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  • 1
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    Performance considerations for the astrometric telescope facility on the phase 1 space station (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The Astrometric Telescope Facility (ATF) is an optical telescope facility of extreme astrometric precision whose principle scientific purpose is the detection and study of planetary systems about nearby stars. With the recent change in the space station program to two phases, the suitability of initial operations from the phase 1 station need to be evaluated. This paper presents the results of such an evaluation for the Astrometric Telescope Facility.
    Keywords: ASTRONOMY
    Type: NASA-TM-100040 , A-88021 , NAS 1.15:100040
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Performance considerations for the astrometric Telescope Facility on the Phase I Space Station (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: The Astrometric Telescope Facility (ATF) is an optical telescope facility of extreme astrometric precision whose principal scientific purpose is the detection and study of planetary systems about nearby stars. With the recent change in the space station program to two phases, the suitability of initial operations from the phase 1 station need to be evaluated. This paper presents the results of such an evaluation for the Astrometric Telescope Facility.
    Keywords: ASTRONOMY
    Type: Optoelectronic technologies for remote sensing from space; Nov. 19, 20, 1987; Cannes; France
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Steady Secondary Momentum and Enthalpy Streaming in the Pulse Tube Refrigerator (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: Our study investigates the steady secondary streaming that occurs in the pulse tube refrigerator through application of the conservation laws and support by flow visualization experiments. A series expansion of the mass, momentum and energy conservation laws for an axisymmetric system yields a set of linear differential equations. The series solution is expanded in the small parameter epsilon = 1/Str where Str is the Strouhal number. The O(1) basic flow problem is solved for the case of a compressible ideal gas oscillating within a cylindrical tube. The phase and amplitude of the boundary conditions on axial velocity are treated as independent parameters. The basic solution for the gas domain is solved for the case of temperature and heat flux coupling to the tube wall. The temperature coupled solution shows how the Fourier number of the tube wall affects the gas temperature, phase angle, and time-averaged enthalpy flow. The basic solution is also examined for the time-averaged Reynolds stresses which are shown to be the driving force that produces steady secondary momentum streaming. Calculated solutions to the steady momentum streaming are shown to be in qualitative agreement with flow visualization experiments.
    Keywords: Engineering (General)
    Type: International Cryocooler Conference; Jun 28, 1994 - Jun 30, 1994; Vail, CO; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    FPA Needs for NASA Missions (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: NASA has identified needs for a broad range of specialized, optimized infrared detectors and IR detector arrays to meet its future mission requirements. Space infrared missions will be conducted in a number of discipline areas, including astrophysics, earth and atmospheric science, planetary systems, and space physics. To allow investigators to meet scientific goals, specific technical requirements for infrared detectors have been developed. These challenging and often unique requirements include, for example, achieving background-limited performance in a cryogenic space telescope; developing long-wave IR arrays which achieve near background-limited performance at elevated (approximately 60 kelvin) operating temperatures; achieving IR arrays with large two-dimensional formats, excellent uniformity and linearity, and low power dissipation; demonstrating an imaging array technology for very long-wavelength (less than 100 microns) IR sensing, and IR devices with extremely low dark current levels; and demonstrating stable, low-noise, low-dissipation readouts. These requirements can in some cases be met by adaptation or extension of technologies originally developed by DoD. In other cases, the novel spectral range or other characteristics require unique solutions. Examples are given of recent scientific results which have been made possible with IR arrays. These serve as a preview of the kinds of science return which can be enabled by advanced IR focal plane technology from space platforms.
    Keywords: Optics
    Type: Infrared Information Symposium Detector Specialty Group Meeting; Aug 17, 1994 - Aug 18, 1994; Boulder, CO; United States
    Format: text
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  • 5
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    A Microgravity Helium Dilution Cooler (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: We are developing a He-3-He-4 dilution cooler to operate in microgravity. It uses charcoal adsorption pumps and heaters for its operation; it has no moving parts. It currently operates cyclically to well below 0.1 K and we have designed a version to operate continuously. We expect that the continuous version will be able to provide the long-duration cooling that many experiments need at temperatures down to 0.040 K. More importantly, such a dilution cooler could provide the precooling that enables the use of adiabatic demagnetization techniques that can reach temperatures below 0.001 K. At temperatures below 0.002 K many fascinating microgravity experiments on superfluid He-3 become possible. Among the possibilities are: research into a superfluid He-3 gyroscope, study of the nucleation of the B-phase of superfluid He-3 when the sample is floating out of contact with walls, study of the anisotropy of the surface tension of the B-phase, and NMR experiments on tiny free-floating clusters of superfluid He-3 atoms that should model the shell structure of nuclei.
    Keywords: Space Processing
    Type: 1994 Microgravity Low-Temperature Physics Workshop; Jan 19, 1994 - Jan 21, 1994; Washington, DC; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    Efficiency Calculations For a Magnetic Refrigerator Operating Between 2K and 10K (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: An adiabatic demagnetization refrigerator (ADR) is being developed at NASA-Ames Research Center. The ADR will operate between 2 K and 10 K and will provide 50 mW of cooling at 2 K. The refrigerant in the ADR is Gadolinium Gallium Garnet (GGG). Absorption of heat at 2 K and heat rejection at 10 K in this fully static refrigerator is made possible by the incorporation of 2 K and 10 K heat switches. Physical layout and experimental results are presented in a parallel paper. The present paper discusses the thermal losses associated with components of the ADR as they occur in various parts of the refrigeration cycle. The results are summarized in terms of a prediction for the ADR efficiency.
    Keywords: Mechanical Engineering
    Type: 8th International Cryocooler Conference; Jun 28, 1994 - Jun 30, 1994; Vale, CO; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 7
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    Modeling Thermal Contact Resistance (1994)
    In:  Other Sources
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    Publication Date: 2019-07-17
    Description: One difficulty in using cryocoolers is making good thermal contact between the cooler and the instrument being cooled. The connection is often made through a bolted joint. The temperature drop associated with this joint has been the subject of many experimental and theoretical studies. The low temperature behavior of dry joints have shown some anomalous dependence on the surface condition of the mating parts. There is also some doubts on how well one can extrapolate from the test samples to predicting the performance of a real system. Both finite element and analytic models of a simple contact system have been developed. The model assumes (a) the contact is dry (contact limited to a small portion of the total available area and the spaces in-between the actual contact patches are perfect insulators), (b) contacts are clean (conductivity of the actual contact is the same as the bulk), (c) small temperature gradients (the bulk conductance may be assumed to be temperature independent), (d) the absolute temperature is low (thermal radiation effects are ignored), and (e) the dimensions of the nominal contact area are small compared to the thickness of the bulk material (the contact effects are localized near the contact). The models show that in the limit of actual contact area much less than the nominal area (a much less than A), that the excess temperature drop due to a single point of contact scales as a(exp -1/2). This disturbance only extends a distance approx. A(exp 1/2) into the bulk material. A group of identical contacts will result in an excess temperature drop that scales as n(exp -1/2), where n is the number of contacts and n dot a is constant. This implies that flat rough surfaces will have a lower excess temperature drop than flat polished surfaces.
    Keywords: Engineering (General)
    Type: International Cryocooler Conference; Jun 28, 1994 - Jun 30, 1994; Colorado; United States
    Format: text
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