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  • Other Sources  (4)
  • 1995-1999  (4)
  • 1950-1954
  • 1999  (4)
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  • 1995-1999  (4)
  • 1950-1954
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  • 1
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    Europa: Extreme Communication Technologies for Extreme Conditions (1999)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Keywords: Communications and Radar
    Type: Deep Space Communication and Navigation Symposium; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Vacuum Plasma Spray (VPS) Forming of Solar Thermal Propulsion Components Using Refractory Metals (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The Thermal Spray Laboratory at NASA's Marshall Space Flight Center has developed and demonstrated a fabrication technique using Vacuum Plasma Spray (VPS) to form structural components from a tungsten/rhenium alloy. The components were assembled into an absorber cavity for a fully-functioning, ground test unit of a solar then-nal propulsion engine. The VPS process deposits refractory metal onto a graphite mandrel of the desired shape. The mandrel acts as a male mold, forming the required contour and dimensions of the inside surface of the deposit. Tungsten and tungsten/25% rhenium were used in the development and production of several absorber cavity components. These materials were selected for their high temperature (greater than 25000 C [greater than 4530 F]) strength. Each absorber cavity comprises 3 coaxial shells with two, double-helical flow passages through which the propellant gas flows. This paper describes the processing techniques, design considerations, and process development associated with forming these engine components.
    Keywords: Spacecraft Propulsion and Power
    Type: Advanced Energy; Apr 11, 1999 - Apr 15, 1999; Maui, HI; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Low-Pressure Gas Effects on the Potency of an Electron Beam Against Ceramic Cloth (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: An 8-kv electron beam with a current in the neighborhood of 100 mA from the Ukrainian space welding "Universal Hand Tool" (UHT) burned holes in Nextel AF-62 ceramic cloth designed to withstand temperatures up to 1,427 C. The burnthrough time was on the order of 8 scc at standoff distances between UHT and cloth ranging from 6-24 in. At both closer (2 in.) and farther (48 in.) standoff distances the potency of the beam against the cloth declined and the burnthrough time went up significantly. Prior to the test it had been expected that the beam would lay down a static charge on the cloth and be deflected without damaging the cloth. The burnthrough is thought to be an effect of partial transmission of beam power by a stream of positive ions generated by the high-voltage electron beam from contaminant gas in the "vacuum" chamber. A rough quantitative theoretical computation appears to substantiate this possibility.
    Keywords: Engineering (General)
    Type: NASA/TM-1999-209762 , NAS 1.15:209762 , M-951
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    How an Electron Beam (Eventually) Penetrates Ceramic Cloth (1999)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: In anticipation of the International Space Welding Experiment (ISWE) the effect of an electron beam was investigated on Nextel AF-62 ceramic cloth designed to withstand temperatures up to 1427 C. It was anticipated that the cloth would take a static charge that would repel the beam and remain undamaged. It was found that after some seconds the impinging beam penetrated penetrated the cloth. Further, the penetration time went up significantly both at longer and at closer standoff distances. A tentative explanation appears to fit the observed facts. The electrons in the beam generate positive ions by collisions with the contaminant gas molecules in the vacuum chamber. The positive ions transfer a small but significant fraction of the beam power to the cloth. Under the impingement of the positive ions the cloth heats up until sufficient outgassing occurs to initiate arcing. Once arcing occurs the full beam power impinges on the cloth and, almost instantaneously, burns a hole.
    Keywords: Mechanical Engineering
    Type: Apr 26, 2000 - Apr 28, 2000; Chicago, IL; United States
    Format: text
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    NASA TECHNICAL REPORTS
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