Passive Freeze Protection for the International Space Station Photovoltaic Radiators

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.