We propose an approach for coarse alignment of a segmented space telescope using science instrument images. The recommended steps go from large post launch rigid body misalignments to within the capture range of coarse phasing where segment piston error is the predominant residual wavefront error. These steps include five data collection and analysis methods comprising of metrology capture, segment capture and identification, segment translation, segment stacking, and fine alignment. Using a proposed architecture for the NASA Habitable Worlds Observatory (HWO) we describe the details of our recommended approach for each telescope alignment step. We then compare this recommended sequence to alternative alignment progressions used in existing segmented testbeds and telescopes in terms of number of data collections required. This model-based demonstration establishes that the recommended coarse and fine alignment sequence performs more efficiently in time and resource cost, handing off to coarse and fine phasing activities further along the telescope commissioning process.

Current approaches for phasing of segmented space telescopes require complex dedicated optics and mechanisms, such as Dispersed Hartmann sensors or grisms. These methods do not scale well as the number of segments increases. The Broadband Phasing (BPH) approach used at the Keck Observatory does scale well and can work on space telescopes without the need for any additional hardware. We show that this method implemented as White Light Interferometry (WLI), using a standard imaging detector and filters, has a capture range limited only by the range of the segment actuators and can easily phase the mirrors to within the capture range of single wavelength phasing methods. An analysis of the Keck BPH performance is presented and used to develop a formula for implementation of WLI on other segmented telescopes. As an example, a WLI implementation for the NASA Habitable Worlds Observatory (HWO) telescope (Exploratory Analytic Case 1 (EAC1)) is developed and demonstrated via detailed wave-optics simulations. The implementation, performance and limitations of the proposed WLI method are discussed in detail in the paper.

The Habitable Worlds Observatory (HWO) is a future NASA flagship mission which will use a segmented telescope and coronagraphic instruments to discover and characterize exoplanets, including exoEarths - Earth-like planets orbiting other stars. HWO will require extraordinary optical stability, with wavefront drift performance measured in the picometers. This paper explores how active control of the telescope optics, using metrology systems that include laser distance gauges, segment edge sensors, and picometer precision actuators, can provide the needed telescope stability. Together with wavefront sensing and deformable mirrors in the coronagraph, this approach can control the entire coronagraphic beam train, to stabilize the electric field in the coronagraph. The HWO Technology Assessment Group is developing three "Exploratory Analytic Cases," which are conceptual designs for HWO that differ in some aspects, to provide a basis for detailed analysis. This paper addresses EAC1, a deployed-aperture concept that draws on JWST heritage. EAC1 uses 19 1.8-meter hexagonal segments to form its off-axis Primary Mirror (PM), as sketched in Figure 1. EAC2 will use fewer, larger "keystone" segments in a non-deployed off-axis PM configuration, and EAC3 will be a larger, on-axis deployed telescope using smaller keystone shaped segments.

Lentil is a Python package for developing high-performance diffraction simulations. Lentil provides an easy to use framework for modeling optical systems and simulating the wave propagation of light through them. Traditional Fourier optics-based approaches for numerically modeling diffraction rely on the Fast Fourier Transform (FFT) for simulating free space propagation. Despite computational efficiencies provided by the FFT, these simulations can be slow and memory-intensive due to very large array sizes needed to satisfy numerical sampling requirements imposed by the FFT algorithm. Modeling large apertures, highly aberrated or misaligned systems, or small features like primary mirror segment gaps demand even finer sampling, further degrading performance. Directly computing the discrete Fourier transform (DFT) in diffraction calculations provides greater flexibility and increased performance when compared with computing an equivalent FFT. Lentil offers generalized diffraction propagation routines using the DFT that improve simulation performance substantially, with additional optimizations for modeling segmented apertures. Lentil also implements a hybrid propagation algorithm blending physical and geometric optics to greatly improve performance in simulations where representing large tilts is required. Additionally, Lentil includes tools for modeling static and dynamic wavefront errors, radiometry, and focal plane arrays. The Lentil package and its accompanying documentation are freely available as open-source software.

