The National Aeronautics and Space Administration’s (NASA) first dedicated exoplanetary spectroscopy mission, the Colorado Ultraviolet Transit Experiment (CUTE), is used to search for signatures of atmospheric escape, the process by which constituent gases depart a planetary atmosphere. Through transit spectroscopy, the signs of escape driven by the high level of ultraviolet (UV) radiation from their parent stars are detectable around close-in planets. CUTE is a 6U CubeSat developed and operated by the Laboratory for Atmospheric and Space Physics (LASP) of the University of Colorado in Boulder, Colorado, United States; it looks for these signs of escape by surveying close-in extrasolar planets in the near-UV (2479 to 3306 Å) with 208×84 mm Cassegrain telescope-fed, UV-enhanced charged coupled device. Funded through a NASA ROSES proposal in 2017 and forced to deal with a worldwide pandemic during the heart of its fabrication and test program, CUTE has demonstrated the capability of small satellites to launch on schedule and perform challenging astronomical measurements. We will highlight the CUTE mission’s science objectives, implementation, and tribulations on its road to delivering a successful science program while discussing lessons learned pertaining to the development of CubeSat programs and the application of those lessons for a CUTE-style follow-on mission in the future.

Electroforming replication technology at the Marshall Space Flight Center has a long heritage of producing high-quality, full-shell X-ray mirrors for various applications. Nickel alloys are electroformed onto a super-polished mandrel in the electroforming process and then separated to form the replicated full-shell optic. Various parameters in the electroplating configuration could result in the non-uniformity of the shell’s thickness. Thickness non-uniformities primarily occur due to the non-uniform electric field distribution in the electroforming tank during deposition. Using COMSOL Multiphysics simulations, we studied the electric field distributions during the deposition process. Using these studies, we optimized the electric field distribution and strength inside the tank using customized shields and insulating gaskets on the mandrel. These efforts reduced the thickness non-uniformity from over 20% to under 5%. Improving the thickness uniformity of the shell aids in better mounting and aligning shells in the optics module. Optimization of the electroforming process, in some cases, improved the optical performance of the shells. Using finite element modeling, we estimated the effect of electroforming stress on the figure errors of the replicated optics. We observed that the electroforming stress predominantly affects the figure toward the ends of the optics. We presented COMSOL optimization of the electroforming process and the experimental results validating these simulations. We also discuss modeling experimental results of the replication figure errors due to electroforming stresses.

The mirror repositioning system is one critical system in large-size deployable space telescopes that aids in correcting errors in mirror orientation once deployed. Stewart mechanism is employed for reorienting the mirror due to its potential for use in high-precision applications, and a high-range and high-accuracy Stewart platform for positioning the mirror was designed using dual-resolution actuators. System characterization is crucial for understanding, optimizing, and evaluating the performance of a system. It provides insight into a system’s behavior, strengths, weaknesses, and limitations, aiding in troubleshooting, design decisions, and quality assurance. Overall, it forms the foundation for ensuring the functionality, efficiency, and reliability of a system throughout its lifecycle. We discuss the techniques adopted for characterizing the mirror repositioning system and the methods employed for error reduction in the system.

Future space telescope coronagraph instruments hinge on the integration of high-performance masks and precise wavefront sensing and control techniques to create dark holes essential for exoplanet detection. Recent advancements in wavefront control algorithms might exhibit differing performances depending on the coronagraph used. This research investigates three model-free and model-based algorithms in conjunction with either a vector vortex coronagraph or a scalar vortex coronagraph under identical laboratory conditions: pairwise probing with electric field conjugation, the self-coherent camera with electric field conjugation, and implicit electric field conjugation. We present experimental results in narrowband and broadband light from the In-Air Coronagraph Testbed at the Jet Propulsion Laboratory. We find that model-free dark hole digging methods achieve broadband contrasts comparable to model-based methods, and we highlight the calibration costs of model-free methods compared with model-based approaches. This study also reports the first time that electric field conjugation with the self-coherent camera has been applied for simultaneous multi-subband correction with a field stop. This study compares the advantages and disadvantages of each of these wavefront sensing and control algorithms with respect to their potential for future space telescopes.

We present the integration of a new calibration system into the Faint Intergalactic-medium Redshifted Emission Balloon-2 (FIREBall-2), which added in-flight calibration capability for the recent September 2023 flight. This system is composed of a calibration source box containing zinc and deuterium lamp sources, focusing optics, electronics, sensors, and a fiber-fed calibration cap with an optical shutter mounted on the spectrograph tank. We discuss how the calibration cap is optimized to be evenly illuminated through non-sequential modeling for the near-UV (191 to 221 nm) for spectrograph slit mask position calibration, electron multiplying charged-coupled device (EMCCD) gain amplification verification, and wavelength calibration. Then, we present the pre-flight performance testing results of the calibration system and their implications for in-flight measurements. FIREBall-2 flew in 2023, but did not collect calibration data due to early termination of the flight.

