Although in development since the 1960s, NASA has recently completed two years of cycling in low earth orbit to prove the sodium sulfur cell's viability for future space missions.
It uses sodium and sulfur as the electrodes, and a solid beta alumina ceramic as the electrolyte. The end result is a battery that produces 150 W-hr/kg on the cell level, and weighs half as much as nickel-hydrogen technology.
Chuck Donet, Air Force Research Laboratory, Space Vehicles Directorate, 3550 Aberdeen Ave. S.E., Kirtland AFB, NM 87117-5776; (505) 846-4899.