We report contrast measurements of a sodium resonance guide star against the daylight sky when observed through a tuned magneto-optical filter (MOF). The guide star was created by projection of a laser beam at 589.16 nm into the mesospheric sodium layer and the observations were made with a collocated 1.5-m telescope. While MOFs are used with sodium light detecting and ranging systems during the day to improve the signal-to-noise ratio of the measurements, they have not so far been employed with laser guide stars to drive adaptive optics (AO) systems to correct atmospherically induced image blur. We interpret our results in terms of the performance of AO systems for astronomy, with particular emphasis on thermal infrared observations at the next generation of extremely large telescopes now being built.

This PDF file contains the editorial “Special Section Guest Editorial: Future large-aperture ultraviolet/optical/infrared space observatory” for JATIS Vol. 2 Issue 04

This PDF file contains the editorial “Special Section Guest Editorial: In Memoriam, Richard G. (Rick) Lyon” for JATIS Vol. 2 Issue 04

NASA is currently carrying out science and technical studies to identify its next astronomy flagship mission, slated to begin development in the 2020s. It has become clear that a Large Ultraviolet/Optical/IR (LUVOIR) surveyor mission (d_primary≈12  m, Δλ≈1000  Å, 2  μm spectroscopic bandpass) can carry out the largest number of NASA’s exoplanet and astrophysics science goals over the coming decades. The science grasp of an LUVOIR surveyor is broad, ranging from the direct detection of potential biomarkers on rocky planets to the flow of matter into and out of galaxies and the history of star-formation across cosmic time. There are technical challenges for several aspects of the LUVOIR surveyor concept, including component level technology readiness maturation and science instrument concepts for a broadly capable ultraviolet spectrograph. We present the scientific motivation for, and a preliminary design of, a multiplexed ultraviolet spectrograph to support both the exoplanet and astrophysics goals of the LUVOIR surveyor mission concept, the combined high-resolution and imaging spectrograph for the LUVOIR surveyor (CHISL). CHISL includes a high-resolution (R≈120,000; 1000 to 1700 Å) point-source spectroscopy channel and a medium-resolution (R≥14,000 from 1000 to 2000 Å in a single observation and R∼24,000 to 35,000 in multiple grating settings) imaging spectroscopy channel. CHISL addresses topics ranging from characterizing the composition and structure of planet-forming disks to the feedback of matter between galaxies and the intergalactic medium. We present the CHISL concept, a small sample of representative science cases, and the primary technological hurdles. Technical challenges include high-efficiency ultraviolet coatings and high-quantum efficiency, large-format, photon counting detectors. We are actively engaged in laboratory and flight characterization efforts for all of these enabling technologies as components on sounding rocket payloads under development at the University of Colorado. We describe two payloads that are designed to be pathfinder instruments for the high-resolution (CHESS) and imaging spectroscopy (SISTINE) arms of CHISL. We are carrying out this instrument design, characterization, and flight-testing today to support the new start of an LUVOIR surveyor mission in the next decade.

The design and scale of a future mission to directly image and characterize potentially Earth-like planets will be impacted, to some degree, by the expected yield of such planets. Recent efforts to increase the estimated yields, by creating observation plans optimized for the detection and characterization of Earth-twins, have focused solely on coronagraphic instruments; starshade-based missions could benefit from a similar analysis. Here we explore how to prioritize observations for a starshade given the limiting resources of both fuel and time, present analytic expressions to estimate fuel use, and provide efficient numerical techniques for maximizing the yield of starshades. We implemented these techniques to create an approximate design reference mission code for starshades and used this code to investigate how exoEarth candidate yield responds to changes in mission, instrument, and astrophysical parameters for missions with a single starshade. We find that a starshade mission operates most efficiently somewhere between the fuel- and exposuretime-limited regimes and, as a result, is less sensitive to photometric noise sources as well as parameters controlling the photon collection rate in comparison to a coronagraph. We produced optimistic yield curves for starshades, assuming our optimized observation plans are schedulable and future starshades are not thrust-limited. Given these yield curves, detecting and characterizing several dozen exoEarth candidates requires either multiple starshades or an η_Earth≳0.3.

