The fact that Discovery and its crew of astronauts returned to Earth safely Tuesday was, of course, the most important news emanating from America's resumption of manned space shuttle flights.

But beneath that dominant news must be acknowledged the important influence of space shuttle Columbia in making the just-completed mission a success. It was because of the Columbia tragedy on Feb. 1, 2003, that this mission had unprecedented inspection, photography and other shuttle data-gathering systems in place that exposed problems and potential dangers and allowed them to be corrected or, at least, properly evaluated, prior to the trip back to Earth.

Discovery blasted off with a redesigned fuel tank, also the result of the Columbia catastrophe, and it was regarding the fuel tank that the first benefits of the new photography capability proved its worth. The cameras in place for the liftoff showed a potentially deadly one-pound chunk of foam insulation come off the fuel tank, revealing that NASA had not resolved the problem that doomed Columbia.

That problem, along with the need to determine why two pieces of filler material were found dangling from Discovery's belly as it orbited Earth, has led NASA to rule against any more shuttle flights until the problems are solved.

One of the shuttle astronauts was able during a spacewalk to remove the two pieces of filler material, which slipped out of the narrow gaps between the shuttle's thermal tiles - putting to rest the concern that they could lead to a repeat of the Columbia tragedy.

Until that spacewalk, astronauts had never ventured beneath an orbiting shuttle or made repairs to a shuttle's thermal shielding.

Meanwhile, NASA's stepped-up safety-consciousness in the wake of Columbia resulted in extensive evaluation - even wind-tunnel testing - regarding a torn thermal blanket under Discovery's cockpit window. That evaluation and testing determined that the tear posed little risk as re-entry shrapnel that could doom Discovery.

Understandably, Discovery's return was a source of great anxiety as a result of what happened to Columbia. Millions of people across America were watching and praying as the shuttle made its descent. The return of a shuttle was no longer the routine process that it seemed to have become prior to the Columbia disaster.

After the shuttle rolled safely to a stop at Edwards Air Force Base in California, Bill Parsons, shuttle program manager, expressed the right sentiment when he noted that "today we honored the Columbia crew. We brought Discovery home safely."

And, he was right in his assessment that "I hope this shows people that we're coming back."

From across America the message Tuesday was "Welcome home, Discovery." It was indeed a mission well done.