On-board assemblages of equipment to generate, store, and distribute electrical energy on satellites and spacecraft. A reliable source of electrical power is required for supplying energy to the spacecraft and its payloads during launch and through several years of operational lifetime in a space environment. Present-generation spacecraft fly power systems from tens of watts to several kilowatts. Each of the three fuel cells on the space shuttle delivers 12 kW continuous power and 16 kW peak power. The International Space Station's solar arrays will generate 110 kW total power, with approximately 46 kW available for research activities.