This PDF file contains the front matter associated with SPIE Proceedings Volume 12777, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

SUAVE (Solar Ultraviolet Advanced Variability Experiment) is a far UV imaging solar telescope (Lyman Alpha, 121.6 nm, Herzberg continuum, 200-242 nm, etc.) of novel design for ultimate thermal stability and long lasting performances over several years instead of, often, a few weeks or months in this wavelength range. SUAVE is a 80 mm Ritchey-Chrétien off-axis telescope with "mushroom type" SiC mirrors and no entrance window for long and uncompromising observations in the UV (no coatings of mirrors, flux limited to less than 2 solar constants on filters to avoid their degradation), associated with an ultimate thermal control (no central obscuration resulting in limited thermal gradients and easier heat evacuation, focus control, stabilization). Design and performances will be detailed as well as results of thermal/optical tests performed on the SiC primary mirror and its regulated support plate also in SiC. Plans for the realization of a representative breadboard for testing of both optical and thermal properties are presented. SUAVE is the main instrument of the Solar/Climate microsatellite SoSWEET mission (Solar ultraviolet variability and Space Weather Extreme EvenTs).

Helianthus is a technological development project funded by the Italian Space Agency for a Phase A study of a space weather station with solar photonic propulsion. Helianthus will have a synchronous orbit with the Earth-Moon barycenter, positioned at about 7 millions km from Earth towards the Sun, thus much closer to the Sun with respect to historical Space Weather instrumentation, which are typically orbiting the Earth or L1. This sub-L1 halo orbit is maintained by radiation pressure on a solar sail as the propulsion mechanism: once in flight, the spacecraft will have a huge square sail, about 40 m long. The scientific payload will be hosted at the center of the sail and will comprise remote-sensing and in situ instruments. Remote sensing: an X-ray detector to detect Solar Flares and SailCor, a coronagraph with a wide field of view. In situ: a plasma analyzer and a magnetometer. For this ”Sailcraft”, a scientific payload with reduced mass and envelope is under study. The maximum allowed mass for the entire scientific payload shall not exceed 5 kg. Both the X-Ray detector and the in situ instruments have a flight heritage. This study aims at developing a laboratory prototype of a coronagraph matching the constraints of mass and envelope of the Helianthus payload. SailCor is a 20 cm long coronagraph with a field of view ranging heliocentric heights 3-30 solar radii. The external occulter is mounted on an extendable boom that will be deployed once in flight. SailCor presents an innovative solution that combines the diffraction apodization by the external occulter and the internal occulter positioning so that no Lyot stop is required. The classical design of externally occulted coronagraphs foresees the positioning of an internal occulter as a conjugated element to the external occulter with respect to the primary objective. The function of the internal occulter is to block the image of of the diffraction from the external occulter edge. Then, a secondary objective generates the coronal image on the detection system. The SailCor solution takes advantage of the focusing effect that the entrance aperture of the instrument induces on the light diffracted by the external occulter. This effect is used to calculate the position of the internal occulter with respect to the primary focal plane. With this approach, there is no need for a Lyot stop and the detection system can be placed at the first focal plane, with a significant reduction of envelope and mass. This contribution describes the design of the prototype of SailCor, used in laboratory to experimentally define the geometry of the occultation system. The activity has been carried out in the INAF OPSys facility clean environment (ISO5/6) hosted at ALTEC S.p.A. (Torino). The source is a solar divergence simulator.

After the 10th February 2020 launch (04:03 UTC), Solar Orbiter has recently begun its Nominal Mission Phase and is collecting imaging data as never seen before due to its peculiar orbit. The Metis coronagraph produces maps of the linearly polarized visible light corona in the wavelength band 580-640 nm and UV maps in the Lyman alpha H i 121.6 nm line. Metis is a coronagraph characterized by an innovative external occultation system that has a twofold function: reduce the thermal load and remove the diffraction due to the external occulter support. The positions of the entrance pupil (which is called Inverted External Occulter, IEO) and of the actual occulter are switched so that the pupil is the surface facing the solar disk and the occultation is performed by a spherical mirror, M0. M0 is positioned 800 mm behind IEO and reflects the disk light back through the IEO aperture. An Internal Occulter (IO) is conjugated to the IEO with respect to the primary mirror. IO is mounted on a motorized 2-axis stage that allows to perform in-flight fine adjustments to its position. During the on-ground calibration campaign the contribution of the stray light due to the diffraction from the IEO and scattering off the optics was measured. The measurement was carried out by using the OPSys facility in Torino (Italy), which is equipped with a clean environment and a source that simulates the solar disk divergence. A stray light measurement in flight is not trivial due to the presence of the solar corona. Nevertheless, an IO position optimization campaign has been conducted in order to reduce the stray light. A procedure was developed in order to minimize the stray light level on the instrument focal plane. This contribution reports on the procedure and on the results.

On-board the Solar Orbiter ESA/NASA mission there is Metis, a coronagraph designed to study the solar corona by providing an artificial solar eclipse. Metis features two channels working at the ultraviolet Lyman-α (121.6 nm) and in the visible light (580-640 nm). On-ground, the Metis radiometric performance has been tested using a flat-field panel (uniform illumination); the stability of the performance can be verified in-flight through the analysis of the stars passing in the Metis Field of View. Care must be taken to ensure the quality of the calibration, both before launch and for the long period associated with the space mission lifetime. For this reason, we are carrying out long period research of stars that cross the Field of View of Metis. In this paper, we describe the vignetting function acquired: on-ground, simulated via a raytracing code and in-flight derived from on-ground measurements (performing some adjustments to account for the real Metis flight configuration). These vignetting functions are then compared with the vignetting data derived from the passage of the star Theta Ophiuchi in March and December 2021. Additional presentation content can be accessed on the supplemental content page.

AEOLUS underwent a long development led by Airbus Defence and Space both for the LIDAR instrument (ALADIN) in France, and the platform in the UK, and was successfully launched into a Sun-synchronous 320 km dawn-dusk orbit by a Vega launcher in August 2018. The ALADIN Doppler wind LIDAR is pioneering the application of such kind of instrument in space and widens the field for space based LIDAR applications. Initially the mission was designed to be a demonstrator but can be actually considered as operational as the data are used routinely with positive impact on the Numerical Weather Predictions (NWP) models after less than one year of operations in-orbit. After four years of operational lifetime, and also thanks to a strong support to in-flight operations, AIRBUS has learnt, together with ESA customer and scientist user teams, many things about ALADIN LIDAR instrument behavior and its performance monitoring in orbit. While temperature and power telemetries monitoring are quite standard in post-delivery, the follow up of the instrument optical alignment and performance is less direct and lesson learnt show it can be however very profitable in particular for the first UV LIDAR in orbit. The ALADIN architecture is recalled with its measurement principle, and its calibration mode and measurement mode, summarizing the available data for monitoring its behavior in orbit: this covers far field pattern from the atmospheric echo, or near field pattern from the atmospheric echo or internal calibration path; this allows to derive alignment stability of the transmitter and receiver part of the instrument. Also, spectral calibration curves trends allow to retrieve information’s about spectrometers stability. In addition, energy monitoring trend are presented with several means available, and linked lessons learnt are driven. As an important contributor for ALADIN performances, the telescope stability is analyzed and thermal correlation presented with representative Earth albedo maps. The telescope stability is shown as a contributor to link budget but also to spectrometers systematic error limitation due to their sensitivity to variations of divergence and line of sight (angle of incidence). As other key element, the CCD sensor "hot pixel" observation is described with the workaround solution operation at instrument allowing to remove their negative impact on measurement data. Overall conclusion is driven with lessons learnt and perspective for a follow on instrument.

In cooperation with the European Space Agency (ESA) and Airbus Defense and Space (DS), the German Aerospace Center (DLR) developed the ALADIN Airborne Demonstrator (A2D). Also operating at 355 nm wavelength, it is the prototype of the first direct-detection Doppler wind lidar instrument in space - ALADIN (Atmospheric Laser Doppler Instrument) - the single payload of ESA’s Aeolus mission. The A2D was deployed for extensive ground-based measurements and airborne campaigns in the years of mission preparation, with the goal to test operational procedures and refine the algorithms for the processing chain. Experience gained with the A2D supported the ground tests conducted with ALADIN before the launch of Aeolus in 2018. It also laid the foundation for the continuous performance monitoring of the mission, performed within the Data Innovation and Science Cluster (DISC), led by DLR. After launch, DLR executed four airborne campaigns with a focus on validating the Aeolus wind products during different phases of the mission and in diverse geographical and meteorological conditions. During these campaigns, the DLR Falcon aircraft was equipped with the A2D and a high-accuracy scanning heterodyne-detection 2-µm Doppler wind lidar (DWL), used as a reference. Complementary and synergistic results from both DWLs do not only allow for the characterization of the Aeolus and A2D wind errors, but also provide recommendations for the optimization of the Aeolus wind retrieval. Fielding the A2D as a test-bed and validation tool for the Aeolus mission has been a milestone for space lidars and vital for the success of Aeolus, as it has been providing efficient access to instrument specifics in the technological, analytical and scientific domains. The paper covers selected aspects of the airborne technology demonstration program that has supported Aeolus in becoming a successful explorer mission, able to provide high impact data for numerical weather prediction institutions around the world on an operational basis.

During ICSO 2020, the development & characterization of a compact low-resource Correlation Lidar (CWL) for the 3-D atmospheric wind measurements has been reported1 . It was demonstrated that 3-D vector winds could be measured with a ground demonstrator scanning in azimuth. In addition to 3-D winds, it was shown that backscattering & extinction coefficients could also be extracted from the atmospheric lidar profiles. An essential part of the vector wind information retrieval was the development of suitable algorithms to implement the data processing. The demonstration was implemented by means of CCA algorithms based on MATLAB Image processing routines. The present work presents the ongoing effort for the development, characterization & testing of an optimized dataprocessing Algorithm & its implementation on a Raspberry Pi board. The present work will describe the definition & evaluation of an optimized algorithm using synthetic Data. We will compare the performance and stability of both CCA & Point Cloud Optical Flow algorithms. The key issues are wind accuracy and the stability of the wind product under adverse conditions (limited SNR etc), the processing resources required for on-board implementation with a view to the development of a spaceborne instrument. The Optimized algorithm & processor has been tested with a ground CWL instrument. The wind data obtained have been verified and fit well with co-located empirical Data. The results of the processor development & field tests will be presented and discussed with a view to operation from a future Space-based implementation. The further development of the current Processor to a future Spaceborne wind sensor using a FPGA-based processor implementation for Meteorological applications will be given. Keywords: Lidar, Photon Counting, Signal Processing

The European Space Agency’s (ESA) Aeolus satellite was launched on 22 August 2018 from Centre Spatial Guyanais in Kourou, French Guyana. The Aeolus data has been extensively analysed by a number of meteorological centres and found to have a positive impact on NWP forecasts, particularly in the tropics and polar regions. These positive results, along with the successful in-orbit demonstration of the measurement concept and associated technologies utilised on Aeolus, resulted in a statement of interest from EUMETSAT in a future, operational DWL mission in the 2030 to mid-2040’s timeframe and a request to ESA to carry out the necessary pre-development activities for such a mission. This paper will describe the current status of instrument pre-development activities that are being performed in the frame of a potential Aeolus-2 mission. The main inputs for a future Doppler Wind Lidar (DWL) instrument that have been used are: lessons learned from the Aeolus development phases and the in-orbit operations and performance; initial inputs from EUMETSAT including a total mission lifetime of higher than 10-15 years utilizing 2 spacecraft (implying a lifetime of 5.5 years for each) with a launch of the first satellite in 2030, increased robustness and operability of the instrument, and an emphasis on reduction of recurrent costs; the maximum utilization of the demonstrated design heritage; and a number of recommendations for the requirements of a future DWL mission from the Aeolus Scientific Advisory Group (ASAG). These inputs have been collated and combined into a set of preliminary requirements which have been used as the basis for a dedicated Instrument Consolidation Study. An extensive review and trade-off of the above inputs by Airbus Defence & Space, ESA, and independent experts, resulted in the decision to baseline a bi-static instrument design. In addition, three instrument subsystem pre-development activities are currently running: two laser transmitter pre-developments and the pre-development of an improved detector. These developments have the aim to demonstrate that issues identified from the above are resolved and that the technology levels are sufficiently mature for the follow-on DWL mission. The status of these pre-developments will be summarise

Optical imagery from space-based telescopes is one of the most valuable tools for understanding various large and small-scale processes on planetary bodies. Whether in orbit around the Earth or another body in the solar system, it is desirable to obtain the highest resolution imagery possible of the central body. The traditional approach to achieving higher resolution imagery is to increase the size of the optical payload’s aperture. However, larger aperture payloads become prohibitively difficult to manufacture and excessively expensive to design, build, launch, and operate. Application of rotating synthetic apertures (RSA), which is a form of dilute aperture imaging system, to space telescope designs have the potential to unlock the design space of low mass and cost, high resolution space telescopes. RSAs employ a high aspect ratio rectangular aperture that is spun about its principal optical axis. A complete image is formed after a 180° rotation during which multiple frames are acquired to fully sample the imaging system’s optical transfer function. The sampling strategy, which involves the number of individual frames captured and the rate of spin about the principal optical axis, is a function of the RSA’s aperture dimensions. The purpose of this work is twofold. First, an expression for resolution in reconstructed images is derived as a function of orbital altitude, RSA aperture dimensions, and amount of spatial oversampling of the target scene. This expression is used to predict potential science data return for a given orbit, RSA design, and sampling strategy. Second, a multi-objective optimization analysis is performed between reconstructed image resolution and optical telescope assembly (OTA) cost from which a Pareto frontier is defined. This analysis informs an ensuing discussion of optimal RSA aperture dimensions for achieving optimal conditions in resolution and cost. Additionally, the effects of different RSA aperture dimensions on sampling strategies are discussed. Based on these results and discussions, a high-level design for an RSA demonstration mission is proposed. Additional presentation content can be accessed on the supplemental content page.

The latest high-performance telescopes for deep space observation employ very large primary mirrors that are made of smaller segments, like the JWST which employs monolithic beryllium hexagonal segments. A very promising development stage of these systems is to make them active and to operate on their reflective surfaces to change their shape and compensate for aberrations as well as to perform a very precise alignment. This is possible by employing a reference body that stores actuators to modify the shape of the shell, like in the SPLATT project where voice coil actuators are used. However, the lack of physical contact between the main body and shell places – along with the many advantages related to the physical decoupling of the two bodies - some concerns related to the retaining of the shell under all the possible acceleration conditions affecting the system during the mission lifetime. This paper aims to study the acceleration environment affecting the spacecraft during its lifetime and to use it as a baseline for operational requirements of a retaining system for the shells. Any solution is selected in this paper to leave complete freedom for the development of a constraining system, just some are qualitatively discussed.

A concept of optical interferometric imager was proposed by Lockheed-Martin in the early 2010s. In this concept, the aperture is paved by lenses. The optical signals collected by these lenses are combined in photonic integrated circuits, allowing the simultaneous measurement of the Fourier components of the observed object at a number of spatial frequencies. This concept allows one to consider a very significant reduction of the size of optical telescopes, e.g., for Earth observation. Indeed, the transverse dimension of a device based on this concept remains close to that of a telescope of the same resolution since the transverse size determines the spatial resolution. On the other hand, its size along the optical axis is much smaller than that of a conventional telescope. After a quick description of this concept, its intrinsic performance will be analyzed. The field of this device, its spatial resolution, the spectral constraints imposed by the interferometric measurement will be presented. Based on these preliminary considerations, the noise on the measurement will be evaluated. The measurement noise will be compared to that obtained with a focal plane imaging instrument. The geometry of combination of the signals collected by the lenses, or aperture configuration, is a key issue to minimize the size of the device and optimize the quality of the reconstructed image at a given spatial resolution. The literature proposes solutions leading to a partial frequency coverage. In this communication, solutions will be presented leading to a frequency coverage that is more suitable for applications such as Earth observation.

Curved imaging sensors bring significant size, weight and cost reduction to imaging systems while mitigating off-axis optical aberrations, as opposed to current flat sensors. Unlocking these key features has captured the interest of major players over the last two decades. SILINA has been developing a CMOS Image Sensor (CIS) curving process, which adapts to various sensor characteristics. This enables the design of image focal planes to various shapes to specifically maximize the optical performance of every single imaging system. We demonstrated the manufacturing of spherical and aspherical CIS in 2021, opening a new area of compact, fast, wide-angle and high-resolution optical system solutions. From concave to convex, spherical, aspherical, cylindrical, toroidal, or even freeform shapes can be reached. These new degrees of freedom offered to CIS can significantly simplify optical systems through a reduction of the number of elements and improve optical performance in many different ways. The field of view, the contrast, the F-number can be increased while optical aberrations and distortion can be minimized. At the end, the different costs related to manufacturing, metrology, integration, and alignment are reduced. This is of great importance for applications requiring compact payload, high resolution, high transmission factor and shorter integration time. In this paper we address the challenges caused by the adoption of curved image sensors, notably the different approaches for the adaptation of existing designs with a highlight on the optimization and tolerancing methodology. We describe our approach to enhance existing designs by including a curved focal plane, from the first analysis to the last optimization run, in order to improve key performance criteria while maintaining first order parameters. We discuss the improvement expected for space observation through a focus on a two-mirror telescope design based on the Hubble Space Telescope characteristics.

The demonstration of interoperability of the deep-space optical ground demonstration infrastructures of the two space agencies, NASA and ESA, will reinforce optical communication for the use case of fast deep-space data return. The operational experience gained by this joint demonstration will enable future mission designers to efficiently trade the option of using optical communication as data-return vehicle for upcoming deep-space missions. ESA is investigating potential mission scenarios at Mars for which this technology demonstration and validation is considered essential. In this paper ESA's ground demonstration infrastructure for optical data return from the Psyche mission is outlined. The deep-space mission to the asteroid Psyche will host a technology demonstration payload, the Deep Space Optical Communication (DSOC) system, developed by NASA. The mission’s objective is to investigate the asteroid and its unique metallic surface. In addition to its primary objective, the mission will demonstrate an optical communication link between the spacecraft and earth with a separation of up to 2.5 AU. Here we provide link budget calculations for the data up- and the data downlink. Optical communication has the potential to deliver 10- to 100 times higher data rate compared to radio frequency, at lower size, weight and power consumption.