The fifth Sloan Digital Sky Survey Local Volume Mapper (LVM) is a wide-field integral field unit survey that uses an array of four 160 mm fixed telescopes with siderostats to minimize the number of moving parts. An individual telescope observes the science or calibration field independently and is synchronized with the science exposure. We developed the LVM Acquisition and Guiding Package (LVMAGP)-optimized telescope control software program for LVM observations, which can simultaneously control four focusers, three K-mirrors, one fiber selector, four mounts (siderostats), and seven guide cameras. This software is built on a hierarchical architecture and the SDSS framework and provides three key sequences: autofocus, field acquisition, and autoguide. We designed and fabricated a proto-model siderostat to test the telescope pointing model and LVMAGP software. The mirrors of the proto-model were designed as an isogrid open-back type, which reduced the weight by 46% and enabled reaching thermal equilibrium quickly. In addition, deflection due to bolting torque, self-gravity, and thermal deformation was simulated, and the maximum scatter of the pointing model induced by the tilt of optomechanics was predicted to be 4′.4, which can be compensated for by the field acquisition sequence. We performed a real sky test of LVMAGP with the proto-model siderostat and obtained field acquisition and autoguide accuracies of 0″.38 and 1″.5, respectively. It met all requirements except for the autoguide specification, which will be resolved by more precise alignment among the hardware components at Las Campanas Observatory.

Time delay error is a significant error source in adaptive optics (AO) systems. It arises from the latency between sensing the wavefront and applying the correction. Predictive control algorithms reduce the time delay error, providing significant performance gains, especially for high-contrast imaging. However, the predictive controller’s performance depends on factors such as the wavefront sensor (WFS) type, the measurement noise level, the AO system’s geometry, and the atmospheric conditions. We study the limits of prediction under different imaging conditions through spatiotemporal Gaussian process models. The method provides a predictive reconstructor that is optimal in the least-squares sense, conditioned on the fixed times series of WFS data and our knowledge of the atmospheric conditions. We demonstrate that knowledge is power in predictive AO control. With a Shack–Hartmann sensor-based extreme AO instrument, perfect knowledge of the wind and atmospheric profile and exact frozen flow evolution lead to a reduction of the residual wavefront phase variance up to a factor of 3.5 compared with a non-predictive approach. If there is uncertainty in the profile or evolution models, the gain is more modest. Still, assuming that only effective wind speed is available (without direction) led to reductions in variance by a factor of ∼2.3. We also study the value of data for predictive filters by computing the experimental utility for different scenarios to answer questions such as how many past telemetry frames should the prediction filter consider and whether is it always most advantageous to use the most recent data. We show that within the scenarios considered, more data provide a consistent increase in prediction accuracy. Furthermore, we demonstrate that given a computational limitation on how many past frames, we can use an optimized selection of n past frames, which leads to a 10% to 15% additional improvement in root mean square over using the n latest consecutive frames of data.

The goal of deformable mirrors (DMs) is to correct aberrated optical wavefronts in spaceborne electro-optical (EO) payloads. It is used as part of an active/adaptive optics system. A continuous-surface, metal-based DM is highly reliable and less complex to assemble, has better stability of the active surface, is less expensive, and can be manufactured quickly. In addition, metal DM with actuation away from the active surface makes the overall configuration scalable. Continuing our previous work on deformable metal mirrors, this work presents the design, validation, and qualification of an aluminum DM using 25 piezoelectric actuators, which include an actuator in the center of the mirror, to improve the spherical aberration correction accuracy. The optomechanical design and analysis of the deformable mirror assembly (DMA) are also presented for performance and survival loads. Later, a qualification model (QM) was built with vacuum-compatible closed-loop piezoelectric actuators. The correction accuracy was demonstrated at the QM by correcting aberrations in the mirror itself. The QM was successfully tested in the space environment in the ThermoVac for operating temperature limits of 20°C±5°C and demonstrated survivability for storage temperature limits of 20°C±40°C. Likewise, the survivability of QM for launch environments such as sinusoidal and random vibration loads is demonstrated. The successful completion of all these tests has improved the maturity of this technology to the technology readiness level of 7 and is now ready to be configured for the appropriate spaceborne EO payload.

Several proposed future X-ray missions will require thin (≤0.5 mm thick) mirrors with precise surface figures to maintain high angular resolution (≤0.5 arcsec). To study methods of meeting these requirements, adjustable X-ray optics have been fabricated with thin-film piezoelectric actuators to perform figure correction. The fabrication and actuator performance for an adjustable X-ray mirror that forms a conical approximation to a Wolter-I telescope are reported. The individual responses of actuator cells were measured and shown to induce a figure change of 870 nm peak-to-valley on average. These measured responses were compared with predicted responses generated using a finite-element analysis algorithm. On average, the measured and predicted cell responses agreed to within 60 nm root mean square. A set of representative mirror distortions and the measured cell responses were used to simulate figure corrections and calculate the half-power diameter (HPD, single reflection at 1 keV) achieved. These simulations showed an improvement in 4.5 to 9 arcsec mirrors to 0.5 to 1.5 arcsec HPD. The disagreements between the predicted and measured cells’ performance in actuation and figure correction were attributed to a high spatial frequency metrology error and differences in mirror bonding considerations between the finite-element analysis model and the as-built mirror mount.

The Indian Institute of Astrophysics is developing a Multi-Conjugate Adaptive Optics system for the Kodaikanal Tower Telescope. In this context, we measured the daytime turbulence strength profile at the Kodaikanal Observatory. The first method based on wavefront sensor images, called solar differential image motion monitor+, was used to estimate the higher altitude turbulence up to a height of 5 to 6 km. The second method used balloon-borne temperature sensors to measure the near-Earth turbulence up to 350 m. We also carried out simulations to validate the performance of our system. We report the first-ever daytime turbulence strength profile measurements at the observatory. We identified the presence of a strong turbulence layer ∼3 km above the observatory. The measured near-Earth turbulence matches the trend that is expected from the model for a daytime component of turbulence and gives an integrated r0 of ∼4 cm at 500 nm. This is consistent with earlier seeing measurements. This shows that a low-cost setup with a small telescope and a simple array of temperature sensors can be used for estimating the turbulence strength profile at the site.