President Bush phoned Discovery's (search) astronauts on Tuesday, thanking them for being "risk takers for the sake of exploration."

In a telephone hook up with the space shuttle crew, the president wished the crew "Godspeed for your mission."

"Thanks for being such great examples of courage for a lot of our fellow citizens," Bush said.

Discovery Commander Eileen Collins (search) told Bush, "We really enjoy what we're doing. We really believe in our mission."

She praised the virtues of "safe exploration...and seeing what's out there."

Bush called as the space shuttle crew prepared for a high-stakes task: an unrehearsed maneuver in which a spacewalker will go beneath the craft on Wednesday to repair filler sticking out from ship's thermal tile belly. NASA says the protruding material could cause dangerous overheating during re-entry and lead to another Columbia-type disaster.

"I know you've got important work to do ahead of you," Bush said.

"We are with you and wish you all the very best. Thanks for taking my phone call. Now get back to work," the president said.

Bush stood with a phone in his hand, watching the astronauts on large flat-screen television embedded in a tall wooden cabinet in the Roosevelt Room of the White House. All nine astronauts could be seen gathered tightly around Collins.

"Thank you for being risk takers for the sake of exploration," Bush said.

"A lot of Americans will be praying for a safe return," he added.

Collins told the president, "The steps we're taking right now are really worth it."

Bush noted that his wife Laura had joined his brother, Florida Gov. Jeb Bush, to watch Discovery's liftoff at Cape Canaveral last week.

Collins noted that, "We did fly over Texas" earlier Tuesday.