ATLAST is a particular realization of the Large Ultraviolet Optical Infrared telescope (LUVOIR), a ∼10-m diameter space telescope being defined for consideration in the 2020 Decadal Review of astronomy and astrophysics. ATLAST/LUVOIR is generally thought of as an ambient temperature (∼300  K) system, and little consideration has been given to using it at infrared wavelengths longward of ∼2  μm. We assess the scientific and technical benefits of operating such a telescope further into the infrared, with particular emphasis on the study of exoplanets, which is a major science theme for ATLAST/LUVOIR. For the study of exoplanet atmospheres, the capability to work at least out to 5.0  μm is highly desirable. Such an extension of the long wavelength limit of ATLAST would greatly increase its capabilities for studies of exoplanet atmospheres and provide powerful capabilities for the study of a wide range of astrophysical questions. We present a concept for a fiber-fed grating spectrometer, which would enable R=200 spectroscopy on ATLAST with minimal impact on the other focal planet instruments. We conclude that it is technically feasible and highly desirable scientifically to extend the wavelength range of ATLAST to at least 5  μm.

Metallic aluminum mirrors remain the best choice for high reflectance applications at ultraviolet wavelengths (90 to 320 nm) and maintain good performance through optical and infrared wavelengths. Transparent protective coatings are required to prevent the formation of an oxide layer, which severely degrades reflectance at wavelengths below 250 nm. We report on the development of atomic layer deposition (ALD) processes for thin protective films of aluminum fluoride that are viable for application at substrate temperatures <200°C. Reflectance measurements of aluminum films evaporated in ultrahigh vacuum conditions, and protected mirrors encapsulated with ALD AlF₃ are used to evaluate the far ultraviolet (90 to 190 nm) and near ultraviolet (190 to 320 nm) performance of both the ALD material and the underlying metal. Optical modeling is used to predict the performance of optimized structures for future astronomical mirror applications.

An architecture and conceptual design for a robotically assembled, modular space telescope (RAMST) that enables extremely large space telescopes to be conceived is presented. The distinguishing features of the RAMST architecture compared with prior concepts include the use of a modular deployable structure, a general-purpose robot, and advanced metrology, with the option of formation flying. To demonstrate the feasibility of the robotic assembly concept, we present a reference design using the RAMST architecture for a formation flying 100-m telescope that is assembled in Earth orbit and operated at the Sun–Earth Lagrange Point 2.

It is generally recognized (e.g., in the National Aeronautics and Space Administration response to recent congressional appropriations) that future space observatories must be serviceable, even if they are orbiting in deep space (e.g., around the Sun–Earth libration point, SEL2). On the basis of this legislation, we believe that budgetary considerations throughout the foreseeable future will require that large, long-lived astrophysics missions must be designed as evolvable semipermanent observatories that will be serviced using an operational, in-space infrastructure. We believe that the development of this infrastructure will include the design and development of a small to mid-sized servicing vehicle (MiniServ) as a key element of an affordable infrastructure for in-space assembly and servicing of future space vehicles. This can be accomplished by the adaptation of technology developed over the past half-century into a vehicle approximately the size of the ascent stage of the Apollo Lunar Module to provide some of the servicing capabilities that will be needed by very large telescopes located in deep space in the near future (2020s and 2030s). We specifically address the need for a detailed study of these servicing requirements and the current proposals for using presently available technologies to provide the appropriate infrastructure.

The Advanced Technology Large Aperture Space Telescope (ATLAST) team identified five key technology areas to enable candidate architectures for a future large-aperture ultraviolet/optical/infrared (LUVOIR) space observatory envisioned by the NASA Astrophysics 30-year roadmap, “Enduring Quests, Daring Visions.” The science goals of ATLAST address a broad range of astrophysical questions from early galaxy and star formation to the processes that contributed to the formation of life on Earth, combining general astrophysics with direct-imaging and spectroscopy of habitable exoplanets. The key technology areas are internal coronagraphs, starshades (or external occulters), ultra-stable large-aperture telescope systems, detectors, and mirror coatings. For each technology area, we define best estimates of required capabilities, current state-of-the-art performance, and current technology readiness level (TRL), thus identifying the current technology gap. We also report on current, planned, or recommended efforts to develop each technology to TRL 5.

Our recently completed study for the Advanced Technology Large-Aperture Space Telescope (ATLAST) was the culmination of three years of initially internally funded work that built upon earlier engineering designs, science objectives, and technology priorities. Beginning in the mid-1980s, multiple teams of astronomers, technologists, and engineers developed concepts for a large-aperture UV/optical/IR space observatory intended to follow the Hubble Space Telescope (HST). Here, we summarize since the first significant conferences on major post-HST ultraviolet, optical, and infrared (UVOIR) observatories the history of designs, scientific goals, key technology recommendations, and community workshops. Although the sophistication of science goals and the engineering designs both advanced over the past three decades, we note the remarkable constancy of major characteristics of large post-HST UVOIR concepts. As it has been a priority goal for NASA and science communities for a half-century, and has driven much of the technology priorities for major space observatories, we include the long history of concepts for searching for Earth-like worlds. We conclude with a capsule summary of our ATLAST reference designs developed by four partnering institutions over the past three years, which was initiated in 2013 to prepare for the 2020 National Academies’ Decadal Survey.

