The Far- and Lyman-ultraviolet imaging demonstrator (FLUID) is a rocket-borne arcsecond-level ultraviolet (UV) imaging instrument covering four bands between 92 and 193 nm. FLUID will observe nearby galaxies to find and characterize the most massive stars that are the primary drivers of the chemical and dynamical evolution of galaxies and the co-evolution of the surrounding galactic environment. The FLUID short wave channel is designed to suppress efficiency at Lyman-α (121.6 nm) while enhancing the reflectivity of shorter wavelengths. Utilizing this technology, FLUID will take the first ever images of local galaxies isolated in the Lyman UV (90–120 nm). As a pathfinder instrument, FLUID will employ and increase the technology readiness level of band-selecting UV coatings and solar-blind UV detector technologies, including microchannel plate and solid-state detectors; technologies that are prioritized in the 2022 NASA Astrophysical Biennial Technology Report. These technologies enable high throughput and high sensitivity observations in the four co-aligned UV imaging bands that make up the FLUID instrument. We present the design of FLUID, status on the technology development, and results from initial assembly and calibration of the FLUID instrument.

Flat-fabrication technology may enable the next generation of gigantic deployable architectures devoted to the detection of faint cosmological signals. We assess the applicability of a multifunctional roll-out structure based on shape memory polymer technology for the realization of a large space observatory to measure the cosmological Dark Ages radio signal. Roll-out solutions offer advantageous properties for probe class missions, such as the capability to morph the shape to achieve sufficient structural performance while ensuring high packaging efficiency. We characterize the feasibility of a roll-out observatory in the context of a 5 years-long heliocentric mission scenario. Our preliminary study demonstrates how a four-250 m-long arms architecture with 150 evenly spaced short dipole antennas potentially meets the basic mission requirements dictated by the Dark Ages science case. We conduct a quasi-static structural analysis considering axial and bending loads acting on the arms to assess the structural properties of the proposed architecture, identifying geometric ranges which enable the structure to withstand expected loads while satisfying mass and size constraints. Printable electronics are considered in the design due to the ease of integration with the polymer substrate. In this regard, we explore two distinct electronics configuration options—centralized and decentralized—discussing their benefits in terms of power demand and data management. If successful, such a design may set the stage for future technological development aiming to realize tomographic measurements of the cosmological Dark Ages.

Photonic lantern nulling (PLN) is a method for enabling the detection and characterization of close-in exoplanets by exploiting the symmetries of the ports of a mode-selective photonic lantern (MSPL) to cancel out starlight. A six-port MSPL provides four ports where on-axis starlight is suppressed, while off-axis planet light is coupled with efficiencies that vary as a function of the planet’s spatial position. We characterize the properties of a six-port MSPL in the laboratory and perform the first testbed demonstration of the PLN in monochromatic light (1569 nm) and in broadband light (1450 to 1625 nm), each using two orthogonal polarizations. We compare the measured spatial throughput maps with those predicted by simulations using the lantern’s modes. We find that the morphologies of the measured throughput maps are reproduced by the simulations, though the real lantern is lossy and has lower throughputs overall. The measured ratios of on-axis stellar leakage to peak off-axis throughput are around 10−2, likely limited by testbed wavefront errors. These null-depths are already sufficient for observing young gas giants at the diffraction limit using ground-based observatories. Future work includes using wavefront control to further improve the nulls, as well as testing and validating the PLN on-sky.

The atmospheric dispersion corrector (ADC) of the Gemini Planet Imager (GPI) corrects the chromatic dispersion caused by differential atmospheric refraction (DAR), making it an important optic for exoplanet observation. Despite requiring <5 mas of residual DAR to avoid potentially affecting the coronagraph, the GPI ADC averages ∼7 and ∼11 mas of residual DAR in H and J band, respectively. We analyzed GPI data in those bands to find explanations for the underperformance. We found the model GPI uses to predict DAR underestimates humidity’s impact on incident DAR, causing on average a 0.54 mas increase in H band residual DAR. Additionally, the GPI ADC consistently undercorrects in H band by about 7 mas, causing almost all the H band residual DAR. J band does not have such an offset. Perpendicular dispersion induced by the GPI ADC, potentially from a misalignment in the prisms’ relative orientation, causes 86% of the residual DAR in J band. Correcting these issues could reduce residual DAR, thereby improving exoplanet detection. We also made an approximation for the index of refraction of air from 0.7 to 1.36 microns that more accurately accounts for the effects of humidity.

