The International Space Station's (ISS) electric power system (EPS) employs nickel-hydrogen (Ni-H2) batteries as part of its power system to store electrical energy. The batteries are charged during insolation and discharged, providing station power, during eclipse. The batteries are designed to operate at a maximum 35-percent depth of discharge during normal operation.
Thirty-eight individual pressure vessel Ni-H2 battery cells are series-connected and packaged in an orbital replacement unit (ORU), and two ORUs are series-connected, using a total of 76 cells, to form one battery. When the ISS is in its assembly-complete form, the electrical power system will have a total of 24 batteries (48 ORUs) on-orbit. The ISS is the first application for low-Earth-orbit cycling of this quantity of series-connected cells.
ISS battery subassembly ORU.
Each battery ORU was designed to meet the following requirements:
The cells selected for use in the battery ORUs are manufactured by Eagle Picher Technologies. They are RNH-81-5 EPI individual pressure vessel NiH2 cells that have a back-to-back plate configuration. They were activated with a 31-wt% aqueous solution of potassium hydroxide electrolyte. The ORUs were assembled and acceptance tested by Space Systems/Loral.
The first set of 12 battery ORUs was integrated into the P6 (port side) integrated equipment assembly (IEA) and was successfully launched on November 30, 2000. The on-orbit battery cycling started in early December 2003. The remaining 36 battery ORUs have been delivered to the Kennedy Space Center and have been integrated into the next three IEAs, which are awaiting launch in 2004 and 2005.
The telemetered on-orbit data clearly show that the batteries are performing within their design specifications over the operational range. Because of the lower-than-anticipated power demands of the station, the P6 battery life is expected to meet or exceed the ISS 6.5-year life requirement.
All aspects of the ISS battery hardware, including design, development, assembly, test, and operation, are managed by the NASA Glenn Research Center. In addition to the current battery, Glenn is investigating advanced technologies as future replacements for the ISS.
Find out more about the research of Glenn's Electro-Chemistry Branch.
Glenn contact: Penni J. Dalton, 216-433-5223, Penni.J.Dalton@nasa.gov
Author: Penni J. Dalton
Headquarters program office: OSF
Power and Propulsion
Last updated: September 24, 2004
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