The Habitable Worlds Observatory (HWO), NASA’s next flagship science mission, follows in the tradition of the Nancy Grace Roman Space Telescope (Roman) and other preceding great observatories. HWO will directly image and characterize Earth-like exoplanets and their atmospheres, with the capability to detect biosignatures and potentially answer the question “are we alone?” HWO will also serve as a powerful general astrophysics observatory, enabling breakthroughs in galaxy evolution, stellar astrophysics, and dark matter studies. Currently in preformulation, the project has established Exploratory Analytic Cases (EACs), a series of architectural concept designs used to assess the mission’s demanding science objectives while exploring challenging engineering parameters. We describe the first three EACs, starting with observing strategies and error budget formulation and then progressing to design formulations, trade studies, and lessons learned; we also discuss the integrated modeling pipeline, a key multidisciplinary system-level analysis capability, and analysis findings as applied to the first EAC. These activities set the stage for the follow-on EACs 4 and 5, which will further explore the trade space and prepare for the baseline design that will support the Mission Concept Review (MCR).

The upcoming Roman Coronagraph will be the first high-contrast instrument in space capable of high-order wavefront sensing and control technologies, a critical technology demonstration for the proposed Habitable Worlds Observatory (HWO) that aims to directly image and characterize habitable exoEarths. The nominal Roman Coronagraph observing plan involves alternating observations of a science target and a bright, nearby reference star. High contrast is achieved using wavefront sensing and control, also known as "digging a dark hole", where performance depends on the properties of the reference star, requiring V<3, a resolved stellar diameter <2 mas, and no stellar multiplicity. The imposed brightness and diameter criteria limit the sample of reference star candidates to high-mass main sequence and post-main sequence objects, where multiplicity rates are high. A future HWO coronagraph may have similarly restrictive criteria in reference star selection. From an exhaustive literature review of 95 stars, we identify an initial list of 40 primary and 18 reserve reference star candidates relevant to both the Roman Coronagraph and HWO. We present results from an initial survey of these candidates with high-resolution adaptive optics imaging and speckle interferometry and identify no new companions. We discuss the need for higher-contrast observations to sufficiently vet these reference star candidates prior to Roman Coronagraph observations along with the implications of reference star criteria on observation planning for Roman and HWO.

The Habitable Worlds Observatory (HWO), NASA's next flagship science mission, follows in the tradition of the Nancy Grace Roman Space Telescope and other preceding great observatories. HWO will directly image and characterize Earth-like exoplanet and their atmospheres, with the capability to detect biosignatures and potentially answer the question of whether we are we alone. HWO will also serve as a powerful general astrophysics observatory, enabling breakthroughs in galaxy evolution, stellar astrophysics, and dark matter studies. Currently in pre-formulation, the project has established Exploratory Analytic Cases (EACs), a series of architectural concept designs used to assess the mission's demanding science objectives while exploring challenging engineering parameters. This paper describes the first three EACs, starting with observing strategies and error budget formulation and then progressing to design formulations, trade studies and lessons learned; this paper also discusses the integrated modeling pipeline, a key multidisciplinary system-level analysis capability, and analysis findings as applied to the first EAC. These activities set the stage for the follow on EACs 4 and 5, which will further explore the trade space and prepare for the baseline design that will support the Mission Concept Review (MCR).

Roman is set to launch in weeks! The Coronagraph Instrument - technology pathfinder for future direct imaging missions - is ready to fly too. According to predictions, laboratory tests and high fidelity simulations, it will open a new contrast regime enabling the imaging of mature, giant planets in visible reflected light. The Community Participation Program is responsible for preparing a comprehensive observing program with associated data processing software and calibrations. We give a brief update about the on-going "baseline" calibration plan for the first months. Additionally, we describe a pilot program aiming for the stellar companion HD 29992 B at moderate 1e-5 to 1e-6 Band 1 (575 nm) contrast, to be carried out as soon as the instrument is operational. The idea is to generate a canonical data set with a self luminous companion that is easily recoverable. This functional checkout will be precious to best prepare our community, exercise our calibration plan and suite of tools.

