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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 NTRS1987

Space ten-meter telescope (STMT) - Structural and thermal feasibility study of the primary mirror

The structural and thermal behavior of a ten-meter primary mirror for a space optical/near-IR telescope in geosynchronous orbit is studied. The glass-type lightweighted mirror is monolithic, of the double arch type, and is supported at only three points. The computer programs SSPTA (thermal), NASTRAN (finite element), and ACCOS V (optical) are used in sequence to determine the temperature, deformation, and optical performance of the mirror. A mirror temperature of 130 K or less appears to be obtainable by purely passive means. With a fused silica or standard Zerodur blank, thermally-induced deformation is unacceptable and cannot be fully corrected by an active secondary mirror over the desired field. Either active thermal control or a blank of lower thermal expansion coefficient would be required.

Bely, Pierre Y.↗
NASA NTRS1989

Composite deformable mirror

A mathematical model for a spherical hexagon mirror is described along with the model verifications. A flat hexagon epoxy mirror with aluminum core is used in test procedures in addition to a flat aluminum honeycomb mirror. Deformable reflector concepts are discussed and piezoelectric actuators are analyzed. The concept of a deformable mirror can be used to improve the overall RMS error of the mirror as presently designed and/or make necessary on-orbit adjustments.

Kuo, C. P.↗
NASA NTRS1989

Fabrication of light-weighted Si/SiC lidar mirrors

Small models of lightweight Si/SiC lidar mirrors have been fabricated via a scalable and cost-effective chemical vapor deposition (CVD) process. These mirrors are about 7.5 cm in diameter and consist of a Si-cladded SiC faceplate and lightweight structure made of SiC. The lightweight structure consists of an outer hexagonal cell with six triangular inner cells. The mirrors were polished to a figure better than 1/5 of a wave and a finish of better than 5A rms. The CVD route to fabrication of mirrors is fast and has the potential to yield several mirrors in a few weeks time from a signel reactor.

Goela, Jitendra S.↗
NASA NTRS1989

A comparison of the merits of open-back, symmetric sandwich, and contoured back mirrors as light-weighted optics

A parametric study of contoured back mirrors, symmetric sandwich mirrors, and open-back mirrors is presented. Each mirror type is examined with regard to self-weight-induced deflection, efficiency, and fabrication constraints. A chart of fabrication and mounting factors as well as stiffness and weight factors is presented for assistance in choosing an appropriate mirror type in a given application.

Valente, Tina M.↗
NASA NTRS1990

SIRTF primary mirror design, analysis, and testing

The primary mirror assembly (PMA) requirements and concepts for the Space Infrared Telescope Facility (SIRTF) program are discussed. The PMA studies at NASA/ARC resulted in the design of two engineering test articles, the development of a mirror mount cryogenic static load testing system, and the procurement and partial testing of a full scale spherical mirror mounting system. Preliminary analysis and testing of the single arch mirror with conical mount design and the structured mirror with the spherical mount design indicate that the designs will meet all figure and environmental requirements of the SIRTF program.

Sarver, George L., III↗
NASA NTRS1994

AXAF VETA-I mirror ring focus measurements

The AXAF VETA-I mirror ring focus measurements were made with an HRI (microchannel plate) X-ray detector. The ring focus is a sharply focused ring formed by X-rays before they reach the VEAT-I focal plane. It is caused by spherical aberrations due to the finite source distance and the despace in the VETA-I test. The ring focus test reveals some aspects fo the test system distortions and the mirror surface figure which are difficult or impossible to detect at the focal plane. The test results show periodic modulations of the ring radius and width which could be caused by gravity, thermal, and/or epoxy shrinkage distortions. The strongest component of the modulation had a 12-fold symmetry, because these distortions were exerted on the mirror through 12 flexures of the VETA-I mount. Ring focus models were developed to simulate the ring image. The models were compared with the data to understand the test system distortions and the mirror glass imperfection. Further studies will be done to complete this work. The ring focus measurement is a very powerful test. We expect that a similar test for the finally assembled mirror of AXAD-I will be highly valuable.

Tananbaum, H. D.↗
NASA NTRS1995

Effects of low earth orbit on the optical performance of multi-layer enhanced high reflectance mirrors

Two mirror designs developed for space applications were flown along with a standard mid-infrared design on the leading and trailing edges of the Long Duration Exposure Facility (LDEF). Preliminary observations of induced changes in optical performance of ZnS-coated mirrors and impact-related microstructural and microchemical effects are described in the proceedings of the First LDEF Post-Retrieval Symposium. In this paper, effects of the induced environment and meteoroid/debris impacts on mirror performance are described in more detail. Also, an analysis of reflectance spectra using the results of Auger and secondary ion mass spectroscopy (SIMS) profiling measurements are used to identify an optical-degradation mechanism for the ZnS-coated mirrors. Structural damage associated with a high-velocity impact on a (Si/Al2O3)-coated mirror was imaged optically and with scanning electron and atomic force microscopy (SEM and AFM). Scanning Auger and SIMS analysis provided chemical mapping of selected impact sites. The impact data suggest design and fabrication modifications for obtaining improved mechanical performance using a design variation identified in preflight laboratory simulations. Auger surface profile and SIMS imaging data verified the conclusion that secondary impacts are the source of contamination associated with the dendrites grown on the leading-edge ZnS-coated test samples. It was also found that dendrites can be grown in the laboratory by irradiating contaminated sites on a trailing-edge ZnS-coated sample with a rastered electron beam. These results suggest a mechanism for dendrite growth.