In this paper, we introduce a system based on transfer learning for detecting segment misalignment in multimirror satellites, such as future CubeSat designs and the James Webb Space Telescope (JWST), using image-based methods. When a mirror segment becomes misaligned due to various environmental factors, such as space debris, the images can become distorted with a shifted copy of itself called a "ghost image". To detect whether segments are misaligned, we use pre-trained, large-scale image models trained on the Fast Fourier Transform (FFT) of patches of satellite images in grayscale. Multi-mirror designs can use any arbitrary number of mirrors. For our purposes, the tests were performed on simulated CubeSats with 4, 6, and 8 segments. For system design, we took this into account when we want to know when a satellite has a misaligned segment and how many segments are misaligned. The intensity of the ghost image is directly proportional to the number of segments misaligned. Models trained for intensity classification attempted to classify N-1 segments. Across eight classes, binary models were able to achieve a classification accuracy of 98.75 intensity classification were able to achieve an accuracy of 98.05

The Habitable Worlds Observatory is expected to carry a coronagraph instrument capable of direct imaging of Earth-like exoplanets in the habitable zone of distant stars. Such an instrument requires stability of its wavefront to a few picometers RMS in phase, and << 1% in amplitude over one observational cycle of approximately 12 hours. These tight requirements demand an adaptive optics system with extreme long term internal stability. In this paper, we show how phase shifting interferometry helps enable this long term stability by suppressing sources of 1/f noise while also providing measurement of both the phase and amplitude of the beam. Additionally, we show how a new type of noncommon path interferometer with a photonic phase shifter enables inclusion of this type of modulation into existing coronagraph layouts.

The Habitable Worlds Observatory will have uniquely stringent wavefront stability requirements, in the single-digit picometers for observations lasting days, to preserve coronagraph contrast for imaging earth-like exoplanets. This need will be addressed using high-precision Wavefront Sensing and Control methods, including continuous picometerprecision metrology and control of the Optical Telescope Assembly (OTA). This paper reviews methods for initializing and maintaining the OTA wavefront, evolved from those used for the James Webb Space Telescope, but extended to much higher precision. It concludes by identifying performance targets for WFSC technology development, to help guide NASA technology investments.

In this paper, we present a concept for an active, 6-meter space telescope (6MST) for space-based general astrophysics and consider its potential for coronagraphy. The telescope operates in spectral regions from about 100nm up to $\boldsymbol{2}\upmu\mathrm{m}$ , thus having the range comparable to Large Ultraviolet Optical Infrared Surveyor (LUVOIR) and Habitable Exoplanet Observatory (HabEx) in the longer wavelength end. In this paper, we produce the design for a vector-vortex coronagraph instrument for exoplanet work. We evaluate the impact of Primary Mirror (PM) segment gaps on the 20% broadband contrast floor when a charge 4 or charge 6 vortex mask and two $\boldsymbol{64}\mathrm{x}\boldsymbol{64}$ actuators sequential Deformable Mirrors (DM's) are used in the coronagraph, and compare the performance of a Lyot-mask and a pupil apodization mask relative to one another.

Coronagraphic space telescopes for imaging Earth-like exoplanets, such as the projected Habitable Worlds Observatory, will require extraordinary optical stability, with wavefront drift performance measured in the picometers. This paper considers how active means, using sensing and control subsystems, can control the entire coronagraphic beam train, from the telescope’s segmented primary mirror, through the coronagraph’s deformable mirrors, to stabilize the electric field in the coronagraph. Integrated telescope and coronagraph models are used to show how this can work to preserve contrast at the 10-10 level and provide important observational efficiencies. In future work, the models will also be used to identify needed performance levels for the various control system components, to help inform NASA’s technology funding priorities.

