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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.

The start-up of a capillary pumped loop under a fully flooded condition is often difficult. The problem is due to the presence of a high superheat at the onset of nucleate boiling, and the associated large pressure spike that results in possible vapor penetration through the wick. To overcome the start-up difficulty, a capillary starter pump has been developed. The starter pump is similar to the traditional evaporator pump except for a bayonet tube that is connected directly from the reservoir to the inside of the pump. Such an evaporator design is selfpriming since all displaced liquid must pass through the pump. The starter pump can replace the traditional capillary pump to provide capillary pumping for heat transport. It can further be integrated into a cold plate to receive heat from distributed sources such as spacecraft instruments. Isothermalization of the cold plate can be accomplished by incorporating heat pipes into the cold plate.