This is a list of reviewers who served the Journal of Astronomical Telescopes, Instruments, and Systems in 2020.

We develop a simple coordinate transformation that can be employed to compensate for the nonlinearity introduced by a microwave kinetic inductance detector’s (MKID) homodyne readout scheme. This coordinate system is compared to the canonically used polar coordinates and is shown to improve the performance of the filtering method often used to estimate a photon’s energy. For a detector where the coordinate nonlinearity is primarily responsible for limiting its resolving power, this technique leads to increased dynamic range, which we show by applying the transformation to data from a hafnium MKID designed to be sensitive to photons with wavelengths in the 800- to 1300-nm range. The new coordinates allow the detector to resolve photons with wavelengths down to 400 nm, raising the resolving power at that wavelength from 6.8 to 17.

The Origins Space Telescope will trace the history of our origins from the time dust and heavy elements permanently altered the cosmic landscape to present-day life. How did galaxies evolve from the earliest galactic systems to those found in the Universe today? How do habitable planets form? How common are life-bearing worlds? To answer these alluring questions, Origins will operate at mid- and far-infrared (IR) wavelengths and offer powerful spectroscopic instruments and sensitivity three orders of magnitude better than that of the Herschel Space Observatory, the largest telescope flown in space to date. We describe the baseline concept for Origins recommended to the 2020 US Decadal Survey in Astronomy and Astrophysics. The baseline design includes a 5.9-m diameter telescope cryocooled to 4.5 K and equipped with three scientific instruments. A mid-infrared instrument (Mid-Infrared Spectrometer and Camera Transit spectrometer) will measure the spectra of transiting exoplanets in the 2.8 to 20  μm wavelength range and offer unprecedented spectrophotometric precision, enabling definitive exoplanet biosignature detections. The far-IR imager polarimeter will be able to survey thousands of square degrees with broadband imaging at 50 and 250  μm. The Origins Survey Spectrometer will cover wavelengths from 25 to 588  μm, making wide-area and deep spectroscopic surveys with spectral resolving power R  ∼  300, and pointed observations at R  ∼  40,000 and 300,000 with selectable instrument modes. Origins was designed to minimize complexity. The architecture is similar to that of the Spitzer Space Telescope and requires very few deployments after launch, while the cryothermal system design leverages James Webb Space Telescope technology and experience. A combination of current-state-of-the-art cryocoolers and next-generation detector technology will enable Origins’ natural background-limited sensitivity.

Quantum capacitance detectors (QCDs) are photon shot noise-limited terahertz detectors based on a single Cooper-pair box superconducting qubit. The QCD has demonstrated photon shot noise-limited performance for 1.5 THz radiation under loading conditions between ^{10  −  20} and 10^−  18  W and single-photon detection and counting at that frequency. We report here fabrication and preliminary characterization of a 441 pixel array of QCDs with readout frequencies between 700 and 850 MHz.

The Origins Space Telescope mission concept includes an exoplanet transit spectrometer that requires detector arrays with ultrahigh pixel-to-pixel stability. Superconducting nanowire single-photon detectors, or SNSPDs, have the potential to meet these stringent stability requirements due to their digital-like output. Traditionally used for applications at near-IR telecom wavelengths, SNSPDs have demonstrated near-unity detection efficiencies, ultralow dark-count rates, and high dynamic ranges. Until recently, however, SNSPD operation at the mid-infrared (mid-IR) wavelengths of interest for Origins had not been demonstrated, and SNSPD formats were limited to small arrays and active areas. Recent advances in SNSPD fabrication techniques have pushed SNSPD sensitivity to wavelengths beyond 7  μm and have enabled millimeter-scale active areas and kilopixel arrays. We report here on this progress and the outlook toward developing arrays of ultrastable superconducting nanowire single-photon detectors for mid-IR astronomy applications.

The Origins Space Telescope is one of four flagship missions under study for the 2020 Astrophysics Decadal Survey. With a 5.9-m cold (4.5 K) telescope deployed from space, Origins promises unprecedented sensitivity in the near-, mid-, and far-infrared from 2.8 to 588  μm. This mandates the use of ultrasensitive and stable detectors in all of the Origins instruments. At the present, no known detectors can meet Origins’ stability requirements in the near- to mid-infrared or its sensitivity requirements in the far-infrared. We discuss the applicability of transition-edge sensors, as both calorimeters and bolometers, to meet these requirements, and lay out a path toward improving the present state-of-the-art.