Donovan, Terence↗
NASA NTRS1995

The Alignment Test System for AXAF-I's High Resolution Mirror Assembly

The AXAF-1 High Resolution Mirror Assembly (HRMA) consists of four nested mirror pairs of Wolter Type-1 grazing incidence optics. The HRMA assembly and alignment will take place in a vibration-isolated, cleanliness class 100, 18 meter high tower at an Eastman Kodak Company facility in Rochester, NY. Each mirror pair must be aligned such that its image is coma-free, and the four pairs must be aligned such that their images are coincident. In addition, both the HRMA optical axis and focal point must be precisely known with respect to physical references on the HRMA. The alignment of the HRMA mirrors is measured by the HRMA Alignment Test System (HATS), which is an integral part of the tower facility. The HATS is configured as a double-pass, autocollimating Hartmann test where each mirror aperture is scanned to determine the state of alignment. This paper will describe the design and operation of the HATS.

Waldman, Mark↗
NASA NTRS1994

Optical Analysis of an Ultra-High resolution Two-Mirror Soft X-Ray Microscope

This work has summarized for a Schwarzschild microscope some relationships between numerical aperture (NA), magnification, diameter of the primary mirror, radius of curvature of the secondary mirror, and the total length of the microscope. To achieve resolutions better than a spherical Schwarzschild microscope of 3.3 Lambda for a perfectly aligned and fabricated system. it is necessary to use aspherical surfaces to control higher-order aberrations. For an NA of 0.35, the aspherical Head microscope provides diffraction limited resolution of 1.4 Lambda where the aspherical surfaces differ from the best fit spherical surface by approximately 1 micrometer. However, the angle of incidence varies significantly over the primary and the secondary mirrors, which will require graded multilayer coatings to operate near peak reflectivities. For higher numerical apertures, the variation of the angle of incidence over the secondary mirror surface becomes a serious problem which must be solved before multilayer coatings can be used for this application. Tolerance analysis of the spherical Schwarzschild microscope has shown that water window operations will require 2-3 times tighter tolerances to achieve a similar performance for operations with 130 A radiation. Surface contour errors have been shown to have a significant impact on the MTF and must be controlled to a peak-to-valley variation of 50-100 A and a frequency of 8 periods over the surface of a mirror.

Shealy, David L.↗
NASA NTRS1996

Computation of Static Shapes and Voltages for Micromachined Deformable Mirrors with Nonlinear Electrostatic Actuators

In modeling micromachined deformable mirrors with electrostatic actuators whose gap spacings are of the same order of magnitude as those of the surface deformations, it is necessary to use nonlinear models for the actuators. In this paper, we consider micromachined deformable mirrors modeled by a membrane or plate equation with nonlinear electrostatic actuator characteristics. Numerical methods for computing the mirror deformation due to given actuator voltages and the actuator voltages required for producing the desired deformations at the actuator locations are presented. The application of the proposed methods to circular deformable mirrors whose surfaces are modeled by elastic membranes is discussed in detail. Numerical results are obtained for a typical circular micromachined mirror with electrostatic actuators.

Wang, P. K. C.↗
NASA NTRS1997

Foil Mirrors and Multilayer Developments at Goddard

This paper summarizes progress at Goddard toward incorporating refinements into the foil mirror technology that extend its utilization in astronomical research well into the future. The Japan/US collaborative mission ASCA has demonstrated both the strengths of first generation foil mirrors but also the areas where improvements will be needed. A radical change in the way we smooth the foil surface has already been implemented and represents an important first step that has considerably improved the imaging capability of our second generation mirrors. Additional breakthroughs are still needed, however, if foil mirrors are to play a major role in the Next Generation X ray Observatory era. Foil mirrors offer, additionally, a number of attractive attributes as regards the use of multilayers to extend imaging spectroscopy to tens of keV. Preliminary results of multilayers deposited on our new foil reflectors are very encouraging.

Serlemitsos, Peter J.↗
NASA NTRS2000

Metrology and Alignment of Light Weight Grazing Incidence X-Ray Mirrors

Metrology and alignment of light weight X-ray optics have been a challenge for two reasons: (1) that the intrinsic mirror quality and distortions caused by handling can not be easily separated, and (2) the diffraction limits of the visible light become a severe problem at the order of one arc-minute. Traditional methods of using a normal incident pencil or small parallel beam which monitors a tiny fraction of the mirror in question at a given time can not adequately monitor those distortions. We are developing a normal incidence setup that monitors a large fraction, if not the whole, of the mirror at any given time. It will allow us to align thin X-ray mirrors to-an accuracy of a few arc seconds or to a limit dominated by the mirror intrinsic quality.

