An early NASA idea developed to rescue astronauts in the event of a space shuttle being disabled. The rescue ball was a strong, deflated bag with a small viewing port. The marooned astronaut curled up inside, zipped up the bag, and activated the life-support system that inflated the bag and supplied air for 20 minutes. Astronauts arriving on a rescue shuttle would recover the stranded crew members by taking space walks to manoeuvre the balls into the second vehicle.