Prior to the shuttle Discovery's liftoff a week ago, space-agency engineers put the risk of a fatal incident involving Discovery at 1 in 100.

Following liftoff, having learned that a one-pound 33-inch trapezoidal chunk of foam had broken away from the shuttle's external fuel tank, those engineers realized Discovery came perilously close to being that one fatal happenstance in 100 shuttle flights - as were Challenger and Columbia. Said deputy shuttle program manager Wayne Hale: If that piece had fallen off at a lower altitude and struck the orbiter, "we think this would have been really bad."

As it was, it was bad enough to ground the shuttle fleet indefinitely. "Until we fix this, we're not ready to fly again," said program manager William Parsons. "I don't know if it's (going to be) a month; I don't know if it's three months. We have a lot of work to do, and we'll do it."

Parsons' statement goes to the heart of the issue facing the nation's manned space program. In the 29 months since the loss of the shuttle Columbia, the National Aeronautics and Space Administration was supposed to fix foam and ice and tile problems. It didn't. NASA may have fallen short in diligence - and maybe not. Maybe the age of the shuttle fleet renders it incapable of a sufficient safety fix given the state of our technological understanding.

Of course, the immediate concerns are Discovery and its crew: Despite in-flight checking by robots and cameras, the integrity of the shuttle protective systems will not be known for sure until the crew is safely back on the ground a week from now. Angst - anxious questions, anxious times.

Aside from the immediate question of Discovery and its crew is the fate of manned space flight.

Last week the voice of launch control announced liftoff this way: "Liftoff of space shuttle Discovery, beginning America's new journey to the moon, Mars and beyond." That trapezoidal piece of foam may have altered the path.

The truth is that public enthusiasm for manned space flight began waning well before the flight of Apollo 17, which completed the lunar-landing program in December 1972. Since then, various presidents - including the incumbent - have tried to fire up the national spirit for manned space flight, with but few blips of heightened interest.

But it was all evanescent and fleeting. Congress never got the message and so funding lagged. Morale at NASA slumped, and with it perhaps NASA expertise. Now we have three shuttles (Discovery, Endeavour, and Atlantis) built in the 1970s with 1970s (or earlier) technology. And we have unfixed problems with foam, ice and spatial debris dinging a Rube Goldberg system of brittle heat-shield tiles that are the last line of defense - the only line, really - between shuttle success and disaster.

And we're not speaking of flights to "the moon, Mars and beyond." We're talking about Earth-orbiting flights in near-space.

Hear The Washington Post's John Schwartz: Continued...