Over the past few years, we have developed a concept for an evolvable space telescope (EST) that is assembled on orbit in three stages, growing from a 4×12-m telescope in Stage 1, to a 12-m filled aperture in Stage 2, and then to a 20-m filled aperture in Stage 3. Stage 1 is launched as a fully functional telescope and begins gathering science data immediately after checkout on orbit. This observatory is then periodically augmented in space with additional mirror segments, structures, and newer instruments to evolve the telescope over the years to a 20-m space telescope. We discuss the EST architecture, the motivation for this approach, and the benefits it provides over current approaches to building and maintaining large space observatories.

Direct spectroscopic biosignature characterization (hereafter “biosignature characterization”) will be a major focus for future space observatories equipped with coronagraphs or starshades. Our aim in this article is to provide an introduction to potential detector and cooling technologies for biosignature characterization. We begin by reviewing the needs. These include nearly noiseless photon detection at flux levels as low as <0.001  photons s⁻¹ pixel⁻¹ in the visible and near-infrared. We then discuss potential areas for further testing and/or development to meet these needs using noncryogenic detectors (electron multiplying charge coupled devices, HgCdTe array, HgCdTe APD array), and cryogenic single-photon detectors (microwave kinetic inductance device arrays and transition-edge sensor microcalorimeter arrays). Noncryogenic detectors are compatible with the passive cooling that is strongly preferred by coronagraphic missions but would add nonnegligible noise. Cryogenic detectors would require active cooling, but in return, deliver nearly quantum-limited performance. Based on the flight dynamics of past NASA missions, we discuss reasonable vibration expectations for a large UV-Optical-IR space telescope (LUVOIR) and preliminary cooling concepts that could potentially fit into a vibration budget without being the largest element. We believe that a cooler that meets the stringent vibration needs of a LUVOIR is also likely to meet those of a starshade-based Habitable Exoplanet Imaging Mission.

Large space telescope missions have always been limited by their launch vehicle’s mass and volume capacities. The Hubble Space Telescope was specifically designed to fit inside the Space Shuttle and the James Webb Space Telescope was specifically designed to fit inside an Ariane 5. Astrophysicists desire even larger space telescopes. NASA’s “Enduring Quests Daring Visions” report calls for an 8- to 16-m Large UV-Optical-IR (LUVOIR) Surveyor mission to enable ultrahigh-contrast spectroscopy and coronagraphy. Association of Universities for Research in Astronomy’s “From Cosmic Birth to Living Earth” report calls for a 12-m class High-Definition Space Telescope to pursue transformational scientific discoveries. NASA’s “Planning for the 2020 Decadal Survey” calls for a Habitable Exoplanet Imaging (HabEx) and an LUVOIR as well as Far-IR and an X-ray Surveyor missions. Packaging larger space telescopes into existing launch vehicles is a significant engineering complexity challenge that drives cost and risk. NASA’s planned Space Launch System (SLS), with its 8- or 10-m diameter fairings and ability to deliver 35 to 45 mt of payload to Sun-Earth-Lagrange-2, mitigates this challenge by fundamentally changing the design paradigm for large space telescopes. This paper introduces the mass and volume capacities of the planned SLS, provides a simple mass allocation recipe for designing large space telescope missions to this capacity, and gives three specific mission concept implementation examples: a 4-m monolithic off-axis telescope, an 8-m monolithic on-axis telescope, and a 12-m segmented on-axis telescope.

Our joint NASA GSFC/JPL/MSFC and STScI study team has used community-developed science goals to derive mission needs, design parameters, notional instruments, and candidate mission architectures for a future large-aperture, noncryogenic UVOIR space observatory. We describe the feasibility assessment of system dynamic stability that supports coronagraphy. The observatory is in a Sun–Earth L2 orbit, which provides a stable thermal environment and excellent field of regard. Reference designs include a 36-segment 9.2-m aperture telescope that stows within a 5-m diameter launch vehicle fairing. This paper presents results from the latest cycle of integrated modeling through January 2016. The latest findings support the feasibility of secondary mirror support struts with a thickness on the order of an inch. Thin struts were found not to have a significant negative effect on wavefront error stability. Struts with a width as small as 1 in. may benefit some coronagraph designs by allowing more optical throughput.

