Endeavour decision expected Sunday morning

Technicians are working inside Endeavour's aft compartment this afternoon, hoping to determine if the shuttle could be ready for another launch attempt Monday afternoon.

Managers plan to meet at 9 a.m. Sunday and hold a press conference afterward to announce whether a Monday launch is still possible.

The targeted launch time would be 2:34 p.m. on the dot.

Troubleshooting teams entered the orbiter's left aft compartment this afternoon at launch pad 39A after Endeavour's external tank had been fully drained.

Friday's planned 3:47 p.m. launch scrubbed when heaters on a fuel line linked to the orbiter's hydraulic power system failed to turn on. The fuel line in question feeds one of three auxiliary power units on the ship.

Immediate checks today of a cockpit control fuse panel turned up no problems, NASA reported.

Teams then turned their attention to thermostats that may have failed. Troubleshooting plans called for spritzing a thermostat with cold mist in an effort to trigger it on.

Initial tests reported the thermostat that failed Friday still was not working, but that was expected. More tests were needed to determine if the thermostat was receiving electrical current or if there's another problem, possibly with a switch box that would take longer to repair.

Work was expected to continue through the night.

A Monday launch was considered possible if the problem was limited to thermostats. If the switch box called the Load Control Assembly is at fault, that could take days to swap out and retest.

Endeavour has launch opportunities through Wednesday before NASA will give way to the planned Friday launch of an Atlas V rocket and military satellite from Cape Canaveral Air Force Station.

The next possible opportunity would be as early as May 8, but possibly later because of a potential conflict with a Russian spacecraft that would be scheduled to depart the International Space Station at the same time as Endeavour.

On the next to last shuttle mission, Endeavour and its crew of six are scheduled to fly a two-week mission to deliver spare parts and a $2 billion science instrument to the station.

IMAGE: NASA diagram of auxiliary power system components inside a shuttle orbiter.