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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

New Method for Characterizing the State of Optical and Opto-Mechanical Systems

James Webb Space Telescope Optical Telescope Element (OTE) is a three mirror anastigmat consisting of a 6.5 m primary mirror (PM), secondary mirror (SM) and a tertiary mirror. The primary mirror is made out of 18 segments. The telescope and instruments will be assembled at Goddard Space Flight Center (GSFC) to make it the Optical Telescope Element-Integrated Science Instrument Module (OTIS). The OTIS will go through environmental testing at GSFC before being transported to Johnson Space Center for testing at cryogenic temperature. The objective of the primary mirror Center of Curvature test (CoC) is to characterize the PM before and after the environmental testing for workmanship. This paper discusses the CoC test including both a surface figure test and a new method for characterizing the state of the primary mirror using high speed dynamics interferometry.

Optical Testing↗
NASA NTRS1977

The application of thermally stable graphite composites to a space telescope structure

An optical bench and associated mirror support structural components were designed and fabricated for the HEAO-B satellite. Stringent dimensional stability criteria dictated the use of a graphite/epoxy composite as the basic structural material. Design, analysis, and fabrication aspects are discussed for the resulting structures, which pioneer the use of advanced composite materials for significant applications to orbital flight hardware.

Prunty, J.↗
NASA NTRS2002

Silicon Lightweight Mirrors (SLMS) for Ultraviolet and Extreme Ultraviolet Imaging Mirrors

Subtopic 01-S1.06 requires mirrors with a diameter of 0.5-2.4 meters, areal density less than 20 kg/sq m, a figure specification of 0.02-0.005 waves root mean square (rms) at 633 nanometers, a surface roughness 0.5-1 nanometers rms, and a midfrequency error of 1.0-2.5 nanometers rms for use in the infrared (IR) to extreme ultra violet (EUV) waveband. Schafer's Phase II objective is to use Silicon Lightweight Mirrors (SLMS), a novel, all-silicon, foam-core, lightweight mirror technology, to build three imaging mirrors for the Next Generation Space Telescope Near Infrared Camera (NIRCam) Engineering Test Unit: M0 (a flat), M2 (a concave sphere) and M3R (an oblate spheroid). The surface figure error specification for the NIRCam imaging mirrors is 8 nanometers rms (0.013 waves rms at 633 nanometers), equivalent to that required for ultraviolet (UV) and EUV mirrors, and this figure must be maintained at the 35 K operational temperature of NGST. The surface roughness required is 30 A rms since NIRCam operates in the visible to infrared (VIS/IR) (0.65-5 microns). We will produce mounts for mirrors M2 and M3R using the complementary thermally matched C/SiC material demonstrated by Schafer under another NASA SBIR, NAS8-98137.

Goodman, W. A.↗
NASA NTRS2008

James Webb Space Telescope: Frequently Asked Questions for Scientists and Engineers

JWST will be tested incrementally during its construction, starting with individual mirrors and instruments (including cameras and spectrometers) and building up to the full observatory. JWST's mirrors and the telescope structure are first each tested individually, including optical testing of the mirrors and alignment testing of the structure inside a cold thermal-vacuum chamber. The mirrors are then installed on the telescope structure in a clean room at Goddard Space Flight Center (GSFC). In parallel to the telescope assembly and alignment, the instruments are being built and tested, again first individually, and then as part of an integrated instrument assembly. The integrated instrument assembly will be tested in a thermal-vacuum chamber at GSFC using an optical simulator of the telescope. This testing makes sure the instruments are properly aligned relative to each other and also provides an independent check of the individual tests. After both the telescope and the integrated instrument module are successfully assembled, the integrated instrument module will be installed onto the telescope, and the combined system will be sent to Johnson Space Flight Center (JSC) where it will be optically tested in one of the JSC chambers. The process includes testing the 18 primary mirror segments acting as a single primary mirror, and testing the end-to-end system. The final system test will assure that the combined telescope and instruments are focused and aligned properly, and that the alignment, once in space, will be within the range of the actively controlled optics. In general, the individual optical tests of instruments and mirrors are the most accurate. The final system tests provide a cost-effective check that no major problem has occurred during assembly. In addition, independent optical checks of earlier tests will be made as the full system is assembled, providing confidence that there are no major problems.