Directly imaging Earth-like exoplanets (``exoEarths'') with a coronagraph instrument on a space telescope requires a stable wavefront with optical path differences limited to tens of picometers RMS during exposure times of a few hours. While the structural dynamics of a segmented mirror can be directly stabilized with telescope metrology, another possibility is to use a closed-loop wavefront sensing and control system in the coronagraph instrument that operates during the science exposures to actively correct the wavefront and relax the constraints on the stability of the telescope. In this paper, we present simulations of the temporal filtering provided using the example of LUVOIR-A, a 15~m segmented telescope concept. Assuming steady-state aberrations based on a finite element model of the telescope structure, we (1)~optimize the system to minimize the wavefront residuals, (2)~ use an end-to-end numerical propagation model to estimate the residual starlight intensity at the science detector, and (3)~predict the number of exoEarth candidates detected during the mission. We show that telescope dynamic errors of 100~pm~RMS can be reduced down to 30~pm~RMS with a magnitude 0 star, improving the contrast performance by a factor of 15. In scenarios where vibration frequencies are too fast for a system that uses natural guide stars, laser sources can increase the flux at the wavefront sensor to increase the servo-loop frequency and mitigate the high temporal frequency wavefront errors. For example, an external laser with an effective magnitude of -4 allows the wavefront from a telescope with 100~pm~RMS dynamic errors and strong vibrations as fast as 16~Hz to be stabilized with residual errors of 10~pm~RMS thereby increasing the number of detected planets by at least a factor of 4.

Technology development enables space flight missions. This paper reviews lessons learned for how to formulate and implement an intentional technology development process. We describe four elements of this disciplined approach. First, start with Science Driven Systems Engineering. Define the Level 0 science requirements and derive a science traceability matrix for required measurements. Technology innovation and maturation does not happen in a vacuum. It is tied to the fulfillment of well-articulated science goals. Second, study, analyze and develop multiple notional mission concepts to identify and prioritize technology gaps. Third, invest in the maturation of mid-TRL technologies. And fourth, consistent oversight of the efficacy of those investments. Technology grants, cooperative agreements and contracts need to have active and close management and reporting of their progress, milestones, TRL advancements and final outcomes, to meet the goal of promoting and increasing the technology infusion rates in future space flight missions. The cumulative value of lessons learned from flight projects and expertise gained in the last decade enables more effective ways to promote advances via an intentional technology maturation model, a significant variation of the classical pull technology model.

We present a design for an active telescope for space astronomy. The telescope is capable of both exoplanet work and general astronomy over wavelengths from similar to 100 nm up to 5 mu m. The primary mirror is 6 m in diameter, formed by 16 mirror segments that are precisely phased and supported on rigid body actuators and with segment optical surface figures finetuned using surface figure actuators. The active primary forms a large deformable mirror (DM) with wavefront error (WFE) correction at the entrance pupil. Thus the largest source of WFE can be removed at the source and is corrected over the entire field of view. This enables diffraction-limited performance at 400 nm and a more efficient optical system over a broader wavelength range than could be achieved by a small DM at a downstream relayed pupil. The telescope is passively cooled to below 100 K at Sun-Earth L2, enabling astronomical -background-limited observations out to 5 mu m. Launched on a SpaceX Starship or alternatively National Aeronautics and Space Administration's Space Launch System, the telescope requires minimal deployments. A 72-m-diameter starshade provides a contrast ratio better than 10(-10) for exoplanet science. Near the visible region, with a 108% working bandwidth from 300 to 1000 nm, a working distance of 120 Mm provides a 51-mas inner working angle (IWA). This band can be moved to shorter or longer wavelengths by adjusting the starshade range from the telescope. Our first-ever thermal analysis of such a starshade shows that a temperature below 100 K can be achieved over a broad range of observing directions, permitting the possibility of working into the infrared. We model the yield in exoplanets that can be observed. A starshade and associated spectrograph offer significant advantages for exoplanet characterization. They enable a much broader instantaneous spectral bandwidth (here 108%) than current coronagraphs (similar to 10% to 20% bandwidth), allow both polarizations to be observed simultaneously, and have higher throughput. The IWA is twice as small as can be achieved with a coronagraph and there is no outer working angle. These differences are particularly pronounced in the UV, where corona graph performance would be strongly affected by throughput losses, wavefront aberrations, Fresnel polarization effects at surfaces, and thermal instability.

