All their assigned duties were completed and final precautionary tests had turned up no problems Sunday, leaving weather the only question facing the astronauts on the space shuttle Discovery as they looked forward to a return to Earth.

Mission Control on Sunday gave the shuttle crew permission to try for a landing Monday at the Kennedy Space Center in Florida, clearing all lingering technical questions on the shuttle heat shield and the system that provides hydraulic power for landing.

Piers Sellers (top, L) covers his head as his crewmates laugh after he was described as the spacewalker who lost the spatula during a crew news conference from aboard the International Space Station in this view from NASA TV July 14, 2006. The members of the crew are front row (L-R) Pilot Mark Kelly, ISS Commander Pavel Vinogradov, Jeff Williams, and back row, Sellers, Stephanie Wilson, Lisa Nowak and Mike Fossum. [Reuters]

"We feel very confident that Discovery is safe to come home," landing director Steve Stich said in a news conference Sunday. Re-entry is one of the two most dangerous parts of a shuttle flight, along with the launch. A damaged heat shield caused Columbia to disintegrate during re-entry in 2003.

The somewhat weary Discovery crew members were looking forward to returning to their families on Monday, Stich told The Associated Press.

"We're getting ready to come home and we're just about there," Discovery commander Steve Lindsey told NBC News on Sunday.

Lindsey said his crew members accomplished every one of their preflight goals and did a little extra.

"I hope our legacy was that we closed out the return-to-flight test portion of the program following the Columbia accident and we set the stage for space station assembly to continue," he said Sunday. "Those were our two primary goals and I think we achieved those goals."

Final inspections for heat shield damage on Friday and Saturday revealed no problems caused by dust-size micro-meteorites.

And a test of a leaky power unit on Sunday looked good. The unit, one of three on the shuttle, powers hydraulic systems used for steering and braking during landing.

That left NASA with only one worry: the weather.

The concern involved a patch of rain expected to drift toward the Kennedy Space Center from the north on Monday. The question was whether it would affect either of the two possible landing times: 9:14 a.m. EDT and 10:50 a.m. EDT.

Stich said there was a "fairly reasonable" chance that the rain would hold off long enough to allow Discovery to land.

If the weather prevents a landing Monday in Florida, Stich said, he will try to bring the shuttle home on Tuesday at Kennedy or the backup site at Edwards Air Force Base in California.

After Wednesday, the shuttle will run out of oxygen for its fuel cells and breathing, deputy shuttle program manager John Shannon said.

Kennedy is the preferred landing site. A landing at Edwards costs NASA $1.7 million to fly the shuttle back to Florida atop a modified jumbo jet and could add a week to the schedule for the shuttle's preparations for its next flight, due in late August.

Wherever Discovery lands, it will have the benefit of four new tires and wheels, each of which are two inches larger and 27 pounds heavier than previous shuttle equipment. The new tires will increase the shuttle's load capacity by 20 percent and speed by 10 percent, Stich said.

"For the shuttle, they are the monster tires - tires and wheels," Stich said.

Another addition for this landing is a global positioning system, like the equipment used in airliners and available in cars and airplanes, that should provide a slight improvement for navigation, he said.

The astronauts said being in orbit put the violence in the Middle East in perspective, with astronaut Stephanie Wilson saying: "looking down at Earth reminds us that it's a wonderful place and that we should all live in peace and harmony if we can."

"We just flew over the Middle East and I have to tell you, from up here it looks peaceful and quiet just like the rest of the planet," astronaut Piers Sellers told ABC News. "I think all of us are mindful from flying around and around, this one little Earth, that it's all we have."