The main problem is power. Each shuttle has three fuel cells that mix liquid hydrogen and liquid oxygen, and that reaction generates all the crew's electricity (as well as its clean drinking water). But the shuttle stocks only enough oxygen and hydrogen to keep the fuel cells running for 14 days. After that, the shuttle would go completely dark. It wouldn't be able to maneuver or send radio transmissions, and lifesupport systems would shut down. "You couldn't even cook breakfast," says Michael Curie, a spokesperson for NASA space operations. "You wouldn't be able to return to Earth. Basically, the shuttle would be space junk."