In deep-space optical communications, one particular challenge encountered at the ground receiver side are the wavefront deformations caused by atmospheric turbulence. This gives rise to reduced signal-to-background ratios and signal fades, especially during daytime. Background rejection is therefore a fundamental requirement for optical links operating in the low-photon-count regime with a strong solar background. Both, spectral and spatial filtering subsystems are essential for this application. To this end, we have analyzed several spectral filters and wavefront sensing approaches. In laboratory experiments, a combination of a bandpass filter and a Fabry-Pérot etalon delivered the required bandwidth of 0.17 nm and transmission of 90%, while a SWIR Shack-Hartmann sensor, combined with custom-built wavefront reconstruction software, directed the adaptive optics loop. We have obtained improvements in the Strehl ratio for signal-to-background ratios down to 0.2

We show that utilizing pulse position modulation and photon number resolving detectors together with techniques such as quantum pulse gating allows to approach ultimate quantum limit on optical communication capacity in the presence of background noise in the weak output power regime. This shows that for communication over long distances by means of current existing technology it is possible to attain optimal performance, limited only by laws of quantum mechanics.

The growing interest into exploration of the Moon poses several technological challenges, one of them is surely the need to ensure that the future Moon robots andinhabited colonies will be able to rely on a solid and performing communication infrastructure both within the Lunar environment and with Earth control centers. In this view, a study with ESA (OCRSG) has been carried out by TASI, SSSA and TASCH, in order to start the design of such infrastructure. Severaloptical terminals have been sized to guarantee a downlink from the Moon to Earth at <2 Gbps, and the same performance between Moon orbiters and Moon surface users, and among orbiters themselves, including the future Lunar Gateway. The design is based on state-of-the-art technologies; we also compared the existing radio-frequency subsystem performance, demonstrating the advantages of optical technologies. The optimalmodulation scheme for each scenario has been individuated, starting from high-photon-efficiency modulation (HPE/PPM) but preferring, when possible, more “conventional” schemes, like OOK and DPSK (to exploit a better technological availability). This optimization was possible thanks to the consideration of high power optical boosters which are now available for terrestrial applications. Another part of the study focused on the definition of FoR (Field of Regard)requirements for the different use cases: this realization can be done in different ways, e.g. using a single mirror mechanism up to a fully hemispherical gimballed or periscopic telescope. The study conclusion also draws a technological roadmap, addressing the critical technologies in the gap between the state-of-the-art and the baseline design

The ALTIUS Mission (Atmospheric Limb Tracker for Investigation of the Upcoming Stratosphere) aims at the development of a limb sounder based on a small satellite concept to monitor the distribution and evolution of stratospheric ozone at high vertical resolution in support of operational services and long-term trend monitoring. The ALTIUS instrument consists of three spectral imagers flying at an altitude of approximately 700 km Sun-Synchronous Orbit. The three hyperspectral channels are based on Acousto-Optic Tuneable Filters (AOTFs) in the Visible (440-675nm) and NIR (600-1020nm) range, and a cascade of Fabry-Pérot Interferometers (FPI) in the UV (250-355nm). The use of tuneable active spectral filters will allow the ALTIUS Instrument to perform observations with a spectral resolution ranging between 1nm and 10nm in an extremely versatile operational concept. This paper presents the key technical challenges to be controlled on the design and technologies of the ALTIUS 2D imager for limb sounding. A particular insight will be given on its optical concept including the choice of tuneable spectral filters in each channel and the key development of optical elements such as mirrors, filters and coatings, ensuring the straylight performances of the instrument. The paper also provides a deep dive into the structural and thermal design of the instrument ensuring the pointing accuracy, and the way to achieve L1 radiometric performances from L0 instrument performances through calibration needs and data processing strategies. Along the lines, the stringent cleanliness and contamination control and related envisaged strategy to ensure sustained optical performances will be also described

The FLuorescence Explorer (FLEX) is the 8th Earth Explorer mission currently being developed by ESA with the objective to measure solar induced vegetation fluorescence. This will advance our understanding of photosynthesis and the health of vegetation. Vegetation fluorescence is a very faint signal, and this brings many challenges for the instrument design, development and test, in particular for the very stringent straylight requirement. The development of the FLEX payload (FLORIS instrument) is led by Leonardo (Italy) with OHB (Germany) in its core industrial team. A major milestone has been achieved by completing the instrument Critical Design Review beginning of 2022, allowing now to move into the phase of flight hardware integration. Most of the instrument flight components and subsystems are already manufactured and ready for integration. An extensive test campaign has been already performed on an optically representative engineering model. This campaign provided very useful results in particular for the validation and optimization of the instrument alignment procedures, of cleanliness & contamination preventive measures and the assessment of the optical performances predictions, in particular straylight in flight representative conditions. In this paper an overview of the instrument design, status and development progress is provided including an outlook of the follow up project activities to get ready for FLEX mission launch in 2025. The main results of the engineering model test campaign will be provided with emphasis on the achieved optical performance results. In addition to the project status this paper highlights also some of the most important lessons learnt during the project development as reported in section 4.

A new category of SmallSat research missions, called Scouts, is introduced by ESA. Scout missions distinguish themselves from Earth Explorers by relying on the New Space paradigm, by giving industry and non-profit R&D/academia a more pro-active role. This allows a low-cost approach (≤30M€) and a rapid development cycle (3 years from KO to launch) while using disruptive sensing techniques. CubeMAP is one of the two first Scout missions selected for implementation. CubeMAP is a constellation of three identical 12U satellites, each being designed to perform limb-sounding measurements of atmosphere transmission. Each satellite carries a payload made of two kinds of instruments. The first one, the High-resolution Infra-Red Occultation Spectrometer (HIROS), is a high spectral resolution spectrometer operating in LWIR narrow spectral range (1 cm^-1) with high resolution (0.005 cm^-1). It is based on the measurement of the interferences between the observed Sun scene and an on-board Quantum Cascade Laser (QCL), whose signals propagate through a Hollow Wave Guide (HWG). This configuration limits the sensitivity to shot noise in a compact design with low volume and mass. The second one, the Hyperspectral Solar Disk Imager (HSDI), is a multi-spectral Sun Disk imager. It aims at providing accurate pointing reference to the payload as well as pressure and aerosol measurements. The overall payload allows a spectroscopic measurement of the atmosphere transmission with high vertical resolution (~ 1 km FWHM) between 6 and 50 km altitude

The TRUTHS (Traceable Radiometry Underpinning Terrestrial and Helio Studies) mission is a concept initially proposed by NPL which will enhance our understanding of the Earth’s changing radiation budget by an order of magnitude. This is a UK led mission within the ESA Earthwatch programme with prime, platform and instrument being led by Airbus UK. At the heart of the payload is the ability to calibrate the high resolution hyperspectral imager with a SI calibration traceable to national standards using the payload’s on-board calibration system (OBCS). This in turn provides accurate continuous measurements from the top of atmosphere of reflected, lunar and spectral solar radiance. This paper will concentrate on the hyperspectral instrument part of the payload. The optical design boasts low polarisation sensitivity, good MTF and Smile, and has a compact accommodation to optimise the instruments size and weight footprint within the Payload. The electro-optical back end consists of one Teledyne CHROMA-D MCT detector, with low noise and high SNR achieved through cold operation through a passive cooling system. Pixel correction, customised spectral and spatial binning and compression provided by the electronics front end produces an output dataset with a Spatial Sampling Distance (SSD) of 50m over a spectral range from 320 to 2400nm with a Spectral resolution between 0.3 and 7 nm. This paper will summarise the design status of the TRUTHS hyperspectral imager at the end of phase A/B1. The current spatial and spectral performance will be presented as well as the accommodation and thermal performance.

MERLIN (Methane remote sensing LIDAR mission) is a joint DLR/CNES mission, which will measure column densities of methane in the Earth atmosphere. The heart of the instrument is the laser transmitter subsystem, developed and built by Airbus (Ottobrunn, Germany) in cooperation with the Fraunhofer Institute for Laser Technology (Aachen, Germany), being in charge of the laser’s optomechanical assembly. The project is currently in Phase D with an expected instrument delivery date to the satellite prime in 2026 and launch in 2028. The laser system features key technologies, as already demonstrated successfully in the frame of the FULAS project, to enable reliable long term and high-stability laser performance operation under space conditions. The technologies are optimized with respect to thermal and mechanical stability and developed with special attention on LIC (laser induced contamination) issues by aiming for a fully inorganic design, avoiding any critical organic and outgassing materials. This publication provides an insight into the system design. Furthermore first results from the ongoing qualification model assembly and integration activities are presented, including evidence of the technology maturity for space, based on subassembly and component level qualifications as well as representative bread board activities. Additional presentation content can be accessed on the supplemental content page.

As part of the European Space Agency's AEOLUS mission, the global wind distribution in the atmosphere is currently being measured with a satellite based Doppler lidar. For the AEOLUS-2 mission, a more powerful laser is required which can emit single frequency pulses of 150 mJ energy at a pulse repetition rate of 50 Hz and a wavelength of 355 nm. Fraunhofer ILT is currently developing an engineering model of the laser beam source in cooperation with Airbus Defense and Space Germany. The work on the laser housing and heat removal system is performed by Airbus whereas the work on the laser opto-mechanical assembly is performed by ILT. This work is based on the results of previous projects and focuses on maximizing the use of heritage: The required optical parameters in the infrared have been validated by means of a breadboard demonstrator within the NIRLI project and the optomechanical platform suitable for AEOLUS-2 has been developed in the frame of the OPTOMECH, FULAS and MERLIN projects. For the engineering model presented in this article the proven optical design supplemented by a frequency tripling unit is transferred to the proven and to a large extent space qualified optomechanical platform with an adapted heat removal system. The design is ready, pending the detailed review.

Airbus Defense and Space GmbH, in cooperation with Fraunhofer ILT, is currently developing an engineering model (EM) of the laser transmitter for the AEOLUS-2 mission in frame of the ESA contract ALTA. . For this follow-up mission, a more powerful Laser transmitter is required, to provide single frequency laser pulses of 150 mJ energy. The design focuses on maximizing the use of the heritage from previous space-borne laser designs of the projects FULAS (ESA, EM-like Technology Demonstrator) and MERLIN (DLR/CNES, French-German Climate Mission). The FULAS laser comprises INNOSLAB based MOPA delivering IR laser pulses in the 100 mJ class at 100 Hz PRF. It has undergone a test program demonstrating outstanding thermal insensitivity and robustness and optical and mechanical stability, showing no degradation or misalignment at all after seven years. The laser transmitter of MERLIN, evolved from FULAS, comprises a scaled MOPA, combined with a subsequent Optical Parametric Oscillator (OPO) for frequency conversion. While the Laser opto-mechanical assembly (LASO) is developed by Fraunhofer ILT, Airbus Defence and Space GmbH is in charge of the system concept and the hermetically sealed Laser Housing (LASH) as well as the innovative thermal control system. This publication will provide insight in the transfer of the FULAS and MERLIN system concepts to the Doppler Wind LIDAR Transmitter. Emphasis will be on the robust thermo-mechanical design, with its thermally and mechanically decoupled optical bench and the sophisticated thermal control system based on heat pipes for effective heat removal directly from the individual heat sources of the system. This design is chosen to provide hands off operation of the Transmitter over life time.

We have improved on the characteristics of a diode-pumped, 1064-nm amplifier. The system can deliver 400 mJ @ 100 Hz with very limited wavefront distortion due to thermal effects. It follows that the amplifier can be powered on and reach full energy in a few seconds. The amplifier stable long thermal lens ensures that optical elements used downpath (potentially non-linear crystals for frequency conversion, or a telescope) are at no risk of laser damage, even during the short warm-up time. Additionally, the amplifying system can be operated at any repetition rate up to 100 Hz, and at any energy level, without having to adjust the hardware. The ease of operation, and number of shots saved on the diode lifetime can be a critical advantage in space. The amplifier pumping design enables duplication of the pump source with only 3% increase of the system mass: the doubling of the stacks does not require any additional optical component, nor any moving part. With solar radiation, the diode stacks are among the weakest link of the system, so this unique property is valuable for space applications. The laser amplifier was set-up and characterized as a laboratory breadboard, and a CAD version of a robust system was drawn and analyzed. We will review the properties of this compact amplifying system. Due to its uniform output beam distribution, it is very well suited for non-linear frequency conversion, and for long-range space applications. Additional presentation content can be accessed on the supplemental content page.

The ATHENA (Advanced Telescope for High ENergy Astrophysics) mission is the current 2nd ‘Large’ mission (L2) in the ESA Cosmic Vision programme currently. It is currently at Phase B1 but the mission concept will now enter a reformulation phase that will follow a design-to-cost approach. This paper describes the main technologies behind its reference X-ray telescope based on the modular Silicon Pore Optics (SPO) technology. The large X-ray mirror is the mission enabler being specifically developed for ATHENA, in a joint effort by industry, research institutions and ESA. All aspects of the optics are being addressed, from the mirror plates and their coatings to the mirror modules and their assembly into the ATHENA telescope, as well as the facilities required to build and test the flight optics, demonstrating performance, robustness, and programmatic compliance. An overview of the status of the design and demonstration of the telescope is given. The risks that have successfully been mitigated are made explicit and the remaining risks are identified. Additional presentation content can be accessed on the supplemental content page.

Athena is the European Space Agency’s next flagship telescope, scheduled for launch in the 2030s. Its 2.5 m diameter mirror will be segmented and comprise more than 600 individual Silicon Pore Optics (SPO) mirror modules. Arranged in concentric annuli and following a Wolter-Schwartzschild design, the mirror modules are made of several tens of grazing incidence primary-secondary mirror pairs, each mirror made of silicon, coated to increase the effective area of the system, and shaped to bring the incoming photons to a common focus 12 m away. The mission aims to deliver a half-energy width of 5" and an effective area of about 1.4 m² at 1 keV. We present the status of the optics technology, and illustrate recent X-ray results and the progress made on the environmental testing, manufacturing and assembly aspects of the optics.

Several hundreds of Silicon Pore Optics (SPO) mirror modules need to be integrated and co-aligned onto the ATHENA (Advanced Telescope for High-ENergy Astrophysics) Mirror Assembly Module (MAM). The selected integration process, developed by Media Lario, exploits a full-size optical bench to capture the focal plane image of each mirror module when illuminated by a collimated UV wavefront at 218 nm. Each mirror module, handled by a manipulator, focuses the collimated beam onto a CCD camera placed at the 12 m focal position of the ATHENA telescope. The image is processed in real time to calculate the centroid position and overlap it to the centroid of the already integrated Mirror modules. The 600 mirror modules must be accurately aligned on the ATHENA optical bench, with tolerances of few micrometers and arcseconds. The concept has been demonstrated in a preceding competitive technology development activity. This Assembly Integration and Test (AIT) facility is a vertical optical bench with a collimated UV beam, generated by a 2.6 m Zerodur® parabolic mirror. This UV collimator mirror is already completed and ready to be delivered to Calar Alto Observatory (CAHA, Sierra de Los Filabres, Spain) for the deposition of the reflective coating. In the AIT facility, the ATHENA telescope structure is positioned horizontally on a rigid mechanical structure, called MAIS, and supported by 9 actuators to minimize the gravity effects. One by one, the mirror modules are aligned under the UV beam, ensuring that they all focus into a common point and glued to the dowel pins connecting them to the mirror structure. The building housing the AIT facility is under construction at Media Lario premises near Milan, Italy, and extends 6.5 m below and 17 m above ground. The building is dimensioned to also accommodate the vertical X-ray test facility (Vert-X). The co-location of these two facilities is strategic for the project and will permit regular checks of the mirror module alignment while the MAM is populated. A rail system connects the two facilities.

The ESA Advanced Telescope for High-ENergy Astrophysics (ATHENA) will be the largest X-ray optics ever built. The ground calibration of its mirror assembly raises significant difficulties due to its unprecedented size, mass and focal length. The VERT-X project aims at developing an innovative calibration system which will be able to accomplish this extremely challenging task. The design is based on a 2.5 cm²parallel beam produced by an X-ray source positioned in the focus of a highly performing collimator; in order to cover the whole 2.5m diameter mirror, the beam is accurately moved by a raster-scan mechanism. The same device has the capability to tilt the beam by 3 degrees, in order to test both the off-axis performance and the out-of-field stray-light contamination. By design, VERT-X will be able to measure the ATHENA mirror half energy width (HEW) with a precision of 0.1”, all over the field of view, with the source size, the collimator error and the raster scan tracking accuracy being the most important terms of the error budget. With respect to the traditional long-tubes, the VERT-X facility is much more compact. The entire system will be enclosed in a cylindrical 18m-high vacuum chamber with diameter ranging from 7m as maximum to 4m at minimum. Besides the smaller amount of involved resources, there are important benefits generated by the small scale design. First, it allows a vertical geometry which largely simplifies the mirror support and reduces to zero the PSF degradation due to the lateral gravity. Then, the location of the facility can be chosen flexibly and according to the project needs. Indeed, VERT-X will be built in continuity to the ATHENA mirror assembly integration facility, simplifying the verification and testing procedures. The VERT-X project, started in January 2018, is financed by ESA and conducted by a consortium that includes INAF, EIE, Media Lario, Apogeo Space (former GPAP), and BCV Progetti.

In this paper, we present first results in the experimental demonstration campaign of optical feeder link conducted in November 2021, by using the Laser Utilizing Communication System (LUCAS) onboard the optical data relay GEO satellite. This campaign has been worked under the collaboration for both the National Institute of Information and Communications Technology (NICT) and the Japan Aerospace Exploration Agency (JAXA). In our experiment, we utilize the optical ground station with 1 meter telescope, which is installed in the Okinawa Electromagnetic Technology Center of NICT. This paper mainly discuss received optical power, acquisition and tracking performance, bit error rate performance of the downlink and received optical power of the uplink in an optical feeder link.

Earth Observation missions generate an increasing volume of data as their spatial resolution and swath have constantly increased over the last years. Downloading to ground such amounts of data with limited end-user latency is quite challenging. In this context, optical links offer an effective solution for such image downlink. To demonstrate the feasibility and the relevance of using direct optical links from LEO satellites to ground, to download large volume of data, Airbus DS and CNES have joined to develop LASIN. LASIN, which stands for LASer through the INstrument, is flown onboard the CO3D constellation and will provide a 10 Gbps optical link dedicated to image data downlink. This is achieved thanks to a laser system which transmits directly through the CO3D instrument. LASIN requires only few equipment to turn the instrument into a laser terminal. No pointing mechanisms are required as the beam pointing is achieved thanks to the satellite attitude control capability. LASIN also benefits from the implementation of a new family of high-efficiency LDPC codes recently adopted by the CCSDS and optimized by Airbus DS. In the frame of this demonstration, the optical ground station is developed by CNES and located at the Observatoire de la Côte d’Azur in south of France. The first optical links will take place in 2024. Beyond this demonstration, the goal is to propose a fully operational downlink capability for future EO missions. The system is designed to be compatible with low cost optical ground stations in order to offer innovative and competitive solution for image downlink for the EO export market. Additional presentation content can be accessed on the supplemental content page.

