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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Evaluation of COSTAR mass handling characteristics in an environment. A simulation of the Hubble Space Telescope service mission

The STS-61 Shuttle mission, which took place in December 1993, was solely aimed at servicing the Hubble Space Telescope (HST). Successful completion of this mission was critical to NASA since it was necessary to rectify a flaw in the HST mirror. In addition, NASA had never scheduled a mission with such a high quantity of complex extravehicular activity. To meet the challenge of this mission, the STS-61 crew trained extensively in the Weightless Environment Test Facility at the Johnson Space Center and in the Neutral Buoyancy Simulator at the Marshall Space Flight Center. However, it was suspected that neutral buoyancy training might induce negative training by virtue of the viscous damping effect present in water. The mockups built for this training also did not have the mass properties of the actual orbital replacement units (ORUs). It was felt that the crew should be further trained on mockups with similar mass characteristics. A comprehensive study was designed to address these issues. The study was quantitative, and instrumentation was set up to measure and quantify the forces and moments experienced during ORU mass handling and remote manipulator system run conditions.

Rajulu, Sudhakar L.↗
NASA NTRS2019

Fast Steering Mirror Disturbance Effects on Overall System Optical Performance for the Large Ultraviolet/optical/infrared Surveyor (LUVOIR) Concept Using a Non-Contact Vibration Isolation and Precision Pointing System

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 the specifications on the FSM 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.

Sacks, Lia W.↗
NASA NTRSDate not supplied

Exoplanet Yield Sensitivity for the Hybrid Lyot Coronagraph from end-to-end modeling for LUVOIR-A

NASA's future direct imaging flagship mission will require telescope mirror segmentation to survey a statistically significant population of nearby stellar systems by increasing aperture size beyond that achieved by traditional space-borne monolithic apertures thus far. Segmentation is a path for the size expansion, but it entails a challenge due to the introduction of temporal pupil discontinuities in terms of both phase and amplitude. Modeling of the integrated performance of the coronagraph with the expected dynamical profile of the telescope is an important step toward realistic estimates of the mission's science yields. We present results of a study using the hybrid Lyot coronagraph with a 15-m on-axis, segmented optical telescope assembly (OTA), akin to that of the Large UV / Optical /Infrared (LUVOIR) mission. We have developed a high-fidelity, end-to-end model as part of the Segmented Coronagraph Design and Analysis (SCDA) study that includes diffractive optical propagations at the 1e-10 contrast level across the optical train including the OTA and intermediate re-imaging optics inside the coronagraph instrument. We perform a sensitivity analysis to assess the contrast sensitivity to wavefront perturbations for a set of key telescope terms including segment-level low-order and mid-spatial frequency aberrations and evaluate expected exoplanet yields obtained in the presence of these sets of aberrations. Industry-provided segment-level wavefront aberration datasets involving the following mechanisms are input to the end-to-end model: (1) thermal gradients and accelerations, and (2) telescope dynamics including line-of-sight and segment jitter. Dynamically averaged PSFs in the presence of aberrations are fed into AYO (Altruistic Yield Optimization), a mission design reference simulator, that then assesses the scientific yield sensitivities.

high-contrast imaging↗
NASA NTRS1984

Pointing and control system design study for the space infrared telescope facility (SIRTF)

The design and performance of pointing and control systems for two space infrared telescope facility vehicles were examined. The need for active compensation of image jitter using the secondary mirror or other optical elements was determined. In addition, a control system to allow the telescope to perform small angle slews, and to accomplish large angle slews at the rate of 15 deg per minute was designed. Both the 98 deg and the 28 deg inclination orbits were examined, and spacecraft designs were developed for each. The results indicate that active optical compensation of line-of-sight errors is not necessary if the system is allowed to settle for roughly ten seconds after a slew maneuver. The results are contingent on the assumption of rigid body dynamics, and a single structural mode between spacecraft and telescope. Helium slosh for a half full 4000 liter tank was analyzed, and did not represent a major control problem.

