Initial Operation of the NICMOS Cryocooler on the Hubble Space Telescope

Abstract

The NICMOS Cooling System (NCS) was installed on the Hubble Space Telescope (HST) in March 2002 during HST Servicing Mission 3B (SM3B). It is designed to cool the detectors for the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) to a temperature of approximately 75 K. The system consists of a single-stage turboBrayton cryocooler connected to a cryogenic circulator loop through a gas to gas heat exchanger at the cold end of the cryocooler. Three high-speed miniature turbomachines with self-acting gas bearings and all-metal heat exchangers are used to provide the necessary refrigeration and heat transport with low input power and negligible vibration. The circulating loop transfers heat from the NICMOS detectors to the cold end of the cryocooler through flexible tubes that connect to the NICMOS dewar. Provisions for contamination control of the circulator loop prior to on-orbit integration with the NICMOS dewar were an important part of the pre-launch operations. Following the integration of the NCS with the NICMOS dewar, the system was subjected to a series of tests to verify its operation and to characterize its performance. A separate series of tests was conducted to assess the impact of NCS operation on spacecraft pointing accuracy. This paper describes the NCS, the pre-launch procedures to minimize contamination of the circulator loop, and the performance of the system on orbit.