Large-field telescopes play a significant role in cutting-edge astronomical research fields, such as time-domain astronomy and cosmology. For such telescopes, ensuring symmetrical and uniform imaging across the entire field-of-view (FoV) is pivotal, particularly for areas such as astronomical photometry and astrometry. However, conventional image quality evaluation methods for telescope optical systems have mainly focused on imaging spot size. Other alternative methods, such as ellipticity based methods, also face the challenges of high computational requirements and limited assessment parameters. In addition, establishing a coherent link between the telescope structure and research domains such as photometry has remained a challenge. In response to these challenges, we introduce an assessment approach termed the ray tracing, spot-vector index, and angle (RSVA) approach. This approach offers a fresh perspective on optical systems, prioritizing the depiction of imaging spot shapes. It acts as a valuable supplement to traditional methods and has been effectively employed to analyze four 1-m aperture telescopes with an f-ratio of 3 for a 3 deg FoV. Building on this foundation, the RSVA can be further expanded to explore other research avenues, including exploring the interplay between photometry and telescope systems and guiding large FoV optical design.

Space interferometers could, in principle, exploit the relatively stable space environment and ease of baseline reconfiguration to collect measurements beyond the limitations of ground-based interferometers. In particular, a two-element interferometer could provide excellent uv-plane coverage over a few tens of low Earth orbits. One of the challenges for free-flying interferometers is controlling the optical path distance with subwavelength accuracies despite the collectors flying up to hundreds of meters apart. We consider two approaches: an artificial in-orbit laser guide star (LGS) that provides a phase reference for the space interferometer and fringe tracking on the science target itself. The two approaches (LGS versus no LGS) would require different image processing techniques. In this work, we explore image processing with LGS phase residuals due to global positioning system (GPS) uncertainties. We use GPS uncertainties from the Gravity Recovery and Climate Experiment Follow-On mission to simulate image retrieval with a 300-m baseline laser-guided space interferometer. This is done by fitting the slowly varying phase errors of complex visibility measurements. We also consider a 40-m baseline interferometer with visibility(-modulus)-only measurements. In this case, we simulate the bias in visibility due to fringe tracking in the presence of parasitic forces acting on the spacecraft. We then use a modified version of the hybrid input–output phase retrieval algorithm for image reconstruction. We conclude that under our optimistic assumptions, both approaches could enable general imaging of a few large stars even with CubeSats, although an LGS would significantly improve the best resolution obtainable.

We present Mookodi (meaning “rainbow” in Sesotho), a multipurpose instrument with a low-resolution spectrograph mode and a multi-filter imaging mode for quick-reaction astronomical observations. The instrument, mounted on the 1-m Lesedi telescope at the South African Astronomical Observatory in Sutherland (South Africa), is based on the low-resolution spectrograph for the rapid acquisition of transients (SPRAT) instrument in operation on the 2-m Liverpool Telescope in La Palma (Canary Islands, Spain). Similar to SPRAT, Mookodi has a resolution R≈350 and an operating wavelength range in the visible (∼4000 to 8000 Å). The linear optical design, as in SPRAT, is made possible through the combination of a volume phase holographic transmission grating as the dispersive element and a prism pair (grism), which makes it possible to rapidly and seamlessly switch to an imaging mode by pneumatically removing the slit and grism from the beam and using the same detector as in spectrographic mode to image the sky. This imaging mode is used for auto-target acquisition, but the inclusion of filter slides in Mookodi’s design also provides the capability to perform imaging with a field-of-view ≈10′×10′ (∼0.6″/px) in the complete Sloan Digital Sky Survey filter set.

