Discovery was first slated to launch Monday afternoon for its last flight. The takeoff was first rescheduled for Tuesday but is now planned for 3.52 p.m. (1952 GMT) Wednesday at Kennedy Space Centre on Cape Canaveral, Florida.

NASA technicians had discovered helium and nitrogen leaks in one of the shuttle's engine pods. Discovery is the oldest spacecraft in the US shuttle fleet and will be the first to be officially retired after this final mission, an 11-day trip to the orbiting International Space Station with six astronauts aboard.