(AP) -- Engineers should know Sunday whether Endeavour's six-man crew and their families - including wounded Rep. Gabrielle Giffords - need to stick around for a Monday launch attempt or come back sometime around Mother's Day.
Technicians spent Saturday draining fuel from the shuttle and then getting into the crowded guts of the left rear compartment. Their job is to figure out just what went wrong in a heating system for a power system that controls crucial hydraulics. The problem was severe enough to make NASA postpone Friday's launch, which had become a spectacle.
Kennedy Space Center appeared mostly empty Saturday, foreshadowing what might happen after the shuttle program ends this summer. Gone were the crowds hoping to see the second-to-last shuttle launch and throngs of media for the saga of Giffords, shot in the head by a would-be assassin in January, and her husband, Endeavour commander Mark Kelly.
"It was great to see my friend Rep. Gabby Giffords again this week in Cape Canaveral. She was in good spirits, felt good and looked good," said Rep. Debbie Wasserman Schultz, a Florida Democrat. "She worked hard to be able to make the trip to Florida and I'm thrilled for her and Mark that she will be able to see him off as he launches into space. She is a fighter and a real inspiration."
Astronauts are likely to spend much of the weekend relaxing with their families - presumably including Giffords - at the limited access beach house, said Kennedy Space Center Director Robert Cabana.
"Today is a kind of rest and try to recoup day except for the technicians working to isolate and fix this problem," NASA spokesman Mike Curie said Saturday afternoon.
There are two likely scenarios for NASA's technical glitch. It could be just a thermostat. That's what NASA is hoping for because that is something that can be quickly replaced and put Endeavour on track for a Monday 2:34 p.m. EDT launch attempt. Meteorologists give an 80 percent chance for acceptable weather Monday afternoon with slight worries about winds at the emergency landing site, low clouds and visibility, Curie said.
The other option includes a fault in another part of the electrical system that isn't quite so quickly fixed. It could be a box of switches that would then require at least two days of testing. If that's the case, launch is not likely before May 8. NASA got some partial good news Saturday afternoon when one fuse panel - which would have required a long time to fix and test - proved to be working normally, but there are still other potential problems that could cause a delay of several days.
NASA managers have to make a decision by early Sunday afternoon, if they want to be on track for a Monday launch.
Explore further: NASA braces for Giffords, Obama, huge launch crowd