The Habitable Worlds Observatory (HWO) aims to enable the detection and characterization of Earth-like planets around Sun-like stars to search for possible signs of life elsewhere in our universe. This requires an incredibly sensitive coronagraph instrument that suppresses the light from the star by a factor of 10 billion, which must contend with error terms that have not previously limited high-contrast instrumentation at lower levels of starlight suppression. Polarization aberrations are one such source of error that is particularly problematic for coronagraphy on a large space telescope. Optical rays in large, compact astronomical observatories can have large changes in angle of incidence over the beam, which induce polarization aberrations that decrease sensitivities to faint signals at small angular separations. Limiting variation in angles of incidence along the optical path could lead to longer, less stable observatories. This could negatively impact the total number of exo-Earths HWO would be able to detect. This study links open-source physical optics modeling tools to an exoplanet yield optimizer to understand how polarization aberrations influence science return for HWO. We also explore how polarization aberrations scale with change in angle of incidence, which could drive the primary-secondary mirror distance and overall observatory stability. In the visible, we find that decreasing the EAC-1 barrel from 16m to 12m results in ≈ 10^-10 contrast at the IWA where we expect exo-Earths to be. In the UV we appear to be less sensitive to polarization because exo-Earths are farther from the IWA. We also find a limited range over which the design reference mission of EAC-1 can be optimized to compensate for polarization aberrations using altruistic yield optimization. We then report on mitigation strategies to minimize the presence of polarization aberrations in HWO.

Prior to its delivery to the Goddard Space Flight Center (GSFC) on May 17, 2024, the integrated coronagraph instrument (CGI) underwent testing and verification at the Jet Propulsion Laboratory. We detail the test outcomes of the focus control loop (FCL) and Zernike control loop (ZCL) in the CGI's thermal vacuum (TVAC) test environment. To obtain and maintain the required wavefront stability, the CGI features a dedicated subsystem, the low-order wavefront sensing and control (LOWFSC), which detects wavefront alterations using starlight reflected off the focal plane mask, converts these changes into Zernike modes Z2-Z11, and independently controls Z2/Z3, Z4, and Z5-Z11 through three distinct control loops: line of sight control loop (LCL), FCL, and ZCL. Unlike the LCL, the testing of FCL and ZCL has been unfeasible without an appropriate testbed equipped with the necessary optical stimuli. Thus, the CGI TVAC tests mark the first system-level evaluation of FCL and ZCL prior to the CGI's handover to GSFC. The tests and subsequent analysis affirm that both loops are operating as intended, successfully meeting the key requirements of CGI. This document delineates various test configurations, presents the collected data, and scrutinizes the resulting outcomes. In addition, it includes the dark hole contrast data acquired through the exoplanetary systems camera (EXCAM). By concurrently measuring the EXCAM dark hole images alongside the LOWFSC observation, we were able to assess the CGI's contrast sensitivity to the Zernike wavefront errors, though the accuracy of these measurements suffered from unintentional partial saturation of the dark hole images. (c) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 International License.Distribution or reproduction of this work in whole or in part requires full attribution of the originalpublication, including its DOI.

The Nancy Grace Roman Space Telescope (Roman) is a 2.4-m space telescope scheduled for a 2026 launch. The Coronagraph Instrument (CGI) on Roman is a technology-demonstration instrument with a coronagraph and, for the first time in space, deformable mirrors and active wavefront control. We walk through the algorithmic and system-level architecture of the high-order wavefront sensing and control implementation for CGI, including the use of ground-in-the-loop operations to support computationally expensive operations, and reports on instrument performance measured during thermal vacuum testing in instrument integration and test. CGI achieved better than 5x10(-8) total raw contrast with two independent coronagraph architectures covering 3-9 and 6-20 lambda/D between them and a 360 deg dark hole on each. The contrast limits appear to be driven by the time available for testing and do not appear to represent a floor in the achievable performance of CGI in flight. (c) The Authors.

The Coronagraph Instrument (CGI) on the Roman Space Telescope represents a groundbreaking technology demonstration of advanced coronagraphy in space, enabling the detection and characterization of 10-9 contrast exoplanets in reflected light. Phase retrieval is integral to CGI calibration, supporting deformable mirror registration, wavefront flattening, and high-order wavefront sensing and control. By adapting methods proven in the high-contrast imaging testbed at the Jet Propulsion Laboratory, the CGI phase retrieval process mitigated development risks while meeting stringent performance requirements for repeatability, accuracy, and capture range. Extensive testing using the CGISim model confirmed alignment with these requirements, and successful thermal vacuum testing demonstrated robustness in real hardware scenarios. The phase retrieval algorithm, implemented as a Python package, plays a critical role in enabling CGI's high-contrast imaging capabilities, marking a significant step forward in coronagraph exoplanet imaging.

