NASA’s return to the Moon presents unparalleled opportunities to advance high-impact scientific capabilities. At the cutting edge of these possibilities are extremely high-resolution interferometric observations at visible and ultraviolet wavelengths. Such technology can resolve the surfaces of stars, explore the inner accretion disks of nascent stars and black holes, and eventually enable us to observe surface features and weather patterns on nearby exoplanets. We have been awarded Phase 1 support from NASA's Innovative Advanced Concepts (NIAC) program to explore the feasibility of constructing a high-resolution, long-baseline UV/optical imaging interferometer on the lunar surface, in conjunction with the Artemis Program. A 1996 study comparing interferometers on the Moon versus free-flyers in space concluded that, without pre-existing lunar infrastructure, free-flyers were preferable. However, with the advent of the Artemis Program, it is now crucial to revisit the potential of building lunar interferometers. Our objective is to conduct a study with the same level of rigor applied to large baseline, free-flying interferometers during the 2003-2005 NASA Vision Missions Studies. This preparation is essential for timely and effective utilization of the forthcoming lunar infrastructure. In this paper, we highlight the groundbreaking potential of a lunar surface-based interferometer. This concept study will be a huge step forward to larger arrays on both the moon and free-flying in space, over a wide variety of wavelengths and science topics. Our Phase 1 study began in April 2024, and here we present a concise overview of our vision and the progress made so far.
MoonLITE (Lunar InTerferometry Explorer) is an Astrophysics Pioneers proposal to develop, build, fly, and operate the first separated-aperture optical interferometer in space, delivering sub-milliarcsecond science results. MoonLITE will leverage the Pioneers opportunity for utilizing NASA’s Commercial Lunar Payload Services (CLPS) to deliver an optical interferometer to the lunar surface, enabling unprecedented discovery power by combining high spatial resolution from optical interferometry with deep sensitivity from the stability of the lunar surface. Following landing, the CLPS-provided rover will deploy the pre-loaded MoonLITE outboard optical telescope 100 meters from the lander’s inboard telescope, establishing a two-element interferometric observatory with a single deployment. MoonLITE will observe targets as faint as 17th magnitude in the visible, exceeding ground-based interferometric sensitivity by many magnitudes, and surpassing space-based optical systems resolution by a factor of 50×. The capabilities of MoonLITE open a unique discovery space that includes direct size measurements of the smallest, coolest stars and substellar brown dwarfs; searches for close-in stellar companions orbiting exoplanet-hosting stars that could confound our understanding and characterization of the frequency of Earth-like planets; direct size measurements of young stellar objects and characterization of the terrestrial planet-forming regions of these young stars; measurements of the inner regions and binary fraction of active galactic nuclei; and a probe of the very nature of spacetime foam itself. A portion of the observing time will also be made available to the broader community via a guest observer program. MoonLITE takes advantage of the CLPS opportunity to place an interferometer in space on a stable platform – the lunar surface – and delivers an unprecedented combination of sensitivity and angular resolution at the remarkably affordable cost point of Pioneers.
The mirrors of astronomical interferometers need to be aligned within a fraction of a wavelength relative to one another. This would be especially challenging for optical instruments with mirrors separated by hundreds of meters flying in Earth’s orbit. However, in this work, we show that this alignment can be achieved by means of: (i) flying the mirror cluster in a particular orbital configuration; (ii) closing a coarse positioning loop using GNSS (Global Navigation Satellite System); and (iii) closing a fine wavefront-control loop using light from a laser guide star. The orbital configuration is designed to keep the mirrors passively pointing at the target star (up to a small orbital perturbation) while the interferometer cluster is orbiting and changing its baseline. The laser guide star would be flying in the same orbit but in the opposite direction. In medium- or high-Earth orbit, the interferometer would be able to observe a star for several hours per orbit. In this work, we analyzed the performance of an optical space interferometer consisting of nine 20 cm mirrors mounted on CubeSats and flying 3 km apart (together with a combiner and a laser guide star small satellite). This configuration supports a resolution of 0.04 milliarcseconds - an order of magnitude better than current ground-based interferometers. We estimate the performance of this system imaging stellar surfaces assuming perfect wavefront estimation and control.
