(CNN) -- Thanks to positive results on all pre-flight checks, NASA officials on Saturday unanimously gave the go-ahead for the Monday launch of the Space Shuttle Endeavour.

"The system looks good, the weather looks good, and we should be in good shape for launch," NASA Space Shuttle Program Launch Integration Manager Mike Moses told reporters Saturday. "In our minds, we are good to go."

An estimated 500,000 people are expected to be on hand Monday at the Kennedy Space Center, said NASA's shuttle launch director Michael D. Leinbach. Lift-off is scheduled for 8:56 a.m.

Storms rolled through Florida on Saturday, but Kathy Winters -- the space agency's launch weather officer -- said she expects conditions to gradually improve over the weekend.

She said that there is a 30% chance that strong crosswinds or a low-cloud cover could force a launch delay Monday. Conditions are expected to deteriorate should the mission's start be pushed back to Tuesday, with a 60% chance of postponement. The weather is likely to improve considerably by Wednesday, according to Winters.

The mission will be commanded by Mark Kelly. His wife, U.S. Rep. Gabrielle Giffords, D-Arizona, is expected to be on hand, more than four months after being shot in the head during an apparent assassination attempt at a public event in Tucson, Arizona. After initial treatment in Arizona, she has been undergoing rehabilitation at the TIRR Memorial Hermann center in Houston.

Giffords, along with President Barack Obama, were in Florida on April 29, when Endeavour was originally slated to launch. But that lift-off was scrubbed because of a problem with a heater aboard the shuttle.

Moses said that the issue has been fixed and that -- while additional checks will be conducted on the heater and other systems prior to launch -- no mechanical problems were anticipated.

With the delay, Endeavour is now scheduled to return to Earth on June 1. That is the same day that Atlantis is slated to roll out to the launch pad, in anticipation of the final mission in the space shuttle program's 30-year history.

The shuttle program's end, and the uncertainly surrounding the future of NASA and the U.S. space program, has been a hot topic in recent months. Leinbach acknowledged Saturday that "the mood is a little bit downcast" in the space agency, especially with some NASA employees getting notices this week warning them that they could lose their jobs.

"The timing is a little unfortunate, but we've all known it's been coming," he said.

Endeavour entered service in 1992, as a replacement for the ill-fated Challenger. Leinbach, who was a test director for that inaugural mission, said the orbiter remains in prime condition 19 years later.

"She still looks awfully good out there," said Leinbach. "She's got a lot of life left in her, but that's not meant to be."