The Habitable Worlds Observatory will revolutionize our understanding of the universe by directly detecting biosignatures on extrasolar planets and allow us to answer the question if we are alone in the universe. To accomplish the tight science goals associated with this mission, the development of an ultrastable observatory with a coronagraphic instrument is necessary. The observatory itself may need to stay stable on the order of 10 picometers over a wavefront control cycle, orders of magnitude more stable than what is required on current space missions. The metrology to verify stability requirements must be roughly a factor of ten more stable. The ultrastable laboratory at NASA’s Goddard Space Flight Center has further stabilized its testbed to allow for dynamic measurements on diffuse and specular objects on the order of single picometers, and we are currently measuring drifts on the orders of tens of picometers over different temporal bands. This paper will discuss the mechanical updates to the testbed setup, the analysis performed on several test articles, and the path forward on the road to measuring achieving the required stability for Habitable Worlds Observatory.
NASA’s Habitable Worlds Observatory will consist of a segmented telescope and high contrast coronagraph to characterize exoplanets for habitability. Achieving this objective requires an ultra-stable telescope with wavefront stability of picometers in certain critical modes. The NASA funded Ultra-Stable Large Telescope Research and Analysis – Technology Maturation program has matured key component-level technologies in 10 areas spanning an “ultra-stable” architecture, including active components like segment edge sensors, actuators and thermal hardware, passive components like low distortion mirrors and stable structures, and supporting capabilities like precision metrology. This paper will summarize the final results from the four-year ULTRA-TM program, including advancements in performance and/or path-to-flight readiness, TRL/MRL maturation, and recommendations for future work.
The GMT-Consortium Large Earth Finder (G-CLEF) is a fiber-fed, optical echelle spectrograph that will be a first light instrument for the Giant Magellan Telescope (GMT). G-CLEF is a general-purpose echelle spectrograph with precision radial velocity (PRV) capability. The radial velocity (RV) precision goal of G-CLEF is 10 cm/sec; necessary for detection of Earth-sized exoplanets orbiting Solar-type stars in their habitable zone. This imposes challenging stability requirements on the optical mounts and spectrograph support structures especially when considering the instrument’s operational environment. G-CLEF’s accuracy will be influenced by thermal effects, ambient air pressure, vibration, and micro gravity-vector variations caused by normal telescope slewing. The design and fabrication schedule for G-CLEF spectrograph and ancillary systems will lead the GMT telescope by approximately 5 years, therefore, we will design and build an interim installation configuration for G-CLEF at Magellan’s 6.5m telescopes. This will allow us to complete and commission the spectrograph. During this period, we will collect at least 5 years of data utilizing G-CLEF at Magellan from roughly 2027 to 2032. We also will also optimize major subsystems including spectrograph optics and mechanics, vacuum, thermal control, and vibration isolation. G-CLEF’s challenging technical requirements drove the decision to use low-CTE composites for the optical bench and several optical mounts including its collimator and pupil transfer mirrors and its Echelle Grating Support Structure. This paper discusses the process implemented in designing and procuring the composite structures used in the G-CLEF instrument.
The James Webb Space Telescope (JWST) launched on December 25, 2021, and its optical performance in orbit has been even better than predicted pre-flight. The static wavefront error (WFE) is less than half the value specified for the requirement of having diffraction-limited image quality at 2 microns in the NIRCam shortwave channel, enabling the observatory to deliver both sharper images and higher sensitivity than anticipated. In addition to the excellent image quality, the optical stability has also exceeded expectations, both in terms of high-frequency dynamic contributions (which would be perceived as part of “static WFE”) and in terms of drifts over minutes, hours, and days. Stability over long timescales is critical for several important science cases, including exoplanet transit spectroscopy and coronagraphy. JWST’s stability success was achieved through detailed design and testing, with several important lessons learned for future observatories, especially the Habitable Worlds Observatory that is expected to need even higher levels of stability. We review the stability architecture, how it was technologically demonstrated, the ground test results and improvements, the on-orbit results, and the lessons learned.