Architecture of a 10 Gbauds link between new high complexity optical ground station suitable for feeder link and a geo-stationary satellite is described. Such link is tested in laboratory environment with emulation of power fluctuations representative of the power budget between the optical ground station and the satellite. The software and hardware developed reach the expected performance and the system performance model is demonstrated to be accurate at 1 dB.

Optical free-space data downlinks from LEO satellites benefit considerably from reduced effort on the space segment, when a dedicated pointing mechanism and active tracking of a ground beacon can be avoided. Instead, the attitude of the satellite is dynamically determined from its star cameras and other sensors. Initial calibration for this technique requires recording of the spatial and temporal beam distribution on the Earth’s surface. We describe the measurement of the beam intensity on ground by the power detectors of three ground stations in parallel, exemplarily for one specific downlink. From this data we derive the instantaneous center of gravity of the beam spot, and its dynamic movement during the downlink. By comparison with the satellite’s own recorded attitude data and its error, the dynamic offset to be corrected on the satellite can be calculated, resulting in optimized pointing-control for future operational open-loop downlinks.

Stray light characterization using ultrafast time of flight imaging was demonstrated recently for the testing of refractive telescopes, using a streak tube with a femtosecond laser. It was shown that individual contributors such as ghost reflections and scattering features can be measured individually and identified, allowing unprecedented understanding of stray light properties in telescopes. This opens the door to the development of higher performing instruments, with stray light properties significantly reduced compared to the state of the art. In this paper, we will present the latest advances in the domain of stray light characterization by ultrafast time-of-flight imaging. This includes the characterization of imaging instruments, and the use of the time-of-flight measurements for reverse engineering instruments properties. In addition of using the time-of-flight approach for characterizing instruments, we will show that this method can be used to validate and improve conventional stray light measurement devices and facilities. In the case of large facilities, the typical optical path lengths is of the order of several centimeters to tens of meters. Therefore, in that case streak cameras can be replaced by a less expensive alternative, namely SPAD detectors. We will present the dedicated SPAD detector that we developed and the results obtain in the validation and improvement of the stray light facility for the FLEX Earth observation instrument. This system will be also used in the near future also for the NAC instrument in the ERO mission to Mars

Even high-end optical components exhibit small amounts of imperfections, which can easily limit the performance of optical systems with respect to imaging contrast, optical throughput, imaging ghosts, and increased light scattering. Characterizing the scattering properties of optical components is thus an important step during the development of sophisticated optical systems as well as to identify and steadily improve materials as well as manufacturing and assembling steps. This is illustrated for different optical components as well as optical systems. Furthermore, different characterization concepts are discussed, which allow overcoming typical limits for angles resolved light scattering measurements, such as scattering very close to the specular beam directions (off specular scattering angles < 0.1°) or measurements in retro-reflection, which are important for gratings used in Littrow configuration or optical mirrors for laser-based communication

In this work, we recorded the retro-reflected and back-scattered light from a system of two components i.e, a single side AR coated SiO₂ window and a mirror placed at tilt angle of 10◦ in the transmission of the window. Retro-reflection and back-scattering from components in an optical system can be detrimental for system performance such as the phase measurement errors, ghost images and laser induced damage in gravitational wave interferometry, optical communications, biomedical imaging and high power laser systems, respectively. Therefore, an accurate determination of the retro-reflected and back-scattered light in such systems is imperative for optimized system performance, particularly the systems where extreme phase sensitive measurements are of keen interest such as the gravitational wave detectors LIGO, Virgo, KAGRA, the future planned Einstein Telescope (ET) and Laser Interferometer Space Antenna (LISA). Using a balanced optical low coherence interferometer, we recorded and distinguished the contribution of light retro-reflected and back-scattered from the different optical surfaces of the two-component assembly. This work would pave the way for simultaneous characterization of the spectral properties of light retro-reflected and back-scattered by components in an optical system with the capability to accurately and effectively identify the impact of individual components as well as the global system performance.

The FLuorescence EXplorer (FLEX) European Space Agency (ESA) mission with its payload, the FLuORescence Imaging Spectrometer (FLORIS), aims at performing quantitative measurements of the solar induced chlorophyll fluorescence from space, with the purpose of improving the monitoring of the health of Earth vegetation. The retrieval of a faint signal, such as the one from chlorophyll fluorescence, requires very low Stray-Light (SL) levels. The SL reduction in FLORIS implied constraints impacting the design, by means of using low roughness optical components, the integration, through a strict contamination control, but also the data processing with the need of a very accurate correction strategy making use of numerical models well correlated with experimental data, to be acquired during the On Ground Calibration (OGC) activities. In order to assess and validate the correction strategy, an accurate SL characterization has been anticipated during the FLORIS Optical Model Refurbished (OMR) campaign. Different methods, such as out-of-field and out-of-band measurements, have been investigated in order to avoid the detector blooming affecting measurements with high input signals. By combining the results from the different approaches, it has been possible to achieve up to 9-10 decades of explored dynamic range. The model, correlated with measurements, has finally proved to be capable to correct SL with a reduction factor <10, down to a level less than 40% of the required fluorescence error (10% of a fluorescence level of about 2 mW/m²/sr/nm). Additional presentation content can be accessed on the supplemental content page.

Teledyne e2v is continuing to invest in CCD and CMOS sensors innovation for higher performance in the visible, soft X-Ray and NIR parts of the spectrum for space applications. Space missions are becoming ever more complex and Teledyne e2v, to support this growth, has developed technologies to improve the intrinsic performance of the detector, new features for low noise or data stream approach and improved interfaces to ease integration at system level. As Teledyne also covers commercial and industrial markets it is possible to take advantages of the state-of-the-art development made in those markets to enhance detector performance for space with limited risk and shorter R&D development time. This paper covers the latest innovations for CCD and CMOS technologies and in particular the large area and low noise platform (CIS300 family) and TDI charge domain CIS125. In the last section an overview on the detector electrical interface innovation is given.

ELFIS2 is the second generation of the European Low Flux Image Sensor (ELFIS), developed by Caeleste, manufactured at LFoundry and tested by Airbus on behalf of the European Space agency. As the High flux program was aborted, it was decided to continue ELFIS as a High Dynamic Range (HDR) sensor, enabling the simultaneous integration and readout of the same charge packet on a large and a small conversion capacitance. It is combined with charge domain global shutter, so that motion artefacts, typical for multi-exposure or dual photodiode architectures are completely eliminated. The ELFIS core pixel uses the Global Shutter technology pixel, developed at LFoundry, allowing charge domain Integrate-While-Read operation and on-chip CDS. In order to handle photocharge packets that exceed the full well of the core pixel, there are two low gain overflow capacitors, used alternatingly for signal integration and read-out. Whereas ELFIS1 was a fixed size device, ELFIS2 is designed for stitching. The stitch block of 512*1024 pixels can realize every n*m multiple of 1/2k by 1k pixels, as long as it fits on the wafer. The Initial prototype presented has a 2k*2k format. 4k*4k, 8k*8K, etc. can be realized with the same mask set, as well as elongated (hyperspectral) sensors up to 512*10 k pixels. As each stitch segment has its own output amplifiers, the ultimate frame rate is only determined by the number of rows to be read. Frame rate can be increased by applying row random addressing, which are especially versatile in hyperspectral applications. The initial functional tests of ELFIS2 are promising: without further optimization the noise spec of less than 5 e-rms is reached with a HDR full well of 160 ke- ; the core Global Shutter high gain full well is 10 ke- , resulting in a smooth photon shot noise limited behavior from the high gain noise floor till the low gain saturation. The full functional testing and circuit optimization is now starting and will be finished at the moment of this presentation. Also, radiation pre-qualification is planned. Due to the good SEE results obtained in another Rad-Hard by Design (RHbD) in the same technology we are also confident that the SEE will have a LET < 63 MeV/mg/cm² for both SEL and SEU.

For the last two decades, CNES optoelectronic detection department has studied and evaluated space environment effects on a large panel of CMOS image sensors (CIS), coming from a wide range of commercial foundries and device providers (cf. Table 1). Many environmental tests have been realized in order to bring insights on detection chain degradation in modern CIS for space applications (cf. Table 2). Thanks to their good electro-optical performances, high integration level, low power consumption and tolerance to the space radiation environment, CIS are more and more preferred over Charged Coupled Devices (CCD) in many future space imaging missions. Moreover, the CIS technology has drastically improved during the las decade, reaching very high performances in term of Quantum Efficiency (QE) and spectral selectivity. These improvements are obtained thanks to the introduction of various components in the pixel optical stack such as microlenses^[1], color filters^[2] and polarizing filters^[3]. However, since these parts have been developed for a commercial purpose, it is crucial to evaluate if these technologies can handle space environment for future imaging missions and very few literatures exist on that robustness. Several space imaging systems have thus been able to benefit from these technologies on which these tests have been carried out, such as the Remote Micro-Imager (RMI) in the SuperCam instrument aboard the Mars 2020 rover Perseverance^[4] . This CNES work demonstrates that these kinds of optical stacks show little variation in terms of efficiency when exposed to space environment. It also allowed studying the response of various optical systems at pixel level for various technologies such as microlenses, color filters and polarizing filters (shown respectively in Figures 1, 2 and 3). In the presentation, an overview of environmental tests results (cf. Table 2) on many CIS from different commercial technologies and several optical stacks are compared and show that they are suitable for space applications. Thanks to their robustness, they can significantly increase CIS performances without being a limiting path for them along the mission. Since the full paper containing data and more will be published later in MDPI Sensors^[5] , it is on purpose that we prefer submitting a more consistent abstract with detailed Tables showing the amount of realized tests, and CNES photos of the optical stacks we are talking about. Additional presentation content can be accessed on the supplemental content page.

3D PLUS has developed in the framework of its R&D activities two new high performance camera heads for space applications. The Centre National d’Etudes Spatiales (CNES) is leading the development of these two new cameras: a 12Mpx space camera head (3DCM800), and a 1.3 Mpx Short Waves InfraRed (SWIR) space camera head (3DCM830). Those camera heads have been integrated using 3D PLUS packaging technology and expertise in order to be as compact as possible and provide the high performances of two images sensors associated with a high performance FPGA based electronic architecture to its Space Camera Product line. Particular attention has been paid to ensure radiation and harsh environment tolerance in order to cover a wide range of application, including equipment or key events monitoring, in-flight spacecraft navigation and rendezvous applications, as well as observation and scientific applications benefiting of the high performance of the sensors (earth observation, hyper/multispectral imaging, planetology).

We show that metrology at the working wavelength is possible with a wave front sensor in the Mid-Infrared range (MWIR, 3-5µm). We demonstrate the implementation of an Interband Cascade Laser for double-pass optical qualification with a quadriwave lateral shearing interferometer. To avoid any parasitic interference fringes, which limit the phase accuracy, we modulate the diode driving current with an external analog signal. While the power stability is kept constant, the phase noise is reduced and no artefact limits the measurement accuracy.

The knowledge of the bi-directional scattering distribution function (BSDF) of an optical component is an import requirement for the design and assessment of high-performance optical instruments. However, precise BSDF measurement with high resolution close to the specular beam can be very challenging and require sophisticated instrumentation. In this paper, we present a newly developed scatterometer, the “Enhanced Resolution Light Scattering Analyzer for Curved Gratings (single detector axis)” – ELSA/CG-S which is designed specifically to measure the BSDF of curved optical components with a very high resolution not only close to the specular direction, but throughout the whole angular measurement range with an instrument signature that can compete with the top of the class of current commercially available instruments. The distinguishing feature of the instrument is the use of a high-resolution silicon sCMOS imaging detector which enables fast acquisition times and provides access to a two-dimensional section of the BSDF around the main detection plane of the instrument with an out-of-plane FoV of about ±0.6°. In the following, we will describe the general design of the instrument and explain the measures that have been taken to enable a very low stray light signature with the chosen detection scheme. After this, we will assess the instruments capabilities and present measurements of the instrument signature and BRDF measurements of plane and curved diffraction gratings with high groove densities. These measurements will also demonstrate the additional value that is provided by using an imaging detector. All measurements will be compared to results obtained with ESTEC’s commercial CASI scatterometer from The Scatter Works, that represent the current state of the art.

Cold atom based quantum sensors require robust and miniaturized optical systems for applications on mobile platforms. A micro-integrated optical system (volume ∼25 mL) for trapping and manipulation of neutral atoms is presented. This setup focuses and precisely overlaps two high power laser beams (1064 nm, up to 2W total, wR = 34 µm) launched via a single-mode, polarization maintaining optical fiber, thereby realizing a crossed beam optical dipole trap (ODT). Adhesive bonding is qualified in application relevant geometries and material systems of micro-integrated optical systems for application on mobile platforms or space. Fused silica test blocks (bond area 2 × 4 mm² ) are bonded with four different adhesives on silicon wafers. Theses samples are aged by thermal cycling (up to −55 °C to 150 °C) and/or gamma-radiation (10 000 mSv) and subsequently the bond strength is evaluated by die shear testing according to MIL-STD-883L. The influence of the environmental aging on the bond strength is presented, the failure mode and the influence of fillets discussed. In addition, the effects of plasma cleaning on the bond strength in this geometry is presented.

Joining technologies are of great importance for space-based applications. Given the very low environmental temperatures, high temperature differences, vacuum, and high acceleration loads during rocket launch, the (thermo-)mechanical requirements on the joining technologies are demanding. Plasma-activated bonding (PAB) and silicate bonding (SB) meet all these requirements. We developed PAB and SB to assemble an all-glass four-channel beam splitter. This development was initiated by a satellite mission concept, devoted to transient astronomy. Central part of this satellite mission is a novel beam splitter that divides the incoming telescope beam into four near infrared channels (λ = 800 − 1700 nm), by using a Kosters prism type design. As a final result, we built a demonstrator for the validation of the developed technological concept. Additional presentation content can be accessed on the supplemental content page.

While the next generation of satellite constellations provide improved capacity through the use of optical inter-satellite links, there is still a capacity bottleneck at the RF feeder links between satellites and ground stations, which are an order of magnitude slower in moving data. In order to move to all optical feeder links, there is a challenge to overcome the distortion associated with atmospheric turbulence. Laser Guide Star (LGS) adaptive optics systems are a key enabling technology to help solve this beam wander problem for ground to space optical systems. For guide star lasers suitable for daytime LGS operation, high power is key. To respond to this need, a 100-W continuous-wave (CW) 1178-nm narrow-band polarization-maintaining (PM) Raman fiber amplifier (RFA) has been developed and fully engineered. A linearly-polarized single-frequency 1178-nm seed laser with an output power of only a few mW is amplified up to 100 W in a two-stage RFA counter-pumped by a 200-W 1120-nm PM fiber laser. Techniques for efficient suppression of stimulated Brillouin scattering (SBS) have been optimized, resulting in the RFA SBS threshold being pushed beyond the 100-W level. The narrow linewidth of the seed laser is well preserved in the RFA, without any evidence of linewidth broadening up to 100 W. The RFA is based on true single-mode PM fibers and has excellent polarization purity and output beam quality, key factors for subsequent efficient frequency doubling to the Na absorption line at 589 nm in a resonant frequency-doubling cavity. Similar to the widely-deployed MPBC/TOPTICA SodiumStar 20/2, the new 100-W RFA system is a compact, modular, reliable and ruggedized off-the-shelf system ready for integration. Compared to solid-state alternatives, a guide star laser based on an all-fiber, highly-reliable, 100-W RFA not only provides excellent overall wall-plug efficiency due to its high pump-to-Raman optical conversion efficiency, but also maximizes the important “up time” for the optical channel at ground station facilities since it is a maintenance-free and turn-key system. To confirm the stability and reliability of this next-generation guide star RFA, the system was run 24/7 at the full 100 W for a total of 1300 hours. The test results confirmed that the 100-W RFA system is extremely robust and reliable, with a sufficient built-in 1120-nm pump power margin. Re-measurements of key RFA parameters, such as polarization purity and output beam quality, also confirmed that the RFA performance remained unchanged after the 1300-hour 100-W test. Assuming a conservative conversion efficiency of ~ 80% by a resonant frequency doubler and taking into account typical passive coupling losses into the doubler cavity of < 15%, narrow-linewidth CW guide star lasers with powers < 70 W at 589 nm can confidently be expected for future optical ground station adaptive optics systems. The RFA output power was shown to be solely limited by the SBS threshold. Since all the laser components showed sufficient higher optical power handling potential, it is expected that, with further optimization of the SBS suppression, the RFA output power can be scaled significantly beyond the current 100-W level.

We propose and analyze numerically concurrent intensity modulation/direct detection (IM/DD) optical key distribution (OKD) combined with conventional data transmission over a LEO-to-ground optical link. The idea is validated by numerical simulations which indicate that in a realistic scenario it is possible to generate simultaneously up to 200 Mbits of a secret key and downlink transmit up to 140 Gbits of data during a single nearly-zenithal pass of a LEO satellite. Such lengths of the secret key are three orders of magnitude higher in comparison to typical quantum key distribution systems, although they are generated under different security assumptions. The simplicity and robustness of IM/DD OKD protocols could make them an attractive and cost-effective option to provide security in the physical layer of space communication systems.

Optical feeder links (OFL) are expected to become part of future Very High Throughput Satellite (VHTS) systems in response to the growing demand for higher capacity and lower costs. H2020 VERTIGO (Very High Throughput Satellite Ground Optical Link) project was set to prove key optical communication technologies and to address: 1) Throughput increase with high spectral and power efficiencies. 2) Higher optical power generation and delivery. 3) Atmospheric turbulence mitigation by optical and digital processing. Transmit and receive optical communication models were developed in rack units for assessing, in laboratory and outdoor trials, their intrinsic performance, robustness against atmospheric turbulence and compatibility with other technologies. The models for 25 Gbps OOK/DPSK and RF analog modulation with optically pre-amplified direct or differential detection are reported with the achieved performance. An atmospheric channel emulator fed with time series established by simulations was used to mimic the propagation losses and fading of the optical signal coupled into the receiver. Both the downlink and uplink under weak or strong turbulence were emulated. For digital transmission experiments, the performance metrics include BER curves, detection sensitivity and power penalty. State-of-the-art sensitivities were achieved especially under 25 Gbps DPSK. For RF analog transmission, the performance metrics were constellation diagrams and Error Vector Magnitude (EVM) measured for various modulations from QPSK to 64-QAM. Are reported the results of optical transmission experiments first performed in the laboratory under static and dynamic propagation channels, then in the outdoor trial successfully carried out in July between Jungfraujoch and Zimmerwald in Switzerland.