Zhang, William↗
NASA NTRS1999

An Inexpensive Radiosonde Chilled Mirror Sensor: An Old Technology With New Impact

The availability of an inexpensive chilled mirror dewpoint sensor has made improved atmospheric relative humidity measurements accessible. Comparisons between the chilled mirror sensor and routine radiosonde sensors have provided new information on the limitation and reliability of the routine measurements. The chilled mirror has observed detailed moisture profiles at cirrus cloud levels when cirrus was not visible, a feature that routine sensors fail to observe. Comparison measurements between the chilled mirror, the carbon resistive (hygristor) and, the capacitive sensors will be discussed. Measurements from three locations (Wallops Island; Andros Island, Bahamas; and Camborne, UK) will be highlighted. It is conceivable that the chilled mirror sensor, when its capability is fully understood, may be sufficiently reliable to serve as a reference.

Schmidlin, F. J.↗
NASA NTRS2001

Improved Humidity Sensing with the Chilled Mirror: Really?

Testing of the chilled mirror sensor was initiated at Wallops Island in 1997. The chilled mirror dew point system is integrated with the Sippican, Inc., MK2 radiosonde providing a relatively inexpensive instrument. Early tests suggested that better stratospheric humidity measurements might be available. But, recent tests with different configurations of the mirror's cooler indicated that the systems capability to cool to the very low dew point temperatures required in the stratosphere were not being met with the present system. Nonetheless, the present mirror technology, while still undergoing development gives better humidity information between 400 and 100 hPa than the current routine radiosonde sensor. Comparisons are given of the chilled mirror and the typical operational humidity sensors.

Schmidlin, Francis J.↗
NASA NTRS2001

FIRST Mirror Review

As part of a JPL-funded effort to develop lightweight telescope technology suitable for far-infrared astronomy, COI designed and fabricated a spherical, f/1, 2-meter aperture prototype primary mirror using solely graphite/resin composite materials. To assess the performance of this technology, optical metrology of the mirror surface was performed from ambient to an intended operational temperature for IR-telescopes of 70K. Testing was performed horizontally in a cryogenic vacuum chamber at Arnold AFB, Tennessee. The test design had to accommodate requirements for rapid and uniform cooling across the optic, passivation of the ambient vibrational environment, and de-coupling of the mirror from the thermal strain of the test stand. An IR-wavelength phase shifting interferometer (PSI) was the primary instrument used to measure the mirror surface. From an initial surface figure of 2.1 microns RMS at ambient, a modest 3.9 microns of additional RMS surface error was induced at 70K. The thermally induced error was dominated by low-order deformations, of the type that could easily be corrected with secondary or tertiary optics. In addition to exceptional thermal stability, the mirror exhibited no measurable hysteresis between both ambient and cryo measurements.

Dodson, Kelly↗
NASA NTRS2001

NMSD Mirror Status Review

This presentation provides an overview of the 1.6meter hybrid mirror demonstrator for the Next Generation Space Telescope (NGST) Program. The COI design approach for the NGST program combines the optical performance of glass, with the high specific stiffness capabilities of composite materials. The foundation technologies being exploited in the development of the hybrid mirror focus upon precision composite materials for cryogenic operation, and non-contact optical processing (ion figuring) of the lightweight mirror surface. The NGST Mirror System Demonstrator (NMSD) has been designed and built by Composite Optics, Inc. (COI) and is being optically processed by REOSC The mirror has recently completed the second of three cryogenic optical tests for demonstration of the hybrid technology. The test results will be used for the detailed cryo-figuring of the substrate.

Mehle, Greg↗
NASA NTRS2001

[2-m Diameter NGST Mirror System Demonstrator]

The University of Arizona is manufacturing a 2-m diameter NGST Mirror System Demonstrator. This mirror uses a 2-mm thick glass facesheet as the optical surface. The shape is controlled and adjusted using 166 actuators that are mounted into a composite carbon fiber structure. The overall mass density for the mirror system is 13 kg/sq m, including glass, attachments, actuators, cabling, and support structure. The mirror operates at ambient temperatures and at cryogenic temperatures using custom built actuators and couplings. The status of the mirror fabrication will be presented.

Burge, Jim↗
NASA NTRS2002

COI NMSD Hybrid Mirror

This presentation provides an overview of the development of the 1.6 meter hybrid mirror demonstrator for the NGST Mirror System Demonstrator (NMSD) program. The COI design approach for the NGST program combines the optical performance of glass, with the high specific stiffness capabilities of composite materials The foundation technologies being exploited in the development of the hybrid mirror focus upon precision Composite Materials for cryogenic operation, and non-contact optical processing (ion figuring) of the lightweight mirror surface. The NGST Mirror System Demonstrator (NMSD) has been designed and built by Composite Optics, Inc. (COI) with optical processing performed by SAGEM (REOSC). The sponsors of these efforts are the NASA Marshall and Goddard Space Flight Centers.

Mehle, Greg↗