Gardner, Jonathan P.↗
NASA NTRS2008

Zero CTE Glass in the Hubble Space Telescope

Orbiting high above the turbulence of the Earth's atmosphere, the Hubble Space Telescope (HST) has provided breathtaking views of astronomical objects never before seen in such detail. The steady diffraction-limited images allow this medium-size telescope to reach faint galaxies fainter than 30th stellar magnitude. Some of these galaxies are seen as early as 2 billion years after the Big Bang in a 13.7 billion year old universe. Up until recently, astronomers assumed that all of the laws of physics and astronomy applied back then as they do today. Now, using the discovery that certain supernovae are "standard candles," astronomers have found that the universe is expanding faster today than it was back then: the universe is accelerating in its expansion. The Hubble Space Telescope is a two-mirror Ritchey-Chretien telescope of 2.4m aperture in low earth orbit. The mirrors are made of Ultra Low Expansion (ULE) glass by Corning Glass Works. This material allows rapid figuring and outstanding performance in space astronomy applications. The paper describes how the primary mirror was mis-figured in manufacturing and later corrected in orbit. Outstanding astronomical images taken over the last 17 years show how the application of this new technology has advanced our knowledge of the universe. Not only has the acceleration of the expansion been discovered, the excellent imaging capability of HST has allowed gravitational lensing to become a tool to study the distribution of dark matter and dark energy in distant clusters of galaxies. The HST has touched practically every field of astronomy enabling astronomers to solve many long-standing puzzles. It will be a long time until the end of the universe when the density is near zero and all of the stars have long since evaporated. It is remarkable that humankind has found the technology and developed the ability to interpret the measurements in order to understand this dramatic age we live in.

Wood, H. John↗
NASA NTRS1987

Performance characteristics of phased array and thinned aperture optical telescopes

While phased telescope arrays for general-purpose broadband imaging applications suffer severe sensitivity losses and field-of-view limitations, thinned-aperture telescopes consisting of a dilute, segmented primary mirror with a common secondary mirror are viable second-generation space telescope configurational possibilities yielding resolution and sensitivity an order of magnitude greater than those of the Hubble Space Telescope. Attention is given to thinned-aperture optical systems' image quality characterization problems; the 'practical resolution limit' image quality criterion proposed is defined as the reciprocal of the spatial frequency within which no zeros occur in the modulation transfer function.

Harvey, James E.↗
NASA NTRS2002

Managing Risk on a Technology Development Project/Advanced Mirror System Demonstrator

The risk management study applied to the Advanced Mirror System Demonstrator (AMSD), a precursor mirror technology development for the Next Generation Space Telescope (NGST) is documented. The AMSD will be developed as a segment of a lightweight primary mirror system that can be produced at a low cost and with a short manufacturing schedule. The technology gained from the program will support the risk mitigation strategy for the NGST, as well as other government agency space mirror programs.

Byberg, Alicia↗
NASA NTRS1983

Double arch mirror study. Part 3: Fabrication and test report

A method of mounting a cryogenically cooled, lightweight, double arch, glass mirror was developed for infrared, astronomical telescopes such as the Space Infrared Telescope Facility (SIRTF). A 50 cm, fused silica mirror which was previously fabricated was modified for use with a new mount configuration. This mount concept was developed. The modification of the mirror, the fabrication of the mirror mount, and the room temperature testing of the mounted mirror are reported. A design for a SIRTF class primary mirror is suggested.

