February 04, 2013
Credit: Credit: NASA/JSC
Frank Morring, Jr. Washington
Space station crews are set to replace aging nickel-hydrogen battery packs with new lithium-ion units in 2017. They are not particularly worried about the fire hazard from the technology that has grounded the Boeing 787.
NASA plans to use lithium-ion battery cells manufactured by the same company that built the 787 cells. But the agency has subjected them and the computerized control units that keep the cells from overheating to the same design oversight it uses to human-rate other space hardware. Space quality standards appear to be working as the technology moves into expensive unmanned spacecraft as well. SpaceX founder Elon Musk, who uses lithium-ion batteries in his Tesla electric automobiles as well as the Dragon autonomous cargo carrier, has offered to help Boeing solve its 787 problem.
“We have independent experts who review the whole design and implementation and hazard controls that we have on these,” says Caris “Skip” Hatfield, manager of NASA's International Space Station (ISS) development projects office at Johnson Space Center (JSC). “Within the design itself, we've monitored the manufacturing process of the cells and have done audits of the cell manufacturing to make sure we're satisfied that at the cell level there are no design [or] process issues.”
Boeing, NASA's ISS prime contractor, has a $208.8 million contract to deliver 27 of the batteries—24 for service on the station as orbital replacement units (ORUs), and three as ground spares. Weighing 425 lb. each, and measuring 39 X 39 X 18 in., the batteries include adaptor plates to store the worn-out nickel-hydrogen batteries they replace (see illustration). Batteries charge while the station's solar array wings are in sunlight, and discharge to provide power in darkness.
Lithium-ion batteries are used in human and robotic spacecraft for the same reasons that Boeing selected them for the 787—their high-power density and the weight savings it permits. They are used or planned on a variety of other high-value government and commercial spacecraft, including the James Webb Space Telescope. On the ISS, one lithium-ion battery will replace two nickel-hydrogen units in orbit, Hatfield says.
Precautions taken with space-qualified battery hardware have so far prevented “thermal runaway,” the main risk. The NASA Engineering and Safety Center maintains guidelines to help spacecraft designers address the “inherent high-specific energy combined with flammable electrolytes” in the advanced battery cells.
The lithium-ion cells used in the new ISS batteries were manufactured by Japan's GS Yuansa, the same company that built the cells for the Boeing 787. Pratt & Whitney Rocketdyne is building the battery controllers, which ensure the chemical cells do not get out of balance.