US space shuttle Endeavour sits on launc
US space shuttle Endeavour sits on launch pad 39A on May 15, 2011, one day before the shuttle’s scheduled final launch. NASA readied the space shuttle Endeavour for its final mission with liftoff set for 8:56 am (1256 GMT) Monday on the next-to-last flight for the American shuttle program. Engineers were optimistic that the repaired shuttle would be able to fly on its 16-day mission to the International Space Station, after a technical glitch postponed its attempt last month. (Photo credit: NICHOLAS KAMM/AFP/Getty Images)