CAPE CANAVERAL — NASA was still undecided Sunday when the space shuttle Endeavour might be launched on its final mission. That decision will be made today or Tuesday, with the earliest possible launch on Sunday.
NASA sent Navy Capt. Mark Kelly, commander of Endeavour, and his five-man crew back to Houston to wait for the next attempt. Meanwhile, NASA engineers will try to figure out why an Endeavour switch box failed Friday, forcing the launch to be postponed just 3½ hours before it was scheduled.
If NASA cannot launch Endeavour Sunday, the scheduling gets even more complicated. May 9 is probably not available and May 10 and May 11 would present problems as well, as NASA tries to coordinate Endeavour's schedule at the International Space Station with that of a Russian Soyuz that is already there.
Kelly's wife, Rep. Gabrielle Giffords, D-Ariz., who was wounded in a January assassination attempt but recovered enough to travel Friday to Kennedy Space Center for the launch attempt, returned to her rehabilitation hospital in Houston.
President Barack Obama and his family also attended Friday. It was unclear Sunday whether they would return for the launch.
"Unfortunately, we're not going to be able to make a launch attempt in the next few days," said Mike Moses, chairman of the mission-management team. "I'm here to disappoint everyone by saying I'm not going to tell you what the new launch date is because I have no idea. We have a lot more to evaluate."
Friday's launch attempt was scrubbed because a hydraulic system fuel-line heater failed. Officials had hoped the problem was simply a faulty thermostat, and proposed a launch for today on that chance.
But once technicians got inside the Endeavour's aft equipment bay late Saturday, they realized that the problem originated in a switch box called a load-control assembly. To replace that, engineers have to retest many of the systems that box controls, and those evaluations would take at least a couple of days.