International space station nickel-hydrogen battery on-orbit performance

International space station (ISS) electric power system (EPS) utilizes nickel-hydrogen (Ni-H/sub 2/) batteries as part of its power system to store electrical energy. The batteries are charged during insolation and discharged during eclipse. The batteries are designed to operate at a 35% depth of discharge (DOD) maximum during normal operation. Thirty-eight individual pressure vessel (IPV) Ni-H/sub 2/ battery cells are series-connected and packaged in an orbital replacement unit (ORU). Two ORUs are series-connected utilizing a total of 76 cells, to form one battery. The ISS is the first application for low earth orbit (LEO) cycling of this quantity of series-connected cells. The P6 (port) integrated equipment assembly (IEA) containing the initial ISS high-power components was successfully launched on November 30, 2000. The IEA contains 12 battery subassembly ORUs (6 batteries) that provide station power during eclipse periods. This work discusses the battery performance data after eighteen months of cycling.