The Photon Sieve Space Telescope (PSST) is a space-based ultra high-resolution (5 mas) narrow band (λ/Δλ ≃ 1000) spectral UV imager providing spectral imaging of astronomical objects in Ly - ∝, CIV and NV emission lines. Science obtained with this telescope will revolutionize our understanding of a whole range of astrophysical processes in the local and distant universe. There will be a dramatic increase in the number of observed moderate and large SMBH masses as well as extra-solar protoplanetary disks. The observations will also enable tracing the star formation rates in active galaxies. We present the optical design, the properties and the future implementation of the proposed UV photon sieve space telescope.
Perhaps one of the most ambitious long-term goals of the astronomical community is to map distant exoplanets. This will require instruments that provide sufficient angular resolution to place multiple pixels across an image of an exoplanet. Many other science programs also require orders of magnitude improvement in angular resolution, and for all of these, single aperture telescopes are impractical. In fact, the array of scientific goals that require high angular resolution makes interferometry inevitable. Here, we discuss some of the long-term science needs, and the implications for future interferometers, and then talk about some possible paths towards these future missions.
The infrastructure available on the ISS provides a unique opportunity to develop the technologies necessary to assemble
large space telescopes. Assembling telescopes in space is a game-changing approach to space astronomy. Using the ISS
as a testbed enables a concentration of resources on reducing the technical risks associated with integrating the
technologies, such as laser metrology and wavefront sensing and control (WFSandC), with the robotic assembly of major
components including very light-weight primary and secondary mirrors and the alignment of the optical elements to a
diffraction-limited optical system in space. The capability to assemble the optical system and remove and replace
components via the existing ISS robotic systems such as the Special Purpose Dexterous Manipulator (SPDM), or by the
ISS Flight Crew, allows for future experimentation as well as repair if necessary. In 2015, first light will be obtained by
the Optical Testbed and Integration on ISS eXperiment (OpTIIX), a small 1.5-meter optical telescope assembled on the
ISS. The primary objectives of OpTIIX include demonstrating telescope assembly technologies and end-to-end optical
system technologies that will advance future large optical telescopes.
Stellar Imager (SI) is a space-based, UV/Optical Interferometer (UVOI) with over 200x the resolution of HST. It will
enable 0.1 milli-arcsec spectral imaging of stellar surfaces and the Universe in general and open an enormous new
"discovery space" for astrophysics with its combination of high angular resolution, dynamic imaging, and spectral
energy resolution. SI's goal is to study the role of magnetism in the Universe and revolutionize our understanding of: 1)
Solar/Stellar Magnetic Activity and their impact on Space Weather, Planetary Climates, and Life, 2) Magnetic and
Accretion Processes and their roles in the Origin & Evolution of Structure and in the Transport of Matter throughout the
Universe, 3) the close-in structure of Active Galactic Nuclei and their winds, and 4) Exo-Solar Planet Transits and Disks.
SI is a "Landmark/Discovery Mission" in 2005 Heliophysics Roadmap and a candidate UVOI in the 2006 Astrophysics
Strategic Plan and is targeted for launch in the mid-2020's. It is a NASA Vision Mission and has been recommended for
further study in a 2008 NRC report on missions potentially enabled/enhanced by an Ares V launch. In this paper, we
discuss the science goals and required capabilities of SI, the baseline architecture of the mission assuming launch on one
or more Delta rockets, and then the potential significant enhancements to the SI science and mission architecture that
would be made possible by a launch in the larger volume Ares V payload fairing, and by servicing options under
consideration in the Constellation program.
We evaluate the feasibility of a balloon-borne nulling interferometer to detect and characterize an exosolar planet and the
surrounding debris disk. The existing instrument consists of a three-telescope Fizeau imaging interferometer with thre
fast steering mirrors and three delay lines operating at 800 Hz for closed-loop control of wavefront errors and fine
pointing. A compact visible nulling interferometer would be coupled to the imaging interferometer and in principle,
allows deep starlight suppression. Atmospheric simulations of the environment above 100,000 feet show that balloonborne
payloads are a possible path towards the direct detection and characterization of a limited set of exoplanets and
debris disks. Furthermore, rapid development of lower cost balloon payloads provide a path towards advancement of
NASA technology readiness levels for future space-based exoplanet missions. Discussed are the BENI mission and
instrument, the balloon environment and the feasibility of such a balloon-borne mission.