An exoplanet survey with a near-infrared Doppler (IRD) instrument focused on mid-to-late M-type dwarfs began in February 2019 within the framework of the Subaru Strategic Program. Because mid-to-late M-type dwarfs are brighter in the infrared region than in the visible region, a laser frequency comb (LFC) system was developed as a wavelength reference, covering the near-infrared region from 970 to 1750 nm. To stabilize the comb image on the spectrometer, the original 12.5 GHz comb generated using highly nonlinear fibers was injected into the spectrometer after optical processing, including spectral shaping, depolarization, and mode scrambling. An inline fiber module was introduced to enable any optical system configuration for the optical processor. This fiber-optic configuration in the LFC system allows for long-term stability and easy repair. Moreover, simple remote control of the LFC system using an interactive program enabled LFC generation in approximately 5 min, excluding warm-up time. The observations using the IRD instrument over 4 years have proven that our LFC system is practical and stable. The LFC system operated stably without major problems during this period, helping to maintain a high radial velocity accuracy.

Randomly distributed anti-reflective nanostructures were fabricated on both surfaces of cylindrical lenses and freeform optical elements using a plasma-assisted reactive-ion etching technique. An average spectral transmission of 98% was measured across the wavelength range from 340 to 800 nm. Mid-band full-angle directional scatter measurements show a difference of six orders of magnitude in transmission intensity between specular and off-specular angles. Measurements before and after the etching process show little to no wavefront distortion for the cylindrical lenses. The enhanced transmission optics were used as part of the dual-unit arrayed wide-field astronomical camera system tested on the Harlan J. Smith telescope at the McDonald Observatory, and their performance was contrasted with conventional thin film coated component performance.

Future space missions that aim to detect and characterize Earth-like exoplanets will require an instrument that efficiently measures the spectra of these planets, placing strict requirements on detector performance. The upcoming Roman Space Telescope will demonstrate the performance of an electron-multiplying charge-coupled device as part of the coronagraphic instrument (CGI). The recent LUVOIR and HabEx studies baselined pairing such a detector with an integral field spectrograph to take spectra of multiple exoplanets and debris disks simultaneously. We investigate the scientific impact of a noiseless energy-resolving detector (ERD) for the planned Habitable Worlds Observatory’s (HWO) CGI. By assuming higher quantum efficiency, higher optical throughput, and zero noise, we effectively place upper limits on the impact of advancing detector technologies. We find that ERDs would potentially take spectra of hundreds of additional exoplanets “for free” over the course of an HWO survey, greatly increasing its scientific yield.

Complementary metal-oxide-semiconductor (CMOS) detectors are a competitive choice for current and upcoming astronomical missions. To understand the performance variations of CMOS detectors in the space environment, we investigate the total ionizing dose effects on custom-made large-format X-ray CMOS detectors. Three CMOS detector samples were irradiated with a Co60 source with a total dose of 70 and 105 krad. We test and compare the performance of these detectors before and after irradiation. After irradiation, the dark current increases by roughly 20∼100 times, and the readout noise increases from 3 e− to 6 e−. The bias level at 50 ms integration time decreases by 13 to 18 digital number (DN) at −30°C. The energy resolution increases from ∼150 to ∼170 eV at 4.5 keV at −30°C. The conversion gain of the detectors varies for <2% after the irradiation. Furthermore, there are about 50 pixels in which bias at 50 ms has changed by more than 20 DN after the exposure to the radiation and about 30 to 140 pixels in which the readout noise has increased by over 20 e− at −30°C at 50 ms integration time. These results demonstrate that the performances of large-format CMOS detectors do not suffer significant degeneration in space environment.

Star sensors are an essential instrument used to determine the attitude of satellites by identifying the stars in the field of view. The high cost and large sizes of commercially available star sensors pose challenges for small satellite missions. We at the Indian Institute of Astrophysics have developed a low-cost star sensor, StarberrySense, based on the Raspberry Pi as the main controller and built from commercial off-the-shelf components. The StarberrySense was flown on the PS4 experimental orbital platform module of the Polar Satellite Launch Vehicle C-55 by the Indian Space Research Organization. This work describes the flight hardware, environmental tests in preparation for the flight, and in-orbit performance of our StarberrySense.