The Astro2020 decadal survey recommended a ~6m IR/O/UV telescope equipped with a coronagraph instrument to directly image exoEarths in the habitable zone of their host star. A telescope of such size may need to be segmented to be folded and then carried in current launch vehicles. However, a segmented primary mirror introduces the potential for mid spatial frequency optical wavefront instabilities during the science operations that would degrade the coronagraph performance. A coronagraph instrument with a wavefront sensing and control (WS&C) system can stabilize the wavefront with a picometer precision at high temporal frequencies (<1Hz). In this work, we study a realistic set of aberrations based on a finite element model of a slightly bigger (8m circumscribed, 6.7m inscribed diameter) segmented telescope with its payload. We model an adaptive optics (AO) system numerically to compute the post-AO residuals. The residuals then feed an end-to-end model of a vector vortex coronagraph instrument. The long exposure contrast thus obtained is finally used in an ExoEarth yield method calculation to understand the overall benefits of the adaptive optics system in the flagship mission success.

Abstract. 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? We describe how Origins was designed to answer these alluring questions. We discuss the key decisions taken by the Origins mission concept study team, the rationale for those choices, and how they led through an exploratory design process to the Origins baseline mission concept. To understand the concept solution space, we studied two distinct mission concepts and descoped the second concept, aiming to maximize science per dollar and hit a self-imposed cost target. We report on the study approach and describe the concept evolution. The resulting baseline design includes a 5.9-m diameter telescope cryocooled to 4.5 K and equipped with three scientific instruments. The chosen architecture is similar to that of the Spitzer Space Telescope and requires very few deployments after launch. The cryo-thermal system design leverages James Webb Space Telescope technology and experience.

One of the primary science goals of the Large UV/Optical/Infrared Surveyor (LUVOIR) mission concept is to detect and characterize Earth-like exoplanets orbiting nearby stars with direct imaging. The success of its coronagraph instrument ECLIPS (Extreme Coronagraph for Living Planetary Systems) depends on the ability to stabilize the wavefront from a large segmented mirror such that optical path differences are limited to tens of picometers RMS during an exposure time of a few hours. In order to relax the constraints on the mechanical stability, ECLIPS will be equipped with a wavefront sensing and control (WS C) architecture to correct wavefront errors up to temporal frequencies > 1 Hz. These errors may be dominated by spacecraft structural dynamics exciting vibrations at the segmented primary mirror. In this work, we present detailed simulations of the WS C system within the ECLIPS instrument and the resulting contrast performance. This study assumes wavefront aberrations based on a finite element model of a simulated telescope with spacecraft structural dynamics. Wavefront residuals are then computed according to a model of the adaptive optics system that includes numerical propagation to simulate a realistic wavefront sensor and an analytical model of the temporal performance. An end-to-end numerical propagation model of ECLIPS is then used to estimate the residual starlight intensity distribution at the science detector. We show that the contrast performance depends strongly on the target star magnitude and the spatio-temporal distribution of wavefront errors from the telescope. In cases with significant vibration, we advocate for the use of laser metrology to mitigate high temporal frequency wavefront errors and increase the mission yield.

The National Academies’ Decadal Survey telescope studies have produced mission design concepts that plot pathways into the future to follow on from Hubble, Spitzer, JWST and NGRST. Considering the results of the LUVOIR and HabEx studies in particular, it is clear that segmented mirrors will eventually be needed to provide very large apertures in space and that this architecture presents both a scientific opportunity and an engineering challenge. Furthermore, while HabEx and LUVOIR cover a great deal of spectrum, both fall short of the mid-IR region where general astronomy and astrophysics can be undertaken that would be impossible from terrestrial observatories and where there also exist spectral features of interest in the search for life. A telescope with similar capabilities to Habex/LUVOIR but also capable of exoplanet work in spectral regions up to 5 μm would largely bridge the gap between those proposals and TPF-I (which would have operated from about 7 μm upwards), and is therefore worthy of study. The Active Telescope for Space Astronomy (ATSA) design study presents a possible architecture and is moderately sized (6 m) to enable the use of both starshade and coronagraph technologies. While the segment gaps of a segmented primary mirror present a challenge for coronagraphy, the architecture does allow direct wavefront control at each segment of that mirror, enabling a great degree of control at the primary source of contrast degradation. While active systems (for example, deformable mirrors on WFIRST CGI) are being incorporated into telescope designs today, a fully active mirror system needs further development for a future mission. With this concept in mind, and intending to build on the LUVOIR and HabEx studies, we discuss the elements of a cooled telescope design enabling both general astrophysics and exoplanet studies from the near UV through to the near-IR.

