Thermal Design and Analysis of the NICMOS Cooling System for the Hubble Space Telescope

The Near Infrared Camera and Multi-Object Spectrometer (NICMOS) was installed on the Hubble Space Telescope (HST) during the HST’s Second Servicing Mission (SM-2) in February 1997. Shortly after installation, a thermal short was discovered inside the cryogenic dewar designed to cool the instrument’s detectors. This thermal short introduced a significantly higher parasitic heat load into the solid nitrogen cryogen than predicted and reduced the expected scientific life of NICMOS from approximately 4.8 years to approximately 2.5 years.

The NICMOS Cooling System (NCS) has been designed to restore NICMOS science capabilities by cooling the detectors utilizing a closed loop mechanical cryocooler. The NICMOS Cryocooler (NCC) will deliver neon at cryogenic temperatures to the NICMOS dewar through tubing which was originally designed to subcool the dewar on the ground prior to launch. The NCS will be installed onto NICMOS as an extra vehicular activity during the fourth HST Servicing Mission, designated SM-3B, scheduled for launch in November 2001.

This paper describes the thermal design of the NICMOS Cooling System as well as the thermal analyses performed in conjunction with the design and in support of on orbit control of the cooling system.