High throughput optical satellite communication (SATCOM) systems need to rely on effective and robust technology to enable wavelength-division multiplexing (WDM) in a commercially viable way. The main challenge to implement WDM in optical feeder links deals with the multiplexing of high power channels. Currently the levels of power required for communication, tens of watts per channel, make unfeasible to multiplex several channels in a waveguiding device. A free space architecture is devised to mitigate this issue. The paper describes the architectural choices made, the optical and mechanical design for a multiplexer to be employed in a Optical Feeder Link terminal combining 13 channels, each carrying 50W of optical power. Within the TOmCAT (Terabit Optical communiCation Adaptive Terminal) project a demonstrator of the full system has been realized. The demonstrator multiplexer supports 5 channels, each carrying up to 2W of optical power, with an optical bandwidth of 25 GHz, centered on the 200 GHz ITU grid. The design and the experimental results obtained during the integration of the multiplexer demonstrator are here presented and discussed.

The Mars Sample Return mission is a multiple probe mission to collect rock samples from Mars and bring them to Earth. The Perseverance rover is currently collecting samples on Mars. Tasked with the recovery of the Mars samples in Mars orbit and their return to Earth, the Earth Return Orbiter (ERO) is the last probe of the mission. In order to capture the Orbiting Sample (OS), which contains the Mars rock samples, the ERO will first detect the OS at long distance using its Narrow Angle Camera (NAC). Because the OS will be a faint object of magnitude 12, its detection is a challenge. One part of this challenge is to minimize the straylight caused by the illumination of the camera by much brighter out of field sources, such as the Sun and also the planet Mars. We describe here the design steps taken to minimize straylight, starting with measurement, design principles for the baffle and the objective, then finally simulations and their results.

EarthCARE (Earth Clouds, Aerosols and Radiation Explorer) is the 6th Earth Explorer mission of ESA‘s “Living Planet Earth“ Program. The EarthCARE satellite is about to start its environmental test campaign in autumn 2022. This Core Explorer mission (Core Explorer missions that focus on scientific objectives of a large scientific community) is a large and very complex Earth Explorer mission with 4 Instruments on board. It improves the representation and understanding of Earth's radiative balance for climate and numerical forecast models by advancing our understanding of the role that clouds and aerosols play in reflecting incident solar radiation back into space and trapping infrared radiation emitted from Earth's surface. To achieve this goal, EarthCare is hosting a Multi-Spectral Imager (MSI), an Atmospheric Lidar (ATLID) and a Broad-Band Radiometer (BBR) under European ESA authority and a Cloud Profiling Radar (CPR) under JAXA (Japan Aerospace Exploration Agency) authority. The EarthCare MSI Instrument consists in two camera units, the TIR (Thermal Infrared Radiometer) part with 3 channels (Band7 [8800nm], Band8 [10800nm] and Band9 [12000nm]) and an VNS (Visible, Near-infrared and Short-wave infrared) part with 4 channels (VIS [670nm], NIR [867nm], SWIR1 [1654nm] and SWIR2 [2214nm]) and by an overall weight of around 50kg (including control units, harness and thermal hardware). The Instrument performance qualification consist in a full performance verification testing on instrument level and of regular instrument performance checks (IPCs) on Satellite level after Instrument integration. This performance checks for the MSI concentrate on a simplified test approach and are regularly repeated along the entire S/C AIT campaign until launch. The test results will be compared with first reference IPC measurements from instrument Level. MSI IPC definition does focus on radiometric key performance parameters as noise and responsivity to identify optical or detection chain degradations, as well as detector dead pixels. This paper will present the MSI IPC approach for EarthCare and the first ambient results from S/C Level MSI IPCs performed so far. Furthermore this paper will show that the ambient S/C Level MSI IPC results are in line with the ambient IPC on instrument level but it will also shows good agreement with thermal vacuum results on Instrument level.

Meteosat Third Generation (MTG) is the new European mission for accurate observation of the Earth dedicated to meteorological applications. MTG Program is being realised through the well-established and successful cooperation between EUMETSAT and ESA. MTG system will ensure continuity and enhancement of operational meteorological (and climate) data from Geostationary Orbit as currently provided by the Meteosat Second Generation (MSG) system. The industrial Prime Contractor for the Space segment of MTG is Thales Alenia Space (France) with a core team consortium including OHB (Germany). This contract includes the provision of six satellites, four Imaging satellites (MTG-I) and two sounding satellites (MTG-S), which will ensure a total operational life of the MTG system in excess of 20 years. MTG-I first satellite will be launched end of 2022, starting point of the in-orbit story of MTG. MTG-I embarks the FCI (Flexible Combined Imager), optical payload developed at Thales Alenia Space in France. The FCI is an imaging radiometer which provides simultaneously to the users 16 spectral channels from Visible to Very Long Wave InfraRed (0.4µm – 13.3µm) delivering full disk services (in 10 minutes) at their nominal sampling distance (1 to 2km). Four channels are also delivered at a smaller spatial sampling distance (down to 500m). FCI also provides local area scanning possibilities with a higher repeat cycle (down to 2.5 minutes). The present paper is dedicated to the FCI end-to-end radiometric performance. After an overview of the FCI and the design specificities of its detection chains, its key radiometric performance will be presented. It will focus on FCI PFM test results, which has successfully passed the on-ground fine radiometric calibration and characterization campaign under optical vacuum in 2021. After 10 years of development at Thales Alenia Space, with a fruitful cooperation of many European sub-contractors, the results of the performance characterization and calibration of the FCI have been successfully demonstrated. This work has been achieved thanks to the major support and supervision of ESA.

The Multi-viewing, Multi-spectral, Multi-polarisation Imager (3MI) is one of the payloads that will be on board of the MetOp-SG “Satellite A”, developed to provide information on atmospheric aerosols. 3MI is a space-based, wide field-of-view polarimeter that is designed to acquire sequential images of the same ground target, which are then combined with multiple spectral views in both un-polarized and polarized channels. This article presents the On-Ground calibration results on the 3MI PFM payload. The calibration request the measurement of a set of Key Data Parameters (KDP). These are needed in an instrument model. In the frame of 3MI calibration additionally to the geometrical, spectral and radiometric KDP, polarization and Stray Light are also considered. Because of 3MI wide FOV and polarization performance, dedicated Ground System Equipment GSE have been developed. Test results of the PFM calibration campaign are discussed and lessons learnt for the next campaign are proposed.

EarthCARE is the 3rd Earth Explorer Core Mission of the European Space Agency (ESA) Living Planet Program, with the fundamental objective of improving understanding of the processes involving clouds, aerosols and radiation in the Earth’s atmosphere [2] [3] [5] [6]. EarthCARE data products will be used to improve climate and numerical weather prediction. The data products include vertical profiles of aerosols, liquid water and ice, observations of cloud distribution and vertical motion within clouds, and will allow the retrieval of profiles of atmospheric radiative heating and cooling [4]. For above mission objective, the EarthCARE satellite hosts four complex instruments, the ATLID, (ATmospheric LIDAR from Airbus Toulouse), the CPR (Cloud Profiling Radar, from JAXA/NEC), the MSI (Multi Spectral Imager from SSTL) and the BBR (Broad Band Radiometer from TAS-UK). The instrument performance verification approach is based on (a) the full performance verification testing done on instrument level, and (b) on Instrument Performance Checks (IPCs) to be repeated periodically on instrument and satellite level. IPCs are designed to confirm that the core instrument performance as verified on instrument level does not degrade after integration on the platform and throughout the overall satellite AIT campaign until launch. Five ATLID IPCs have been defined in close cooperation between Airbus instrument and satellite prime teams, considering instrument performance verification needs as well as feasibility of IPC repetition in satellite AIT. This feasibility refers mainly to satellite AIT limitations for laser hazard protection measures, cleanliness (ISO8 environment), complexity of optical setups, need for limited test durations<1 day and more difficult instrument accessibility (instrument integrated at more than 3m height on the satellite). For the ATLID Lidar instrument, the following IPCs have been defined: (1) Transmit Laser Beam Line of Sight (LoS) stability, (2) Activation of Transmit Laser beam steering mechanism, (3) Laser pulse energy knowledge stability, (4) Overall Receive chain optical response check and (5) Detection chain total noise in darkness. IPC test definition as well as test results from instrument level and satellite level IPC testing will be presented. The trend of ATLID IPC test results is found stable along all test repetitions done until today. Additional presentation content can be accessed on the supplemental content page.

Thanks to a large set of available photocathodes with first in class QE, high gain, high collection efficiency, high dynamic range while keeping low dark count rate and single photon resolution capability with excellent timing, MCP-PMTs have emerged as candidates for LIDAR receivers. We present results of Ageing tests and Radiation tests carried out with Photonis and Airbus Defence & Space on High QE, and High linearity MCP-PMT for UV LIDAR receivers. Ageing of the photocathode is usually due to electron-induced ion feedback and molecule desorption from the MCP and anode, causing degradation of the photocathode layer leading to a progressive loss of QE related to the quantity of electron charges generated along lifetime. Expected Coulomb charges generated along a typical and worst-case mission were estimated from the atmosphere profiles. Thanks to a design change of the MCP-PMT and the implementation of Long-Lifetime MCP technology, ageing of the photocathode was drastically reduced. The new design showed no Quantum Efficiency nor Collection Efficiency degradation up to 20 C. Proton radiation tests were performed to evaluate false signal generated, end-of-life impact on performance, loss of transmission depending on the photocathode glass substrate as well as cathodoluminescence and photoluminescence at the photocathode. Quantum Efficiency, Collection Efficiency, PHD shape, Gain, and Linearity were found to be unchanged for fluences of 5x1011 p+/cm² with 60 MeV protons. Only small increase of DCR for about 120 cps/cm² was recorded about 8 weeks after the radiation.

The probe of HERA mission has a semi-autonomous navigation system that will perform fly-byes to the moon of the binary asteroid, called Didymos-B. The navigation is based on information given by the cameras and by the Planetary Altimeter (PALT). PALT is a Time-of-Flight (TOF) LIDAR that emits laser pulses of 2 ns, with 100 µJ of energy, at 1535 nm. PALT has a 70 mm Cassegrain telescope with an APD. PALT can take distance measurements from 500 m to 14 km with an accuracy of 0.5m. Aside from assisting navigation, the instrument will take scientific measurements that will contribute to the characterization of the asteroid topography. In this paper we present the Critical Design Review (CDR), which includes the optical, mechanical, and thermal designs, before manufacture. Regarding the optical system, the two mirrors are made of Zerodur, the secondary mirror is supported by a tripod structure made of carbon fibres, and the lenses are radiation resistant. The mechanical design has an innovative system that comprises a stainless-steel spring blades solution, which has the aim of protecting the optics bench plate and allows the survivability of the optics during launch. The thermal design solution was achieved by isolating the sub-systems with thermal washers and by implementing an optimized isostatic bipod mount structure in the primary mirror, making possible to reduce the stress on the optical component, while keeping the performance of the instrument. Additional presentation content can be accessed on the supplemental content page.

For crisis management and monitoring, a geostationary Earth observation telescope with large segmented aperture is investigated in JAXA. The preliminary study showed the feasibility of the aperture size of 3.6 m consisted with six primary mirror segments and the fundamental optical design. In order to obtain nearly diffraction limited performance with the optical system in the orbit, the aperture synthesis and wavefront error correction have to be conducted through precise alignment procedure, and therefore the system needs to equip several actuators and sensors dedicatedly designed for the purpose. We constructed the system design through the combination of structural-thermal analysis and optical consideration, and then planned the alignment procedure after launch. Those design concept are planned to be tested in the miniature testbed of segmented optical system under construction. We show the testing equipment and procedure for segment co-phasing and wavefront correction intending in space use.

For more than half of a century, Safran Reosc has been a key player in the development of optical components and equipment for space applications. From the Meteosat first generation and the SPOT 1 optics up to the most advanced enabling technology using silicon carbide off axis mirrors that are the key components of the Near Infrared Spectrometer, one of the instrument on board the recently launched James Webb Space Telescope, Safran Reosc has delivered optics for the most advanced scientific and earth observation satellites. This paper will highlight some of the recent developments in space optics and equipment: low CTE ceramics mirrors and silicon carbide free form mirrors and the SEEING instruments suite for nano-satellite earth observation and SSA applications. Ultra stable ceramics mirrors are still widely used for space mirrors application both for earth imaging applications and climate monitoring missions. The demands for extreme light-weighting mirrors are still further pushing the limits of glass machining technology and this trend is well illustrated by the primary mirror of the receiving channel of the MERLIN telescope, one of the most critical component of this mission devoted to the monitoring of the methane concentration in the Earth atmosphere. In the field of silicon carbide mirrors, Safran Reosc has delivered to Airbus Defence the highly aspheric freeform mirrors of the MICROCARB telescope to achieve unprecedented compactness. Safran Reosc has designed and developed the SEEING imagers, a family of 16U- 30U instruments for earth observation of meter class ground resolution. The first imager, the SEEING 130 a wide field of view instrument, will be delivered later this year to the Norwegian Research Defence Establishment and will be part of the NorSat-4 satellite.

ALTIUS is the next ESA limb-sounding mission for monitoring of stratospheric ozone at high vertical resolution and of NOx molecules and aerosols. With a platform based on the PROBA-NEXT concept flying in a Sun-Synchronous orbit, the data provided by the ALTIUS Mission will support the scientific community addressing key questions related to atmospheric chemistry composition and climate changes. The ALTIUS Instrument features wavelength-tuning capabilities in the UV (250-355nm), VIS (440-675 nm) and NIR (600-1020) bands using a Fabry-Perot interferometer (FPI) stack in the UV band and an Acousto-Optic Tunable Filter technologies (AOTF) in the VIS and NIR bands. This Instrument topology allows ALTIUS to perform 2D imaging with high resolution in the vertical profile of the Earth limb. The optical layout of 2D imagers, characterized by a more extensive field of view (FOV), makes them more susceptible to stray light issues in comparison to more conventional optical designs such as grating systems. These particular design aspects in combination with the use of novel technologies (FPI’s and AOTF’s) and the irradiance distribution of the observed bright limb scenes makes the stray light prediction very interesting and complex. An accurate modelling of scatter contributors involving optical and mechanical surfaces is, therefore, required. Due to the cost-effective model philosophy applied for the ALTIUS Instrument, no hardware model is available for stray light correlation purposes prior to the Instrument Proto-flight. Hence, a study was performed to benchmark the stray light analyses results obtained with Optic Studio with the ones obtained with FRED. This paper provides a description of the optical modelling features of the ALTIUS Instrument with specific attention to the novel optical devices, AOTF and FPI stack. It also addresses the particularities and differences observed when modelling the Instrument using two different commercial optical design suites. A comparison of scattered stray light computations for the ALTIUS Instrument ran in OpticStudio and FRED is also presented highlighting reflections on modelling approach and used mathematical models, with an outlook on consistency at L1. Finally, lessons learned from this exercise are presented along with the conclusions and plans for future work. Additional presentation content can be accessed on the supplemental content page.

This paper points out the lack of existing ground infrastructure that will be needed to communicate with the upcoming lunar missions. It discusses basic considerations about site locations and the pros and cons between Radio Frequency and laser-based communications. It also points out the challenges and risks that industry needs to consider for building this infrastructure. Finally, it recommends a hybrid solution for the future.

These last years have seen a raising interest for ground to GEO satellites optical very high throughput links, i.e. GEO-feeder links, or GEO-FL. However, despite their potential, these applications have to overcome atmospheric turbulence, which requires the development of mitigation techniques, such as adaptive optics (AO). In the case of GEO-FL, AO performance is limited by the Point-Ahead Angle (PAA) induced anisoplanatism. We describe here how our feedback on our field experiments helped us to design ONERA’s AO-compensated ground station, FEELINGS, and the status of said ground station in the fall of 2022.

In this paper we speak about the double-axicon unit built for the CaNaPy instrument, the LGS-AO backbone of the ESA ALASCA TRL6 facility, to demonstrate Optical Feeder Links for Satellite Communications in 2023 using Laser Guide Star Adaptive Optics technologies. The ALASCA system will co-propagate a guidestar laser (λ = 589 nm) and an infrared laser (λ = 1075 nm), using the monostatic approach through the entire 1-m Optical Ground Station (OGS) at Teide Observatory, Canary Islands (Spain). Provisions have been made to use either the full aperture or a section of the OGS primary mirror. The OGS telescope secondary mirror would introduce 30% central vignetting losses on the uplink laser beams. In order to minimise the losses, a double-axicon module shapes the gaussian beam as an annulus, thus optimises the laser profile to match the telescope pupil and nulls the losses, achieving the most efficient coupling to the OGS telescope. We present the CaNaPy axicon module design and analysis for the 589-nm laser as well as the ALASCA axicon module design for the OFL; we describe the tests done and the gain achieved in power transmission when shaping the laser compared to propagating a conventional Gaussian beam through a telescope with a non-negligible central obstruction.

For the next generation of very high throughput communication satellites, free-space optical (FSO) communication between ground stations and geostationary telecommunication satellites is a potential solution to overcome the limitations of RF links. To mitigate atmospheric turbulence effects, TNO proposes Adaptive Optics (AO) to apply uplink pre-correction. As a successor of Optics Feeder Link Adaptive Optics (OFELIA) breadboard [1], [2], the Terabit Optical Communication Adaptive Terminal (TOmCAT) project phase 2 aims to demonstrate the AO pre-correction technology for a terabit Optical Ground Station (OGT) in a ground-to-ground link field test over 10 km. Within this demonstrator an upgraded version of the OFELIA breadboard is used as optical bench for the AO (pre-)correction, but moreover the demonstrator enables the (future) integration of equipment for the final OGT configuration including the Beam Multiplexer (BMUX) and communication equipment. Apart from the OGT demonstrator, the overall layout of the field test has been upgraded, including the test site and the Ground Support Equipment (GSE), with the goal to create a better understanding of the encountered link phenomena and the instant (turbulence) conditions at which it was measured. New additions to the GSE are several weather stations placed along the link path to quantify the local turbulence and to relate the measured link performance to the instant turbulence conditions. The test campaign is split in two successive field tests: First the AO Demonstrator evaluates the upgraded AO pre-correction performance with a single non-modulated link, followed by the OGT Demonstrator which will include the multiplexing of multiple uplink channels and RF end-to-end modems to prove the technical feasibility of supporting a terabit communication link. This paper covers the design of the AO demonstrator and GSE, the field test layout and the preliminary results for the AO demonstrator field test. For the downlink correction the residual Wave Front Error (WFE) is presented. The pre-correction performance is depicted in the uplink transmission loss and scintillation, all as function of the encountered turbulence conditions.