Lorell, K. R.↗
NASA NTRS1992

Wavefront sensing, control, and pointing

A majority of future NASA astrophysics missions from orbiting interferometers to 16-m telescopes on the Moon have, as a common requirement, the need to bring light from a large entrance aperture to the focal plane in a way that preserves the spatial coherence properties of the starlight. Only by preserving the phase of the incoming wavefront, can many scientific observations be made, observations that range from measuring the red shift of quasi-stellar objects (QSO's) to detecting the IR emission of a planet in orbit around another star. New technologies for wavefront sensing, control, and pointing hold the key to advancing our observatories of the future from those already launched or currently under development. As the size of the optical system increases, either to increase the sensitivity or angular resolution of the instrument, traditional technologies for maintaining optical wavefront accuracy become prohibitively expensive or completely impractical. For space-based instruments, the low mass requirement and the large temperature excursions further challenge existing technologies. The Hubble Space Telescope (HST) is probably the last large space telescope to rely on passive means to keep its primary optics stable and the optical system aligned. One needs only look to the significant developments in wavefront sensing, control, and pointing that have occurred over the past several years to appreciate the potential of this technology for transforming the capability of future space observatories. Future developments in space-borne telescopes will be based in part on developments in ground-based systems. Telescopes with rigid primary mirrors much larger than 5 m in diameter are impractical because of gravity loading. New technologies are now being introduced, such as active optics, that address the scale problem and that allow very large telescopes to be built. One approach is a segmented design such as that being pioneered by the W.M. Keck telescope now under construction at the Mauna Kea Observatory. It consists of 36 hexagonal mirror segments, supported on a framework structure, which are positioned by actuators located between the structure and the mirrors. The figure of the telescope is initialized by making observations of a bright star using a Shack Hartmann sensor integrated with a white light interferometer. Then, using sensed data from the mirror edges to control these actuators, the figure of the mosaic of 36 segments is maintained as if it were a rigid primary mirror. Another active optics approach is the use of a thin meniscus mirror with actuators. This technique was demonstrated on the European Southern Observatory's New Technology Telescope (NTT) and is planned for use in the Very Large Telescope (consists of four 8-m apertures), which is now entering the design phase.

Pitts, Thomas↗
NASA NTRS2007

Optical Modeling of the Alignment and Test of the NASA James Webb Space Telescope

Optical modeling challenges of the ground alignment plan and optical test and verification of the NASA James Webb Space Telescope are discussed. Issues such as back-out of the gravity sag of light-weighted mirrors, as well as the use of a sparse-aperture auto-collimating flat system are discussed. A walk-through of the interferometer based alignment procedure is summarized, and sensitivities from the sparse aperture wavefront test are included as examples.'

Howard, Joseph M.↗
NASA NTRS2011

Summary of the NASA Science Instrument, Observatories and Sensor Systems (SIOSS) Technology Assessment Roadmap

In August 2010, the NASA Office of Chief Technologist (OCT) commissioned an assessment of 15 different technology areas of importance to the future of NASA. Technology Assessment #8 (TA8) was Science Instruments, Observatories and Sensor Systems (SIOSS). SIOSS assessed the needs for optical technology ranging from detectors to lasers, x-ray mirrors to microwave antenna, in-situ spectrographs for on-surface planetary sample characterization to large space telescopes. This needs assessment looked across the entirety of NASA and not just the Science Mission Directorate. This paper summarizes the SIOSS findings and recommendations.

Stahl, H. Philip↗
NASA NTRS2011

Optical Manufacturing and Testing Requirements Identified by the NASA Science Instruments, Observatories and Sensor Systems Technology Assessment

In August 2010, the NASA Office of Chief Technologist (OCT) commissioned an assessment of 15 different technology areas of importance to the future of NASA. Technology assessment #8 (TA8) was Science Instruments, Observatories and Sensor Systems (SIOSS). SIOSS assess the needs for optical technology ranging from detectors to lasers, x-ray mirrors to microwave antenna, in-situ spectrographs for on-surface planetary sample characterization to large space telescopes. The needs assessment looked across the entirety of NASA and not just the Science Mission Directorate. This paper reviews the optical manufacturing and testing technologies identified by SIOSS which require development in order to enable future NASA high priority missions.

Stahl, H. Philip↗
NASA NTRS2013

Telescope Innovations Improve Speed, Accuracy of Eye Surgery

One of the main components of NASA's vision for the future of space exploration will actually have a keen eye for the past. The James Webb Space Telescope (JWST), scheduled to launch in 2018, will have spectacular sight, after it reaches orbit, one of its main goals is to observe the first galaxies that formed in the early universe. "JWST offers new capabilities in the infrared well beyond what we can see from current telescopes, either on the ground or in space. It will let us explore the early universe, extrasolar planets, and really, all branches of astrophysics," says Lee Feinberg, optical telescope element manager for the JWST at Goddard Space Flight Center. Building such a keen space telescope is an astronomic task. Because JWST will gaze over such incredible distances, it requires very large mirrors. In fact, the primary mirror will be more than two stories in diameter and consists of 18 separate segments. Each segment must be perfectly smooth, flat, and scratch-free in order to deliver a view 13 billion light years away. Construction of the 18 mirror segments involved measuring, grinding, polishing, and testing - and more measuring, grinding, polishing, and testing - and more measuring, grinding, polishing, and testing (you get the idea). One of the most time consuming steps of the mirror development process, the grinding phase, can take years.

