Powering up the Space Station
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Nickel-containing batteries store electricity generated by huge array of solar panels
Nickel magazine, Jun. 02 -- Nearly 400 kilometres above the planet, a superalloy rich in nickel is
playing a crucial role in powering the International Space Station. The nickel-hydrogen batteries that supply
the station's electrical needs are encased in pressure vessels made of
N07718, a tough alloy that contains between 50 and 55% nickel.
"N07718 has been the material of choice for battery cells using the nickel-hydrogen chemistry since their initial development in the 1970s," notes Dan DeBiccari, manager of the battery department, space power directorate, for Space Systems/Loral, which supplies the station's battery orbital replacement units. "It's superior strength allows for a relatively thin wall container which can resist the internal pressure 7 megapascals generated by the chemistry."
Space Systems/Loral, based in Palo Alto, California, U.S.A., manufactures the batteries and their charging/discharging equipment under an agreement with the Boeing Company, the primary contractor for the space station. (Space Systems is chiefly in the business of designing and building satellites.) Alloy for the casing is provided by Special Metals Corporation of Huntington, West Virginia, U.S.A., a producer of high-performance nickel alloys.
Each battery consists of two orbital replacement units, which in turn contain 38 battery cells apiece and are capable of providing peak power of about 6,000 watts. The batteries store and regulate electricity generated by the station's array of solar panels during one-hour periods when the platform is orbiting in sunlight, then discharge power to the station during the 35-minute intervals when it passes through the earth's shadow. In low earth orbit, the batteries undergo 16 of these charge/
discharge cycles per day, or about 30,000 cycles over their projected five-and-a-half-year mission life.
N07718, besides providing protection against rupture, has excellent chemical resistance to the caustic solution that acts as an electrolyte. The chemical reaction creates hydrogen gas, which is responsible for the pressure that builds up inside the cells, and the alloy offers the necessary resistance to hydrogen embrittlement. The cell casings are built in sections and joined using electron-beam welding, so the weldability and resistance to post-weld cracking of N07718 are important properties. The nickel-base alloy contains chromium, molybdenum, niobium and iron and is also used in gas turbines, rocket motors, spacecraft, nuclear reactors and pumps.
The battery cells also contain woven nickel screening and nickel rod and strip for the electrical conductors, while chemically etched nickel foil is used as the substrate for a platinum electrode. The nickel hydroxide electrodes contain sintered nickel powder and nickel nitrate.
The shuttle Endeavor delivered the first battery units to the station in November 2000, increasing by five
times the power available to operate the platform. There are currently six batteries on board, DeBiccari
said, but the number will ultimately reach 24 batteries (a total of 48 orbital replacement units) capable of
generating 150 kilowatts.
 Space Systems/Loral, 3825 Fabian Way, Palo Alto, California, U.S.A. 94303. Tel: 1-650-852-4000 Fax: 1-650-852-6722 E-mail: crockett.cathy@ssd.local.com Website: www.ssloral.com Special Metals Corporation 3200 Riverside Drive Huntington, WV, U.S.A. 25705. Tel: 1-304-526-5628 E-mail: info@smcwv.com Website: www.specialmetals.com |
