Space-Station nickel-hydrogen battery orbital replacement unit test

Abstract

The International Space Station electrical power system utilizes nickel-hydrogen (Ni-H2) 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 maximum during normal operation. Thirty-eight individual pressure vessel Ni-H2 battery cells are series-connected and packaged in an orbit replacement unit (ORU). Two ORUs are series connected, a total of 76 cells, to form one battery. The International Space Station will be the first application for low Earth orbit cycling of this quantity of series connected cells. The Space Station Photovoltaic Electronics Team, consisting of NASA and Rocketdyne personnel, began a unique test program at the Power Systems Facility at the NASA Lewis Research Center. The test plan was created to evaluate near- and long-term performance as a battery as well as charge management characteristics. The testing would also validate the ORU configuration including the ORU box and thermal interface design. This article describes the test program and the results of the 3000 LEO cycles on a Space Station engineering model battery.