Source record↗
NASA NTRSDate not supplied

Influence of evaporation rate and chamber pressure on the FUV reflectance and physical characteristics of aluminum films

Space telescopes for studying astrophysical phenomena from the far ultraviolet (FUV) to the near infrared (NIR) require durable mirror coatings with high and uniform reflectance over a very broad spectral region. While coatings for the optical and NIR region are well developed with proven performance, the FUV band presents significant challenges, particularly below 115 nm. Recent developments in physical vapor deposition (PVD) coating processes of aluminum mirrors that are protected with a metal-fluoride overcoat to prevent oxidation (such as LiF, MgF2, or AlF3) have improved reflectance in the FUV. While the emphasis in these studies has been placed on improving the deposition conditions of the metal-fluoride overcoats, less attention has been devoted to how deposition parameters (such as vacuum conditions or deposition rates) may affect the quality of the aluminum mirrors. This paper presents characterization of Al+MgF2 coupons made by flash evaporation of aluminum followed by resistive evaporation of MgF2. Samples were manufactured under a variety of processing conditions and the relationship between processing variables and mirror FUV reflectivity is analyzed. Performance characterization was based on the measured near-normal reflectance in the FUV (90-180 nm), and normal-incidence transmittance in the visible was done to analyze the possible presence of pinholes in the mirror. We demonstrated pinhole-free Al/MgF2 mirrors deposited at room temperature with a reflectivity of 0.91 at 122 nm wavelength. This reflectivity enhancement was achieved solely through parameter optimization.

Manuel A. Quijada↗
NASA NTRSDate not supplied

Influence of Evaporation Rate and Chamber Pressure on the FUV Reflectance and Physical Characteristics of Aluminum Films

Space telescopes for studying astrophysical phenomena from the far ultraviolet (FUV) to the near infrared (NIR) require durable mirror coatings with high and uniform reflectance over a very broad spectral region. While coatings for the optical and NIR region are well developed with proven performance, the FUV band presents significant challenges, particularly below 115 nm. Recent developments in physical vapor deposition (PVD) coating processes of aluminum mirrors that are protected with a metal-fluoride overcoat to prevent oxidation (such as LiF, MgF2, or AlF3) have improved reflectance in the FUV. While the emphasis in these studies has been placed on improving the deposition conditions of the metal-fluoride overcoats, less attention has been devoted to how deposition parameters (such as vacuum conditions or deposition rates) may affect the quality of the aluminum mirrors. This paper presents characterization of Al+MgF2 coupons made by flash evaporation of aluminum followed by resistive evaporation of MgF2. Samples were manufactured under a variety of processing conditions and the relationship between processing variables and mirror FUV reflectivity is analyzed. Performance characterization was based on the measured near-normal reflectance in the FUV (90-180 nm), and normal-incidence transmittance in the visible was done to analyze the possible presence of pinholes in the mirror. We demonstrated pinhole-free Al/MgF2 mirrors deposited at room temperature with a reflectivity of 0.91 at 122 nm wavelength. This reflectivity enhancement was achieved solely through parameter optimization.

FUV reflectance, aluminum, PVD, deposition rate, A↗
NASA NTRSDate not supplied

Fabrication of monocrystalline silicon x-ray mirrors

Progress within the fi eld of x-ray astronomy depends on astronomical x-ray observations of ever-increasing quality and speed. Fast and high-resolution x-ray observations over a broad spectral range promise amazing new discoveries. These observations, however, require a spaceborne x-ray telescope of unprecedented imaging power. Of the numerous technological concerns associated with the design and construction of such a telescope, the x-ray focusing optics present a particularly complex and arduous set of challenges. An x-ray optical assembly comprises many thousands of x-ray mirrors, a most critical element. Our group at NASA Goddard Space Flight Center (GSFC) pursues the development of an x-ray mirror manufacturing process capable of meeting the stringent quality, production time, and cost requirements of the next-generation of x-ray telescopes. The manufacturing process employs monocrystalline silicon: a lightweight, stiff, thermally conductive, and readily available material which is free of internal stress; it is a nearly ideal material for a thin mirror substrate. The process involves various traditional optical fabrication techniques adapted to x-ray mirror geometry. Presently, our process is capable of fabricating sub-arcsecond half-power diameter (HPD) resolution mirror pairs (primary and secondary) at a mirror thickness of 0.5 mm and of virtually any x-ray optical design (e.g. Wolter-I, Wolter-Schwarzschild, etc.). The mirror substrate surface quality is comparable to, and sometimes exceeding, that of the mirrors on the Chandra X-ray Observatory. This paper describes the various manufacturing steps involved in the production of x-ray mirror substrates and a present status report.

Raul E. Riveros↗
NASA NTRS1978

The High Energy Astronomy Observatory X-ray Telescope

The High Energy Astronomy Observatory-Mission B (HEAO-B) is a satellite observatory for the purpose of performing a detailed X-ray survey of the celestial sphere. Measurements will be made of stellar radiation in the range 0.2 through 20 keV. The primary viewing requirement is to provide final aspect solution and internal alignment information to correlate an observed X-ray image with the celestial sphere to within one-and-one-half arc seconds. The Observatory consists of the HEAO Spacecraft together with the X-ray Telescope. The Spacecraft provides the required attitude control and determination system, data telemetry system, space solar power system, and interface with the launch vehicle. The X-ray Telescope includes a high resolution mirror assembly, optical bench metering structure, X-ray detectors, detector positioning system, detector electronics and aspect sensing system.

Miller, R.↗