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The CAPL 2 Flight Experiment, flown on Space Shuttle STS-69 in 1995, was a flight demonstration of a full-scale prototype of a thermal control system planned for the Earth Observing System (EOS-AM) instruments Flight tests successfully demonstrated various CPL operations with simulated EOS-AM power profiles, including baseline and backup start-up procedures. In general, there were no significant differences in CPL performance between one-G and zero-G. However, some unusual behaviors were observed in several start-ups during the flight test. This paper describes CAPL 2 start-ups in detail, and offers explanations for the notably different zero-G behaviors.

During ground testing and micro-g operation of Capillary Pumped Loops (CPLs), oscillations of the system pressure drop have been observed. In some cases, it is highly probable that they contributed to deprimes of the system when the magnitude of the pressure oscillations exceeded the capillary limit of the wick. A hydrodynamic stability theory was proposed in 1994 to explain the oscillatory behavior of the CPL systems. The theory has given insight to the cause of pressure oscillations in CPL systems and their effect on system operation. The theory indicates that the pressure oscillations are a function of the system design parameters and the operational conditions. One of the system parameters which affects the pressure oscillations is the wick spring constant of the porous wick structure in the evaporator. The wick spring constant is determined from porosity, pore size and permeability of the wick.