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Having been in operation for over 15 years, the Hubble Space Telescope (HST) had experienced significant changes in both hardware upgrades and operational modes. The changes were necessary to improve performance of some equipment and to replace failed electronics in others. Hardware replacements were done in several servicing missions. To accommodate the change in physical condition of HST, alterations in the way the telescope is operated were also required. The final opportunity to make any hardware changes on HST is during Servicing Mission 4 (SM-4) which is currently scheduled for December of 2007. It is important to make the most appropriate changes in order to ensure that HST will be in good operating condition until its planned termination. In order to provide manifest input to the HST project for the final servicing mission, the HST thermal team must conduct careful evaluation of every single piece of hardware on HST.

Like a Loop Heat Pipe (LHP), a Cryogenic Loop Heat Pipe (CLHP) is a passive two-phase heat transport system that utilizes the capillary pressure developed in a fine pore evaporator wick to circulate the system's working fluid. To demonstrate startup from a supercritical temperature and an operation below ambient temperature for passive bench cooling applications, a CLHP was developed and tested in a thermal vacuum chamber. The system requires startup from a maximum outgassing temperature of 335K over an operating temperature range of 215 to 218K, and an orbital average heat transport capability of 39W. Ethane was selected as the working fluid because it has heat transport properties that are suitable for the operating temperature of 218K. This paper provides a description of the CLHP concept, the development of the design including proof of concept development and testing of a CLHP designed to provide passive cooling of optical instruments.

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.

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.