NASA's Nancy Grace Roman Space Telescope includes the coronagraph instrument (CGI): a technology demonstrator for active coronagraphy that uses deformable mirrors for deep starlight suppression, which enables imaging and spectroscopy of nearby faint companions. We provide an overview of the instrument-level test campaign of the CGI that took place at the Jet Propulsion Laboratory prior to the delivery of this instrument for the Roman payload and observatory integration. This test campaign served to expose the instrument to the environments associated with the Roman launch and space operations and to verify the CGI functional and performance requirements in the most comprehensive way possible prior to launch. An overview of the coronagraph requirements and key results of the test campaign is presented. (c) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 International License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. [DOI: 10.1117/1.JATIS.11.3.031511]

The coronagraph instrument for the Nancy Grace Roman Space Telescope is a complex instrument developed to directly image an exoplanet orbiting a nearby star. To do so, the light from the host star must be blocked to reveal the light from the planet. To accomplish this task, the instrument leverages many key technologies including hybrid-Lyot coronagraphs, shaped-pupil coronagraphs, electric field conjugation, Zernike wavefront sensing, deformable mirrors, precision alignment mechanisms, and precision fabrication of masks based on the development of microdevices. This large, baby grand piano-sized instrument has been delivered to the Roman Payload for integration. The flight instrument optical subsystem was fully aligned and tested prior to delivery. Besides the successful alignment of the optical subsystem, a few issues involving optical elements were revealed and addressed during the integration and test process. We present the final optical design and layout of the instrument, discuss key performance metrics, and discuss issues and lessons learned. (c) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 International License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. [DOI: 10.1117/1.JATIS.11.2.021413]

After nearly a decade's development, the coronagraph instrument (CGI) built for NASA's Nancy Grace Roman Space Telescope (RST) mission was delivered and integrated into the Roman telescope in 2024. CGI's high-order wavefront sensing and control (HOWFSC) modeling has played an important role throughout CGI development phases, from flight design, component risk assessment, and engineering decision-making support, to predelivery system requirement verification, anomaly resolution, etc. All these hinge on the credibility of HOWFSC models to predict key performance metrics. We outline the main evolution of the RST CGI HOWFSC performance model. We start by briefly summarizing past testbed model validation efforts and results and then focus on more recent modeling results during CGI's instrument-level thermal vacuum (TVAC) test campaign. We show that our model's prediction is consistent and in agreement with CGI's TVAC performance on many key contrast performance metrics, extending the good model validation track record. The model verified a critical anomaly discovered during TVAC and provided a credible assessment of the anomaly's on-orbit impact both with and without mitigation. The RST CGI model also shows a good correlation between the contrast drifts observed with the deformable mirror creep-like effect we have modeled. The results, experiences, and lessons learned from CGI HOWFSC modeling efforts are valuable to both future CGI operations and future missions to improve coronagraph technology development where there is a need to understand the bottlenecks of testbed raw contrast performance of various promising coronagraph types that are under development or testing. (c) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 International License.Distribution or reproduction of this work in whole or in part requires full attribution of the originalpublication, including its DOI.

Optical alignment of the Coronagraph Instrument (CGI) was completed in time to begin its full-functional and environmental testing and its integration into the Roman Space Telescope (RST). CGI optics relay the optical pupil of the RST five times so that science operations can be conducted at the internal pupil and image planes. The CGI has multiple active optical assemblies, including a fast-steering mirror, a focus-control mirror, two deformable mirrors, and six precision alignment mechanisms that articulate masks and apertures into the beam. Initial alignment of CGI optics was accomplished using an interferometer to measure the wavefront error (WFE) as optics were added sequentially. The end-to-end WFE was initially verified using surrogate optics in place of active optical assemblies, to allow their simultaneous development. Throughout alignment, pupil and image planes were referenced and coaligned optically. Upon alignment of the pupil-relay optics, the active optical assemblies were integrated and aligned, and the entire CGI alignment was then optimized. The CGI optical subsystem was mapped to fiducials, which will later be used to integrate CGI into the RST observatory. This study details the many alignment steps required to successfully achieve the performance criteria of the CGI. (c) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 International License.Distribution or reproduction of this work in whole or in part requires full attribution of the originalpublication, including its DOI.

