This PDF file contains the front matter associated with SPIE Proceedings Volume 12689, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

The four NASA TROPICS Earth Venture (EVI-3) CubeSat constellation satellites were successfully launched into orbit on May 7 and May 25, 2023. TROPICS will provide nearly all-weather observations of 3-D temperature and humidity, as well as cloud ice and precipitation horizontal structure, at high temporal resolution to conduct high-value science investigations of tropical cyclones. TROPICS will provide rapid-refresh microwave measurements (median refresh rate of approximately 60 minutes for the baseline mission) over the tropics that can be used to observe the thermodynamics of the troposphere and precipitation structure for storm systems at the mesoscale and synoptic scale over the entire storm lifecycle. The TROPICS constellation mission comprises four 3U CubeSats (5.4 kg each) in two low-Earth orbital planes inclined at approximately 33 degrees with a 550-km altitude. Each CubeSat comprises a Blue Canyon Technologies bus and a high-performance radiometer payload to provide temperature profiles using seven channels near the 118.75 GHz oxygen absorption line, water vapor profiles using three channels near the 183 GHz water vapor absorption line, imagery in a single channel near 90 GHz for precipitation measurements (when combined with higher resolution water vapor channels), and a single channel at 205 GHz that is more sensitive to precipitation-sized ice particles. TROPICS spatial resolution and measurement sensitivity is comparable with current state-of-the-art observing platforms. Data is downlinked to the ground via the KSAT-Lite ground network with latencies better than one hour. NASA's Earth System Science Pathfinder (ESSP) Program Office approved the separate TROPICS Pathfinder mission, which launched on June 30, 2021, in advance of the TROPICS constellation mission as a technology demonstration and risk reduction effort. The TROPICS Pathfinder mission continues to yield excellent data over 24+ months of operation and has provided an opportunity to checkout and optimize all mission elements prior to the primary constellation mission. This paper describes the on-orbit results for the successful TROPICS Pathfinder precursor mission and the newly-commissioned TROPICS constellation mission.

RainCube (Radar in a CubeSat) and TEMPEST-D (Temporal Experiment for Storms and Tropical Systems - Demonstration) demonstrated in 2018 that deployment of active and passive microwave sensors to monitor storms and precipitation from space is possible on platforms as small as 6U CubeSats. Despite their implementation as high-risk technology demonstrations, with very low budgets compared to their predecessors, they both survived more than two years in orbit (well beyond their commitments). These demonstrations opened the gates to satisfy several long-standing unmet needs by the scientific and operational weather and climate communities. Among them is the need to observe the evolution of the vertical structure of convective storms in the Tropics at the temporal scales relevant to convective processes (i.e., tens of seconds to few minutes) in order to advance our understanding of convective processes and the environmental conditions behind them via modeling and analysis. The INCUS (Investigation of Convective Updrafts) mission concept aims at addressing this need by deploying 3 small satellites each carrying an augmented version of the RainCube radar. One of the 3 small satellites also includes a millimeter wave radiometer inherited from TEMPEST-D. In this presentation we present the status of the INCUS project at the end of Phase A.

Spatial heterodyne spectroscopy has become increasingly attractive for remote sensing of the atmosphere from microsatellites. Its outstanding light gathering power makes this technology particularly suitable for the detection of faint signals with minimal volume requirements. This paper is about an instrument, which was designed to measure the spectral shape of an atmospheric oxygen emission. The near infrared emission is observed in limb viewing geometry from space. The optical setup and specific characteristics of the design are presented. A focus is on the straylight behaviour of the system. In-field and out-of-field contributions are discussed. Straylight kernels are applied to expected background radiation fields with regard to performance-limiting factors of the system.