The current paper introduces the Twin ANthropogenic Greenhouse Gas Observers (TANGO) instruments and mission. The purpose of TANGO is monitoring and quantifying greenhouse gas emissions, with a focus on characterizing emission sources down to the level of individual facilities. The TANGO mission was developed for the ESA-Scout program by a consortium consisting of ISISpace, TNO, SRON and KNMI. It consists of two agile CubeSat satellites that fly in tandem, with less than 1 minute between observations of the same target, each satellite equipped with a spectrometer of the TNO Spectrolite family of instruments that observes a different part of the spectrum. TANGO-Carbon measures emission of CH₄ and CO₂ in the SWIR1 spectral band. TANGO-Nitro measures emission of NO₂ in the visible spectral range. The Nitro instrument has a multifunctional role, using the NO₂ measurements to improve the detection of (anthropogenic) CO₂ plumes, deriving historic CO₂ emission trends based on available global NO₂ observations, and quantifying the possible CO₂ contribution in mixed CH₄-CO₂ sources. Each TANGO instrument fits in an 8U volume (on a 16U platform) and are all-aluminium, reflective pushbroom spectrometers covering a 30-km swath from a 500-km altitude, with a ground sampling distance of 300 m × 300 m. In this paper we will present the mission, the shared instrument concept, as well as the design and performance of both Carbon and Nitro instruments. Additional presentation content can be accessed on the supplemental content page.

METimage is a cross-purpose, medium resolution, multi-spectral optical imaging radiometer for meteorological applications on-board the MetOp-SG satellites. The fully representative instrument engineering model has been successfully tested and delivered to MetOp-SG. On METimage level this model served for instrument mechanical, thermal and EMC verification, at MetOp-SG level it supports the entire satellite test campaign. The instrument PFM integration is under finalisation by integrating the optical subsystems into the optical head. The preparation of the environmental test campaign and of the calibration and characterization campaign is ongoing.

The Infrared Atmospheric Sounding Interferometer New Generation (IASI-NG) is a key element of the second generation of EUMETSAT European Polar System (EPS SG) dedicated to operational meteorology, oceanography, atmospheric chemistry, and climate monitoring. A series of three IASI-NG instruments will be embarked on the second generation of European Meteorological Operational satellites (METOP SG) developed by ESA. CNES (Centre National d’ Etudes Spatiales) is in charge of IASI-NG overall system including the ground processing, the Technical Expertise Center and the Instrument, which is developed by Airbus Defence and Space. It will continue and improve the IASI mission in the next decades (2020-2040). The performance objective is mainly a spectral resolution and a radiometric error divided by two compared with the IASI first generation. The measurement technique is based on wide field Fourier Transform Spectrometer (operating in the 3.5 - 15.5 µm spectral range) using an innovative Mertz compensated interferometer to manage the so-called self-apodization effect and the associated spectral resolution degradation. We present here a synthesis of the development strategy, including the EM instrument campaign in parallel of the PFM, and the main milestones achieved on PFM instrument, which should be delivered for integration on Satellite in September 2022. In parallel, FM2 subsystems are under integration and first results on focal plane and interferometer should be available in third quarter of 2022. Additional presentation content can be accessed on the supplemental content page.

The detection and quantification of greenhouse gas (GHG) emissions, in particular carbon dioxide (CO2) and methane (CH4), is presently one of the main goals of remote sensing of atmospheric gasses on a global scale, for the strong impact these molecules have on climate change. Of particular urgency is the quantification of emissions from anthropogenic sources, a high-priority task addressed by the ESA Copernicus mission CO2M, which will provide global coverage detection of CO2 and CH4. The observation of CO2M, capable of quantifying emissions from the major sources, can be complemented by other observation systems addressing the smaller, and more numerous, sources. In this domain, static interferometers can offer several advantages. This paper reports on the main results of two activities completed within the ESA Future Missions activities in the Earth Observation Program, for the development of small instruments based on static interferometer designs, for the detection of CO2. The two studies, named Carbon-HIGS and Carbon-CGI, investigated two instruments operating in the SWIR and NIR bands, with a targeted precision of 2 ppm and an accuracy of 1 ppm for CO2 atmospheric concentration, covering a relatively small swath of 50 km at a spatial sampling better than 300 m. We summarize the general detection principles, the result of the design activities, and the estimated instrument performances. Both concepts are suitable candidates to work in conjunction with the Copernicus mission offering a zoom-mode observation, for quantification of medium-sized GHG sources and improved localization and understanding of anthropogenic emissions. Additional presentation content can be accessed on the supplemental content page.

A lot of investigations are ongoing for the development of laser systems with Alexandrite as active laser medium. These laser systems fulfill the general laser requirements for spaceborne Earth observation missions such as altimetry. However, to date, the laser systems and especially the coated Alexandrite crystals do not exceed Technology Readiness Level (TRL) 4. Therefore, the Horizon 2020 project GALACTIC was initiated to develop reproducible, fully European supplier-based functionally coated Alexandrite crystals, which show at least the same optical quality and laser performance in comparison to the components from the leading suppliers on the global market (mainly US and Chinese companies) and further fulfill the qualification to be generally used in space (i.e. verification of TRL 6). We present the high optical quality and good laser performance results of our developed Alexandrite crystals tested in a cavity-dumped Q-switched laser system. Furthermore, we show on the one hand the reproducibility and on the other hand the competitiveness of our crystals by a comparison study with our GALACTIC samples and crystals from two non-European suppliers. Additional presentation content can be accessed on the supplemental content page.

We report a lighter version of SuperCam laser for LIBS only operation. We investigate through CAD simulation the potential of an unsealed passively Q-switched Nd:YAG laser. We are able to reach a less than 100 g laser within 122 x 38 x 50 mm. Table top experiments are conducted. The final version leads to a 12.6 mJ, 4 ns laser with M² = 1.2.

Spaceborne precision frequency reference is one of the essential technologies for extensive applications in metrology, astronomy, remote sensing and global navigation satellite system, and we have researched and developed a high-precision microwave generation system which is based on an optical frequency reference. In our system, a highly-stable optical frequency is generated from an iodine-stabilized laser whose frequency is down-converted to the microwave region without degradation by using an optical frequency comb. The frequency stability of the iodine-stabilized laser would reach 10−15 level. In this conference, we will mainly present the development of the optical frequency comb. Nonlinear amplifying loop mirror (NALM)-type mode-locked fiber lasers have two kinds of configurations, figure-8 and figure-9. The figure-9 laser is widely used as an oscillator for the optical frequency comb due to its excellent low phase noise, and there are few reports of the figure-8 mode-locked fiber laser-based optical frequency comb. On the other hand, the operation of the figure-8 would be very stable against external perturbations because of its all polarization-maintaining fiber configurations. Therefore, we have developed low-phase-noise figure-8 lasers for our optical frequency comb because its robustness is suitable for the spaceborne system. One of the significant points of our figure-8 laser is that two types of erbium-doped fibers with different concentrations are used as the gain media of the oscillator. The repetition rate, the center wavelength and the width of the optical spectrum of our figure-8 laser are 51 MHz, 1560 nm and 58 nm, respectively. Though any NALM type mode-locked fiber laser needs initial impulse for starting mode-locking operation, our figure-8 laser can start mode-locking automatically without special procedure, which is called self-starting. We tried the operation test repeatedly for about 1600 times whose success rate reaches 99.94%. The disturbance tests and the thermal vacuum tests have been applied to our figure-8 laser, and under the conditions of both tests, our figure-8 laser shows the stable mode-locked operation without any break of mode-locking. In the radiation exposure test, we have confirmed the stable operation of our figure-8 laser till 30 krad radiation dose, and at higher radiation doses the mode-locking operation stopped.

A radiation tolerant Erbium fiber based optical frequency comb has been developed and environmentally tested. The system remained operable after an accumulated dose of 1 kGy^∗

. The underlying femtosecond fiber oscillator and Erbium fiber amplifiers have been manufactured from speciality doped fibers. The fiber optic system has been assembled and packaged using low outgassing components in a flight representative package before it was irradiated under active operation in two stages a 500 kGy. The accelerated ageing with dose rates of 10 mGy/s in water was tested using the calibrated Cobalt 60 source of the ESA-ESTEC facilities. The comb laser remained fully functional while the oscillator lost up to 30% of output power after the full exposure to the accumulated dose of 1 kGy. The fiber amplifiers lost 5-7% of output power.

BEaTriX (Beam Expander Testing X-ray facility) is the new facility available at the INAF-Osservatorio Astronomico Brera (Merate, Italy) for the calibration of X-ray optics. Specifically designed to measure the point spread function (PSF) and the effective area (EA) of the mirror modules (MM) of the ATHENA X-ray telescope at their production rate, BEaTriX gives the unique possibility to test the optics with a source that approximate an astronomical source, i.e. with a large, parallel X-ray beam (170 × 60 mm²) that fully covers the entrance pupil of the MM. For a fast and precise testing, BEaTriX is a compact facility (9 × 18 m²) with fast vacuum pump-down (to 10^-6 mbar), and an optical setup able to create the X-ray beam with a residual divergence of about 2-3 arcsec, HEW, and with a flux of 60 photons/s/cm². The first beam line at the energy of 4.51 keV is now operative, and a second beam line, working at the energy of 1.49 keV, will be implemented in the coming future. The unique characteristics of the BEaTriX X-ray beam are obtained with an X-ray microfocus source placed in the focus of a paraboloidal mirror, a monochromation stage with 4 symmetrically cut crystals, and an expansion stage where the beam is diffracted and expanded by an asymmetrically-cut crystal. The beam, reflected by the MMs, is then imaged at 12 m distance, where a directly-illuminated CCD camera is placed. This paper presents the facility, the calibration of the beam and the latest results with the ATHENA MMs.

MINERVA is an X-ray beamline designed to contribute to the development of the ATHENA^{1, 14} mission (Advanced Telescope for High Energy Astrophysics) at the ALBA synchrotron2 (Barcelona, Spain). Originally based on the monochromatic pencil beam XPBF 2.0 at the Physikalisch-Technische Bundesanstalt (PTB at BESSY II), MINERVA will be furnished with the necessary equipment to produce and characterize the mirror modules (MM) of ATHENA by adjusting and assembling 4 SPO stacks together (manufactured by cosine measurement systems) ^4,5. The construction of MINERVA is also an opportunity to bring some innovations in order to improve the characterization time of each MM produced⁶. Full interoperability with XPBF 2.0 is secured to allow operators to work on both beamlines the same way. The MINERVA project started in March 2020 and the last past months were dedicated to the definition, design, procurement, partial assembly and installation of the different beamline components. MINERVA is funded by the European Space Agency (ESA) and the Spanish Ministry of Science and Innovation and will be completed for operation at the turn 2022/2023.

At the PANTER X-ray test facility of the Max Planck Institute for Extraterrestrial Physics the testing of optics for ESAs ATHENA Mission is ongoing, as part of work towards the mission acceptance review. The ATHENA 2.6-m diameter mirror assembly comprises an aluminium support structure that holds the 600 Silicon Pore optic Modules (SPOs) that focus the X-rays coming from the sources in the universe. At PANTER, these lightweight SPO modules are being tested individually or mounted in a petal that represents a sixth of the mirror structure. MM-0051 is the last iteration of a single mid-radius SPO to be tested at PANTER. A detailed description of the MM-0051 measurements is presented here. The characterization of three ATHENA “row 8” SPO optics produced to be inserted into the test petals shows that they will provide the necessary precision on the localization of the PSF on the detector to allow the verification of the thermal models of different mirror structure designs by the primes Airbus Defense and Space and Thales Alenia Space. Currently the opto-thermo-mechanical tests are ongoing at PANTER

LEXI is a wide-field X-ray imager using bare-glass slumped micropore optics. The LEXI optic was recently characterized at PANTER to measure both the point spread function and the effective area as a function of energy. The effective area measurements were made with a continuum source in order to characterize the effective area curve at moderate energy resolution over the 0.2-4.0 keV range. Comparison of measurements with ray-tracing suggests a number of ways modeling can be improved in the future.

Quantum Key Distribution (QKD) is the most mature quantum technology, having achieved on-ground applications and commercially available products. In this domain, satellite platforms are essential to achieve a communication range reaching the intercontinental scale, acting thus as enablers for the future global quantum internet operation. This paper will report on the main results of the TNO-Eutelsat-TAS Italy project aiming to evaluate a novel hybrid approach for improved QKD performance particularly suited for geostationary orbits (GEO); the Dutch TKI HTSM sponsors the overall activity. We will present the results of lab-based tests of a novel QKD free-space approach that simultaneously implements the BBM92 protocol in both trusted and trust-free mode, following a joint Eutelsat-TNO patent. The trust-free mode between two ground receivers is the standard BBM92 protocol that uses entangled photons and there is no need for further security assumptions on the satellite payload. In trusted mode operation, one of the two entangled photons is measured directly on board. Key material is generated between ground and satellite. Security measures will be needed in the space segment, which therefore needs to be trusted. Further, we will present a demonstration roadmap aiming at free space field test to validate loss and key rate models for a free space link up to 2.5km in one of the arms. We also present a perspective on potential future GEO-based quantum applications beyond QKD. Additional presentation content can be accessed on the supplemental content page.

In the frame of the Secure And cryptoGrAphic (SAGA) project under ESA ARTES 4.0 program, we report the design and the test of a High-Performance Entangled Photon Source (HP-EPS) dedicated to QKD satellite-based communication, by using the Conventional-band optical fiber telecom components. We developed an asynchronous time binning higher than 10 bits/sec and 5 bits/sec for respectively a 60 dB (LEO) and a 65 dB (GEO) transmission loss budgets (both downlinks combined). The compactness and simplicity of the optical design, the low electrical consumption and the low mass combined with the robustness of the all-fibered design to the space environment (mechanical vibrations, shock, and radiations) make the HP-EPS a valuable and serious candidate for the satellite-based QKD quest.

In recent years, quantum key distribution (QKD) has seen the first proof-of-concept demonstrations from space. Next on the agenda towards a full-blown global quantum internet is to address the more practical aspects, such as efficiency, flexibility, and accessibility of QKD services. One of the main challenges that remains to be solved in this regard is to enable operation in the presence of daylight noise. Here, we present a complete framework for modelling daylight QKD from an orbiting satellite. We include the effects of atmospheric turbulence and adaptive optics correction at the receivers. We consider single- and multi-mode fibre coupling as a means of spatial filtering, for which we derived simple formulas for estimating coupling efficiencies of signal as well as noise. Using our framework, we identify the most critical system parameters for daylight operation and discuss the choice of signal wavelength and detection technology. Finally, we provide simulation results for various parameter combinations in a hypothetical daylight QKD between Berlin and Munich via a satellite in a low Earth orbit. The results show a clear advantage of 800 nm signal wavelength over 1550 nm with the currently available technology. Moreover, we show the relevance of single-mode fibre coupling and the importance of detectors with low timing jitters. We anticipate our work will provide valuable insight and tools to aid the future feasibility studies of daylight QKD in dual-downlink configurations. Additional presentation content can be accessed on the supplemental content page.

Quantum key distribution (QKD) enables tap-proof exchange of cryptographic keys guaranteed by the very laws of physics. One of the last remaining roadblocks on the way towards widespread deployment of QKD is the high loss experienced during terrestrial distribution of photons, which limits the distance between the communicating parties. A viable solution to this problem is to avoid the terrestrial distribution of photons via optical fibers altogether and instead transmit them via satellite links, where the loss is dominated by diffraction instead of absorption and scattering. First dedicated satellite missions have demonstrated the feasibility of this approach, albeit with relatively low secure key rates. In order for QKD to become commercially viable, the design of future satellite missions must be focused on achieving higher key rates at lower system costs. Current satellite missions are already operating at almost optimal system parameters, which leaves little room for enhancing the key rates with currently deployed technology. Instead, fundamentally new techniques are required to drastically reduce the costs per secret bit shared between two distant parties. Entanglement-based protocols provide the highest level of security and offer several pathways for increasing the key rate by exploiting the underlying quantum correlations. In this contribution, we review the most relevant advances in entanglement-based QKD which are implementable over free-space links and thus enable distribution of secure keys from orbit. The development of satellite missions is notoriously lengthy. Possible candidates for a new generation of quantum payloads should therefore be scrutinized as early as possible in order to advance the development of quantum technologies for space applications.

TRUTHS (Traceable Radiometry Underpinning Terrestrial – and Helio- Studies) is a hyperspectral climate mission which, with the support of an on board calibration system traceable to national standards, will enhance our understanding of the Earths changing radiation budget by an order of magnitude. The payload being developed by consortium led by Airbus UK includes three major subsystems: a hyperspectral imager capable of high resolution spatial and spectral lunar and earth measurements, a cryogenic radiometer with three high precision temperature controlled cavities traceable to national standards and a transfer systemto convert this calibration into one of diffused radiance for comparability with measurements made with the hyperspectral imager. The on board calibration system also includes a solar monochromator and a range of mechanisms and distribution optics to enable the calibration sequence and the required modes of the instrument. This paper will summarise the design concept for the on board calibration chain developed during the Phase A/B1 instrument studies carried out in 2020-2022. The presentation will discuss the main engineering challenges and tradeoffs and the outlook and development plan for the Phase B2CD programme will be presented.

The PROBA-3 double-spacecraft formation flying mission of the European Space Agency (ESA) has been presented in recent papers with details about the mission profile, the operation objectives, and the implemented technologies. PROBA-3 will fly the externally occulted coronagraph ASPIICS (Association of Spacecraft for Polarimetric and Imaging Investigation of the Corona of the Sun), with the telescope on one satellite and the occulter on the other one, at 144m. The scientific objective is to realize an artificial total solar eclipse to observe the lower Sun corona. The high accuracy metrology control is the core of the mission and several sub-systems will be verified and validated to realize the coronagraphic formation. Between these, the Shadow Position Sensors (SPS), composed of eight photo-multipliers mounted around the ASPIICS entrance pupil monitoring the solar penumbra symmetry, will return the 3D positioning of the formation with the highest accuracy. The SPS on-ground calibration was completed in 2021 and one of the main aspects of the test has been the implementation of an illumination scheme to simulate the same conditions the SPS will experience in flight. This was realized using a suite of LED sources properly assembled in a testbed used to reproduce the expected observation configurations. This testbed is supported by a dedicated software able to simulate the different illumination conditions and to drive the control of the LEDs in order to feed each SPS sensor with the proper light flux. In this paper, we review the SPS metrology system, the calibration testbed setup, and we discuss the interface control software, the simulation tool, and the data acquisition procedure adopted to calibrate the LED sources. Additional presentation content can be accessed on the supplemental content page.