Vukobratovich, D.↗
NASA NTRS2010

JWST Mirror Technology Development

Since the initial Design Studies leading to JWST, Mirror Technology was identified as a (if not the) critical capability necessary to enable the next generation of large aperture space telescopes required to achieve the science goals of imaging the earliest galaxies and proto-galaxies after the big bang. Specific telescope architectures were explored via three independent design concept studies conducted during the summer of 1996. Achieving the desired science objectives required a never before demonstrated space telescope capability, one with an 8 meter class primary mirror that is diffraction limited at 2 micrometers and operating in deep space at temperatures well below 70K. Beryllium was identified in the NASA "Yardstick" design as the preferred material because of its ability to provide stable optical performance in the anticipated thermal environment as well as its excellent specific stiffness. Because of launch vehicle constraints, two very significant architectural constraints were placed upon the telescope: segmentation and areal density. Each of these directly resulted in specific technology capability requirements. First, because the maximum launch vehicle payload fairing diameter is approximately 4.5 meters, the only way to launch an 8 meter class mirror is to segment it, fold it and deploy it on orbit - resulting in actuation and control requirements. Second, because of launch vehicle mass limits, the primary mirror allocation was only 1000 kg - resulting in a maximum areal density specification of 20 kilograms per square meter.

Stahl, H. Philip↗
NASA NTRS2002

Segmented mirror coarse phasing with white light interferometry: modeling and experiment on NGST's wavefront control testbed

A method of coarse phasing segmented mirrors using white light interferometry (WLI) has been developed for Next Generation Space Telescope (NGST) wavefront sensing and control. Using the broadband point spread function (PSF) of the segmented mirrors taken during a segment piston scan, the WLI can accurately detect small residual piston errors. WLI does not rely on any extra optics and uses only the final imaging camera. With its high sensitivity to small segment piston error WLI can be used as a complementary phasing algorithm to the dispersed fringe sensor (DFS) for NGST. The paper will present the results from modeling and experiment on the NGST's Wavefront Control Testbed (WCT).

Space↗
NASA NTRS2016

Phase-Retrieval Uncertainty Estimation and Algorithm Comparison for the JWST-ISIM Test Campaign

Phase retrieval, the process of determining the exitpupil wavefront of an optical instrument from image-plane intensity measurements, is the baseline methodology for characterizing the wavefront for the suite of science instruments (SIs) in the Integrated Science Instrument Module (ISIM) for the James Webb Space Telescope (JWST). JWST is a large, infrared space telescope with a 6.5-meter diameter primary mirror. JWST is currently NASA's flagship mission and will be the premier space observatory of the next decade. ISIM contains four optical benches with nine unique instruments, including redundancies. ISIM was characterized at the Goddard Space Flight Center (GSFC) in Greenbelt, MD in a series of cryogenic vacuum tests using a telescope simulator. During these tests, phase-retrieval algorithms were used to characterize the instruments. The objective of this paper is to describe the Monte-Carlo simulations that were used to establish uncertainties (i.e., error bars) for the wavefronts of the various instruments in ISIM. Multiple retrieval algorithms were used in the analysis of ISIM phase-retrieval focus-sweep data, including an iterativetransform algorithm and a nonlinear optimization algorithm. These algorithms emphasize the recovery of numerous optical parameters, including low-order wavefront composition described by Zernike polynomial terms and high-order wavefront described by a point-by-point map, location of instrument best focus, focal ratio, exit-pupil amplitude, the morphology of any extended object, and optical jitter. The secondary objective of this paper is to report on the relative accuracies of these algorithms for the ISIM instrument tests, and a comparison of their computational complexity and their performance on central and graphical processing unit clusters. From a phase-retrieval perspective, the ISIM test campaign includes a variety of source illumination bandwidths, various image-plane sampling criteria above and below the Nyquist- Shannon critical sampling value, various extended object sizes, and several other impactful effects.

Design Analysis↗
NASA NTRS1990

A soft actuation system for segmented reflector articulation and isolation

Segmented reflectors have been proposed for space based applications such as optical communication and large diameter telescopes. An actuation system for mirrors in a space based segmented mirror array was developed as part of NASA's Precision Segmented Reflector program. The actuation system, called the Articulated Panel Module (APM), provides 3 degrees of freedom mirror articulation, gives isolation from structural motion, and simplifies space assembly of the mirrors to the reflector backup truss. A breadboard of the APM was built and is described.