We report on our investigation into adapting the design of the James Webb Space Telescope (JWST) to the needs and requirements of the Origins Space Telescope. The modifications needed to the equipment and insulation of the JWST design to achieve the 4.5-K design temperature for Origins are introduced and detailed. The Webb thermal model is modified to the Origins design and used to predict the heat loads at 18 and 4.5 K. We also describe the needed development of the JWST Mid-Infrared Instrument’s cryocooler needed to reach the temperature necessary for Origins. The capabilities of the various modified cryocoolers are discussed. We show that three modified coolers are needed to achieve the performance required for Origins. Finally, we show that the baseline instruments and needed coolers can be accommodated for volume, mass, and power in the Webb architecture.

The Heterodyne Receiver for Origins (HERO) is the first detailed study of a heterodyne focal plane array receiver for space applications. HERO gives the Origins Space Telescope the capability to observe at very high spectral resolution (R  =  10⁷) over an unprecedentedly large far-infrared (FIR) wavelengths range (111 to 617  μm) with high sensitivity, with simultaneous dual polarization and dual-frequency band operation. The design is based on prior successful heterodyne receivers, such as Heterodyne Instrument for the Far-Infrared /Herschel, but surpasses it by one to two orders of magnitude by exploiting the latest technological developments. Innovative components are used to keep the required satellite resources low and thus allowing for the first time a convincing design of a large format heterodyne array receiver for space. HERO on Origins is a unique tool to explore the FIR universe and extends the enormous potential of submillimeter astronomical spectroscopy into new areas of astronomical research.

The Origins Space Telescope’s (Origins) significant improvement over the scientific capabilities of prior infrared missions is based on its cold telescope (4.5 K) combined with low-noise far-IR detectors and ultrastable mid-IR detectors. A small number of new technologies will enable Origins to approach the fundamental sensitivity limit imposed by the natural sky background and deliver groundbreaking science. This paper describes a robust plan to mature the Origins mission, enabling cryocooler technology from current state-of-the-art (SOA) to Technology Readiness Level (TRL) 5 by 2025 and to TRL 6 by mission Preliminary Design Review. Entry TRLs corresponding to today’s SOA are 4 or 5, depending on the technology in question.

The Origins Space Telescope’s orders-of-magnitude improvement over the scientific capabilities of prior infrared (IR) missions is based on its cold telescope (4.5 K) combined with low-noise far-IR detectors and ultra-stable mid-IR detectors. A number of trades were made in favor of a design with staged cooling, avoiding warm objects in the cold zones and minimizing the number of deployments and their complexity. The result is an architecture that is easily to analyze thermally and straightforward to test in existing facilities.

Our paper discusses the optical design of the Origins Space Telescope. Origins is one of four large missions under study in preparation for the 2020 Decadal Survey in Astronomy and Astrophysics. Sensitive to the mid- and far-infrared spectrum (between 2.8 and 588  μm), Origins sets out to answer a number of important scientific questions by addressing NASA’s three key science goals in astrophysics. The Origins telescope operates at f  /  14. The design includes a 5.9-m-diameter primary mirror. The large on-axis primary consists of 18 “keystone” segments of two different prescriptions arranged in two annuli (six inner and twelve outer segments) that together form a circular aperture in the goal of achieving a symmetric point spread function. To accommodate the 46  ×  15  arc min full field of view (FOV) of the telescope at the design wavelength of λ  =  30  μm, a three-mirror anastigmat configuration is used. The design is diffraction-limited across its instruments’ FOV. A brief discussion of each of the three baselined instruments within the Instrument Accommodation Module is presented: (1) Origins Survey Spectrometer, (2) Mid-infrared Spectrometer, Camera transit spectrometer channel, and (3) Far-Infrared Polarimeter/Imager. In addition, the upscope options for the observatory are laid out as well including a fourth instrument: the Heterodyne Receiver for Origins.

The Origins Space Telescope (Origins) study team prepared and submitted a Mission Concept Study Report for the 2020 Decadal Survey in Astrophysics. During the study, a Materials Working Group was formed to evaluate materials for Origins. The Materials Working Group identified material candidates and evaluated the candidates using driving requirements and key material considerations. The evaluation resulted in several options to aid the study team in making a materials selection for the mission concept. Our paper details the approach to the materials evaluation and the results.

Athena, a future high-energy mission, is expected to consist of a large aperture x-ray mirror with a focal length of 12 m. The mirror surface is to be coated with iridium and a low Z overcoat. To define the effective area of the x-ray telescope, the atomic scattering factors of iridium with an energy resolution less than that (2.5 eV) of the x-ray integral field unit are needed. We measured the reflectance of the silicon pore optics mirror plate coated with iridium in the energy range of 9 to 15 keV and that near the iridium L-edges in steps of 10 and 1.5 eV, respectively, at the synchrotron beamline SPring-8. The L3, L2, and L1 edges were clearly detected around 11,215, 12,824, and 13,428 eV, respectively. The measured scattering factors were ∼3  %   smaller than the corresponding values reported by Henke et al., likely due to the presence of an overlayer on the iridium coating, and were consistent with those measured by Graessle et al. The angular dependence of the reflectivity measured indicates that the iridium surface was extremely smooth, with a surface roughness of 0.3 nm.