Stellar Imager (SI) is a proposed NASA space-based UV imaging interferometer to resolve the stellar disks of nearby
stars. SI would consist of 20 - 30 separate spacecraft flying in formation at the Earth-Sun L2 libration point. Onboard
wavefront sensing and control is required to maintain alignment during science observations and after array
reconfigurations. The Fizeau Interferometry Testbed (FIT), developed at the NASA/Goddard Space Flight Center, is
being used to study wavefront sensing and control methodologies for Stellar Imager and other large, sparse aperture
telescope systems. FIT initially consists of 7 articulated spherical mirrors in a Golay pattern, and is currently undergoing
expansion to 18 elements. FIT currently uses in-focus whitelight sparse aperture PSFs and a direct solve broadband
phase retrieval algorithm to sense and control its wavefront. Ultimately it will use extended scene wavelength, with a
sequential diversity algorithm that modulates a subset of aperture pistons to jointly estimate the wavefront and the
reconstructed image from extended scenes. The recovered wavefront is decomposed into the eigenmodes of the control
matrix and actuators are moved to minimize the wavefront piston, tip and tilt in closed-loop. We discuss the testbed,
wavefront control methodology and ongoing work to increase its bandwidth from 1 per 11 seconds to a few 10's of
Hertz and show ongoing results.
Stellar Imager (SI) is a proposed NASA space-based UV imaging interferometer to resolve the stellar disks of nearby
stars. SI would consist of 20 - 30 separate spacecraft flying in formation at the Earth-Sun L2 libration point. Onboard
wavefront sensing and control is required to maintain alignment during science observations and after array
reconfigurations. The Fizeau Interferometry Testbed (FIT), developed at the NASA/Goddard Space Flight Center, is
being used to study wavefront sensing and control methodologies for Stellar Imager and other large, sparse aperture
telescope systems. FIT initially consists of 7 articulated spherical mirrors in a Golay pattern, and is currently undergoing
expansion to 18 elements. FIT currently uses in-focus whitelight sparse aperture PSFs and a direct solve phase retrieval
algorithm to sense and control its wavefront. Ultimately it will use extended scene wavelength, with a sequential
diversity algorithm that modulates a subset of aperture pistons to jointly estimate the wavefront and the reconstructed
image from extended scenes. The recovered wavefront is decomposed into the eigenmodes of the control matrix and
actuators are moved to minimize the wavefront piston, tip and tilt in closed-loop. We discuss the testbed, wavefront
control methodology and ongoing work to increase its bandwidth from 1 per 11 seconds to a few 10's of Hertz and show
ongoing results.
KEYWORDS: Imaging systems, Sensors, Telescopes, Spatial frequencies, Mirrors, Space telescopes, Interferometry, Adaptive optics, Wavefronts, Signal to noise ratio
Stellar Imager (SI) will be a Space-Based telescope consisting of 20 to 30 separated apertures. It is designed
for UV/Optical imaging of stellar surfaces and asteroseismology. This report describes details of an alternative
optical design for the beam combiner, dubbed the Spatial Frequency Remapper (SFR). It sacrifices the large
field of view of the Fizeau combiner. In return, spectral resolution is obtained with a diffraction grating rather
than an array of energy-resolving detectors. The SFR design works in principle and has been implemented with
MIRC at CHARA for a small number of apertures. Here, we show the number of optical surfaces can be reduced
and the concept scales gracefully to the large number of apertures needed for Stellar Imager.
We also describe a potential application of this spatial frequency remapping to improved imaging with filled-aperture
systems. For filled-aperture imaging, the SFR becomes the core of an improved aperture masking
system. To date, aperture-masking has produced the best images with ground-based telescopes but at the
expense of low sensitivity due to short exposures and the discarding of most of the light collected by the telescope.
This design eliminates the light-loss problem previously claimed to be inherent in all aperture-masking designs.
We also argue that at least in principle, the short-integration time limit can also be overcome. With these
improvements, it becomes an ideal camera for TPF-C; since it can form speckle-free images in the presence of
wavefront errors, it should significantly relax the stability requirements of the current designs.
