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Performance tests and analysis of a new flexible Variable Conductance Heat Pipe (VCHP) design are reported. The unit features a single liquid passage through most of the length and incorporates flexible sections to reduce transverse bending stiffness to less than 175 N/m. A feedthru plate is accommodated to enable installation of the heat pipe in a dual environment. The unit accepts a high heat flux heat input of more than 50 W/cm2 and has a demonstrated thermal conductance of ∼50 W/°C (at 14 W per cm of evaporator length). The demonstrated room temperature heat transport limit is approximately 150 W-m for this 1 cm OD design as configured. The unit was first tested as a Constant Conductance Heat Pipe (CCHP) to validate ammonia charge quantity and heat transport. It was then reworked to include a gas reservoir, and the performance was again validated. The test data was then compared with the thermohydraulic model predictions and shown to be in excellent agreement.

This paper describes the results of Engineering Development Unit (EDU) testing of a graded-groove Variable Conductance Heat Pipe (VCHP). This EDU pipe contains all the essential design features of an end-item unit, including multiple bends, flex sections, stainless steel transport section and high heat flux evaporator. Testing covered a wide range of environments including hot and cold condenser temperatures, hot and cold reservoir sink temperatures, and varying evaporator powers. A control algorithm was also developed which was designed to minimize warm-up time of the evaporator, minimize overshoot of the evaporator temperature, and maintain a stable evaporator temperature after warm-up. Testing was performed to determine whether the VCHP reservoir needed to be cooled during testing in an ambient environment. Results of the model correlation are also presented.

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.

This paper describes modeling results for the on-orbit thermal response of spacecraft propellant used for orbit stationkeeping. The specific objectives of the work are to improve analytical models of a transient thermal Propellant Gauging System (PGS) in use on communications satellites. This simple method uses tank wall heaters and temperature sensors and a transient energy balance to obtain periodic measurements of remaining propellant fill. The fill levels must be related to the on-orbit sensor measurements through a thermal model of the system. In the past, relatively simplified representations have been used due to the complex liquid/gas geometry when in a weightless state. In the current work, advanced modeling tools are utilized to allow a more detailed representation of the actual liquid/gas geometry. Model results are presented for a range of fill levels later in life to assess PGS measurement resolution.