Agronin, Michael L.↗
NASA NTRS1974

LST secondary mirror articulation mechanism

The analysis, design, manufacture, test, and delivery of one secondary mirror articulation mechanism for the large space telescope (LST) are reported. The mechanism provides angular freedom about two axes that are perpendicular to the optical axis of the secondary mirror. Motion in each axis is controlled from two sources; one source provides alignment, the other source provides stabilization. Two articulation mechanism configurations were evaluated. In one configuration the stabilization system was assembled with piezoelectric actuators. In the second configuration the stabilization system utilized flexure torque motor actuators. The alignment system was the same for both configurations. System testing confirmed performance that met or exceeded all operational requirements. The two types of stabilization actuators had different performance characteristics. Both types demonstrated position resolution and frequency response better than specified limits.

Source record↗
NASA NTRSDate not supplied

Obtaining Cryogenic Molecular Transport Data for Analysis

The James Webb Space Telescope (JWST) has a primary mirror, made of 18 segments, and a secondary mirror (SM) that are used to direct the light of desired targets. While on orbit, the secondary mirror assembly (SMA) was stowed for approximately 10 days and was subject to molecular contamination outgassing from the cavity of the secondary mirror support structure (SMSS) in-board hinge (IBH) which contains cables, motors, resolvers, and coatings. The main concern during this period before SMA deployment is the accumulation of ice due to the lack of a heater on the SMA. The temperature differentials between the IBH surfaces and SMA could cause redistribution of contaminants. To address this concern, single layer insulation (SLI) was used to create adequate venting and path redirection of outgassing from the IBH. Two separate thermal vacuum tests were performed to quantify this contamination: one Z307 ASTM E 1559 materials test of the radiator paint used on the motor of the IBH and a separate test on a primary mirror backplane assembly (PMBA) qualification engineering test unit (ETU) of the IBH. These tests approximately followed the predicted SMA pre-deployment thermal environment. To quantify source rates in case of a leak, the motor and resolver sides were separated and quartz crystal microbalances (QCM) were used to measure the deposition of water. The SLI redesign and implementation and outgassing measurements to understand leak effects from the IBH were essential to mitigate the deposition of contamination on the SMA. "

James Webb Space Telescope↗
NASA NTRSDate not supplied

Obtaining cryogenic molecular transport data for analysis

The James Webb Space Telescope (JWST) has a primary mirror, made of 18 segments, and a secondary mirror (SM) that are used to direct the light of desired targets. While on orbit, the secondary mirror assembly (SMA) was stowed for approximately 10 days and was subject to molecular contamination outgassing from the cavity of the secondary mirror support structure (SMSS) in-board hinge (IBH) which contains cables, motors, resolvers, and coatings. The main concern during this period before SMA deployment is the accumulation of ice due to the lack of a heater on the SMA. The temperature differentials between the IBH surfaces and SMA could cause redistribution of contaminants. To address this concern, single layer insulation (SLI) was used to create adequate venting and path redirection of outgassing from the IBH. Two separate thermal vacuum tests were performed to quantify this contamination: one Z307 ASTM E 1559 materials test of the radiator paint used on the motor of the IBH and a separate test on a primary mirror backplane assembly (PMBA) qualification engineering test unit (ETU) of the IBH. These tests approximately followed the predicted SMA pre-deployment thermal environment. To quantify source rates in case of a leak, the motor and resolver sides were separated and quartz crystal microbalances (QCM) were used to measure the deposition of water. The SLI redesign and implementation and outgassing measurements to understand leak effects from the IBH were essential to mitigate the deposition of contamination on the SMA.

James Webb Space Telescope, contamination, cleanro↗
NASA NTRS1973

Active optics simulation system

The active optics simulation system (AOSS) is a set of computer programs and associated software to be used in the development, design, and evaluation of a primary mirror control system for a large space telescope, (e.g., the tentatively proposed 3-meter telescope). The mathematical models of component subsystems and the solution of the physical processes that occur within the mirror surface control system were obtained, and based on these models AOSS simulates the behavior of the entire mirror surface control system as well as the behavior of the component subsystems. The program has a modular structure so that any subsystem module can be replaced or modified with minimum disruption of the rest of the simulation program.

Chi, C. H.↗