The Stellar Imager (SI) is a UV/optical, space-based interferometer designed to enable 0.1 milli-arcsecond (mas) spectral
imaging of stellar surfaces and, via asteroseismology, stellar interiors and of the Universe in general. SI's science focuses
on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. SI's
prime goal is to enable long-term forecasting of solar activity and the space weather that it drives, in support of the
Living with a Star program in the Exploration Era. SI will also revolutionize our understanding of the formation of
planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically
controlled processes in the Universe. SI is a "Flagship and Landmark Discovery Mission" in the 2005 Sun Solar System
Connection (SSSC) Roadmap and a candidate for a "Pathways to Life Observatory" in the Exploration of the Universe
Division (EUD) Roadmap (May, 2005). We discuss herein the science goals of the SI Mission, a mission architecture
that could meet those goals, and the technologies needed to enable this mission. Additional information on SI can be
found at: http://hires.gsfc.nasa.gov/si/.
The Stellar Imager (SI) is a UV-Optical, Space-Based Interferometer designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general and asteroseismic imaging of stellar interiors. SI is identified as a "Flagship and Landmark Discovery Mission" in the 2005 Sun Solar System Connection (SSSC) Roadmap and as a candidate for a "Pathways to Life Observatory" in the Exploration of the Universe Division (EUD) Roadmap (May, 2005). SI will revolutionize our view of many dynamic astrophysical processes: its resolution will transform point sources into extended sources, and snapshots into evolving views. SI's science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. SI's prime goal is to enable long-term forecasting of solar activity and the space weather that it drives. SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. The results of the SI "Vision Mission" Study are presented in this paper. Additional information on the SI mission concept and related technology development can be found at URL: http://hires.gsfc.nasa.gov/si/.
The Stellar Imager (SI) is a far-horizon or "Vision" mission in the NASA Sun-Earth Connection (SEC) Roadmap, conceived for the purpose of understanding the effects of stellar magnetic fields, the dynamos that generate them, and the internal structure and dynamics of the stars in which they exist. The ultimate goal is to achieve the best possible forecasting of solar/stellar activity and its impact on life in the Universe. The science goals of SI require an ultra-high angular resolution, at ultraviolet wavelengths, on the order of 0.1 milliarcsec and thus baselines on the order of 500 meters. These requirements call for a large, multi-spacecraft (>20) imaging interferometer, utilizing precision formation flying in a stable environment, such as in a Lissajous orbit around the Sun-Earth L2 point. SI's resolution (several 100 times that of HST) will make it an invaluable resource for many other areas of astrophysics, including studies of AGN's, supernovae, cataclysmic variables, young stellar objects, QSO's, and stellar black holes. In this paper, we present an update on the ongoing mission concept and technology development studies for SI. These studies are designed to refine the mission requirements for the science goals, define a Design Reference Mission, perform trade studies of selected major technical and architectural issues, improve the existing technology roadmap, and explore the details of deployment and operations, as well as the possible roles of astronauts and/or robots in construction and servicing of the facility.
Metrology and pointing will be enabling technologies for a new generation of astronomical missions having large and distributed apertures and delivering unprecedented performance. The UV interferometer Stellar Imager would study stellar dynamos by imaging magnetic activity on the disks of stars in our Galaxy. The X-ray interferometer Black Hole Imager would study strong gravity physics and the formation of jets by imaging the event horizons of supermassive black holes. These missions require pointing to microarcseconds or better, and metrology to nm accuracy of optical elements separated by km, for control of optical path difference. This paper describes a metrology and pointing system that meets these requirements for the Stellar Imager. A reference platform uses interferometers to sense alignment with a guide star. Laser gauges determine mirror positions in the frame of the reference platform, and detector position is monitored by laser gauges or observations of an artificial star. Applications to other astronomical instruments are discussed.
The Fizeau Interferometer Testbed (FIT) is a ground-based laboratory experiment at Goddard Space Flight Center (GSFC) designed to develop and test technologies that will be needed for future interferometric spacecraft missions. Specifically, the research from this experiment is a proof-of-concept for optical accuracy and stability, closed-loop control algorithms, optimal sampling methodology of the Fourier UV-plane, computational models for system performance, and image synthesis techniques for a sparse array of 7 to 30 mirrors. It will assess and refine the technical requirements on hardware, control, and imaging algorithms for the Stellar Imager (SI), its pathfinder mission, and other sparse aperture and interferometric imaging mission concepts. This ground-based optical system is a collaborative effort between NASA's GSFC, Sigma Space Corporation, the Naval Research Laboratory, and the University of Maryland. We present an overview of the FIT design goals and explain their associated validation methods. We further document the design requirements and provide a status on their completion. Next, we show the overall FIT design, including the optics and data acquisition process. We discuss the technologies needed to insure success of the testbed as well as for an entire class of future mission concepts. Finally, we compare the expected performance to the actual performance of the testbed using the initial array of seven spherical mirrors. Currently, we have aligned and phased all seven mirrors, demonstrated excellent system stability for extended periods of time, and begun open-loop operations using "pinhole" light sources. Extended scenes and calibration masks are being fabricated and will shortly be installed in the source module. Installation of all the different phase retrieval/diversity algorithms and control software is well on the way to completion, in preparation for future tests of closed-loop operations.
