Recent Leonid meteor showers have rekindled general awareness that meteoroid/orbital debris (M/OD) will impact the International Space Station (ISS) hardware and may cause damage and disruption of service. Large surface areas, photovoltaic (PV) arrays and PV radiators, have a higher probability of such an impact.
The power generation, storage, and distribution system on the ISS is a channelized system, such that a malfunction affects only one channel. At assembly complete configuration, the ISS consists of eight power channels, and a temporary loss of one channel can be easily accommodated. However, during early stages, the ISS consists of only one PV module, which has two power channels, and a loss of one channel results in a significant loss of capability.
Each PV module is supported by a photovoltaic thermal control system (PV TCS), which consists of two independent recirculating cooling loops. Each coolant loop collects heat from actively cooled components and radiates it to space via a radiator. An M/OD impact may rupture a tube in the radiator causing the coolant to escape and half of the PV TCS to shut down. Without active cooling, electrical components will overheat and shutdown, resulting in the loss of one power channel.
The first PV module also contains an Early External Active Thermal Control System (EEATCS), which consists of two independent re-circulating coolant loops. The EEATCS collects waste heat from the US Laboratory (USL) and radiates it to space via its own two radiators. The radiators used for the PV TCS and EEATCS are almost identical in design and both systems use the same coolant - anhydrous ammonia.
This paper describes features incorporated in the PV module design to permit restoration of full power capability following M/OD impact on a PV radiator or other events resulting in loss of ammonia. These design features enable isolation of the leaky radiator channel, refilling the PV TCS loop with ammonia, rerouting of the coolant loop to one of the EEATCS radiators, and restart of the power channel.