The solutions to a number of astrophysical problems require access to the ultraviolet, optical, and infrared from space-based facilities, with capabilities beyond those available with Hubble Space Telescope or James Webb Space Telescope. A large ultraviolet-optical-infrared telescope will need to have a large collecting area and milliarcsecond angular resolution capabilities plus highly efficient instruments, providing a revolutionary enhancement in capability. During 2013, the European astronomical community was involved in an exercise to outline the big science that could be achieved with such a facility; the proposal was called EUVO (as per European Ultraviolet-Visible Observatory). Inspired by that work, we describe a proposal on future science and instrumentation to be carried out with a 10-m class telescope.

The international x-ray observatory ASTRO-H was renamed “Hitomi” after launch. It covers a wide energy range from a few hundred eV to 600 keV. It is equipped with two soft x-ray telescopes (SXTs: SXT-I and SXT-S) for imaging the soft x-ray sky up to ∼12  keV, which focus an image onto the respective focal-plane detectors: CCD camera (SXI) and a calorimeter (SXS). The SXTs are fabricated in a quadrant unit. The angular resolution in half-power diameter (HPD) of each quadrant of the SXTs ranges between 1.1 and 1.4 arc min at 4.51 keV. It was also found that one quadrant has an energy dependence on the HPD. We examine the angular resolution with “spot scan” measurements. In order to understand the cause of imaging capability deterioration and to reflect it to the future telescope development, we carried out spot scan measurements, in which we illuminate all over the aperture of each quadrant with a square beam 8 mm on a side. Based on the scan results, we made “maps” of image blurring and a focus position. The former and the latter reflect figure error and positioning error, respectively, of the foils that are within the incident 8  mm×8  mm beam. As a result, we estimated those errors in a quadrant to be ∼0.9 to 1.0 and ∼0.6 to 0.9 arc min, respectively. We found that the larger the positioning error in a quadrant is, the larger its HPD is. The HPD map, which manifests the local image blurring, is very similar from quadrant to quadrant, but the map of the focus position is different from location to location in each telescope. It is also found that the difference in local performance causes energy dependence of the HPD.

Physikalisch-Technische Bundesanstalt (PTB) has more than 20 years of experience in the calibration of space-based instruments using synchrotron radiation to cover the ultraviolet (UV), vacuum UV (VUV), and x-ray spectral range. Over the past decades, PTB has performed calibrations for numerous space missions within scientific collaborations and has become an important partner for activities in this field. New instrumentation at the electron storage ring, metrology light source, creates additional calibration possibilities within this framework. A new facility for the calibration of radiation transfer source standards with a considerably extended spectral range has been put into operation. The commissioning of a large vacuum vessel that can accommodate entire space instruments opens up new prospects. Finally, an existing VUV transfer calibration source was upgraded to increase the spectral range coverage to a band from 15 to 350 nm.

High-resolution broadband spectroscopy at near-infrared (NIR) wavelengths (950 to 2450 nm) has been performed using externally dispersed interferometry (EDI) at the Hale telescope at Mt. Palomar, with the TEDI interferometer mounted within the central hole of the 200-in. primary mirror in series with the comounted TripleSpec NIR echelle spectrograph. These are the first multidelay EDI demonstrations on starlight. We demonstrated very high (10×) resolution boost and dramatic (20× or more) robustness to point spread function wavelength drifts in the native spectrograph. Data analysis, results, and instrument noise are described in a companion paper (part 1). This part 2 describes theoretical photon limited and readout noise limited behaviors, using simulated spectra and instrument model with noise added at the detector. We show that a single interferometer delay can be used to reduce the high frequency noise at the original resolution (1× boost case), and that except for delays much smaller than the native response peak half width, the fringing and nonfringing noises act uncorrelated and add in quadrature. This is due to the frequency shifting of the noise due to the heterodyning effect. We find a sum rule for the noise variance for multiple delays. The multiple delay EDI using a Gaussian distribution of exposure times has noise-to-signal ratio for photon-limited noise similar to a classical spectrograph with reduced slitwidth and reduced flux, proportional to the square root of resolution boost achieved, but without the focal spot limitation and pixel spacing Nyquist limitations. At low boost (∼1×) EDI has ∼1.4× smaller noise than conventional, and at >10× boost, EDI has ∼1.4× larger noise than conventional. Readout noise is minimized by the use of three or four steps instead of 10 of TEDI. Net noise grows as step phases change from symmetrical arrangement with wavenumber across the band. For three (or four) steps, we calculate a multiplicative bandwidth of 1.8:1 (2.3:1), sufficient to handle the visible band (400 to 700 nm, 1.8:1) and most of TripleSpec (2.6:1).