Hyperspectral infrared sounders measure the profiles of temperature and water vapor in the atmosphere and the concentration of trace gas species. Instruments such as NASA Atmospheric Infrared Sounder (AIRS) on the Aqua spacecraft have proven their value for weather and climate research, atmospheric composition research, and high impact to the operational forecast at NWP centers worldwide. Reducing the size, weight and power of these instruments is key to enabling more rapid revisit when deployed in Low Earth Orbit (LEO), enabling new measurements such as 3D Atmospheric Motion Vector (AMV) winds, and reducing the cost of these instrument for future deployment in LEO, Geostationary Earth Orbit (GEO) and aircraft platforms. NASA and NOAA have sponsored technology maturation at JPL of the CubeSat Infrared Atmospheric Sounder (CIRAS) to demonstrate the use of wide field grating spectrometer optics and large format FPA technologies included in CIRAS for infrared sounding. These include a 2D format High Operating Temperature-Barrier Infrared Detector (HOT-BIRD), a silicon Immersion Grating, and Black Silicon for the CIRAS entrance slit and blackbody. Thermal Vacuum (TVac) performance testing of CIRAS has been completed achieving TRL 5 for a full scale brassboard of the instrument. Testing included spatial, spectral, and radiometric response of the instrument including measurements of the transmission in a gas cell. Results show excellent performance from the system with the exception of a high background flux from the Integrated Dewar Cryocooler Assembly (IDCA). The IDCA is not planned for flight use and projections of the performance in the flight configuration are discussed. Through this testing the instrument has reached TRL 5. Recently, the NASA Earth Science Technology Office (ESTO) awarded JPL a contract to fly the CIRAS in an aircraft, called the Pyro-atmosphere Infrared Sounder (PIRS), to measure the convective environment around wildfires.

We present the design of the objective lens for the DRAGO-2 optical system, a compact SWIR camera designed for the space environment. DRAGO-2 is the long-focal variant of the DRAGO (Demonstrator of Remote Analysis of Ground Observations) series, developed for the ALISIO-1 mission of the IACTEC-Space team at the Instituto de Astrofísica de Canarias (IAC). The objective lens has a refractive design covering the two bands in the SWIR range (1.1 and 1.6 μm) which is passively athermalized for operation between -20 °C and 40 °C, with a focal length of 150 mm and a focal length variation over the whole temperature range of under 0.2%. The system has an f/# of 4.5, both transmission and relative illumination above 90%, and low distortion under 0.05%. The optical quality is excellent, with an as-built modulation transfer function (MTF) value at 30 cy/mm over 55% on axis and over 40% at the edge of the 6.2 mm diagonal image field to ensure pixel-limited performance. Straylight and finite-element analysis ensure optimal optical performance as well as survival to the environment. Several units of the objective lens have been manufactured with special attention to environmental requirements in terms of both assembly processes and material selection, and their optical performance has been found to be in excellent compliance with the projected as-built optical quality.

Small satellites are performing more demanding tasks than ever, from navigation to precision time transfer and high-speed communications. Until now, terrestrial products have been sufficient for all except high-speed communication applications over orbital distances. An experimental system has been made that utilizes technology in high-speed communication systems and applies it to relative navigation systems while greatly reducing cost from complexity. The primary areas of interest for these improvements are in the laser transmitters, fiber amplifiers, precision timing systems, low-jitter optical receivers, and beam steering capabilities. Using shorter, highly doped fiber amplifiers both reduces nonlinearities in amplification and decreases the spooling complexity for small packages. Bi-directionally pumping an erbium-doped fiber amplifier (EDFA) enables increased amplification while imparting less jitter onto the optical signal.1 This layout enables the usage of low power diode lasers and achieves pulse energies greater than 1 mJ. These lasers can emit optical pulse widths of 100 ps or greater, with picosecond level timing knowledge due to the usage of gallium nitride field-effect transistors (GaN FETs). The amplified output beam is steered with a sub-micro radian precision fine steering mirror. Avalanche photodiodes (APDs) with under 60 ps timing jitter are used to detect the optical pulses as they are transmitted and received from over 100 km ranges, with the filtered and amplified outputs passing into an analog demultiplexer. This signal is then sent to either a high-speed analog-to-digital converter or to a time-to-digital converter referenced to a chip scale atomic clock for precision timing.