The Galaxy Evolution Probe (GEP) is a concept for a mid- and far-infrared space observatory to measure key properties of large samples of galaxies with large and unbiased surveys. GEP will attempt to achieve zodiacal light and Galactic dust emission photon background-limited observations by utilizing a 6-K, 2.0-m primary mirror and sensitive arrays of kinetic inductance detectors (KIDs). It will have two instrument modules: a 10 to 400 mu m hyperspectral imager with spectral resolution R = lambda/Delta lambda >= 8 (GEP-I) and a 24 to 193 mu m, R = 200 grating spectrometer (GEP-S). GEP-I surveys will identify star-forming galaxies via their thermal dust emission and simultaneously measure redshifts using polycyclic aromatic hydrocarbon emission lines. Galaxy luminosities derived from star formation and nuclear supermassive black hole accretion will be measured for each source, enabling the cosmic star formation history to be measured to much greater precision than previously possible. Using optically thin far-infrared fine-structure lines, surveys with GEP-S will measure the growth of metallicity in the hearts of galaxies over cosmic time and extraplanar gas will be mapped in spiral galaxies in the local universe to investigate feedback processes. The science case and mission architecture designed to meet the science requirements is described, and the KID and readout electronics state of the art and needed developments are described. This paper supersedes the GEP concept study report cited in it by providing new content, including: a summary of recent mid-infrared KID development, a discussion of microlens array fabrication for mid-infrared KIDs, and additional context for galaxy surveys. The reader interested in more technical details may want to consult the concept study report. (C) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License.

Notes on the forward model for a Zernike wavefront sensor, with details on numerical implementation. 1. REVIEW OF ZWFS ESTIMATORS First we recall the ZWFS Y± = F † h 1 R ⇣ 1 e±i⇡/2 ⌘ R i FAe so that the output pupil field is Y± = Ae i (1⌥ i)F †RFAei B = F †RFAei ⌘ |B|e B0 ⌘ F †RFA (1) Note that we know A = p I0. These relations give exactly I± = |A| 2 + 2|B| |B||A|Re (1± i)e i e = |A| + 2|B| 2 p 2 |B||A| Re n e±i⇡/4e i e o This shows that I± = |A| 2 + 2|B| 2 p 2 |B||A| cos n ( )± ⇡ 4 o (2) Assuming we know B, this gives cos n ( )± ⇡ 4 o = ( 1)  I± |A|2 2|B|2 2 p 2 |B||A| (3) We also have I+ I = 2 p 2 |B||A| Re n⇣ e e i⇡/4 ⌘ e i e o = 2 p 2 |B||A| Re (2i) sin(⇡/4)e i e = 4|B||A| Re ie i e = +4|B||A| sin { }

We consider the scientific benefits and technical feasibility of a 6-m, non-deployed, cold space telescope mission concept, covering the ultraviolet, visible, near-infrared, and mid-infrared wavebands, for direct imaging of exoplanets and a broad range of astronomical investigations. The concept uses the largest practical aperture size that can be launched without deployment, for lower risk and cost. An innovative, rigid outer barrel and sunshield control temperature and stray light in a compact, Spitzer-like configuration that provides a 100-K telescope. Additional active and passive thermal features provide millikelvin temperature stability. The ultraviolet and visible instruments are based on the suite developed for the Habitable Exoplanet Observatory concept. The cold telescope enables the scientifically important addition of mid-infrared imaging and spectroscopy modes, providing background-limited imaging to 5 um wavelength. The telescope uses actively-controlled mirrors to compensate for cool-down aberrations, other optical uncertainties, and tolerances or errors that may occur in manufacturing, assembly, launch, and on-orbit operations. A starshade provides high-dynamic-range imaging and spectroscopy of exoplanets, potentially augmented by a coronagraph for exoplanet search and orbit measurement. Special attention has been paid to contamination control, assessing the feasibility of UV imaging with a cryogenic telescope. The paper will provide design details and assessment of scientific yield and technology readiness, while addressing real and perceived issues for a space telescope capable of covering this wide wavelength range.