The Fizeau Interferometer Testbed (FIT) is a ground-based system that will be used for the development and testing of technologies relevant to Stellar Imager (SI) and other sparse aperture/Fizeau imaging interferometer mission concepts. The testbed will utilize image-based wavefront sensing and control to co-phase and maintain closed-loop control over a Sparse Aperture Array (SAA) consisting of spherical mirror elements. The SAA is a re-configurable assembly baselined to incorporate between seven (initially) and thirty 12.5mm diameter (R = 4000mm) mirror elements. In this paper we describe the fabrication, alignment, and initial calibration of the phase I (7 primary elements) FIT hardware and discuss various factors impacting the performance and stability of the testbed.
The standard approach to achieving TPF-level starlight suppression has been to couple a few techniques together. Deployment of a
low- or medium-performance external occulter as the first stage of starlight suppression reduces manufacturing challenges, mitigates
under-performance risks, lowers development costs, and hastens launch date for TPF. This paper describes the important aspects of a
conceptual 4-metre apodized square aperture telescope system utilizing a low-performance external occulter. Adding an external
occulter to such a standard TPF design provides a benefit that no other technique offers: scattered and diffracted on-axis starlight
is suppressed by orders of magnitude before reaching the telescope. This translates directly into relaxed requirements on the
remainder of the optical system.
Stellar Imager (SI) is a potential NASA space-based UV imaging interferometer to resolve the stellar disks of nearby stars. SI would consist of 20 - 30 separate spacecraft flying in formation at the Earth-Sun L2 libration point. Onboard wavefront control would be required to initially align the formation and maintain alignment during science observations and after array reconfiguration. The Fizeau Interferometry Testbed (FIT) is a testbed currently under development at the NASA/Goddard Space Flight Center to develop and study the wavefront control methodologies for Stellar Imager and other large, sparse aperture telescope systems. FIT consists of 7 articulated spherical mirrors in a Golay pattern, expandable up to 30 elements, and reconfigurable into multiple array patterns. FIT’s purpose is to demonstrate image quality versus array configuration and to develop and advance the wavefront control for SI. FIT uses extended scene wavelength, focus and field diversity to estimate the wavefront across the set of apertures. The recovered wavefront is decomposed into the eigenmodes of the control matrix and actuators are moved to minimize the wavefront piston, tip and tilt. Each mirror’s actuators are 3 degrees of freedom, however, they do not move each of the mirrors about a point on each mirrors surface, thus the mapping from wavefront piston, tip/tilt to mirror piston, tip/tilt is not diagonal. We initially estimate this mapping but update it as part of wavefront sensing and control process using system identification techniques. We discuss the FIT testbed, wavefront control methodology, and show initial results from FIT.
In this manuscript, we further develop our concepts for the free-flying occulter space-based mission, the Umbral Missions Blocking Radiating Astronomical Sources (UMBRAS). Our optical simulations clearly show that an UMBRAS-like mission designed around a 4-m telescope and 10-m occulter could directly image terrestrial planets. Such a mission utilizing existing technology could be built and flown by the end of the decade. Moreover, many of the other proposed concepts for Terrestrial Planet Finder (TPF) could significantly benefit by using an external occulter.
We present simultations for an optical design comprising a square aperture telescope plus square external occulter. We show that the entire diffraction pattern, which is propagated from occulter to telescope and through telescope to focal plane, may be characterized by two parameters, the Fresnel number and the ratio of the telescope diameter to the occulter width. Combining the effects of a square occulter with apodization provides a much more rapid roll-off in the PSF intensity between the diffraction spikes than may be achieved with an unapodized telecope aperture and occulter. We parameterize our results with respect to wavefront quality and compare them against other competing methods for exo-planet imaging. The combination of external occulter and apodization yields the required contrast in the region of the PSF essential for exo-planet detection.