Our understanding of the origin, movement, and storage of water on the Moon remains largely unconstrained. Measurements of water absorption features over the same swaths as a function of time of day from a nearly polar orbit, the science goal proposed for the BIRCHES (Broadband InfraRed Compact High-resolution Exploration Spectrometer) payload designed and built for the Lunar Ice Cube orbiter, was intended to provide such essential constraints. BIRCHES was a compact version of OVIRS (Origins Spectral Interpretation Resource Identification Security Regolith Explorer Visible InfraRed Spectrometer) plus a compact cryocooler. IR spectrometer capabilities have been greatly advanced, since its selection in 2015 for the NASA NEXT STEP program, in terms of sensitivity, spectral coverage, and less active cooling demand as exemplified by the NASA GSFC Compact Thermal Imager (CTI), which utilizes a Type II SLS (Strained Super Lattice) combined with the ACADIA processor, follow on to the OVIRS SIDECAR (System Image, Digitizing, Enhancing, Controlling, And Retrieving) ASIC. Although initially developed for astronomical applications, the CTI has, with the addition of a cryocooler, already been modified for lunar surface applications. The ‘Next generation’ orbital mission and surface package concepts discussed here would utilize advanced versions of BIRCHES, of comparable mass, power and volume but with superior performance, and would likely be significantly more robust and ‘roomy’, due to availability of high-performance thermal protection components and a larger 12U platform. A compact textual camera and internal calibration source would thus be added.

A CubeSat polarimeter for the earth’s oxygen 135.6 nm ionospheric emission, which can be used to measure electron density, has been developed and calibrated. The 135.6 nm spin-forbidden line when viewed from orbit is optically thin, undergoes minimal resonance scattering events, and is expected to be polarized. The polarimeter optical system fits within a CubeSat 1U module and employs a planar mirror at the Brewster angle that functions as the polarization analyzer and a concave reflection grating. The grating focuses the 135.6 nm and nearby spectrum onto a linear array of silicon photodiodes and disperses longer wavelengths away from the detector thereby providing 10⁵ rejection of visible light. The rejection factor is increased to 10¹⁰ by application of narrowband AR coatings to the mirror, grating, and detector. A single optical channel measures the signals in the S and P polarizations as the CubeSat spins. The polarization of the oxygen 130.5 nm allowed line, which is optically thick and unpolarized owing to multiple resonance scatterings, is also measured and serves as a null polarization measurement that monitors the polarimeter on-orbit functionality and polarization calibration. Signal levels are calculated for 135.6 nm polarization in the range from 0.446, the polarization expected from one resonance scattering event, down to no polarization that could potentially result from multiple scatterings in some atmospheric regions. The prototype polarimeter has been calibrated in the grating’s first diffraction order using 275 nm to 405 nm sources, and signal levels are calculated in the second order for typical 135.6 nm and 130.5 nm ionospheric emissions.

The Tiny Remote-sensing Instrument for Thermospheric Oxygen and Nitrogen (TRITON) is being developed by the U.S. Naval Research Laboratory (NRL) for detection of neutral components of the daytime thermosphere. TRITON measures naturally occurring, far ultraviolet (FUV) emissions of the upper atmosphere that are produced as a result of solar excitation. The sensor concept is based primarily on multiple sensors previously developed at NRL with recent spaceflight heritage. The legacy optics have been under evaluation and development for extension to new emission targets and brighter ambient environments. Recent TRITON development work has included characterization of a new photomultiplier tube and comparison to performance of a previously used model. In addition, several bandpass filters are evaluated for their effectiveness in providing the out-of-band rejection needed to isolate the FUV and MUV emissions of interest. The primary optical layout of TRITON sensors will be described to highlight the components that have been changed or adapted for use in the new configuration. The results of recent lab tests will also be shown to demonstrate the expected performance of TRITON relative to prior, legacy components and subsystems.

The NOAA Space Weather Follow On (SWFO) Program supports NOAA's goal of reducing the impact of severe space weather events, which responds to the 2020 Promoting Research and Observations of Space Weather to Improve the Forecasting of Tomorrow Act. The SWFO Program will ensure continuity of space weather operational Solar Wind and Coronal Mass Ejection (CME) data to its operational users. The SWFO Program includes a SWFO-L1 observatory which will host a Solar Wind Plasma Sensor, a Magnetometer, a SupraThermal Ion Sensor, and a Compact Coronagraph. The SWFO Program will take rideshare with NASA’s IMAP mission scheduled for FY 2025.