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This paper describes the flight verification of a nitrogen triple-point Cryogenic Thermal Storage Unit (CTSU), which flew as part of the CRYOTSU payload on STS-95 in late 1998. The CTSU flight unit is a dual-volume device with a 140 cc beryllium cryogenic heat exchanger and a 17 liter stainless steel ambient storage tank. During the flight, the CTSU demonstrated 3 kJ of energy storage at 63.15 K with variable heat loads from 5-9 W. An additional test was performed which demonstrated nitrogen's solid-solid transition at 35 K with 1 kJ of energy storage. The zero-g environment had no measurable impact on CTSU operation.

This paper describes the development, operation and testing of an across-gimbal ambient thermal transport system (GATTS) for carrying cryocooler waste heat across a 2-axis gimbal. The principal application for the system is space-based remote sensing spacecraft with gimbaled cryogenics optics and/or infrared sensors. GATTS uses loop heat pipe (LHP) technology with ammonia as the working fluid and small diameter stainless steel tubing to transport 100–275 W across a two-axis gimbal. The tubing is coiled around each gimbal axis to provide flexibility (less than 0.68 N-m [6 lbf-in] of tubing-induced torque per axis) and fatigue life. Stepper motors are implemented to conduct life cycling and to assess the impact of motion on thermal performance. An LHP conductance of approximately 7.5 W/C was demonstrated at 200 W, with and without gimbal motion. At the time this paper was written, the gimbal had successfully completed over 500,000 cycles of operation with no performance degradation.

This paper describes the Cryogenic Thermal Storage Unit (CTSU) flight experiment, which flew as part of the CRYOTSU payload on STS-95 in late 1998. The CTSU flight unit is a dual-volume nitrogen triple-point device with a 140 cc beryllium cryogenic heat exchanger and a 17 liter stainless steel ambient storage tank. During the 9-day flight, the CTSU completed all testing goals including 22 full freeze-thaw and 18 partial freeze-thaw cycles at power levels from 5-9 W. All tests were successful and demonstrated 3000 J of energy storage at 63.15 K. An additional test was performed which demonstrated nitrogen’s solid-solid transition at 35 K with 1000 J of energy storage. The zero-g environment had no discernible impact on CTSU operation.