Those of us who covered the Challenger explosion predicted for 15 years that this day would happen, hoping it never would but realizing it was inevitable.

When you delve into the nuts and bolts of the shuttle, as we did back then, you realize the intricate dangers that lurk within.

The question with the shuttle, the question that will be rehashed once again, is whether human space flight is intrinsically dangerous no matter the vehicle, or whether the shuttle is inherently flawed to the point it can’t be trusted.

Before Challenger, NASA deluded itself with safety predictions that listed the chance of catastrophic failure as one in thousands. After Challenger, a presidential panel destroyed that myth.

Richard Feynman, a Nobel physicist and one of the most brilliant men of the 20th century, said anyone who truly understood the flaws in the space ship would be crazy to fly in it.

And so NASA stopped shuttle launches for more than 2 1/2 years. It undertook a massive redesign of the shuttle, re-engineering everything from the booster that caused the Challenger tragedy to the faulty brakes in the orbiter.

For 87 launches the shuttle flew without serious incident.

That was, in my mind, NASA’s greatest accomplishment, even more amazing than the moon landings.

But then came troubling signs from the space agency, indications that it once again was getting overconfident in the reliability of its shuttle.

Less than two years ago, NASA put the odds of a shuttle failure at 483-to-1.

That seemed a preposterous number given that it factored in two potentially explosive booster rockets, a troublesome main engine and all the glitches that can cause a failure–cracked fuel lines, a wrench left in the engine, the delicate insulation tiles being damaged at liftoff and so on.

As the former chief of quality control at the Marshall Space Flight Center once told me, “Everybody talks about the safety record of Apollo. You know why we didn’t lose a spacecraft? Pure, dumb luck.”

The more times you launch, the greater the odds of that luck running out.

Another indication of NASA’s confidence in the shuttle came when it recently cranked back up its teacher in space program. The Challenger panel harshly criticized the agency for putting teacher Christa McAuliffe on what amounted to a dangerous, experimental spacecraft.

The fact that NASA was planning to put another teacher on a shuttle indicated the confidence it had in its space plane.

And in a recent interview at the Orlando Sentinel, NASA Administrator Sean O’Keefe talked about what a marvelous workhorse the shuttle had become and how it could last for decades more.

Now come the inevitable questions.

Can the shuttle really be trusted?

How thorough of an investigation can we undertake given that there is a space station under construction?

Will President Bush, like Ronald Reagan, set up a panel to investigate? That would add months to the investigation process.

If a panel is not formed, can NASA be trusted to investigate itself? The answer is no for those of us who witnessed the agency’s behavior following Challenger. Rival NASA centers got embroiled in backbiting and blame shifting.

Is it possible NASA may have to launch again before the cause of this disaster is fully understood, or before a remedy is undertaken and completed?

How damning will the truth be? I guarantee that whatever went wrong, there will be piles of memos from engineers warning that it could go wrong. Such is the nature of engineered space flight. Each critical component is analyzed over and over, and each worst-case scenario examined.

Will the public and politicians deem that the failure mechanism responsible for this disaster should have been foreseen and prevented? That is why NASA took such a beating after Challenger — the flaws in the booster rocket were well known and engineers argued the shuttle should not have been launched that morning.

Can the remaining fleet of shuttles service the space station? And if they can’t, does the nation embark on building a next-generation spacecraft, or does it throw money into the past and build yet another shuttle?