NASA’s Habitable Worlds Observatory will consist of a segmented telescope and high contrast coronagraph to characterize exoplanets for habitability. Achieving this objective requires an ultra-stable telescope with wavefront stability of picometers in certain critical modes. The NASA funded Ultra-Stable Large Telescope Research and Analysis – Technology Maturation program continues to mature key component-level technologies for this new regime of “ultra-stable optical systems,” including active components like segment edge sensors, actuators and thermal hardware, passive components like low distortion mirrors and stable structures, and supporting capabilities like precision metrology. This paper will present an update to the latest results from hardware testbeds and simulations in the areas listed above. It will also contain a correction to previously published results of Ball’s Integrated Demo, which consists of a capacitive sensor and three actuators operating in closed loop.
The recently released Astro2020 Decadal Survey recommends a large IR/O/UV space telescope that can observe potentially habitable exoplanets. Achieving this goal requires a telescope with wavefront stability on the order of picometers in some modes. The Ultra-Stable Large Telescope Research and Analysis – Technology Maturation (ULTRATM) program has matured key component-level technologies for this new regime of “ultra-stable optical systems,” including active components like segment edge sensors, actuators and thermal sensing and control hardware, as well as passive components like low distortion mirror mounts and stable composites for structures. Hardware testbeds have demonstrated component performance in the desired regime and with path-to-flight properties and simulations have applied those results to the flight system. These component level demonstrations are a critical step to enable subsequent subsystem and system level demonstrations of an ultra-stable telescope.
To achieve the ambitious science goal of performing direct imaging of earth-like exoplanets with a high contrast coronagraph, future space-based astronomical telescopes will require wavefront stability several orders of magnitude beyond state-of-the-art. The Ultra-Stable Large Telescope Research and Analysis – Technology Maturation (ULTRA-TM) program is maturing key component-level technologies for this new regime of “ultra-stable optical systems” through hardware testbeds that demonstrate component performance in the desired picometer regime and with path-to-flight properties. This paper describes the initial results from these testbeds – which address key capabilities across the ultrastable architecture and include active components like segment edge sensors, actuators and thermal sensing and control hardware, as well as passive components like low distortion mirror mounts and stable composites for structures. These promising experimental results are the first steps in our team’s technical maturation plan to credibly enable a large, ultrastable telescope in space. The resulting component, sub-system and system roadmaps are meant to support planning for technology development efforts for future NASA missions.
To achieve the ambitious goal of directly imaging exo-Earths with a coronagraph, future space-based astronomical telescopes will require wavefront stability several orders of magnitude beyond state-of-the-art. The Ultra-Stable Large Telescope Research and Analysis – Technology Maturation (ULTRA-TM) program will mature critical technologies for this new regime of “ultra-stable optical systems” through component-level hardware demonstrations.
This paper describes the progress towards demonstrating performance of these technologies in the picometer regime and with flight-like properties – including active systems like segment sensing and actuation and thermal sensing and control, as well as passive systems like low distortion mirror mounts and composite structures. Raising the TRL of these technologies will address the most difficult parts of the stability problem with the longest lead times and provide significant risk reduction for their inclusion in future mission concepts.
As the optical performance requirements of space telescopes get more stringent, the need to analyze all possible error sources early in the mission design becomes critical. One large telescope with tight performance requirements is the Large Ultraviolet / Optical / Infrared Surveyor (LUVOIR) concept. The LUVOIR concept includes a 15-meter-diameter segmented-aperture telescope with a suite of serviceable instruments operating over a range of wavelengths between 100nm to 2.5um. Using an isolation architecture that involves no mechanical contact between the telescope and the host spacecraft structure allows for tighter performance metrics than current space-based telescopes being flown. Because of this separation, the spacecraft disturbances can be greatly reduced and disturbances on the telescope payload contribute more to the optical performance error. A portion of the optical performance error comes from the disturbances generated from the motion of the Fast Steering Mirror (FSM) on the payload. Characterizing the effects of this disturbance gives insight into FSM specifications needed to achieve the tight optical performance requirements of the overall system. Through analysis of the LUVOIR finite element model and linear optical model given a range of input disturbances at the FSM, the optical performance of the telescope and recommendations for FSM specifications can be determined. The LUVOIR observatory control strategy consists of a multi-loop control architecture including the spacecraft Attitude Control System (ACS), Vibration Isolation and Precision Pointing System (VIPPS), and FSM. This paper focuses on the control loop containing the FSM disturbances and their effects on the telescope optical performance.