We present a preliminary design for a neutron detection system that is compact, lightweight, and low power consuming, utilizing the CubeSat platform making it suitable for space-based applications. This is made possible using the scintillating crystal lithium indium diselenide (⁶LilnSe₂), the first crystal to include ⁶Li in the crystalline structure, and a silicon avalanche photodiode. The schematics of this instrument are presented as well as the response of the instrument to initial testing under alpha radiation. A principal aim of this work is to demonstrate the feasibility of such a neutron detection system within a CubeSat platform. The entire end-to-end system presented here is 10×10×15  cm³, weighs 670 g, and requires 5 V direct current at 3 W.

The focal plane of the X-Ray Integral Field Unit (X-IFU) instrument of the Advanced Telescope for High-Energy Astrophysics observatory is composed of 3840 microcalorimeters. These sensors, based on superconducting transition edge sensors (TES), are read out through a frequency multiplexer. A “base-band feedback” suppresses all the carriers of the multiplexed signal in the superconducting quantum interference devices input coil (cryogenic readout). However, the loop gain of this feedback is too small (less than 10 in the present baseline of the phase A mission) to strongly compensate the readout gain drifts. An onboard x-ray source is considered to calibrate the gain of the full instrument. However, in-flight calibration time must be minimized, which leads to a requirement on the gain stability larger than 10−4 over a long duration (between each calibration) to reach the challenging energy resolution goal of 2.5 eV at 6 keV of the X-IFU. A significant part of this gain is provided by a low-noise amplifier in the warm front-end electronics (WFEE). To reach such gain stability over more than a dozen minutes, this noncooled amplifier has to cope with the temperature and supply voltage variations. Moreover, mainly for noise reasons, a common large loop gain with feedback cannot be used. We propose a new amplifier topology using diodes as loads of a differential amplifier to provide a fixed voltage gain, independent of the temperature and of the bias fluctuations. This amplifier is designed using 350-nm SiGe BiCMOS technology and is part of an integrated circuit developed for the WFEE. Our simulations provide the expected gain and noise performances. Comparison with standard resistive loaded differential pair clearly shows the advantages of the proposed amplifier topology with a gain drift decreased by more than an order of magnitude. Performances of this diode loaded amplifier are discussed in the context of the X-IFU requirements.

We describe the development and implementation of a light-weight, fully autonomous 2-axis pointing and stabilization system designed for balloon-borne astronomical payloads. The system is developed using off-the-shelf components such as Arduino Uno controller, HMC 5883L magnetometer, MPU-9150 inertial measurement unit, and iWave GPS receiver unit. It is a compact and rugged system which can also be used to take images/video in a moving vehicle or in real photography. The system performance is evaluated from the ground, as well as in conditions simulated to imitate the actual flight by using a tethered launch.

In preparation of future multiobject spectrographs (MOS) whose one of the major role is to provide an extensive statistical studies of high redshifted galaxies surveyed, the demonstrator CANARY has been designed to tackle technical challenges related to open-loop adaptive optics (AO) control with jointed Natural Guide Star and Laser Guide Star tomography. We have developed a point spread function (PSF) reconstruction algorithm dedicated to multiobject adaptive optics systems using system telemetry to estimate the PSF potentially anywhere in the observed field, a prerequisite to postprocess AO-corrected observations in integral field spectroscopy. We show how to handle off-axis data to estimate the PSF using atmospheric tomography and compare it to a classical approach that uses on-axis residual phase from a truth sensor observing a natural bright source. We have reconstructed over 450 on-sky CANARY PSFs and we get bias/1-σ standard-deviation (std) of 1.3/4.8 on the H-band Strehl ratio (SR) with 92.3% of correlation between reconstructed and sky SR. On the full-width at half-maximum, we get, respectively, 2.94 mas, 19.9 mas, and 88.3% for the bias, std, and correlation. The reference method achieves 0.4/3.5/95% on the SR and 2.71 mas/14.9 mas/92.5% on the FWHM for the bias/std/correlation.