For this month's launch, the "Return to Flight" after the Columbia accident, specialized cameras and radars were trained on the shuttle and its rockets. They captured images of flying debris, including the large piece of insulation foam that later triggered the grounding.

Because of concerns about safety, Lind said, "NASA has to take this extremely seriously."

Harry Ames, deputy director of the Space Dynamics Laboratory at Utah State University, said he does not expect this will be an extremely long grounding, "but I do know that the shuttle folks are very disappointed that any foam came off the tank.

"They spent a lot of time and energy working that particular safety issue, and yet a piece of foam came off."

NASA and industry experts redesigned the procedure for applying insulation onto the enormous tank, which holds extremely cold liquid hydrogen and liquid oxygen fuel. They investigated ways to apply the foam, calculated optimum density and figured how thick the layer should be, he said.

"Apparently that simply didn't work," Ames said.

Patrick Wiggins, a member of the Salt Lake Astronomical Society, said if repairs to the shuttle turn out to be too expensive, it may not be practical to keep the fleet flying.

Last year, President Bush announced the end of the shuttle fleet. It was to be phased out in 2010 and replaced by a new generation of space vehicles that can take humans back to the moon.

"We're simply running old, complicated hardware, and it's time to get something that's maybe a bit more 21st century," Wiggins said.

For now, the shuttle is essential to completing the International Space Station, he said. No other launch vehicle is able to lift heavy components to the ISS.

"If the shuttle does get canceled, in effect ISS is going to get canceled," Wiggins added. "I don't even want to think about that."

Lind also emphasized the need to complete the orbiting station and said he hopes repairs to the shuttle fleet turn out to be straightforward.

However, he said, "if this section has been repaired in the past and it didn't work, that's a big deal. . . . That would be absolutely unique in NASA. My experience is, if NASA has a problem, they go ahead and solve the problem."

Based on nothing more than what he has heard in the media and his personal feelings, Lind said, he thinks NASA will analyze and repair the shuttle and finish the flights it has committed to. Besides completing the space station, he believes it should be used to repair the Hubble space telescope.

"I really can't imagine this is the end of the shuttle flights," Lind said.