Within the DLR project COMPASSO, optical clock and link technologies will be evaluated in space on the Bartolomeo platform attached to the Columbus module of the ISS. The system utilizes two iodine-based frequency references, a frequency comb, an optical laser communication and ranging terminal and a GNSS disciplined microwave reference. While COMPASSO is specifically dedicated to test optical technologies relevant for future satellite navigation (i.e. Galileo), the technologies are also crucial for future missions related to Earth observation and science. The optical frequency reference is based on modulation transfer spectroscopy (MTS) of molecular iodine near a wavelength of 532 nm. An extended cavity diode laser (ECDL) at a wavelength of 1064 nm is used as light source, together with fiber-optical components for beam preparation and manipulation. The laser light is frequency-doubled and sent to a mechanically and thermally highly stable free-beam spectroscopy board which includes a 20 cm long iodine cell in four-pass configuration. The iodine reference development is lead by the DLR-Institute of Quantum Technologies and includes further DLR institutes, space industry and research institutions. Phase B of the project will be finalized soon and an Engineering Model of the iodine reference, which represents the flight models in form, fit and function, will be realized by mid 2023. The launch of the COMPASSO payload is planned for 2025. Additional presentation content can be accessed on the supplemental content page.

The Meteosat Third Generation is the new generation of European operational geostationary meteorological system. The MTG series will comprise 4 imaging (MTG-I) and 2 sounding (MTG-S) satellites. The MTG-S sounding satellites, whose development is led by OHB System (Wessling, Germany), will carry 2 instruments: an Infrared Sounder (IRS) and an Ultraviolet Visible Near-Infrared spectrometer (UVN). The aim of IRS instrument is to provide detailed vertical profiles of atmospheric temperature and water vapor at a high spatial resolution of 4km. These data will be used in the future for numerical weather prediction and nowcasting. In the framework of this project, AMOS (Liège, Belgium), as a subcontractor of OHB, is the responsible for the design, manufacturing, integration, alignment and testing of the Geometrical and Spectral Test Assembly (GESTA) for the performance tests and calibration if the IRS under operational conditions. GESTA is an Optical Ground Support Equipment (OGSE) used for optical measurements during the alignment and test phases of the Infra-Red Sounder (IRS) instruments. The GESTA is composed of three different main subassemblies: The source Assembly (SA), designed by Bertin Technologies (Aix-en-Provence, France) is composed of a heated pattern plate mounted on an XY translation stage enabling to position it across the focal plane of the collimator. A Cold Black Body, operated at 90K, ensures the necessary contrast for the geometrical measurements. An Integrated Sphere is fed with MWIR and LWIR laser outputs, which are located outside of the vacuum chamber, and hence generates a uniform monochromatic output towards the collimator and ultimately the IRS. The Gas Cell, designed by Centre Spatial de Liège (CSL – Liège, Belgium), consists of a Hot Black Body, operated at high temperature (295K, 523K), as broad-band MWIR/LWIR light source and an atmospheric gas cell, operated at 293K with the possibility to fill it with up to 4 different gases in order to check the spectral and radiometric sensitivities of the IRS. The collimator, designed by AMOS, consists in a four mirror anastigmatic telescope with focal length of 2600 mm and an entrance pupil size of 320mm, operated at ambient temperature (293K). The collimator mirrors are made out of light-weighted aluminum structure with gold coating. The mirrors are mounted on a baseplate, which is of the same material and allows low stresses and deformations due to differential thermal dilatation. In view of its qualification, GESTA underwent an extensive testing campaign including thermal control performances, alignment stability and radiometric performances under operational conditions (i.e. same conditions as the ones encountered with the IRS instrument in front of GESTA). The results of the tests allow to demonstrate the compliance of the GESTA OGSE to the requirements. Additional presentation content can be accessed on the supplemental content page.

LiDAR remote sensing of the atmosphere requires a photons detection chain with a high sensitivity and a high dynamic range associated with a good temporal resolution. To meet these requirements, a specific CMOS read out circuit (ROIC) has been studied, design and realized at CEA/Leti within the frame of the H2020 project HOLDON. This ROIC is based on a CTIA amplifier with four different current/voltage conversion gain thanks to capacitance ranging from 10 fF to 10 pf. Other functionalities like on chip sampling, auto-reset or programmable low pass filtering have been implemented to optimize the detector for different measurement chain. Based on this circuit architecture, two versions of the ROIC with different way to connect the circuit to the photodiodes have been manufactured and tested. The first one is design to be directly hybridized to a small array of photodiodes with a format imposed by the ROIC design in term of pixel pitch and array size. For the second ROIC version, the photodiode array is hybridized to an interconnection circuit used as a fan-out of electrical connections to a bonding pad. This module is then wire-bonded to the ROIC to get the final detector assembly. This configuration allows us to couple the ROIC with different APD geometry adapted to a specific application need. The performances of one of the first hybridized devices were previously presented during ICSO 2020[1]. For this review, we focus on the second version of the ROIC. The tested detector module is made of an array of 76 HgCdTe APD in parallel with a pixel pitch of 15 µm. The array forms a 150 µm diameter macro-photodiode. The device was tested at 78K within a liquid nitrogen cooled cryostat. Under photon flux, we have obtained a linear response of the device with an incoming flux varying over more than six orders of magnitude without varying the APD gain. This wild dynamic is associated with a high sensitivity with a noise standing below the unique photon. The response to a brief laser pulse gives a rise time ranging from 175 ns for the highest CTIA gain to 6 ns for the lowest CTIA gain.

LYNRED (formerly Sofradir) is a global leader in designing and manufacturing high quality infrared technologies for aerospace, defense and commercial markets. Its vast portfolio of infrared detectors covers the entire electromagnetic spectrum from near to very far infrared, especially thanks to a well-mastered wavelength tunable MCT technology. Over the past 20 years, LYNRED has been involved in numerous space applications requiring SWIR detectors for Earth observation like atmosphere chemistry (such as TROPOMI instrument on-board Sentinel 5 precursor satellite) or hyperspectral imaging (such as PRISMA or HYSIS satellites). Most of these instruments used the well-known SATURN detector. These kind of missions are increasing and will keep growing in the near future in order to provide new measurement tools to control, measure and preserve our environment. Pulled by this trend, the need corresponding to short wavelength infrared detectors is evolving in order to match with these mission’s expectations. In particular, spatial and spectral resolutions of instruments are more demanding, resulting in requirements for larger detectors with better radiometric performances. In this paper, we introduce our new generation of SWIR detectors answering future Earth observation missions. In the first part, we will describe the key requirements to be considered when developing infrared sensors for such applications. We will then present our dedicated space product line based on the mature NGP detector (1024x1024, 15µm pixel pitch) that is currently in production and the new COBRA detector proposed in two versions (COBRA-L = 1840x1112 and COBRA-S = 1380x640, 20µm pixel pitch). Their state-of-the-art features and main performances will also be detailed. Finally, examples of passive and active detector packages well adapted to these IRFPAs will be proposed.

Within the framework of the ESA Copernicus Carbon Dioxide Monitoring (CO2M) mission, the Short-wave infrared (SWIR) Next-Generation Panchromatic (NGP) detector, designed and manufactured by Lynred, has been extensively characterized to assess its suitability for the mission. We present here the results of the remanence measurement tests, as well as the exploitation of the data, carried out on the detector, using a bench dedicated to the measurement of remanence. This characterization made it possible to identify three remanence effects, two are linked to the ROIC and one linked to the sensitive layer effect. We demonstrated that the ROIC effects, are, respectively, removed, by the use of a non-destructive reading for the first, and by a slight increase of the reset time for the second. The third effect, the LAG, has been characterized with a very high accuracy (better than two electrons). This characterization shows that the LAG is fully linear with the illumination magnitude. This allowed us to build a numerical correction model that has been tested on real data. Using real measurement data, the residuals after correction are assessed lower than 10 electrons. The purpose of this test campaign, and among others the results presented here, made it possible to demonstrate the feasibility of the CO2M mission using the NGP detector. This feasibility was difficult to obtain because the main instrument of the CO2M satellite, named CO2I, is very sensitive to remanence, especially when it is nonlinear with illumination magnitude. If the measurements and the design of the test bench were made by Thales Alenia Space, this work is part of a collaborative technical work between Thales Alenia Space, Lynred, and the European Space Agency.

Photodetectors for the non-visible region of the electromagnetic spectrum are vital for security, defense and space as well as industrial and scientific applications. The research activities at Fraunhofer IAF contribute to Europe’s non-dependence on critical components and support the European strategy for critical space technologies. A broad range of III-V material systems is developed to address the spectral region adjacent to the visible regime. For the ultraviolet (UV) spectral region, AlGaN is the material of choice with an adjustable bandgap between 3.4 and 6.0 eV, depending on the Al content, addressing the wavelength regime between 365 to 210 nm. The short-wavelength infrared (SWIR) region from 0.9 up to 3.0 µm is covered by two approaches: Lattice matched InGaAs absorber material on InP substrates for a cut-off wavelength at 1.7 µm and InGaAsSb lattice matched on GaSb substrates for 1.7 up to 3.0 µm. Through the choice of appropriate layer thickness, InAs/(In,Ga)(As,Sb) type-II superlattices (T2SLs) can be tailored to cover the wavelength range from mid- to long- up to very-long-wavelength infrared (MWIR, LWIR, VLWIR) in the spectrum of 3-15 µm.

Low reflectance, blinded HgCdTe pixels would allow the effects of drifts in the supply voltage and operating temperature to be accounted for when trying to resolve very faint objects. This paper describes the progress of an ESA / Leonardo contract in developing such a layer. The structure chosen offers significant levels of blocking for the masked pixels as well as minimal reflection to prevent optical cross-talk to neighbouring pixels.

Copernicus, the European Union’s programme for observing and monitoring the Earth, represents one of the most successful space programmes coordinated and managed by the European Commission in partnership with ESA, the Member States and Agencies. 2020 marked a major step of the Copernicus expansion programme with the selection of six missions to enter into B2CD implementation, namely CHIME, LSTM, CO2M, CRISTAL, ROSE-L, and CIMR. The CHIME mission (Copernicus Hyperspectral Imaging Mission for the Environment) space segment was awarded to an industrial consortium led by Thales Alenia Space (FR), as Mission Prime, and OHB (DE), as Instrument Prime. Within the instrument team, the responsibility of the design and development of the spectrometer system (SPS) have been assigned to AMOS (BE). The SPS is the centrepiece of the CHIME instrument, ensuring the accurate spectral dispersion of the imaged ground swath over wide focal planes. The SPS consists of three identical spectrometer units drawn from the compact de-magnifying freeform Offner optical solution developed at AMOS. Its throughput is guaranteed by a broadband convex diffraction grating, while the image quality and distortion control are enabled using freeform mirrors. This paper describes the mathematical modelling and prototyping activities, including manufacturing and testing of grating samples, carried by AMOS raising the maturity of the CHIME diffraction grating achieving Technology Readiness Level 6 (TRL6).

Holography represents a very elegant and versatile method for the manufacturing of high-performance diffraction gratings. This is particularly true within the frame of space applications, e.g., for utilization in customized, high end optical spectrometers. Holography enables both symmetrical (sinusoidal or binary) and blazed groove profiles on arbitrarily shaped substrates, ranging from plane over spherical to freeform surfaces. In addition, holographic recording of grating lines is not restricted to straight lines of constant density (either on a plane surface or on a plane projection plane above a curved substrate figure) but can rather be deterministically controlled to yield defined groove distortions and locally varying groove densities. Being able to control not only the groove density but also grooves local curvature represents a major advantage for the optical design of spectrometers, since it adds another degree of freedom to the design – enabling improved focusing and / or aberration correction features within the grating surface. In contrast to frequently encountered misbeliefs, it is shown that holography can also address very low groove density gratings with periods well above 10 µm (i.e. g < 100 lines/mm). Furthermore, two strategies are presented that allow for flattening a grating’s spectral diffraction efficiency (which is often of particular importance for gratings with low groove density): (1) multi-zone gratings with zone-wise varying blaze wavelength and (2) “kinked” groove profiles with more than just one effective blaze facet within the grating period.

In next generation space and ground-based instrumentation for Earth and Universe Observation, new instrument concepts include often non planar gratings. Their realization is complex and costly. We propose a new technology for designing and realizing convex blazed gratings for high throughput spectrographs. For this purpose, the requirements are driven by a Digital-Micromirror-Device-based (DMD) MOS instrument we are developing, called BATMAN. The two-arm instrument is providing in parallel imaging and spectroscopic capabilities. The objects/field selector is a 2048 x 1080 micromirrors DMD, placed at the focal plane of the telescope; it is used as a programmable multi-slit mask at the entrance of the spectrograph. The compact Offner-type spectrograph design contains a low density convex grating to disperse light. For optimization of the spectrograph efficiency, this convex grating must be blazed. A blazed reflective grating has been designed with a period of 3300 nm and a blaze angle of 5.04°, and fabricated into convex substrates with 225 mm radius of curvature and a footprint diameter of 63.5 mm. The blaze is optimized for the center wavelength of 580 nm within the spectral range of 400 – 800 nm. Such grating has been fabricated by using lithography, angular Ar ion etching, transfer of the blazed grating from a flat surface onto a convex substrate with a flexible stamp, etched into the substrate by RIE etching. and finally coated with a silver-based layer. With a final 7° blaze angle over the whole surface, efficiency close to 90% on the 1st diffraction order at 700nm has been obtained, measured on BATMAN spectroscopic arm. An optimized device with the exact required blaze angle would reach the same efficiency and be centered on the mid of 400-800nm wavelength band: its realization is on-going. The wavefront error of the diffracted beam will also be optimized. The grating brings a significant contribution in the total amount of straylight at instrument level. Their straylight level remains a critical issue, and its reduction by specific and controlled implementation of improvements in manufacturing process is a challenge to tackle. Straylight measurement has been done and shows a BRDF cosθ values of 10^-8 sr^-1 on the optical surface and 10^-7 sr^-1 on the structured features. This new type of non-planar reflective gratings will be the key component for future high throughput spectrographs in space missions

In this contribution we will present different methods for analyzing straylight measurements in spectrometer gratings. For this purpose two different but very common types of gratings are investigated: a binary high resolution littrow grating and a silicon-crystel echelle reflection grating. We will present several measurements and simulations on such gratings. The focus lies in particular on the difference between grating ghosts and homogeneous scattering background. It is worked out, that the homogenous background must be evaluated by the well-established concept of ”angle resolved scattering”. Though, it is advantegeous to use the concept of ”angle resolve efficiency” for ghost analysis. Further, a simulation method is presented that allows to calculate straylight in diffraction gratings. The method is applied for ghost and background analysis and it is shown that not only the particular type of disturbance but also the grating geometry itself affects the straylight level and distribution.

We address the applicability of quantum key distribution (QKD) with continuous-variable (CV) coherent and squeezed signal states of light over long-distance satellite-based links, considering low Earth orbits in the advantageous downlink scenario and taking into account strong varying channel attenuation (referred to as fading), atmospheric turbulence and finite data ensemble size effects. The study is motivated by the possibility to use highly efficient homodyne detection for CV protocols, which can serve as filter of background radiation due to matching of the quantum signal to a narrowband intense local oscillator beam. Considering feasible Gaussian modulation, compatible with the most advanced security proofs, we obtain tight security bounds on the untrusted excess noise at the channel output, which suggest that the protocols are very sensitive to the channel noise at the respective loss levels. In this regime, either a set-up stabilization resulting in drastic decrease of noise or relaxation of security assumptions to individual or passive collective attacks is required for implementation over the low Earth orbit satellites. Relaxation of security assumptions can be particularly motivated by the possibility of line-of-sight control of the absence of equipment capable of active collective eavesdropping attacks using quantum memories. Furthermore, splitting the satellite pass into discrete segments and extracting the keys from each rather than from the overall single pass allows one to effectively improve robustness against the untrusted channel noise and establish a secure key even under active collective attacks. Such satellite pass segmentation provides another viable option to reduce channel fading thus improving the secure key rate and allowing to establish the secure link with satellites at higher altitudes. We show that the use of signal squeezing can make the protocols more applicable in the satellite links, allowing for higher attenuation and levels of noise at the given security assumptions, and it has to be optimized in the collective attacks scenario. On the other hand, in the case of trusted noise assumption and at high repetition rates, squeezed-state CV QKD can tolerate attenuation levels up to 42 dB, allowing for higher orbit altitudes or smaller receiving telescope apertures. The obtained results are promising for satellite-based QKD, potentially applicable in daylight conditions.

The Atmospheric moNitoring to Assess the availability of Optical LInks through the Atmosphere (ANAtOLIA) is a station developed in the framework of a project funded by the European Space Agency which aims to ground-sites selection and assess their availabilities for optical links through the atmosphere. In addition to cloud cover, space-to-ground optical communications are limited by aerosols and atmospheric turbulence. Therefore, we are developing in the framework of the ANAtOLIA project, an innovative and efficiency instrumentation and studies to specify, accurately measure, analyze, characterize, and ultimately predict critical atmospheric parameters for the purposes of the selection of the Optical Ground Station (OGS) sites and the evaluation of their availability. The main objectives of ANAtOLIA project are to design, manufacture, procure and assembly a self-standing and autonomous ground support equipment, comprising cloud, aerosol and turbulence monitoring to deliver precise measurements of the atmosphere transmission. Then, to install and commission of these atmosphere monitors at selected ground locations in ESA member states or in their vicinity and to record continuously local cloud, aerosol information and atmospheric turbulence conditions for 24 months. The last objective is to correlate these local ground measurements with data available from other sources of atmospheric conditions. The main goal of these correlations is to improve knowledge of the optical link availability for selected OGS locations and to carry out a long-term validation of the optical link availability prediction methods. ANAtOLIA is a compact 24h mobile station consisting of the Generalized Monitor of Turbulence (GMT), the Reuniwatt Sky Insight camera and the Cimel photometer CE318-T.

In this study a feasibility analysis of a satellite-to-ground QKD link employing the Decoy-State BB84 protocol for both LEO and MEO satellite constellations is presented. Considering realistic atmospheric conditions and system assumptions, a comparison of the QKD performance between low and medium satellite orbits over an existing OGS network is reported.

