Astronauts Depart KSC After Launch Delay

The Endeavour astronauts are en route to Ellington Field in Houston in the wake of a decision to delay the tentatively scheduled launch Monday of NASA's next-to-last shuttle mission.

Mission commander Mark Kelly and five crewmates departed Kennedy Space Center's Shuttle Landing Facility about 10:10 a.m. in a Gulfstream 2 and are scheduled to arrive at Ellington about 12:15 p.m. Eastern Daylight Time.

The NASA 2 aircraft that brought Kelly's wife -- critically wounded U.S. Rep. Gabrielle Giffords -- to the Space Coast to watch Endeavour's launch flew to Patrick Air Force Base from Ellington early today. The plane is scheduled to depart Patrick at 12:10 p.m. and arrive at Ellington at 2:23 p.m. EDT.

Endeavour's first launch attempt was scrubbed Friday after trouble cropped up with heaters on one of three Auxiliary Power Units that provide hydraulic power needed to steer shuttle main engines in flight and control the orbiter's wing elevons, rudder-speedbrake, landing gear and brakes during atmospheric reentry and landing.

NASA tentatively rescheduled the launch for 2:34 p.m. Monday. But engineers traced the problem to a Load Control Assembly that routes power to the hydraulic power unit. Launch managers decided to replace the faulty switch box and then test the spare. The testing alone will take two days, and its highly unlikely NASA can launch Endeavour before Wednesday -- the last day in its current window of opportunity

A United Launch Alliance Atlas V rocket is scheduled to launch a new-generation missile warning satellite Friday. Air Force tracking and range safety systems must be prepped for that flight on Thursday. So Endeavour could not launch that day.

The earliest shuttle launch opportunity after the scheduled Atlas mission is Sunday. However, United Launch Alliance has a backup day to launch the Atlas on Saturday. A launch Saturday would push the earliest shuttle launch opportunity to Monday, May 9. However, NASA cannot launch Endeavour on May 9 because the shuttle's departure from the International Space Station would occur on May 23, the same day a Russian Soyuz spacecraft and three station crew members are scheduled to undock at the outpost and return to Earth.

NASA would have a period between May 10 and May 29 to launch Endeavour.

Launch managers have tentatively scheduled a news conference for 2 p.m. Click the NASA TV box on the right to launch our NASA TV viewer and live coverage of the briefing.