If an astronaut became untethered during a spacewalk, as the characters did in "Gravity," his or her spacesuit—the extravehicular mobility unit, or EMU, in NASA lingo—would still provide oxygen and remove carbon dioxide for as long as eight-and-a-half hours [source: NASA]. But if the suit failed, or an astronaut was somehow subjected to the airless, pressure-less void of space without such protection, he or she would lose consciousness within 15 seconds [source: NASA].
Death would quickly ensue, as a grisly textbook example illustrates. In 1971, three Soviet cosmonauts were about 104 miles (167 kilometers) above Earth when a valve in their life-support system ruptured, making them the only humans ever exposed directly to the vacuum of space. When their capsule, which was being guided by an automatic re-entry system, landed, recovery teams were shocked to find them dead in their seats, with dark-blue blotches on their faces and blood seeping from their noses and ears [source: Dhar].