2005, pp 633-639

The NICMOS Turbo-Brayton Cryocooler — Two Years in Orbit

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Abstract

A turbo-Brayton cryocooler was installed on the Hubble Space Telescope in March 2002 to restore cooling to the Near Infrared Camera and Multi-Object Spectrograph (NICMOS). The cryocooler delivers its refrigeration to the NICMOS cryostat by means of a separate cryogenic circulating loop that was packaged with the cryocooler. During two years of on-orbit operation, the cooler has maintained the NICMOS detectors within specified bounds of temperature at approximately 77 K. The cryocooler relies on temperature feedback from the gas stream into and out of the cryostat for temperature control. Compressor frequency is adjusted to increase or reduce net refrigeration available from the cryocooler to accommodate changes in the thermal environment and parasitic heat loads. This paper reviews the cryocooler design, describes the means for temperature control, and reviews operational history during the first two years in space.