Search Results

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 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.

Loop Heat Pipes (LHPs) are passive two-phase heat transport devices that have been baselined for many spacecraft thermal management applications. The design life of a spacecraft can extend to 15 years or longer, thus requiring a robust thermal management system. Based on conventional aluminum/ammonia heat pipe experience, there exists a potential for the generation of noncondensible gas in LHPs over the spacecraft lifetime. In addition, some applications would have the LHP evaporator attached directly to spacecraft equipment having large thermal mass. To address the potential issues associated with LHP operation with noncondensible gas and large thermal mass attached to the evaporator, a test program was implemented to examine the effect of mass and gas on ammonia LHP performance. Many laboratory test programs for LHPs have heat delivered to the evaporator through light-weight aluminum heater blocks.

The ADRAD deployable radiator is in development at Swales Aerospace to provide additional heat rejection area for spacecraft without envelope impact. The ADRAD design incorporates ALPHA loop heat pipes, an aluminum honeycomb radiator with embedded condenser, OSR optical coating, spherical bearing hinges, pyrotechnic release devices and snubbers. This paper describes the design of ADRAD to a set of “generic” GEO requirements, including a nominal heat rejection capacity of 1250 W. Thermal, structural and mechanism considerations are described along with the comprehensive systems approach necessary to produce an integrated subsystem.

This paper describes the development and testing status of several novel components and integration tools for space-based cryogenic applications. These advanced devices offer functionality in the areas of cryogenic thermal switching, cryogenic thermal transport, cryogenic thermal storage, and cryogenic integration. As such, they help solve problems associated with cryocooler redundancy, across-gimbal thermal transport, large focal plane array cooling, fluid-based cryogenic transport, and low vibration thermal links. The devices discussed in the paper include a differential thermal expansion cryogenic thermal switch, an across-gimbal thermal transport system, a cryogenic loop heat pipe, a cryogenic capillary pumped loop, a beryllium cryogenic thermal storage unit, a high performance flexible conductive link, a kevlar cable structural support system, and a high conductance make-break cryogenic thermal interface.

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.