JANUS (Jovis Amorum Ac Natorum Undique Scrutator) is a high-resolution camera operating in the spectral range 340-1080 nm and designed for the ESA space mission JUICE1 (Jupiter Icy moons Explorer) planned for launch in 2023 and arrival at Jupiter in 2031. The main scientific goal of the mission is the detailed investigation of Jupiter and its Galileian moons: after three years in Jupiter orbit and many fly-bys with the icy moons, JUICE will be the first spacecraft to be inserted in orbit around Ganymede in 2032. During the final stage of the mission, JANUS is expected to provide images of the moon surface with ground sampling up to 7.5 m/pixel in both panchromatic and narrow band spectral ranges. Leonardo Spa is the JANUS prime contractor and is in charge, on behalf of the Italian Space Agency (ASI) and in collaboration with the science team led by Parthenope University and the Italian Institute of Astrophysics (INAF), of developing and integrating the Opto-Mechanical Structure of JANUS Optical Head Unit (OHU). The present paper will discuss the procedure adopted for the integration of the OHU and the results in terms of optical quality of the system in flight conditions. Ensuring a Modulation Transfer Function (MTF) close to the diffraction limit at the Nyquist frequency of 71.4 cy/mm constitutes the main challenge for the telescope integration and sets the maximum acceptable transmitted wavefront error to be at most a few tens of nm over the whole field of view.

The EnVisS (Entire Visible Sky) instrument is one of the payloads of the European Space Agency Comet Interceptor mission. The aim of the mission is the study of a dynamically new comet, i.e. a comet that never travelled through the solar system, or an interstellar object, entering the inner solar system. As the mission three-spacecraft system passes through the comet coma, the EnVisS instrument maps the sky, as viewed from the interior of the comet tail, providing information on the dust properties and distribution. EnVisS is mounted on a spinning spacecraft and the full sky (i.e. 360°x180°) is entirely mapped thanks to a very wide field of view (180°x45°) optical design selected for the EnVisS camera. The paper presents the design of the EnVisS optical head. A fisheye optical layout has been selected because of the required wide field of view (180°x45°). This kind of layout has recently found several applications in Earth remote sensing (3MI instrument on MetOp SG) and in space exploration (SMEI instrument on Coriolis, MARCI on Mars reconnaissance orbiter). The EnVisS optical head provides a high resolved image to be coupled with a COTS detector featuring 2kx2k pixels with pitch 5.5µm. Chromatic aberration is corrected in the waveband 550-800nm, while the distortion has been controlled over the whole field of view to remain below 8% with respect to an Fθ mapping law. Since the camera will be switched on 24 hours before the comet closest encounter, the operative temperature will change during the approaching phase and crossing of the comet’s coma. In the paper, we discuss the solution adopted for reaching these challenging performances for a space-grade design, while at the same time respecting the demanding small allocated volume and mass for the optical and mechanical design. The view expressed herein can in no way be taken to reflect the official opinion of the European Space Agency.

METimage is an advanced multispectral radiometer for weather and climate forecasting developed by Airbus Defence & Space under the auspices of the German Space Administration (DLR) for the EUMETSAT Polar System-Second Generation (EPS-SG). The instrument is equipped with a continuously rotating scan mirror with a 1.7s period followed by a static telescope. The scan mirror permits an extended Earth view of 108° per revolution and regular views to on-board calibration sources. A derotator assembly, which is half-speed synchronised with the scanner, is inserted in the optical beam after the telescope to compensate the image rotation in the focal plane. The derotator optical arrangement is a five-mirror concept that minimises the polarisation sensitivity. The derotator design is constrained by optical performance, mass and compactness, which led to the selection of a full silicon carbide (SiC) concept. The stringent alignment requirements of the derotator optics lead to an excellent pointing accuracy, confirmed by the measurements performed with a dedicated OGSE. The measured wavefront error of the system is very small, thanks to fine polishing of the five optics. In this paper, we will present the overall design of the derotator, discuss the manufacturing of the key SiC elements and present the results of the FM1 test campaign.

Thermal and dynamic qualification loads on spacecraft are usually very high and the design of space components requires to use strong material to withstand them. However optical payloads usually mount brittle materials for optics and lenses. Two of them are the crystal CaF2 and the OHARA glass S-FPL51. Allowable design values for this kind of materials are hard to define, also considering that the numerical values for strength are low and the safety factor to use for design of brittle materials are really high. These two optical glass/crystal shall be used for three of the s ix lens es mounted on each one of the 26 Telescope Optical Units (TOU) of PLATO (PLAnetary Transits and Oscillation of stars), an ESA satellite that will be launched in 2026 to discover exoplanets. These brittle lenses, together with the mounts on which they are bonded, have been tested on a breadboards campaign checking their resistance to cryogenic temperatures (down to -115 °C), random loads up to failure and their behavior under shock loads. The results presented in this article show an unexpected and very high performance of each lens and its mount considering both thermal and dynamical behavior.

State-of-the-art semiconductor lasers can deliver average power, linewidth, and beam quality suitable for supporting differential absorption (DIAL) instruments that are competitive with fiber and solid-state lasers. An all-semiconductor transmitter architecture can enable a drastic reduction in size, weight, and power consumption (SWaP) of the instrument, while allowing for beneficial wavelength agility. Crucially, this reduction in SWaP can enable the implementation of compact airborne and spaceborne profiling DIAL instruments with high power output, while the broad spectral coverage of semiconductor laser technology allows the adaption and tuning of the transmitter design across a variety of operating scenarios. In this work, we present the first demonstration of volumetric ranging based on an all-semiconductor intensity-modulated CW (IMCW) transmitter. For this proof-of-concept demonstration, we used Rayleigh backscattering in optical fiber to emulate the atmospheric backscattering return echo. The range-resolved profile is reconstructed using matched filtering of the return echo, a technique widely adopted in CW radar. Finally, we present a theoretical analysis grounded in CW radar theory, showing excellent agreement with the results measured across a wide range of transmitted waveforms and return target configurations.

The Methane Remote Sensing LIDAR Mission (MERLIN) is a joint French-German cooperation on the development, launch and operation of a climate monitoring satellite, executed by the French Space Agency CNES and the German Space Agency DLR. It is focused on global measurements of the spatial and temporal gradients of atmospheric Methane (CH4) with a precision and accuracy sufficient to determine Methane fluxes significantly better than with the current observation network. Merlin is a LIDAR Instrument using the Integrated Path Differential Absorption (IPDA) principle. This instrument principle relies on the different absorption of the laser signal by atmospheric Methane at two laser wavelengths – online and offline – both around 1645 nm, reflected by the Earth surface. The attenuation is strong at the online wavelength; the offline “reference” wavelength is selected to be only marginally affected by Methane absorption. Being an active instrument with its own light source, the MERLIN LIDAR Instrument does not rely on sun illumination of the observed areas and therefore operates continuously over the orbit. Airbus DS GmbH was selected by DLR as the industrial Prime Contractor for the Mission Phase C/D to build the MERLIN Payload, which is the first realization of an IPDA LIDAR for space in Europe. This presentation will concentrate on the Architecture and the Design of the MERLIN Payload, which passed the CDR in 2020 and is now progressing in Phase D. Further details of the instrument development status will be shown by an overview of the current hardware and design status of the major subsystems. A spotlight of this paper will be a finding when performing a low-bandwidth spectral characterization of an Avalanche Photo Diode (APD), which revealed features which were not expected: Next to the known global spatial and spectral variations, the scans have shown an unexpected narrowband spectral dependence, as well as a spatial dependence, which was a factor of two worse than originally expected. Further tests also showed a thermal dependence of the QE related to the APD operating temperature, which strongly exceeded the expected variations. These unexpected effects would have led to a highly increased Radiometric Systematic Error (RSE) in the Differential Absorption Optical Depth (DAOD). The root-cause was identified as an Etalon effect caused by the APD substrate, which in addition varied over the APD due to slight changes in the layer thickness. The effect is strongly field angle dependent, which made a review of the scan setup necessary. Therefore, the setup was adapted via a stepwise increase of the field angle, which reduced the Etalon effect. Consequentially, the Etalon effect as root cause for these observations has been confirmed by experiments, as well as theoretical analysis, which was shown to be in line with the measurement results.

This paper presents a new concept of frequency comb LIDAR instrument for atmospheric CO₂ mapping. The French space agency (CNES) has initiated the development of an airborne proof of concept. The main originality of this instrument lies in the use of two probe combs crossing the same atmospheric path and used for self-phase correction. This technique, named Double Heterodyne Detection (DHD), allows us to coherently average interferograms beyond the coherence time of the laser source. The LIDAR airborne instrument is designed for real-conditions atmospheric CO₂ measurements at 1.572 μm and mainly relies on commercial telecom components. We present experimental results on a breadboard laboratory version of the instrument and our data processing method. Then, we extend the study to a space instrument and provide a first estimation of radiometric performances.

A highly efficient mirrorless OPO tunable in the mid-infrared around 2 μm has been developed and characterized in an original pumping configuration comprising a tunable high power hybrid Ytterbium laser MOPA (Master Oscillator Power Amplifier) in the nanosecond regime. The hybrid pump laser is based on a fiber laser seeder continuously tunable over several GHz at 1030 nm, which is shaped in the time domain with acousto-optic modulators (AOM), and power amplified in a dual stage Ytterbium doped fiber amplifiers, followed by two Yb:YAG bulk amplifiers. The pump delivers up to 3.5 mJ of energy within narrowband 15 ns pulses with a 5 kHz repetition rate. The output was focused into Periodically Poled KTP (PPKTP) crystals with a quasi-Phase Matching (QPM) period of 580 nm, producing Backward Optical Parametric Oscillation (BWOPO), with a forward signal wave at 1981 nm and a backward traveling idler at 2145 nm. We report significant optical to optical efficiencies exceeding 70 % depending on crystal length and input power. As theoretically expected, the forward wave could be continuously tuned over 10 GHz following the pump frequency sweep, while the backward wave remains almost stable, both being free from mode hops. These properties obtained from an optical arrangement without free-space cavities are attractive for future space Integrated Path Differential Absorption (IPDA) Lidar applications, which require robust and efficient tunable frequency converters in the mid-infrared. Additional presentation content can be accessed on the supplemental content page.

In the last few years the concept of an active space telescope has been greatly developed, to meet demanding requirements with a substantial reduction of tolerances, risks and costs. This is the frame of the LATT project (an ESA TRP) and its follow-up SPLATT (an INAF funded R&D project). Within the SPLATT activities, we outline a novel approach and investigate, both via simulations and in the optical laboratory, two main elements: an active segmented primary with contactless actuators and a pyramid wavefront sensor (PWFS) to drive the correction chain. The key point is the synergy between them: the sensitivity of the PWFS and the intrinsic stability of a contactless-actuated mirror segment. Voice-coil, contactless actuators are in facts a natural decoupling layer between the payload and the optical surface and can suppress the high frequency vibration as we verified in the lab. We subjected a 40 cm diameter prototype with 19 actuators to an externally injected vibration spectrum; we then measured optically the reduction of vibrations when the optical surface is floating controlled by the actuators, thus validating the concept at the first stage of the design. The PWFS, which is largely adopted on ground-based telescope, is a pupil-conjugated sensor and offers a user-selectable sampling and capture range, in order to match different use cases; it is also more sensitive than Shack-Hartmann sensor especially at the low-mid spatial scales. We run a set of numerical simulations with the PWFS measuring the misalignment and phase steps of a JWST-like primary mirrors: we investigated the PWFS sensitivity in the sub-nanometer regime in presence of photon and detector noise, and with guide star magnitudes in the range 8 to 14. In the paper we discuss the outcomes of the project and present a possible roadmap for further developments.

Most optical instruments for space applications in the areas of earth observation, science and optical communication require high performance optical mirrors. Driving requirements are typically low Surface Form Error (SFE), high structural stiffness over a wide temperature range, a low micro roughness and low mass. A promising material combination for optical mirrors is the usage of the aluminium alloy AlSi40 as mirror substrate and electroless Nickel phosphorous (NiP) as coating for the optical surface. The main advantage of this combination is the CTE compatibility of AlSi40 and NiP over a large temperature range. In addition, NiP coated surfaces can be easily diamond turned and polished. This material combination thus enables relatively fast production cycles even for a mirror surface roughness in the few-nm range. Within the ESA GSTP SME4ALM program, the feasibility to produce optical mirrors from AlSi40 by additive manufacturing (AM) was demonstrated. Main objectives were the determination of AlSi40 AM parameters and material properties as well as the demonstration of advantages of AM (e.g. topology optimization, monolithic design, lattice structures). By consequent improvement of the Laser Powder Bed Fusion (LPBF) manufacturing process, similar material properties to bulk AlSi40 were obtained. Up to 40% improvement were achieved for relevant material properties such as stiffness and SFE. Based on the good results of the first project, a follow up program was launched by ESA (also in the context of ESA-GSTP) with the objective to design and print an optical mirror with TRL ≥ 5. This paper will summarize the development program and results of the follow-up project, in particular: · Design and testing of lattice structures · Definition of a cleaning process · Transfer of AlSi40 processing strategies to industrial-scale machines · Design and testing of a mirror demonstrator, which is representative for space applications.

The current paper describes the optical and mechanical design of a compact Three-Mirror Anastigmate (TMA) telescope which is installed at the ISS as an earth observation demonstrator for the thermal-infrared spectral range. The TMA bases on a Korsch type design. It has a focal length of 150 mm and an aperture of F/3 and allows for a diffraction limited performance at the design wavelength of 10 μm. The ground resolution reaches 80 m from the ISS. The mechanical design fits into a design space of 80x80x150 mm³ which would correspond to 1.5 U of a typical CubeSat for the telescope or 3U for the whole instrument, respectively.

Since 1999, MERSEN BOOSTEC designs, manufactures and sells products made of sintered silicon carbide (SiC) mainly for space applications. Improvement of the state of surface of SiC substrates is essential to reduce scattering losses. In collaboration with CNES, a comparative study of microstructural, mechanical, and optical performances of different ceramic processes has been involved to optimized SiC substrates. Then, the comparative study has been extended to scattering losses in collaboration with the Institut FRESNEL which is expert in light scattering metrology. Comparative measurements on the developed substrates have been performed on Spectrally and Angularly resolved Light Scattering characterisation Apparatus (SALSA). This communication will present the results of this study which are already very promising for the development of the next generation SiC optics.

The CubeSat Laser Infrared CrosslinK (CLICK) mission is a technology demonstration of a low size, weight, and power (SWaP) crosslink optical communication terminal. The 3U CLICK-A spacecraft is the first phase of the mission with a 1.2U optical communication downlink terminal. The twin 3U CLICK-B/C spacecraft are the second phase of the mission each with a 1.5U crosslink optical communication transceiver terminal. This work discusses the flight functional and environmental testing for the CLICK-A terminal as well as the optomechanical design and testing for the CLICK-B/C terminals. The CLICK-A terminal serves as a risk reduction effort for the CLICK-B/C terminals, whose goal is to establish a 20 Mbps intersatellite link at separations from 25 to 580 km. The CLICK-B/C terminals communicate with M-ary pulse position modulation (PPM) using a 200 mW erbium-doped fiber amplifier (EDFA). The payloads are capable of ranging up to a precision of 50 cm. CLICK-B & C will both be deployed from the International Space Station (ISS) at the same time and fly in the same orbital plane. We begin by discussing the final integration and environmental testing results from the CLICK-A terminal, which was launched to the ISS in July 2022 and expected to be deployed in September 2022, as well as preparation of the CLICK optical ground station in Westford, MA. Second we present the CLICK-B/C flight terminal development. We describe the optomechanical design of the optical bench and its interface with the terminal. A prototype optical bench with the initial version of the CLICK-B/C optomechanical design has been built and tested. We also capture the lessons learned that have informed the building of an engineering development unit (EDU).

The CubeSat Laser Infrared Crosslink (CLICK) B/C mission seeks to demonstrate laser crosslinks for full-duplex communications and two-way ranging and time-transfer between two 3U CubeSats: CLICK-B and CLICK-C. Laser crosslinks between satellites can provide enhanced performance, with high data transfer rates and high precision range and timing information, using low size, weight, and power (SWaP) optical transceiver terminals. CLICK-B and CLICK-C will demonstrate laser crosslinks with data rates of at least 20 Mbps over separation distances ranging from 25 km to 580 km. CLICK-B/C will also demonstrate a ranging precision of better than 50 cm and a time transfer precision of better than 200 ps single shot over these distances. We present the design and development status and recent testing results of the laser transmitter and fine pointing, acquisition, and tracking (PAT) system, which are key to achieving these capabilities. The 1550 nm laser transmitter follows a master oscillator power amplifier (MOPA) design using an erbium-doped fiber amplifier (EDFA) for an average output power of 200 mW. A semiconductor optical amplifier (SOA) is used to achieve the pulse position modulation (PPM), ranging in order from 4 PPM - 128 PPM. The PAT system uses a microelectromechanical systems (MEMS)-based fast steering mirror (FSM) for fine pointing. A quadrant photodiode (quadcell) provides feedback for the actuation and steering of the FSM.

In the framework of the TELEO demonstration, a space optical instrument is being developed by a European consortium led by Airbus at Toulouse. This laser communications terminal will be placed on GEO orbit during the year 2023. Our flight laboratory will demonstrate new technologies (such as pointing mechanisms, optical amplifier, Infra-Red camera) and the associated concepts such as Pointing Acquisition and Tracking (PAT) strategy. The optical instrument is composed of a 26 cm telescope steered by a mechanism. The whole structure design ensures high performance of the optics thanks to a low distortion thermo-mechanical concept. A compact Focal Plane Assembly is accommodated under this telescope. It is used to manage with tremendously high rejection efficiency the high optical power Tx and the received beacon and Rx beams. Dedicated electronics also compose the terminal for highly stable thermal regulation, modes and PAT algorithms management, power distribution, mechanisms drivers, detector acquisition, laser sources and optical amplifiers. All the building blocks of the TELEO instrument are now being manufactured and their performances are being measured, before integration and final environment tests on the satellite. Additional presentation content can be accessed on the supplemental content page.

Quantum Key Distribution (QKD) is currently the only known technique that is able to guarantee information-theoretic secure communications. While many countries have already started developing use-cases based mostly on terrestrial links, the high losses that afflict fiber-basedchannels make them unsuitable for very-long-distance communications. Taking the quantum networks to a national and global scale thus requires the use of satellite-based quantum communications, as the attenuation experienced by photons in space communications is order of magnitudes lower than the one that characterizes terrestrial networks. Thales Alenia Space in Italy (TAS-I) is positioning itself as a key actor in the development of the technology needed to perform space quantum communications. In this work, we present an overview of the initiatives that are currently being carried out by TAS-I, and define a roadmap whose steps are planned to take the current laboratory experimentation towards the development of a fully operational QKD constellation meant to provide secret keys on a global scale. We also describe a possible implementation of an Italian demonstrator mission based on a LEO satellite that acts as a trusted node to distribute shared keys among a certain number of ground stations; we study the effects of some major system choices and assess the overall achievable performance in terms of Secret Key Volume (SKV).