We summarize the current best polychromatic (similar to 10% to 20% bandwidth) contrast performance demonstrated in the laboratory by different starlight suppression approaches and systems designed to directly characterize exoplanets around nearby stars. We present results obtained by internal coronagraph and external starshade experimental testbeds using entrance apertures equivalent to off-axis or on-axis telescopes, either monolithic or segmented. For a given angular separation and spectral bandwidth, the performance of each starlight suppression system is characterized by the values of "raw" contrast (before image processing), off-axis (exoplanet) core throughput, and post-calibration contrast (the final 1-sigma detection limit of off-axis point sources, after image processing). Together, the first two parameters set the minimum exposure time required for observations of exoplanets at a given signal-to-noise, i.e., assuming perfect subtraction of background residuals down to the photon noise limit. In practice, residual starlight speckle fluctuations during the exposure will not be perfectly estimated nor subtracted, resulting in a finite post-calibrated contrast and exoplanet detection limit whatever the exposure time. To place the current laboratory results in the perspective of the future Habitable Worlds Observatory (HWO) mission, we simulate visible observations of a fiducial Earth/Sun twin system at 12 pc, assuming a 6 m (inscribed diameter) collecting aperture and a realistic end-to-end optical throughput. The exposure times required for broadband exo-Earth detection (20% bandwidth around lambda=0.55 mu m) and visible spectroscopic observations (R=70) are then computed assuming various levels of starlight suppression performance, including the values currently demonstrated in the laboratory. Using spectroscopic exposure time as a simple metric, our results point to key starlight suppression system design performance improvements and trades to be conducted in support of HWO's exoplanet science capabilities. These trades may be explored via numerical studies, lab experiments, and high-contrast space-based observations and demonstrations.

Optical alignment of the Coronagraph Instrument (CGI) was completed in time to begin its full-functional and environmental testing in late 2023 and its integration into the Roman Space Telescope (RST) in summer 2024. The optics of the CGI relay the optical pupil of the RST five times so that science operations, such as coronagraphy and wavefront control, can be conducted in the different internal pupil and image planes. Within the pupil relays, the CGI has multiple active optical assemblies, including a fast-steering mirror, a focus-control mirror, two deformable mirrors, and six precision alignment mechanisms that articulate different masks and apertures into the beam. Initial alignment of the CGI optics was completed in the reverse direction, using a commercial dynamic Twyman-Green interferometer to measure the wavefront error through each relay as optics were added sequentially from back to front. The end-to-end wavefront error was initially verified using surrogate optics in place of the active optical assemblies, to allow their simultaneous development and test. Throughout alignment, pupil and image planes were referenced and coaligned optically using fiducials, including spherically mounted retroreflectors (SMRs) that were positioned by a laser tracker and measured by the interferometer camera. Upon end-to-end alignment of the pupil-relay optics, the active optical assemblies were integrated and aligned individually, and the entire CGI alignment was then optimized. The CGI optical subsystem was also mapped to SMR fiducials, which will later be used to integrate CGI into the RST observatory and verify its alignment to the Telescope's line of sight. This paper details the many alignment steps required to successfully achieve the performance criteria of the CGI. (c) 2024. California Institute of Technology.

The Roman Space Telescope Coronagraph Instrument uses phase retrieval for instrument multiple calibrations. We describe the how phase retrieval is performed and evaluate estimation error in the presence of instrument non-idealities.

The Roman Space Telescope will have the first advanced coronagraph in space, with deformable mirrors for wavefront control, low-order wavefront sensing and maintenance, and a photon-counting detector. It is expected to be able to detect and characterize mature, giant exoplanets in reflected visible light. Over the past decade the performance of the coronagraph in its flight environment has been simulated with increasingly detailed diffraction and structural/thermal finite element modeling. With the instrument now being integrated in preparation for launch within the next few years, the present state of the end-to-end modeling is described, including the measured flight components such as deformable mirrors. The coronagraphic modes are thoroughly described, including characteristics most readily derived from modeling. The methods for diffraction propagation, wavefront control, and structural and thermal finite-element modeling are detailed. The techniques and procedures developed for the instrument will serve as a foundation for future coronagraphic missions such as the Habitable Worlds Observatory.

NASA’s Nancy Grace Roman Space Telescope mission includes a Coronagraph Instrument (CGI) to demonstrate active Wavefront Sensing and Control (WFSC) for future direct imaging and characterization of exoplanets. CGI is in the instrument integration and testing phase and is scheduled to be delivered next year for integration into the Roman observatory. Key flight components, such as Deformable Mirrors (DMs) and detectors, have been recently characterized and integrated into the CGI optical system. A series of system level coronagraph requirement verifications in a vacuum chamber will take place starting later this year. Among them is the static raw contrast with a coronagraph stimulus source. This is the only time CGI will have the opportunity for dark hole digging before In-Orbit Commissioning (IOC). CGI High Order Wavefront Sensing and Control (HOWFSC) modeling has played an important role in assisting many engineering decisions and risk assessments and mitigations throughout the project phases, including when calibration data of key components and their imperfections became available. Here we present some of the latest modeling studies involving special use cases or properties of the DMs and detectors and give our current-best-estimates on static raw contrasts for the upcoming performance verification. Contrast performance for IOC phase WFSC with a typical reference star and its brightness is also provided. All evaluations are performed with the full features of HOWFSC modeling and extensive engineering details. This work is performed at the Jet Propulsion Laboratory / California Institute of Technology under contract to NASA.