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  • 1
    Publication Date: 2007-10-01
    Print ISSN: 0002-7820
    Electronic ISSN: 1551-2916
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Wiley on behalf of American Ceramic Society.
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  • 2
    Publication Date: 2013-08-29
    Description: A number of unusual effects were observed on the Thermal Control Surfaces Experiment (TCSE) test samples, front cover, and structural components. These effects include atomic oxygen (AO) texturing of the exposed surface of the silver Teflon (Ag/FEP) thermal control material, 'brownish' discoloration of the Ag/FEP material, changes in fluorescence of thermal control paint samples, and meteoroid/debris impact effects on silver Teflon.
    Keywords: NONMETALLIC MATERIALS
    Type: NASA. Langley Research Center, LDEF: 69 Months in Space. First Post-Retrieval Symposium, Part 2; p 919-933
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  • 3
    Publication Date: 2018-06-12
    Description: The strengths of two candidate glass types for use in a space observatory were measured. Samples of ultra-low expansion glass (ULE) and borosilicate (Pyrex) were tested in air and in vacuum at room temperature (20 degrees C) and in vacuum after being heated to 200 degrees C. Both glasses tested in vacuum showed a significant increase in strength over those tested in air. However, there was no statistical difference between the strength of samples tested in vacuum at room temperature and those tested in vacuum after heating to 200 degrees C.
    Keywords: Inorganic, Organic and Physical Chemistry
    Format: application/pdf
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  • 4
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    In:  CASI
    Publication Date: 2019-06-28
    Description: The time dependence of the angular reflectance from molecularly contaminated optical surfaces in the Vacuum Ultraviolet (VUV) is measured. The light scattering measurements are accomplished in situ on optical surfaces in real time during deposition of molecular contaminants. The measurements are taken using non-coherent VUV sources with the predominant wavelengths being the Krypton resonance lines at 1236 and 1600 A. Detection of the scattered light is accomplished using a set of three solar blind VUV photomultipliers. An in-plane VUV BRDF (Bidirectional Reflectance Distribution Functions) experiment is described and details of the ongoing program to characterize optical materials exposed to the space environment is reported.
    Keywords: OPTICS
    Type: NASA-CR-184225 , NAS 1.26:184225 , UAH-5-32180
    Format: application/pdf
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  • 5
    Publication Date: 2019-06-28
    Description: NASA's In Situ Contamination Effects Facility has been used to measure the time dependence of the angular reflectance from molecularly contaminated optical surfaces in the vacuum ultraviolet. The light scattering measurements are accomplished in situ on optical surfaces in real time during deposition of molecular contaminants. The measurements are taken using noncoherent VUV sources with the predominant wavelengths being the krypton resonance lines at 1236 and 1600 angstroms. Detection of the scattered light is accomplished using a set of three solar blind VUV photomultipliers. An in-plane VUV BRDF (bidirectional reflectance distribution function) experiment is described and details of the on-going program to characterize optical materials exposed to the space environment is reported.
    Keywords: OPTICS
    Type: SAE PAPER 901412
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  • 6
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    In:  Other Sources
    Publication Date: 2019-07-18
    Description: The ion milling of sapphire is a complicated operation due to several characteristics of the material itself. It is a relatively hard transparent nonconductive crystalline material that does not transfer heat nearly as well as metals that have been successfully ion milled in the past. This investigation involved designing an experimental arrangement, using existing ion milling equipment, as the precursor to figuring the surface of sapphire and other insulating optical materials. The experimental arrangement employs a laser probe beam to constantly monitor the stresses being induced in the material, as it is being ion milled. The goal is to determine if the technique proposed would indeed indicate the stress being induced in the material so that these stresses can be managed to prevent failure of the optic.
    Keywords: Optics
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  • 7
    Publication Date: 2019-07-18
    Description: The term "specific impulse" is so ingrained in the field of rocket propulsion that it is unlikely that any fundamental argument would be taken seriously for its removal. It is not an ideal measure but it does give an indication of the amount of mass flow (mass loss/time), as in fuel rate, required to produce a measured thrust over some time period This investigation explores the implications of being able to accurately measure the ablation rate and how the language used to describe the specific impulse results may have to change slightly, and recasts the specific impulse as something that is not a time average. It is not currently possible to measure the ablation rate accurately in real time so it is generally just assumed that a constant amount of material will be removed for each laser pulse delivered The specific impulse dependence on the ablation rate is determined here as a correction to the classical textbook definition.
    Keywords: Spacecraft Instrumentation and Astrionics
    Type: Third International Symposium on Beamed Energy Propulsion; Oct 11, 2004 - Oct 13, 2004; Troy, NY; United States
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  • 8
    Publication Date: 2019-07-18
    Description: This work continues on previous investigations of elementary propellants for Ablative Laser Propulsion (ALP). This paper details the experimental methods used for alignment of a non-colinear temporal pulse splitting apparatus. Spatial coincidence of the separate pulses is established, the pulses are delayed, and first data is reported on this pulse spacing effect on time-of-fight (TOF) measurements. This includes ion velocity and number density measurements, and this data is compared to results from a previous work. Also, first data on the experimental determination of the time required for the laser-induced plasma to become purely reflective to incident pulses is presented.
    Keywords: Lasers and Masers
    Type: First International Symposium on Beamed Energy Propulsion; Nov 05, 2002 - Nov 07, 2002; Huntsville, AL; United States
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  • 9
    Publication Date: 2019-07-18
    Description: This is a continuation of studies using a two-pulsed technique for Ablative Laser Propulsion (ALP) extended to force measurements in vacuum. Aluminum samples were ablated using pairs of laser pulses, each of 100 ps width, 532 nm wavelength and 5 mJ energy. The pulses were temporally separated in the 0 - 0.67 ns range. The force imparted on Al targets was measured in situ by means of a piezoelectric force gauge. The preliminary results confirm the previously reported oscillatory behavior of ion velocity and number density observed by means of a time-of-flight energy analyzer. The uncertainties of presented measurements and future directions for the study are discussed.
    Keywords: Lasers and Masers
    Type: Third International Symposium on Beamed Energy Propulsion; Oct 11, 2004 - Oct 13, 2004; Troy, NY; United States
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  • 10
    Publication Date: 2019-07-18
    Description: Bi-directional reflectance distribution function (BRDF) measurements of optical surfaces both before and after molecular contamination were done using UV, VUV and visible light. Molecular contamination of optical surfaces from outgassed material has been shown in many cases to proceed from acclimation centers, and to produce many roughly hemispherical "islands" of contamination on the surface. Vacuum Ultraviolet (VW) wavelengths are used here to measure angularly scattered light from optical surfaces.
    Keywords: Astrophysics
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