Thermal Switching Cryogenic Heat Pipe
Bugby, D. C.
Rodriguez, J. I.
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This paper describes a thermal switching cryogenic heat pipe, which is needed to thermally manage two CCD cameras within the ABC instrument on the NASA/JPL SIM Lite telescope. The primary requirement is to transport 12 W from the 150 K CCD cameras to a 140 K primary radiator 1.4 m away. The heat pipe is a 1.5 cm OD Al axial groove design with methane as the working fluid, which provides 75 W-m of transport capacity at 140 K. A secondary requirement is to periodically heat (decontaminate) the CCD cameras to 293 K with minimal heater power. To meet the decontamination requirement, the heat pipe was modified to provide thermal switching by using small diameter SS tubing to connect it to a liquid trap (LT) cooled by a small secondary radiator (SR) which is thermally isolated from the primary radiator (PR). The LT is a scaled-up version of the LTs used on the CRISM flight system. During normal operation, a small heater keeps the LT filled only with vapor. During decontamination, the LT heater is turned OFF, the PR is heated by midsized heaters and/or heat pipe conduction, the SR-cooled LT captures the working fluid effectively turning the heat pipe OFF, and a small evaporator heater raises the instrument temperature to 293 K. When the LT heater is re-enabled, the system returns to normal operation. This paper describes the design, fabrication, and testing of this demonstration system.