MicroCarb is a space mission designed to monitor the CO2 fluxes at the earth surface in order to better understand exchanges between atmosphere, oceans and vegetation. The specificity of Microcarb is its capacity to measure very precisely the CO2 atmospheric concentration (better than 1ppm) using a microsatellite (180kg). The MicroCarb mission is developed by the French Space Agency CNES through a funding from French Research Agency ANR and with participations from European Union and UK Space Agency. The Microcarb payload is composed of a passive Short Wave InfraRed spectrometer and a visible imager. The innovative concept of the spectrometer allows to acquire 4 narrow bands (0.76μm, 1.27μm, 1.61μm, 2.04μm) on a same detector thanks to the use of an echelle grating and a split-pupil telescope. The performances required for the instrument are very stringent in terms of spectral resolution (R~25000), Instrument Spectral Response Function (ISRF) knowledge (<1%), radiometry and polarization’s sensitivity (~ 0.3%). To achieve such high performances, on ground and in flight spectrometer calibration is a key point for the success of the mission. The payload is developed by Airbus Defence and Space (ADS) France and the assembly phase is now almost complete. First performance results in ambient conditions were obtained with a calibration detector and were in line with the expected values. The instrument activities will continue with the mechanical qualification and Thermal VACuum (TVAC) tests during which all the instrument performances will be measured. Delivery of the instrument is scheduled today at autumn 2022 for further integration on platform. This paper will focus on the technical overview of the instrument and on its critical performances. Then we will present the calibration philosophy and the first tests results.

The Copernicus missions Sentinel-4 (S4) and Sentinel-5 (S5) will carry out atmospheric composition observations on an operational long-term basis to serve the needs of the Copernicus Atmosphere Monitoring Service (CAMS) and the Copernicus Climate Change Service (C3S). Building on the heritage from instruments such as GOME, SCIAMACHY, GOME-2, OMI and S5P, S4 is an imaging spectrometer instruments covering wide spectral bands in the ultraviolet and visible wavelength range (305-500nm) and near infrared wavelength range (750-775 nm). S4 will observe key air quality parameters with a pronounced temporal variability by measuring NO2, O3, SO2, HCHO, CHOCHO, and aerosols over Europe with an hourly revisit time. A series of two S4 instruments will be embarked on the geostationary Meteosat Third Generation-Sounder (MTG-S) satellites. S4 establishes the European component of a constellation of geostationary instruments with a strong air quality focus, together with the NASA mission TEMPO (to be launched end 2022) [9] and the Korean mission GEMS (launched 19 February 2020) [8]. This paper addresses the result of the final and crucial phase for the end to end performance of the PFM instrument: the extensive on-ground Characterization and Calibration of the instrument that is happening during the summer/fall 2022. The paper presents an overview of the calibration campaign objectives, the main performance verification and calibration measurements and preliminary performances of the PFM as-built instrument.

Thales Alenia Space has been selected to design and provide the payloads of the European Copernicus CO2M mission, whose main aim is to provide monitoring of the anthropogenic carbon dioxide emissions from space. Each payload is composed of : • The CO2 instrument, which is the instrument dedicated to measuring atmospheric CO2 and CH4. This dispersive instrument measures the spectral radiance in three bands (747-773, 1590-1675 and 1990-2095nm), used as inputs to the inverse models for determining total column concentrations for atmospheric CO2 and CH4. The instrument is designed for high spatial resolution, high spectral resolution, and high thermal and mechanical stabilities. • The CO2 instrument embeds an imaging spectrometer in the VIS 405-490nm band dedicated to measuring atmospheric NO2 content, permitting native nominal co-registration and optimized relative radiometric performances with the CO2 bands. This translates into an accurate tracing of anthropogenic CO2 plumes from power plants and cities while limiting the additional hardware and qualification procedures • This combined CO2 and NO2 instrument is the core of the payload, and two additional instruments of limited mass and volumes are embarked: a multi-angle polarimeter dedicated to aerosols measurement (MAP) to better account for cloud and aerosols scattering effects, and a cloud imager (CLIM) with high spatial resolution to accurately filter the data for cloud-contaminated samples. This article presents the payload design and development status.

CHIME, the Copernicus Hyperspectral Imaging Mission for the Environment, is one of six new missions that the EU and ESA are developing to expand the current suite of Copernicus Sentinels. The CHIME mission will provide systematic hyperspectral images to map changes in land cover and help sustainable agricultural practices. The contract for the development of two CHIME Satellites has been awarded in November 2020 to Thales Alenia Space France as Industrial Prime together with OHB Germany as Instrument Prime responsible for the novel Hyperspectral Imager (HSI). Compared to the two hyperspectral precursor missions, EnMAP (DLR) and PRISMA (ASI), CHIME will provide an enhancement allowing continuous and fully operational hyperspectral mapping of the Earth’s surface. The Hyperspectral Imager (HSI) on both satellites is a high-performance pushbroom imaging spectrometer type of instrument. Each instrument records ~130km of swath at 30m x 30m ground sampling. The spectral sampling interval is 10nm, covering a continuous spectral range from 400 nm to 2500 nm. A high performance Three Mirror Anastigmat (TMA) type telescope with wide-band coated optics collects the light reflected from ground and images it to three highly linear radiometric responsive and almost distortion-free spectrometers attaining very good spectral stability. All optical units are mounted to a torus-like carbon fiber (CFRP) optical bench structure providing the necessary line of sight stability. The electro-optical back end is based on passively cooled Teledyne CHROMA-D digital readout detectors creating robust margin in the predicted Signal-to-Noise performance. In flight, the HSI can be calibrated via on-board devices and using reference targets outside the spacecraft. We present the design of the instrument payload at the stage of the Preliminary Design Review (PDR) mid 2022. We show the predicted instrument performance and discuss several design aspect highlights, like the carbon-fiber torus optical bench and the novel spectral calibration unit based on a combination of diffused sun illumination and absorption glass filters.

NASA Goddard Space Flight Center (GSFC) is developing a master oscillator power amplifier (MOPA) laser transmitter for the Laser Interferometer Space Antenna (LISA) mission. The laser transmitter is one of the potential contributions to the LISA mission from NASA. Our development effort has included a master oscillator (MO), a power amplifier (PA), a frequency reference system (FRS), a power monitor detector (PMON), and laser electronics module (LEM). We are working on their design, performance evaluation, environmental testing, and reliability testing for space flight. We have built TRL 4 laser optical modules based on the MO and PA, which meets most performance requirements. One of the TRL 4 laser optical modules has been delivered to ESA for independent evaluation. TRL 6 versions of MO and PA are being built and evaluated at GSFC. TRL 5 and 6 versions of laser electronics are under development. In this paper, we will describe our progress to date and plans to demonstrate and deliver a TRL 6 laser demonstrator system to ESA by 2024.

The Laser Interferometer Space Antenna (LISA) is a partnership between the European Space Agency (ESA) and NASA to build a Gravitational Wave (GW) observatory. The observatory, which consists of a three-spacecraft constellation with a nominal separation of 2.5 million km between each spacecraft, provides a tool for scientists to directly detect gravitational waves generated from various astronomical phenomena in a waveband that is not accessible from Earth. NASA is developing laser transmitters as one of the potential US contributions to LISA. The NASA laser design leverages lessons learned from previous flight missions and included the latest technologies in photonics packaging and reliability engineering to ensure a laser lifetime of <16 years covering integration and test through a possible extended mission phase. As part of the laser development process, NASA’s Goddard Space Flight Center (GSFC) requested support from the NASA Engineering and Safety Center (NESC) to independently assess the Technology Readiness Level (TRL) of the LISA Laser System (LS). The independent assessment included the following tasks: (a) assess the design for weaknesses and suggest improvements to mitigate risks, (b) assess the laser reliability plan for weaknesses and suggest improvements to mitigate risks and improve effectiveness, and (c) assess the current redundancy plan on laser subsystems for weaknesses and suggest improvements to mitigate risks and improve effectiveness. The NESC team comprised of a team of subject matter experts (SMEs) and performed a 12-month review of every aspect of the laser design. We present the assessment findings and the current development progress of the LISA laser to meet the mission requirements with a delivery of a form, fit, and functional TRL6 laser to the LSIA mission by late 2023

We present the European development of an engineering model Laser Head for LISA. This single box includes a seed laser, an electro-optical phase modulator, a fiber amplifier and all PCBs to operate the Laser Head.

The Laser Interferometer Space Antenna (LISA), with its extreme distance measurement requirements (pm over arm lengths of 2.5 million km), imposes many stringent requirements on the laser sources used for the distance metrological measurements. In particular, meeting the frequency noise, power stability and side band phase noise requirements reliably for multiple laser systems over the mission lifetime presents a considerable technical challenge. These constraints demand a robust state-of-the-art laser design and a particular attention to reliability and procurement strategy, which all pose a significant challenge. Relying on its strong metrology expertise, CSEM, Swiss Center of Electronics and Microtechnology, is, in the frame of an ESA activity, upgrading all of the metrology techniques and hardware, used to characterize a previously developed non NPRO laser system for the LISA mission. These metrology systems are the baseline for assessing the performance of LISA mission laser heads, developed by NASA. Novel metrology techniques have been developed to assess the challenging laser head specifications. The measurement of frequency stability requires combining different frequency references to cover the full frequency range spanning over more than 10 decades. The measurement of power stability requires combining several metrology approaches to cover the full frequency range and dedicated development, in collaboration with NASA, to improve the long-term measurement capability. As already demonstrated in the previous CSEM activity, sideband phase noise measurement is very sensitive to the environment and complex to perform. A dedicated and improved test setup has been implemented. After a presentation of the NASA laser head, dedicated testing philosophy approaches, encountered technical challenges and obtained test results are presented.

The Follow-up telescope (FXT) is one of the instruments on board for the Einstein Probe mission, a dedicated mission to the study of the time-domain high-energy astrophysics due to launch end of 2023. The full calibration tests were carried out at the PANTER X-ray test facility, of the Max-Planck Institute for extraterrestrial Physics in Germany, to validate the performance of the fully flight-compatible optics, both the Qualification Model (QM) and the Flight Model (FM). The eROSITA Wolter-I-type telescope, consisting of 54 X-ray mirror shells was characterised in terms of the angular resolution and effective area. The effective areas were measured using the “Glucksrad” that allows quasi-parallel beam measurements to simulate the in-orbit scenario. The TRoPIC and PIXI detectors were used to take the exposures. A silicon drift detector mounted sidelong in the tube, out of the optic’s field of view, was installed to monitor the X-ray beam simultaneously. The QM telescope experienced a slight degradation of the half energy width (HEW) at Al-K energy (1.49 keV) during the thermal cycle test while the FM satisfied the requirements. Both modules satisfied the effective area requirement at this standard energy. In this work, we discuss the full calibration tests at different energies for the Einstein Probe FXT - QM and FM. The measured HEW, effective area, vignetting, and final focal length at PANTER will be summarized.

The Microchannel X-ray Telescope (MXT) for the Space-based multi-band astronomical Variable Objects Monitor (SVOM), a Franco-Chinese mission (CNES/CNSA), is designed for the soft X-ray range (0.2-10 KeV) to observe gamma-ray bursts (GRBs) from the beginning to the afterglow emission. In the past years, the PANTER test facility has been testing the different MXT optics models. Each optic is made up of an array of 5 x 5 Micro Pore Optic (MPO) plates. We characterized the performance of the SVOM optic at different phases: Bread-Board (BB), Qualification Model (QM), Flight Model (FM), and Flight Spare (FS) for the optic followed by the Performance Model (PM) and Flight Model (FM) for the complete telescope fully integrated with the optic, detector, radiator and electronics. For the FM end-to-end test, in October 2021, the goal was to determine the half-energy width (HEW) on-axis and off-axis, and to characterize the flight telescope's energy-dependent efficiency (effective area) under different thermal loads, i.e. different detector and optics temperatures. The final numbers will be presented in a paper in preparation. This paper provides the overview of various activities: setup, metrology and measurement, carried out at the PANTER facility during the development of the SVOM-MXT towards the end-to-end test.

The BEaTriX (Beam Expander Testing X-ray) facility, now operational at INAF-Brera Astronomical Observatory, will represent a cornerstone in the acceptance roadmap of Silicon Pore Optics (SPO) mirror modules, and will so contribute to the final angular resolution of the ATHENA X-ray telescope. By expansion and collimation of a microfocus X-ray source via a paraboloidal mirror, a monochromation stage, and an asymmetric crystal, BEaTriX enables the full-aperture illumination of an SPO mirror module with a parallel, monochromatic, and broad (140 mm ´ 60 mm) X-ray beam. The beam then propagates in a 12 m vacuum range to image the point spread function of the mirror module, directly on a focal plane camera. Currently the 4.51 keV beamline, based on silicon crystals, is operational in BEaTriX. A second beamline at 1.49 keV, which requires a separate paraboloidal mirror and organic crystals (ADP) for beam expansion, is being realized. As for monochromators, the current design is based on asymmetric quartz crystals. In this paper, we show the current optical design of the 1.49 keV beamline and the optical simulations carried out to predict the achievable performances in terms of beam collimation, intensity, and uniformity. In the next future, the simulation activity will allow us to determine manufacturing and alignment tolerances for the optical components. Additional presentation content can be accessed on the supplemental content page.

Wide-field X-ray Telescope (WXT) is a survey instrument of Einstein Probe, a small-class mission dedicated to time-domain high-energy astrophysics to discover transients and monitor variable objects in the 0.5–4.0 keV X-rays. We aim to characterize the performance of Qualification Model (QM) of the Einstein Probe Wide-field X-ray Telescope (WXT) – to determine the half-energy width (HEW) on-axis and off-axis, and the energy-dependent efficiency. The WXT optics assembly, consisting of 36 Micro Pore Optic (MPO) chips divided into four 3x3 MPO sectors which focus onto separate detectors. The full characterization consists of the focus searches, focal plane mapping and effective area measurements at different energies: C-K, Cu-L, Ti-K, very low Energy band continuum (vlEbc), and low Energy band continuum (lEbc). Measurements were made using the TRoPIC detector (pnCCD), a prototype of the eROSITA camera. The focal plane mapping results show an expected slight degradation towards the furthest off-axis angles as well the known alignment imperfections of some of the MPOs. The effective area results of the Energy band continuum match well with the theoretical model. This work describes the X-ray testing of the WXT QM3 Qualification Model at the PANTER X-ray test facility of the Max-Planck Institute for extraterrestrial Physics in Germany. The test setup, measurements and results are presented.

The Transportable Adaptive Optical Ground Station, which was located at Tenerife (Spain) from 2014 until 2019 was shipped for a refurbishment and several enhancements to Switzerland. Following the refurbishment, a measurement campaign at the Swiss Optical Ground Station and Geodynamics Observatory Zimmerwald (Switzerland) was performed, in July/August 2021. The optical counter terminal for the experiments was the TDP1-LCT at the geostationary Alphasat satellite. In the seven weeks of the campaign, measurements for optical uplink communication at a rural site in Europe at an altitude of 900 meters to a GEO spacecraft were gathered. We give an overview of the improvements of the T-AOGS and the actual status after the refurbishment. We present the results of the link activities, e.g. the uplink budget (ground to space) and the dynamic of the atmosphere (scintillations index, number of fades, fade duration).

There are a number of parametric challenges in designing transmit optical amplifiers for the current deployment of optical communication constellations. Constellations are often aligned to channel wavelengths defined by the Space Development Agency (SDA) Tranche 1 Optical Communications Terminal Standard, which requires duplex operation at 1536.61 and 1553.33nm. We present an experimental characterisation supported by numerical modelling, of duplex operation up to 10W at both channel wavelengths and discuss performance limits. The characterisation includes power, out-of-channel amplified spontaneous emission (ASE) content and in-channel ASE content / noise figure determined from time-domain extinction measurements. For an output power of 10W, stimulated Brillouin scattering (SBS) can readily limit the delivery of optical power over relatively short fiber lengths. We also present the growth of a Stokes wave as a function of output power, delivery fiber length and fiber type experimentally. These results showing good agreement with theory, and set design limits on peak power transmission. These peak power considerations being of particular interest for pulse position modulation (PPM) encoding which are required in both the SDA and Consultative Committee for Space Data Systems (CCSDS) 142.0-B-1 standards. The CCSDS and SDA standards both require a sinusoid amplitude modulated tracking tone. We present the limits of the design space of achievable modulation depth, as function of amplifier design, modulation condition and operating wavelength & power. A good agreement between experimental and numerical results is found.

Cost of in-orbit capacity is an important element to take into account when ordering new satellites in order to remain competitive with terrestrial-based solutions. This can be achieved by minimizing the size, weight, and power consumption (SWaP), volume, reducing spacecraft AIT, etc. Properties of photonics components makes them a natural candidate while designing future generation Satcom payloads. Photonic components offer the advantage of minimizing the SWaP of satellite communication payload and are capable of offering a limitless bandwidth in THz range at around 1550 nm wavelength. Light weight and low volume photonic components offer almost lossless propagation in an optical fibre within a spacecraft and immunity to Electromagnetic Interference (EMI). With the advancement of photonic technology, it is now possible to develop Tbps-like software defined photonic payload of high data rates and frequencies with almost lossless propagation in an optical fibre. However, at present in the satcom industry only a few demonstrations of photonic devices in non-critical equipment with limited degree of integration can be found. This paper presents a space-based photo-digital communication payload called PhLEXSAT and shows how the advantages offered by photonics can be utilized in increasing the capacity of Very High Throughput Satellites (VHTS) while reducing the cost at the same time. PhLEXSAT is a Ka/Q/V/W band communication system that will use novel optical devices for space-based systems, these are currently under design and development stage. The architecture incorporates advanced broadband photonic ADC and photonic DAC with digital processing firmware with a high degree of miniaturization and power-consumption efficiency. This design will be suitable for future Terabit per second satellites. PhLEXSAT project is focusing on the advancement of these key photonic technologies to develop a photo-digital channelizer for flexible HTS. PhLEXSAT project, funded under the European Union H2020 programme, is led by DAS Photonics in cooperation with MDA UK, Eutelsat, Axenic, HHI Fraunhofer and Argotech. Additional presentation content can be accessed on the supplemental content page.