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This paper describes modeling and test results for a two Loop Heat Pipes (LHP) with a condenser designed to be used in a deployable spacecraft radiator system. These units were provided by the two major commercial US vendors of LHPs. The condenser used is a freeze-tolerant, parallel-flow design based on the International Space Station (ISS) deployable radiator design. This condenser allows the deployable radiator to be utilized without freeze-protection heaters.

In recent years, loop heat pipe (LHP) technology has transitioned from a developmental technology to one that is flight ready. The LHP is considered to be more robust than capillary pumped loops (CPL) because the LHP does not require any preconditioning of the system prior to application of the heat load, nor does its performance become unstable in the presence of two-phase fluid in the core of the evaporator. However, both devices have a lower limit on input power: below a certain power, the system may not start properly. The LHP becomes especially susceptible to these low power start-ups following diode operation, intentional shut-down, or very cold conditions. These limits are affected by the presence of adverse tilt, mass on the evaporator, and noncondensible gas in the working fluid.