Conventional two-mirror optical telescope designs are well known. An attempt to improve the performance of a two-mirror telescopic system using freeform surface is reported. Four variants of the optical design that use symmetric and off-axis freeform surfaces for achieving superior performances in the spectral range from 400 to 900 nm are proposed. These designs are compared with the conventional Ritchey–Chretien and equivalent two-mirror off-axis telescope designs with rotationally symmetric surfaces. The optical design with freeform surfaces shows marked improvements compared with its counterpart comprising of conics and higher order aspherics. The incorporation of freeform surfaces is obtained by an overlay of fringe Zernike polynomial either on the base sphere or on the conic itself, which is used as a surface descriptor in the envisaged designs. This approach aids in correction of asymmetrical aberrations and also extends the performances to a wider field, which is quite advantageous in the case of off-axis (de-centered and tilted) optical systems.

The Off-plane Grating Rocket Experiment (OGRE) is a soft x-ray grating spectrometer to be flown on a suborbital rocket. The payload is designed to obtain the highest-resolution soft x-ray spectrum of Capella to date with a resolution goal of R  (  λ  /  Δλ  )    >  2000 at select wavelengths in its 10 to 55 Å bandpass of interest. The optical design of the spectrometer realizes a theoretical maximum resolution of R  ≈  5000, but this performance does not consider the finite performance of the individual spectrometer components, misalignments between components, and in-flight pointing errors. These errors all degrade the performance of the spectrometer from its theoretical maximum. A comprehensive line-spread function (LSF) error budget has been constructed for the OGRE spectrometer to identify contributions to the LSF, to determine how each of these affects the LSF, and to inform performance requirements and alignment tolerances for the spectrometer. In this document, the comprehensive LSF error budget for the OGRE spectrometer is presented, the resulting errors are validated via raytrace simulations, the implications of these results are discussed, and future work is identified.

The development of the Skipper-charge-coupled devices (Skipper-CCDs) has been a major technological breakthrough for sensing very weak ionizing particles. The sensor allows to reach the ultimate sensitivity of silicon material as a charge signal sensor by unambiguous determination of the charge signal collected by each cell or pixel, even for single electron–hole pair ionization. Extensive use of the technology was limited by the lack of specific equipment to operate the sensor at the ultimate performance. A simple, single-board Skipper-CCD controller designed by the authors is presented and aimed for the operation of the detector in high sensitivity scientific applications. Our article describes the main components and functionality of the so-called low threshold acquisition controller together with experimental results when connected to a Skipper-CCD sensor. Measurements show unprecedented deep subelectron noise of 0.039  erms−/pix by nondestructively measuring the charge 5000 times in each pixel.

The Dual-channel Extreme Ultraviolet Continuum Experiment (DEUCE) is a rocket-borne, ultraviolet spectrograph specifically designed to obtain the first flux-calibrated spectra of nearby B stars ϵ and β Canis Majoris (CMa) across the Lyman limit at 912 Å. These observations will help quantify the contribution of such stars to modern ionization in the intergalactic medium. The payload operates in two channels over the 700 to 1150 Å extreme ultraviolet/far ultraviolet (EUV/FUV) bandpass, with resolving powers of 180 (1850) and net effective areas (including slit transmission) of 4  cm² (  .  15  cm²) in its large and small-slit channels, respectively. DEUCE features a large format 200  ×  200  mm² low-noise atomic layer deposition-activated microchannel plate detector of the type baselined for the Large Ultraviolet Optical Infrared (LUVOIR) Surveyor and has demonstrated its flight performance. DEUCE has obtained the first flux-calibrated spectrum of ϵ CMa from 730 to 895 Å. This paper outlines the science objectives, instrument design, calibration, launches, and observations of the mission.

The KM3NeT infrastructure consists of two deep-sea neutrino telescopes being deployed in the Mediterranean Sea. The telescopes will detect extraterrestrial and atmospheric neutrinos by means of the incident photons induced by the passage of relativistic charged particles through the seawater as a consequence of a neutrino interaction. The telescopes are configured in a three-dimensional grid of digital optical modules, each hosting 31 photomultipliers. The photomultiplier signals produced by the incident Cherenkov photons are converted into digital information consisting of the integrated pulse duration and the time at which it surpasses a chosen threshold. The digitization is done by means of time to digital converters (TDCs) embedded in the field programmable gate array of the central logic board. Subsequently, a state machine formats the acquired data for its transmission to shore. We present the architecture and performance of the front-end firmware consisting of the TDCs and the state machine.