An occulter external to the telescope (i.e., in a separate spacecraft, as opposed to a classical coronagraph with internal occulter) reduces light scatter within the telescope by approximately 2 orders of magnitude. This is due to less light actually entering the telescope. Reduced scattered light significantly relaxes the constraints on the mirror surface roughness, especially in the mid-spatial frequencies critical for planet detection. This study, plus our previous investigations of engineering as well as spacecraft
rendezvous and formation flying clearly indicates that the UMBRAS concept is very competitive with, or superior to, other proposed concepts for TPF missions.
We describe a 1-meter space telescope plus free-flying occulter craft mission that would provide direct imaging and spectroscopic observations of Jovian and Uranus-sized planets about nearby stars not detectable by Doppler techniques. The Doppler technique is most sensitive for the detection of massive, close-in extrasolar planets while the use of a free-flying occulter would make it possible to image and study stellar systems with planets comparable to our own Solar System. Such a mission with a larger telescope has the potential to detect earth-like planets. Previous studies of free-flying occulters reported advantages in having the occulting spot outside the telescope compared to a classical coronagraph onboard a space telescope. Using an external occulter means light scatter within the telescope is reduced due to fewer internal obstructions and less light entering the telescope and the polishing tolerances of the primary mirror and the supporting optics can be less stringent, thereby providing higher contrast and fainter detection limits.
In this concept, the occulting spot is positioned over the star by translating the occulter craft, at distances of 1,000 to 15,000 kms from the telescope, on the sky instead of by moving the telescope. Any source within the telescope field-of-view can be occulted without moving the telescope. In this paper, we present our current concept for a 1-m space telescope matched to a free-flying occulter, the Umbral Missions Blocking Radiating Astronomical Sources (UMBRAS) space mission. An UMBRAS space mission consists of a Solar Powered Ion Driven Eclipsing Rover (SPIDER) occulter craft and a matched (apodized) telescope. The occulter spacecraft would be semi-autonomous, with its own propulsion systems, internal power
(solar cells), communications, and navigation capability. Spacecraft rendezvous and formation flying would be achieved with the aid of telescope imaging, RF or laser ranging, celestial navigation inputs, and formation control algorithms.
A number of proposed space missions for high resolution imaging at wavelengths ranging from IR to UV call for ``dilute-aperture'' Fizeau-mode interferometers. We present here details of a software tool developed for high fidelity simulations of images obtained with such instruments. We show simulated images from the Stellar Imager, a mission concept being developed by NASA's GSFC to obtain
high-resolution images of nearby stars in UV-optical wavelengths.
Using the simulator, we study the capability of the proposed SI design to image stellar surfaces. We use the simulator to explore
parameters of image quality such as resolution and dynamic range, and to evaluate proposed designs and the feasibility of science goals.
The Stellar Imager (SI) is envisioned as a space-based, UV-optical interferometer composed of 10 or more one-meter class
elements distributed with a maximum baseline of 0.5 km. It is designed to image stars and binaries with sufficient resolution to enable long-term studies of stellar magnetic activity patterns,
for comparison with those on the sun. It will also support asteroseismology (acoustic imaging) to probe stellar internal structure, differential rotation, and large-scale circulations.
SI will enable us to understand the various effects of the magnetic fields of stars, the dynamos that generate these fields, and the internal structure and dynamics of the stars. The ultimate goal of the mission is to achieve the best-possible forecasting of solar activity as a driver of climate and space weather on time scales ranging from months up to decades, and an understanding of the impact of stellar magnetic activity on life in the Universe. In this paper we describe the scientific goals of the mission, the performance requirements needed to address these goals, the "enabling technology" development efforts being pursued, and the design concepts now under study for the full mission and a possible pathfinder mission.
KEYWORDS: Mirrors, Composites, Space mirrors, Space operations, Interferometers, Monochromatic aberrations, Spherical lenses, Space telescopes, Optical fabrication, Control systems
During the course of performing space flight qualification testing of composite mirrors at NASA GSFC, a serendipitious event was observed which, in retrospect, should have been obvious. Investigation of this phenomenon leads to a promising avenue towards the fabrication of large aperture precision spherical mirrors with very long radius of curvature (>f/100). Such mirrors are required for future missions such as the Stellar Imager. We report on the observation and analysis of the event, optical measurements, and the development of associated active figure control systems.
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