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  • 1
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    Floating Pressure Conversion and Equipment Upgrades of Two 3.5kw, 20k, Helium Refrigerators (2008)
    In:  Other Sources
    Details
    Publication Date: 2019-07-19
    Description: Two helium refrigerators, each rated for 3.5KW at 20K, are used at NASA s Johnson Space Center (JSC) in Building No. 32 to provide cryo-pumping within two large thermal-vacuum chambers. These refrigerators were originally commissioned in 1996. Equipment refurbishment and upgrades to the controls of these refrigerators were recently completed. This paper describes some of the mechanical and control issues that necessitated the equipment refurbishment and controls change-over. It will describe the modifications and the new process control which allows the refrigerators to take advantage of the Ganni Cycle "floating pressure" control technology. The upgrades -- the controls philosophy change-over to the floating pressure control technology and the newly refurbished equipment -- have greatly improved the performance, stability, and efficiency of these two refrigerators. The upgrades have also given the operators more information and details about the operational status of the main components (compressors, expanders etc.) of the refrigerators at all operating conditions (i.e.: at various loads in the vacuum chambers). Capabilities, configuration, and performance data pre, and post, upgrading will be presented.
    Keywords: Engineering (General)
    Type: 25th Space Simulation Conference. Environmental Testing: The Earth-Space Connection; 8; NASA/CP-2008-214164
    Format: text
    Location Call Number Expected Availability
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    NASA TECHNICAL REPORTS
  • 2
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    Modernization of NASA Johnson Space Center's Chamber A to Support Cryogenic Vacuum Optical Testing of the James Webb Space Telescope (JWST) (2018)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Final document is attached. NASA is the mission lead for the James Webb Space Telescope (JWST), the next of the "Great Observatories", scheduled for launch in 2021. NASA is directly responsible for the integration and test (I&T) program that culminated in an end-to-end cryo vacuum optical test of the flight telescope and instrument module in Chamber A at NASA Johnson Space Center. Historic Chamber A is the largest thermal vacuum chamber at Johnson Space Center and one of the largest space simulation chambers in the world. Chamber A has undergone a major modernization effort to support the deep cryogenic, vacuum and cleanliness requirements for testing the JWST. This paper describes the upgrades to the Chamber A facility: Thermal Shrouds, Helium Refrigeration, Liquid Nitrogen System, High Vacuum System, Clean Airflow System, and Utilities.
    Keywords: Optics
    Type: JSC-E-DAA-TN61814 , Space Simulation Conference; Nov 05, 2018 - Nov 08, 2018; Annapolis, MD; United States
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    NASA TECHNICAL REPORTS
  • 3
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    Unknown
    The Liquid Nitrogen System for Chamber A: A Change from Original Forced Flow Design to a Natural Flow (Thermo Siphon) System (2008)
    In:  Other Sources
    Details
    Publication Date: 2019-07-19
    Description: NASA Johnson Space Center (JSC) in Houston is currently supplementing its 20K helium refrigeration system to meet the new requirements for testing the James Web Space Telescope in the environmental control Chamber-A (65 dia x 120 high) in Building 32. The new system is required to meet the various operating modes which include a high 20K heat load, a required temperature stability at the load, rapid (but controlled) cool down and warm up and bake out of the chamber. This paper will present the proposed modifications to the existing helium system(s) to incorporate the new requirements and the integration of the new helium refrigerator with the existing two 3.5KW 20K helium refrigerators. In addition, the floating pressure process control philosophy to achieve high efficiency over the operating range (40% to 100% of the refrigeration system capacity), and the required temperature stability of +/- 0.25 K at the load will be discussed. The refrigeration systems ability to naturally seek the operating conditions under various loads and thus minimizing operator involvement and the over all improvements to the system operability and the reliability will be explained.
    Keywords: Space Sciences (General)
    Type: 25th Space Simulation Conference. Environmental Testing: The Earth-Space Connection; 6; NASA/CP-2008-214164
    Format: text
    Location Call Number Expected Availability
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    NASA TECHNICAL REPORTS
  • 4
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    Affect of Air Leakage into a Thermal-Vacuum Chamber on Helium Refrigeration Heat Load (2008)
    In:  Other Sources
    Details
    Publication Date: 2019-07-19
    Description: NASA s Johnson Space Center (JSC) Building 32 houses two large thermal-vacuum chambers (Chamber A and Chamber B). Within these chambers are liquid nitrogen shrouds to provide a thermal environment and helium panels which operate at 20K to provide cryopumping. Some amount of air leakage into the chambers during tests is inevitable. This causes "air fouling" of the helium panel surfaces due to the components of the air that adhere to the panels. The air fouling causes the emittance of the helium panels to increase during tests. The increase in helium panel emittance increases the heat load on the helium refrigerator that supplies the 20K helium for those panels. Planning for thermal-vacuum tests should account for this increase to make sure that the helium refrigerator capacity will not be exceeded over the duration of a test. During a recent test conducted in Chamber B a known-size air leak was introduced to the chamber. Emittance change of the helium panels and the affect on the helium refrigerator was characterized. A description of the test and the results will be presented.
    Keywords: Engineering (General)
    Type: 25th Space Simulation Conference. Environmental Testing: The Earth-Space Connection; 9; NASA/CP-2008-214164
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    NASA TECHNICAL REPORTS
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