Future large astronomical telescopes in space will have architectures that will have complex and demanding requirements to meet the science goals. The Large UV/Optical/IR Surveyor (LUVOIR) mission concept being assessed by the NASA/Goddard Space Flight Center is expected to be 8 to 16 meters in diameter, have a segmented primary mirror, active control, and be diffraction limited at a wavelength of 500 nanometers. The optical stability is expected to be in the picometer range for minutes to hours. Architecture studies to support the NASA Science and Technology Definition teams (STDTs) are underway to evaluate systems performance. A wave front error budget has been developed to help define the technology needs and assess performance. The budget includes both spatial and temporal domain aspects for the active, adaptive and passive elements in the optical design.
The JWST Optical Telescope Element (OTE) assembly is the largest optically stable infrared-optimized telescope currently being manufactured and assembled, and is scheduled for launch in 2018. The JWST OTE, including the 18 segment primary mirror, secondary mirror, and the Aft Optics Subsystem (AOS) are designed to be passively cooled and operate near 45K. These optical elements are supported by a complex composite backplane structure. As a part of the structural distortion model validation efforts, a series of tests are planned during the cryogenic vacuum test of the fully integrated flight hardware at NASA JSC Chamber A. The successful ends to the thermal-distortion phases are heavily dependent on the accurate temperature knowledge of the OTE structural members. However, the current temperature sensor allocations during the cryo-vac test may not have sufficient fidelity to provide accurate knowledge of the temperature distributions within the composite structure. A method based on an inverse distance relationship among the sensors and thermal model nodes was developed to improve the thermal data provided for the nanometer scale WaveFront Error (WFE) predictions. The Linear Distance Weighted Interpolation (LDWI) method was developed to augment the thermal model predictions based on the sparse sensor information. This paper will encompass the development of the LDWI method using the test data from the earlier ‘pathfinder’ cryo-vac tests, and the results of the notional and as tested WFE predictions from the structural finite element model cases to characterize the accuracies of this LDWI method.
The Large UV/Optical/IR Surveyor (LUVOIR) is one of four 2020 Decadal Survey Missions, a concept for ‘flag-ship’ class space-borne observatory, operating across the multi-wavelength UV/Optical/NIR spectra. An Optical Telescope concept being considered is the segmented primary mirror architecture with composite backplane structure. In order to achieve the high-contrast imaging required to satisfy the primary science goals of this mission would require, roughly, 10 pico-meter wavefront RMS stability over a wavefront control time step of approximately 10 minutes. The LUVOIR primary mirror backplance support structure (PMBSS) requires active thermal management to maintain operational temperature while on orbit. Furthermore, the active thermal control must be sufficiently stable to prevent time-varying thermally induced distortions in the PMBSS. This paper describes a systematic approach to developing a thermal architecture of a modular composite section of the mirror support structure heavily guided by the sensitivity studies of the composite Coefficient of Thermal Expansion (CTE) values. Thermal and finite-element models, sensitivity studies against the absolute values and their variations of the composite CTE, the early findings from the thermal and thermaldistortion analyses are presented.
