Grant Cates, a former NASA engineer who now works at the Aerospace Corporation, a government-backed think tank, argues that the situation needs to change. NASA learned through hard-won experience that redundancy is key: Having two spacecraft—a lunar lander and a command module—made Apollo 13's escape from disaster possible, while the Columbia tragedy might have been avoided had NASA sent a rescue rather than attempting to return the damaged Space Shuttle to Earth. China keeps a backup spacecraft ready for launch in case of problems that require a crew evacuation of its new space station.