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This paper describes the flight test results of the fifth generation cryogenic capillary pumped loop (CCPL-5) which flew on the Space Shuttle STS-95 in October of 1998 as part of the CRYOTSU Flight Experiment. This flight was the first in-space demonstration of the CCPL, a lightweight heat transport and thermal switching device for future integrated cryogenic bus systems. The CCPL-5 utilized nitrogen as the working fluid and operated between 75K and 110K. Flight results indicated excellent performance of the CCPL-5 in a micro-gravity environment. The CCPL could start from a supercritical condition in all tests, and the reservoir set point temperature controlled the loop operating temperature regardless of changes in the heat load and/or the sink temperature. In addition, the loop demonstrated successful operation with heat loads ranging from 0.5W to 3W, as well as with parasitic heat loads alone.

In typical loop heat pipe (LHP) applications, the LHP design calls for a dedicated evaporator and a dedicated condenser. Applications exist for reversible loop heat pipes (LHPs), which can transport heat in either direction. In the reversible LHP design, two evaporator pumps are plumbed together, one which acts as an evaporator while the other acts as a condenser. The two pumps can reverse roles, simply by reversing the temperature gradient across the loop. Thus, either pump can be used as an evaporator or a condenser, depending upon the environment. Reversible LHPs can be used to share heat between components, or to cross-strap opposing spacecraft radiators. A reversible LHP was built and tested to demonstrate feasibility and to characterize its performance capabilities and attributes. The device was tested by either alternately heating each evaporator electrically or by inducing a temperature difference between the two ends of the device.

Capillary Pumped Loops (CPLs) have been under development for almost two decades and are emerging as a design solution for many spacecraft thermal control systems. Three Capillary Pumped Heat Transport Systems (CPHTS) using CPL technology have been selected for accommodating the two Earth Observing System (EOS-AM) instruments that require advanced waste heat dissipation. The Capillary Pumped Loop Flight Experiment (CAPL-2) [Ref 7], which was carried on board STS-69, successfully demonstrated an EOS-like capillary system utilizing a prototyped starter pump cold plate (SCP). The CAPL-2 SCP is almost identical to the EOS-AM configuration and was designed, built, and demonstrated to overcome the start-up difficulty under fully flooded conditions. The SCP was rigorous ground tested as part of a simulated EOS-AM / CAPL-2 capillary loop, and the SCP successfully met or surpassed all of its performance requirements.