KEYWORDS: Mirrors, Space telescopes, James Webb Space Telescope, Finite element methods, Thermography, Thermal modeling, Aerospace engineering, Space mirrors, Telescopes, Observatories
The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a concept for a 9.2 m aperture space-borne observatory operating across the UV/Optical/NIR spectra. The primary mirror for ATLAST is a segmented architecture with pico-meter class wavefront stability. Due to its extraordinarily low coefficient of thermal expansion, a leading candidate for the primary mirror substrate is Corning’s ULE® titania-silicate glass. The ATLAST ULE® mirror substrates will be maintained at ‘room temperature’ during on orbit flight operations minimizing the need for compensation of mirror deformation between the manufacturing temperature and the operational temperatures. This approach requires active thermal management to maintain operational temperature while on orbit. Furthermore, the active thermal control must be sufficiently stable to prevent time-varying thermally induced distortions in the mirror substrates. This paper describes a conceptual thermal management system for the ATLAST 9.2 m segmented mirror architecture that maintains the wavefront stability to less than 10 pico-meters/10 minutes RMS. Thermal and finite element models, analytical techniques, accuracies involved in solving the mirror figure errors, and early findings from the thermal and thermal-distortion analyses are presented.
The GMT-CfA, Carnegie, Catolica, Chicago Large Earth Finder (G-CLEF) is a fiber fed, optical echelle spectrograph
that has undergone conceptual design for consideration as a first light instrument at the Giant Magellan Telescope. GCLEF
has been designed to be a general-purpose echelle spectrograph with precision radial velocity (PRV) capability.
We have defined the performance envelope of G-CLEF to address several of the highest science priorities in the Decadal
Survey1. The spectrograph optical design is an asymmetric, two-arm, white pupil design. The asymmetric white pupil
design is adopted to minimize the size of the refractive camera lenses. The spectrograph beam is nominally 300 mm,
reduced to 200 mm after dispersion by the R4 echelle grating. The peak efficiency of the spectrograph is >35% and the
passband is 3500-9500Å. The spectrograph is primarily fed with three sets of fibers to enable three observing modes:
High-Throughput, Precision-Abundance and PRV. The respective resolving powers of these modes are R~ 25,000,
40,000 and 120,000. We also anticipate having an R~40,000 Multi-object Spectroscopy mode with a multiplex of ~40
fibers. In PRV mode, each of the seven 8.4m GMT primary mirror sub-apertures feeds an individual fiber, which is
scrambled after pupil-slicing. The goal radial velocity precision of G-CLEF is ∂V <10 cm/sec radial. In this paper, we
provide a flowdown from fiducial science programs to design parameters. We discuss the optomechanical, electrical,
structural and thermal design and present a roadmap to first light at the GMT.
Generation-X is being studied as an extremely high resolution, very large area grazing incidence x-ray
telescope. Under a NASA Advanced Mission Concepts Study, we have developed a technology plan
designed to lead to the 0.1 arcsec (HPD) resolution adjustable optics with 50 square meters of effective area
necessary to meet Generation-X requirements. We describe our plan in detail.
In addition, we report on our development activities of adjustable grazing incidence optics via the
fabrication of bimorph mirrors. We have successfully deposited thin-film piezo-electric material on the
back surface of thin glass mirrors. We report on the electrical and mechanical properties of the bimorph
mirrors. We also report on initial finite element modeling of adjustable grazing incidence mirrors; in
particular, we examine the impact of how the mirrors are supported - the boundary conditions - on the
deformations which can be achieved.
X-rays provide one of the few bands through which we can study the epoch of reionization, when the first galaxies,
black holes and stars were born. To reach the sensitivity required to image these first discrete objects in the
universe needs a major advance in X-ray optics. Generation-X (Gen-X) is currently the only X-ray astronomy
mission concept that addresses this goal. Gen-X aims to improve substantially on the Chandra angular resolution
and to do so with substantially larger effective area. These two goals can only be met if a mirror technology
can be developed that yields high angular resolution at much lower mass/unit area than the Chandra optics,
matching that of Constellation-X (Con-X). We describe an approach to this goal based on active X-ray optics
that correct the mid-frequency departures from an ideal Wolter optic on-orbit. We concentrate on the problems
of sensing figure errors, calculating the corrections required, and applying those corrections. The time needed
to make this in-flight calibration is reasonable. A laboratory version of these optics has already been developed
by others and is successfully operating at synchrotron light sources. With only a moderate investment in these
optics the goals of Gen-X resolution can be realized.
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