Performance of International Space Station electric power system during station assembly

The International Space Station (ISS) will be an Earth-orbiting laboratory in space. It will house experimental payloads, distribute resource utilities, and support human habitation for conducting research and science experiments in a microgravity environment. The ISS will be assembled on-orbit through 44 assembly and utilization flights using the launch vehicles of the United States, Russian Republic and the European Space Agency (ESA) over a 5-year period. Electrical power is a major utility to support successful achievement of the mission goal. The ISS United States on-orbit segment (USOS) electric power system (EPS) power generation capability will vary throughout the assembly phase with orbital parameters, various assembly configurations, various flight attitudes, and shadowing on the solar arrays. Power capability will be further influenced by EPS operational constraints, such as array pointing biases, battery charging and hardware limitations, natural and induced environment, hardware aging and by ISS operational constraints either to avoid long term solar array shadowing from the adjacent solar array or to accommodate ISS maneuvering during proximity operations with other space vehicles, mating, and departing. Design of the ISS USOS EPS takes into consideration the various equipment degradation modes, operation constraints and orbital conditions to make it compatible with the environments and to meet power, lifetime and performance requirements. This paper emphasizes USOS EPS performance during ISS assembly.