The study of gamma-ray burst (GRB) jets has focused predominantly on the gamma-ray portion of the spectral energy distribution (SED) to understand jet properties and their physics. Recent theoretical development has turned to the lower-energy side of the SED to test competing jet models. We considered the application of wide-field X-ray detectors to extend the observation of the SED and for better distinguishing spectral models, aimed at resolving theoretical features existing at or below the sensitivity of missions such as Fermi and Swift. A proposed SmallSat reference mission is introduced, and analysis is conducted on simulated GRBs to determine its improvement in understanding the SED compared with the Fermi-gamma-ray burst monitor (GBM). Detection rates of the reference mission are simulated using a GRB population model and convolved with the energy flux needed to resolve models to find estimated rates of GRBs that the reference mission can resolve better than Fermi-GBM. We discuss the methods and results along with the scientific context for this type of mission.

Accurate solar observation plays a vital role in space weather prediction. Aditya-L1, ISRO’s first solar observatory mission, carried a Visible Emission Line Coronagraph (VELC) instrument. This instrument provides observations very close to the solar limb with internal occultation. We provide design and development details of detector electronics for continuum, two spectroscopic channels and one spectro-polarimetry channel of the VELC instrument. The developed hardware with imaging detectors (sCMOS in visible and InGaAs in near-infrared spectral region) has very high sensitivity (noise equivalent signal = 0.2 photon/s/pixel). The instrument has onboard intelligence for detection of coronal mass ejection events. Photon-noise-limited detector electronics are developed and qualified for all four channels. Dark noise of ≈1.2e− with dark signal ≈0.035e−/p/s was achieved. Detector electronics cater to very high input dynamic range >120 dB. Stringent contamination control protocols were evolved and implemented during all stages of development. The uniqueness of the VELC instrument is that it makes observations very close to the solar limb (1.05 R) as well as magnetic field measurements and has simultaneous spectroscopic and imaging capability.

We developed the X-ray, gamma-ray, and relativistic electron detector (XGRE) onboard the Tool for the Analysis of RAdiation from lightNIngs and Sprites (TARANIS) satellite, to investigate high-energy phenomena associated with lightning discharges such as terrestrial gamma-ray flashes and terrestrial electron beams. XGRE consisted of three sensors. Each sensor has one layer of LaBr3 crystals for X-ray/gamma-ray detections and two layers of plastic scintillators for electron and charged-particle discrimination. Since 2018, the flight model of XGRE was developed, and validation and calibration tests, such as a thermal cycle test and a calibration test with the sensors onboard the satellite, were performed before the launch of TARANIS on 17 November 2020. The energy range of the LaBr3 crystals sensitive to X-rays and gamma rays was determined to be 0.04 to 11.6 MeV, 0.08 to 11.0 MeV, and 0.08 to 11.3 MeV for XGRE1, 2, and 3, respectively. The energy resolution at 0.662 MeV (full width at half maximum) was 20.5%, 25.9%, and 28.6%, respectively. The results from the calibration test were then used to validate a simulation model of XGRE and TARANIS. By performing Monte Carlo simulations with the verified model, we calculated effective areas of XGRE to X-rays, gamma rays, electrons, and detector responses to incident photons and electrons coming from various elevation and azimuth angles.

The first results of high-speed atomic oxygen (AO) irradiation tests for atomically thin single-layer graphene sheets are presented as space environmental tolerance evaluation tests toward application in astronomy. The single-layer graphene sample was prepared without a metal coating, and high-speed AO irradiation tests were conducted with an averaged velocity of ∼6 km/s using a laser-detonation AO beam source assuming a low Earth orbit (LEO) case. The Raman spectral features were examined before and after the tests with fluence values of 2×1015, 2×1016, 2×1017, 2×1018, and 2×1019 atoms/cm2. It was found that there is no significant change in the observed D/G ratios for fluence up to 2×1017 atoms/cm2. In contrast, the D/G ratios changed from 0.04±0.03 to 0.8±0.4 for 2×1018 atoms/cm2 drastically in both the averaged value and 1-sigma range. Furthermore, the D/G ratio could not be measured beyond 2×1019atoms/cm2 because no peaks were observed in both the G and D bands, which suggests that the degradation occurs between 2×1017 and 2×1018 atoms/cm2 and no graphene sheets exist after the 2×1019 atoms/cm2 irradiation. Scanning electron microscopy images also support this conclusion in terms of the observed image contrast. Consequently, to protect the single-layer graphene sheets from erosion, a special treatment such as coating is needed to survive in an LEO for ≳ a day.

