Every U.S. manned space mission during the past four decades has used fuel-cell power plants built by a division of UTC Power, a United Technologies Corp. company. The Space Shuttle fuel cells — there are three per orbiter — have accumulated more than 91,000 hr of flight operation.

Shuttle fuel cells not only produce electricity, they also produce drinking water for the astronauts. Each alkaline fuel cell produces up to 12 kW and is more than 70% efficient, two to three times better than a typical combustion engine. Cryogenic hydrogen and oxygen feed each of the self-contained units, which are installed under the payload bay, aft of the crew compartment.