NASA is pressing ahead with a plan to install lithium-ion batteries on the International Space Station (ISS), New Scientist has learned. The batteries are similar to those used on Boeing's 787 Dreamliner aircraft, all 50 of which have been taken out of commercial service worldwide since January following battery fires on two planes. NASA says that lithium-ion cells offer compelling benefits, and it is confident that any safety issues can be overcome.
The agency intends to use batteries sourced from GS Yuasa, based in Kyoto, Japan, which also makes lithium batteries for Boeing 787 Dreamliner planes. Boeing has modified the aircraft batteries following the fires, but the new design has yet to gain safety certification from the US Federal Aviation Administration.
NASA is going ahead because, it says, "proper design" of the battery packs will let it take advantage of the lightness and extra power delivered by lithium-ion technology - which is easily better than the current nickel metal-hydride batteries used on the ISS.
"The benefits of [lithium's] higher power density are too compelling to ignore," says NASA spokesman Josh Byerly at the Johnson Spaceflight Center in Houston, Texas. He says the technology would allow launch payloads to be halved. "With space launch costs being extremely high, one can see the benefit in this approach."
Thermal runaway
The Boeing 787 battery packs contained eight lithium-ion cells made by GS Yuasa and assembled by aerospace contractor Thales, a multinational headquartered in France. Boeing says overheating in one cell vented heat to neighbouring cells and caused them to overheat also, an effect known as thermal runaway. One battery caught fire in a jet on the ground at Boston Logan airport in the US while another melted down in flight, causing an emergency landing and evacuation in Japan.
Boeing has redesigned the battery pack to improve issues such as the physical and thermal isolation of the cells and test-flew it earlier this month. But since what exactly started the fire in the lithium cells has not been precisely identified, the FAA and US National Transportation Safety Board are still deliberating over a solution.
Boeing is also the lead contractor on the ISS. NASA says it is working with it, and with its battery-assembling subcontractor Pratt & Whitney Rocketdyne, to do "everything possible to assure that a hazard is mitigated to the maximum possible extent – in this case, that conditions that could cause a cell runaway are designed out of the system and that safety controls are available to maintain the cells within allowable limits," says Byerly.
The design and testing will also ensure, he says, that if a hazardous event does occur, "it is contained and does not propagate into an uncontrolled event".
Near-vacuum
NASA says the situation on the ISS is very different to an aircraft because the batteries are installed outside the pressurised crew modules on a structural joist called a truss.
"In the near-vacuum of low-Earth orbit, while a cell failure resulting in a runaway thermal event would provide its own fuel and oxidiser, with proper design there is nothing available to propagate such an event beyond a single cell, let alone beyond a battery assembly," Byerly says.
What would happen to the space station if an entire battery overheated? "I don't want to get into hypothetical situations," Byerly says. "There is minimal risk."