Electron multiplying charge-coupled devices (EMCCDs) are a variant of standard CCD technology capable of single-optical photon counting at MHz pixel readout rates. For photon counting, thermal dark signal and clock-induced charge (CIC) are the dominant source of noise and must be minimized to reduce the likelihood of coincident events. Thermal dark signal is reduced to low levels through cooling or operation in inverted mode (pinning). However, mitigation of CIC requires precise tuning of both parallel and serial clock waveforms. Here, we present a detailed study of CIC within Teledyne-e2v EMCCDs with a goal of better understanding the physical mechanisms that dominate CIC production in both noninverted and inverted mode operations (IMO). Measurements are presented as a function of parallel and serial clock timings, clock amplitudes, and device temperature. The effects of radiation damage and annealing are also discussed. A widely accepted view is that CIC is signal generated through impact ionization of energetic holes as the clock phase is driven high. While this explanation holds for IMO, we propose that the majority of CIC generated in noninverted mode is in fact due to a secondary effect of light emission from hot carriers. The information from this study is then used to optimize CIC on Teledyne e2v CCD201s operating at 1-MHz pixel rate in NIMO. For the CCD201, we obtained total CIC levels as low as 6.9  ×  10^−  4  e⁻  /  pix  /  frame with ≥90  %   detective quantum efficiency. We conclude with proposals to further reduce CIC based upon modifications to clocking schemes and device architecture.

Contamination is always troublesome in spacecraft development, but it has yet to be investigated because outgassing, transportation, deposition, and re-emission largely depend on spacecraft design. Designing spacecraft requires an accurate estimate of contaminant emission and deposition. Particularly for today’s sophisticated spacecraft, analytical tools would be indispensable—but current simulations need to be improved. Our study addresses the first phase in the occurrence of contamination: improving the outgassing model. We focused on diffusion-limited phenomena because the diffusion rate of outgassing molecules in materials is thought to be much slower than their desorption rate at the surface. A new outgassing test method and analytical procedure was originally devised for extracting the parameters of the diffusion model. In comparing the desorption and diffusion models, we developed a model for the emission of outgassing molecules based on the diffusion theory and updated some functions of Japan’s Spacecraft Induced Contamination Environment analysis software (J-SPICE). From this, we developed J-SPICE2 and installed the diffusion model to the software for calculating outgassing behavior.

Superconducting transition-edge sensors (TESs) carried by x-ray telescopes are powerful tools for the study of neutron stars and black holes. Several methods, such as optimal filtering or principal component analysis, have already been developed to analyze x-ray data from these sensors. However, these techniques may be hard to implement in space. Our goal is to develop a lower-computational-cost technique that optimizes energy and time resolution when x-ray photons are detected by a TES. Current pulses, in TESs, exhibit a non-linear response to photon energy. Therefore, at low energies, we focus on the current-pulse height, whereas at high energies, we consider the current-pulse width, to retrieve energy and arrival time of x-ray photons. For energies between 0.1 and 30 keV and with a sampling rate of 195 kHz, we obtain an energy resolution (full-width at half-maximum) between 1.32 and 2.98 eV. We also get an arrival-time resolution (full-duration at half-maximum) between 163 and 3.85 ns. To improve the accuracy of these results, it will be essential to get a thorough description of non-stationary noise in a TES and develop a robust on-board identification method of pile-up events.

Adaptive optics (AO) has become an indispensable tool for ground-based telescopes to mitigate atmospheric seeing and obtain high angular resolution observations. Predictive control aims to overcome latency in AO systems: the inevitable time delay between wavefront measurement and correction. A current method of predictive control uses the empirical orthogonal functions (EOFs) framework borrowed from weather prediction, but the advent of modern machine learning and the rise of neural networks (NNs) offer scope for further improvement. Here, we evaluate the potential application of NNs to predictive control and highlight the advantages that they offer. We first show their superior regularization over the standard truncation regularization used by the linear EOF method with on-sky data before demonstrating the NNs’ capacity to model nonlinearities on simulated data. This is highly relevant to the operation of pyramid wavefront sensors (PyWFSs), as the handling of nonlinearities would enable a PyWFS to be used with low modulation and deliver extremely sensitive wavefront measurements.

We describe an approach to coronagraphic focal-plane wavefront control that utilizes gradient-based nonlinear optimization along with analytical gradients obtained with algorithmic differentiation to find deformable mirror solutions. In addition to eliminating the cost of calculating a high-dimensional finite-difference Jacobian matrix, we show that this approach leads to improved asymptotic computational efficiency. With very high-actuator deformable mirrors such as the 128  ×  128 actuators baselined for the Large UV/Optical/IR Surveyor mission concept, the proposed algorithm reduces memory consumption by approximately 95  %   compared to a Jacobian-based algorithm.

This erratum corrects errors in Table 2.