"My commitment to NASA is unwavering," Obama said on a video-conference with astronauts aboard the International Space Station. Speaking from the White House, Obama called the outpost orbiting 200 miles above the Earth "a testimony to human ingenuity."

They were Obama's first public comments on NASA since his administration submitted a $19 billion budget to Congress for the agency that would kill the Constellation lunar program begun under former President George W. Bush.

Instead, Obama's budget would spend $6 billion over five years to turn over space transportation to commercial companies, as well as billions of dollars on technology development and extending the life of the space station.

Obama asked crew of the space station and the visiting Endeavour shuttle to discuss research that they could do in space "that you could not be doing back here at home."

Astronauts said the station enabled them to study how flames and cancer cells behave in the absence of gravity and to research materials that could hold up under the rigors of long-term space flight.

"Some of the things you talked about are in line with where we want to see NASA going increasingly," Obama said. "We're very excited about the possibilities of putting more research dollars into some of these transformational technologies."

If humans are to travel to Mars and beyond, Obama said NASA must develop technology "to be sure that folks can get there in one piece and get back in one piece."

Obama's call came during Endeavour's 14-day trip to the space station, with the shuttle due back at the Kennedy Space Center in Florida on Sunday.

Major construction on the $100 billion orbital outpost is complete, and NASA has only four more shuttle missions planned to ferry spare parts and supplies to the station, a project of 16 nations that has been under construction since 1998.

"Any future astronauts here?" Obama asked students who joined him to pose questions to the astronauts. "I wouldn't mind trying that whole floating thing."