The Hawaii-4RG near-infrared detectors offer several output configurations in which the detectors can be interfaced with the European Southern Observatory cryogenic preamplifiers. The buffered mode of output operation has the advantages of higher speed and lower electrical crosstalk between the outputs, reduced unit cell current, etc. One of the effects of the buffered mode operation is increased glow at the bottom of the array due to the operation of the output buffers compared to the unbuffered mode. The excess glow can be a limiting source to achieve low noise in long integrations using the up-the-ramp sampling readout mode. The glow can be significantly reduced by optimally biasing the output buffer stages. This work presents the output buffer glow issue, its quantification in terms of glow per read, glow per unit integration time, its dependency on pixel speed, and its mitigation by optimization of buffered mode operation.

We present moes, a ray tracing software package that computes the path of rays through echelle spectrographs. Our algorithm is based on sequential direct tracing with Seidel aberration corrections applied at the detector plane. As a test case, we model the CARMENES VIS spectrograph. After subtracting the best model from the data, the residuals yield an rms of 0.024 pix, setting a new standard for the precision of the wavelength solution of state-of-the-art radial velocity (RV) instruments. By including the influence of the changes of the environment in ray propagation, we are able to predict instrumental RV systematics at the 1 m/s level.

High-order wavefront sensing and control (HOWFSC) is key to creating a dark hole region within the coronagraphic image plane where high contrasts are achieved. The Roman Coronagraph is expected to perform its HOWFSC with a ground-in-the-loop scheme due to the computational complexity of the electric field conjugation (EFC) algorithm. This scheme provides the flexibility to alter the HOWFSC algorithm for given science objectives. The baseline HOWFSC scheme involves running EFC while observing a bright star such as ζ Puppis to create the initial dark hole followed by a slew to the science target. The new implicit EFC (iEFC) algorithm removes the optical diffraction model from the controller, making the final contrast independent of model accuracy. While previously demonstrated with a single deformable mirror, iEFC is extended to two deformable mirror systems to create annular dark holes. First, an overview of both EFC and iEFC is presented. The algorithm is then applied to the wide-field-of-view shaped pupil coronagraph (SPC-WFOV) mode designed for the Roman Space Telescope using end-to-end physical optics models. Initial noiseless monochromatic simulations demonstrate the efficacy of iEFC as well as the optimal choice of modes for the SPC-WFOV instrument. Further simulations with a 3.6% wavefront control bandpass and a broader 10% bandpass then demonstrate that iEFC can be used in broadband scenarios to achieve contrasts below 10−8 with Roman. Finally, an electron multiplying charge-coupled device (EMCCD) model is implemented to estimate calibration times and predict the controller’s performance. Here, 10−8 contrasts are achieved with a calibration time of ∼6.8 h assuming the reference star is ζ Puppis. The results here indicate that iEFC can be a valid HOWFSC method that can mitigate the risk of model errors associated with space-borne coronagraphs, but to maximize iEFC performance, lengthy calibration times will be required to mitigate the noise accumulated during calibration.

Connecting a coronagraph instrument to a spectrograph via a single-mode optical fiber is a promising technique for characterizing the atmospheres of exoplanets with ground and space-based telescopes. However, due to the small separation and extreme flux ratio between planets and their host stars, instrument sensitivity will be limited by residual starlight leaking into the fiber. To minimize stellar leakage, we must control the electric field at the fiber input. Implicit electric field conjugation (iEFC) is a model-independent wavefront control (WFC) technique in contrast with classical EFC, which requires a detailed optical model of the system. We present here the concept of an iEFC-based WFC algorithm to improve stellar rejection through a single-mode fiber (SMF). As opposed to image-based iEFC, which relies on minimizing intensity in a dark hole region, our approach aims to minimize the amount of residual starlight coupling into an SMF. We present broadband simulation results demonstrating a normalized intensity ≥10−10 for both fiber-based EFC and iEFC. We find that both control algorithms exhibit similar performance for the low wavefront error (WFE) case, however, iEFC outperforms EFC by ≈100x in the high WFE regime. Having no need for an optical model, this fiber-based approach offers a promising alternative to EFC for ground and space-based telescope missions, particularly in the presence of residual WFE.