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The Photovoltaic Radiator (PVR) is designed to reject waste heat of the Early External Active Thermal Control System (EEATCS) and the Photovoltaic Thermal Control System (PV TCS) of the International Space Station (ISS). Two EEATCS PVR units and one PV TCS PVR unit will be on the Assured Early Research (AER) phase of the ISS and all four PV TCS PVR units will be on the assembly complete configuration of the ISS. Thermal environments of the AER mission and assembly complete configuration present challenging thermal designs to maintain the EEATCS and PV TCS PVR units functioning within the temperature operating limits of the structural components and the ammonia fluid.

Due to the extreme cold conditions in space, the International Space Station (ISS) Photovoltaic Radiators (PVR) were in danger of freezing the ammonia within the fluid loops. This would be catastrophic since the pressure buildup during thaw could potentially break the fluid flow lines. Design changes needed to be made to the radiators to insure their worthiness. Freeze tolerant flow tubes, optical coating changes to the manifold covers, multilayer insulation (MLI) around the fluid lines, and thermal isolation of manifold covers by mesh screen isolators are being combined to achieve an acceptable passive design.

The results of design and analysis of a heater system for the photovoltaic radiators (PVR)s on the International Space Station (ISS) is presented. The PVRs are designed to reject heat from batteries being charged by the solar cell arrays. Also, during the early buildup of the ISS, two of the PVRs are dedicated to rejecting waste heat from the man inhabited modules. The PVRs will at times experience environmental conditions that are severe enough to freeze the transport fluid (ammonia) which could cause failure of the coolant delivery lines. The heater system is designed to prevent this situation from occurring in the more vulnerable portions of the PVR. The activities involved in the design process and the thermal analyses used to support the design by aiding in the location of sensor, set point temperatures and failure mode analysis are presented.