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  • 1
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    Space Infrared Telescope Facility (SIRTF) observatory design (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The NASA Space IR Telescope Facility (SIRTF) is a 1-m aperture, cryogenically cooled IR observatory scheduled for launch into orbit in the mid-1990s. SIRTF will operate in the 2-700 micron range and yield a 1000-fold increase in sensitivity over NASA's IRAS observatory. A low inclination orbit compatible with Space Shuttle operations will be used. Results from comparisons of a system error budget allocation for the f/24 optical configuration with recent test data indicate that a figured fused silica mirror and a blade flexure mounting system can be cooled to cryogenic temperature while meeting required wavefront tolerances for substrate deformation. An all-He cooling system will be used in the low inclination orbit.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
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    NASA TECHNICAL REPORTS
  • 2
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    Thermal conductance of pressed brass contacts at liquid helium temperatures (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An apparatus has been designed and fabricated which will measure the thermal conductance of pressed contacts at liquid helium temperatures as a function of applied force, with surface finish as a parameter. The apparatus is automated and was used to measure thermal conductance at temperatures from 1.5 to 6.5 K at applied forces up to 700 N for brass sample pairs having surface finishes from 0.1 to 1.6 micron rms. The experimental data were found to fit a simple power law where the thermal conductance is given by k = alpha T exp n, where k is the thermal conductance, T is the absolute temperature, and alpha and n are empirically determined constants.
    Keywords: ENGINEERING (GENERAL)
    Type: Cryogenics (ISSN 0011-2275); 26; 217-221
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    NASA TECHNICAL REPORTS
  • 3
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    Cryogenic and thermal design for the space infrared telescope facility (SIRTF) (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 23; 25-30
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    NASA TECHNICAL REPORTS
  • 4
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    Temperature control of silica mirrors for cryogenically-cooled telescopes in space (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The SIRTF (Space Infrared Telescope Facility) optical subsystem, including the primary mirror, has been modeled using lumped-parameter techniques and a thermal and cryogenic transient analysis program developed previously. Since silica mirrors have been shown to have significantly less distortion due to cryogenic cooldown, a silica primary mirror of approximately 1 m diameter is being considered. Thermal responses to variations in aperture heat load and heat sink temperature have been explored. Calculations have been made of system noise components from primary mirror spatial and temporal temperature variations. Background-limited infrared observations can be made at wavelengths out to 200 micrometers. Mirror thermal performance with and without copper wires for cooling is also considered.
    Keywords: OPTICS
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    NASA TECHNICAL REPORTS
  • 5
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    Numerical modeling of Helium-II in forced flow conditions (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Thermophysics and Heat Transfer (ISSN 0887-8722); 3; 203-212
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    NASA TECHNICAL REPORTS
  • 6
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    Cryogenic implications of orbit selection of the Space Infrared Telescope Facility (SIRTF) (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An investigation has been conducted to determine how the choice of orbit for NASA's prospective Space IR Telescope Facility (SIRTF), between polar (99-deg) and low inclination (28.5-deg) alternatives, will affect the performance of the all-superfluid He-cooled IR optics employed. While the dewar design met both the service life and 200-micron background-limited performance criteria in the case of the polar orbit mission, the alternative orbit allowed the background-limited criteria to be met only 50 percent of the time. It is accordingly recommended that the 200-micron background-limited observations be made only for a limited portion of the mission, while meeting the 100-micron limit at all times.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
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  • 7
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    Analytical study of He II flow characteristics in the SHOOT transfer line (1988)
    In:  Other Sources
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    Publication Date: 2019-04-02
    Description: Pressure and temperature profiles for He II flow in the transfer line for the Superfluid Helium On-Orbit Transfer (SHOOT) experiment are determined using a finite difference method to solve the one-dimensional two-fluid conservation equations. For practical purposes, forced flow of He II with Re greater than 10 to the 6th can be treated as a classical turbulent flow For a maximum SHOOT transfer rate of 800 cu dm/h, the temperature rise between the pump outlet and the receiver tank is about 80 mk with a 7-W heat load imposed on the 4-m-long transfer line. A pump outlet pressure of 160 torr is required to sustain the 800 cu dm/h flow without causing vapor formation within the transfer line.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Cryogenics (ISSN 0011-2275); 28; 81-85
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  • 8
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    Instrumentation, data acquisition and reduction for a large spaceborne helium dewar (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The data acquisition system monitors five types of transducers: (1) platinum and germanium resistance thermometers; (2) superconducting liquid level indicators for both cryogen tanks; (3) pressure transducers for both tanks; (4) strain gauges at critical structural locations; and (5) flowmeters for monitoring cryogen tank boiloff which are linear voltage output transducers. All the transducers produce a voltage proportional to the parameter they measure; this is routed to a single six and one-half digit voltmeter by way of an 80-channel multiplexer. The data acquisition program has six main functions: (1) definition and modification of the channels to be stimulated; (2) sensor stimulation and measurement; (3) raw data storage; (4) raw data conversion; (5) real-time formatting and output of raw or converted data; and (6) editing. The heart of the program is a driver section that represents approximately 20 percent of the code. The driver mode sequences and controls the six main functions.
    Keywords: ENGINEERING (GENERAL)
    Type: Advances in cryogenic engineering. Volume 27 - Proceedings of the Cryogenic Engineering Conference; Aug 11, 1981 - Aug 14, 1981; San Diego, CA
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  • 9
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    Orbital performance of a one-year lifetime superfluid helium dewar based on ground testing and computer modelling (1982)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The ground-test results of the 550-liter superfluid-He dewar built for IRAS are presented and discussed, and a computer projection of its orbital performance life is developed. The ground-testing program included flow-swap, cold-flow, power-off, hot/cold-viewport, and strap-thermal-efficiency tests. After one set of trials, some design changes were made, and the thermal-network computer model of the system was modified as well. The driving boundary conditions of dewar orbital operation used in this model are vacuum-shell temperature = 170 K, aperture heating = 8.0 mW, and focal-plane power dissipation = 16.2 mW. An operational lifetime of 319 days and an He loss rate of 2.54 mg/sec are predicted.
    Keywords: ENGINEERING (GENERAL)
    Type: Advances in cryogenic engineering. Volume 27 - Proceedings of the Cryogenic Engineering Conference; Aug 11, 1981 - Aug 14, 1981; San Diego, CA
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  • 10
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    Superfluid-supercritical helium tradeoff analysis for the Shuttle Infrared Telescope Facility (SIRTF) (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A comparative study is made of three methods for obtaining the required cooling of the SIRTF. The first is a supercritical helium system in which the 2 K temperatures are obtained by a Joule-Thomson expander; the second is a superfluid (He II) helium system; and the third is a hybrid system in which supercritical helium provides the major cooling and small He II reservoirs supply specific detector cooling. The superfluid helium system is found to offer superior performance; it would be the system to use if funding were available. The comparative study gives equal weight to performance, operations, and cost. From this point of view, the hybrid system is selected as the best compromise to obtain an operational SIRTF.
    Keywords: ENGINEERING (GENERAL)
    Type: Advances in cryogenic engineering. Volume 27 - Proceedings of the Cryogenic Engineering Conference; Aug 11, 1981 - Aug 14, 1981; San Diego, CA
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