Even after an overhaul exceeding $1 billion, NASA knows the space shuttle is still vulnerable, unpredictable, dangerous, unforgiving. With the expected return to space Wednesday, NASA leaders stress this will be a test flight in the true sense, almost like the original Mercury space shots.

In the 2 1/2 years since Columbia plummeted from the sky in a cascade of flames and halted U.S. space travel, NASA has stripped its fuel tanks of excess foam insulation and added launch-surveillance cameras. It's toughened up the spacecraft and cracked down on know-it-all managers. It's created a laser-tipped boom to scour the shuttles' thermal skin for cracks and developed bandages for these ominous sores. It's done everything it can to make the shuttles safer.

Managers believe they have licked the overriding problem of foam shrapnel, but warn that no one will know for sure until Discovery goes up. Ice from the fuel tank could also prove to be a deadly spoiler.

As for those little shuttle bandages, the astronauts don't trust them enough to ride home with them covering any holes, even those considerably smaller than the one that doomed Columbia.

An oversight group found the remedies to be so deficient that it ruled NASA noncompliant with Columbia accident investigators' 2003 insistence on practical space repairs. The task force also found NASA lacking on two other crucial requirements, shuttle hardening and elimination of fuel-tank launch debris.

"Eileen Collins and Vegas Kelly and their associates will be lifting off in the face of unknown risk," NASA Administrator Michael Griffin cautioned employees at the end of June. "This is a very risky venture. The people who are doing this are risking their lives ... and everybody should understand it."

Commander Collins and her co-pilot, James "Vegas" Kelly, will be at Discovery's controls during the eight-minute climb to orbit and the hourlong descent at mission's end.

It used to be only the launches that were nerve-racking, but no more. Columbia's destructive re-entry on Feb. 1, 2003, and the deaths of seven astronauts made landings equally feared.

NASA's traditional post-launch party is off, although beans and cornbread will be served up as usual after liftoff. No one expects to feel like celebrating when there are photos of the shuttle and external fuel tank to be scrutinized, radar to be analyzed, wing sensor and laser boom data to be crunched.

All these devices should produce a mountain of shuttle-health reports that will take nearly a week to sift through.

With so many eyes on Discovery, NASA expects to see more launch debris than on any other mission in the program's 24 years, although in reality it should be the least amount to come off.

"This is a very symbolic mission," said Stephen Robinson, one of Discovery's seven astronauts. "We're getting back on a horse and we're doing it in a much better and wiser and safer way."

Noted crewmate Andrew Thomas: "It is the mission that's going to tell us whether the space shuttle is safe to continue to fly."


When Columbia lifted off on Jan. 16, 2003, the spacecraft was jammed with science experiments. But there was no robot arm, no spacewalker jet pack, no access to the international space station — no obvious way, in other words, for the crew to check Columbia's battered wing, much less fix it.

Commander Rick Husband was notified about the foam strike that occurred 81 seconds after launch, but flight controllers dismissed it as no big deal. Their word was good enough for him.

What Husband didn't know — what hardly anyone knew at the time — was that a handful of lower-level engineers were worried the freed chunk of fuel-tank foam insulation might have pierced the shuttle's thermal shielding. They never expressed their fears to the people in charge, though, and the decision-makers never bothered seeking alternative views.

So when Columbia descended through the atmosphere following its 16-day mission, scorching gases penetrated the hole left by the foam. The stricken left wing melted from the inside out, and the spacecraft lost control and ruptured over Texas, 16 minutes from the Kennedy Space Center landing strip.

It was months before NASA accepted the fact that a 1 1/2-pound piece of foam could bring down a shuttle, and before space agency naysayers realized they could have done something in an attempt to save the crew if only they had known about the hole.

This time, NASA has a strategic plan and, hopefully, a reformed safety culture.

The first layer of defense was the removal of all unnecessary foam from the fuel tank, including the section lost during Columbia's launch. Heaters were added to the foamless areas to prevent ice buildup from the super-cold fuel. Where foam remained, workers were added to oversee the application process.

In all, NASA made nearly 50 improvements to Discovery in the wake of the Columbia tragedy.

Nonetheless, "There's still going to be a possibility that a golden BB could get us," said deputy shuttle program manager Wayne Hale. To make matters worse, "Our testing has now shown us that even a crack, much less a hole, could be catastrophic."

Because of that possibility, NASA embedded dozens of motion and temperature sensors in Discovery's wings to record any impacts during liftoff. More than 100 cameras — on the ground, in the air and aboard Discovery itself — will document the shuttle's climb to orbit in broad daylight. So will radar.

NASA is requiring a daylight launch for the next two missions in order to spot any damage, and also a shuttle on standby for a potential rescue.

Dr. Jon Clark, a NASA neurologist whose astronaut wife Laurel died aboard Columbia, fears for future flights.

"I can tell you, as soon as they can, they're going to start undoing all those things," Clark said. "What they want to do is get back to business as usual as fast as they can."

With a 2010 shuttle retirement date looming and the space station only half built, NASA is admittedly anxious to get things done.

Discovery will carry up badly needed supplies and replacement parts for the space station and, perhaps even more important, haul down trash that's been piling up for close to three years. The Russian cosmonaut living on the station likens the mess to the condition of his country's now defunct Mir outpost.

NASA will keep collecting images of Discovery, even as it's en route to the space station.

In two unprecedented and somewhat risky maneuvers, Discovery will perform flips so the shuttle astronauts can get close-up digital pictures of the departing fuel tank right after liftoff and so the station crew can zoom in on the shuttle's belly right before docking.

Discovery's astronauts also will gather 3-dimensional images of their ship's wings and nose cap, using the brand new 50-foot laser boom that will hook onto the end of Discovery's 50-foot robot arm. Flight director Paul Hill considers this the most hazardous of the groundbreaking procedures.

Imagine a thick, rigid, 100-foot crane being waved for hours around the fragile wings, and you get the worrisome picture.

"If we make contact with the orbiter while we're doing this, I'm looking for another job," Hill said.

The benefits, if the boom works as advertised, will be immense. For the first time, a crew will be able to check out its spacecraft before returning to Earth, "and that's a really big thing," said Robinson, the astronaut.

Spy satellites also will snap pictures of Discovery as dictated by the Columbia investigators, but NASA is keeping mum on the details.

"We've got backups on backups on backups to get this information," said John Shannon, shuttle flight operations manager. "We're going to know if something came off. We're going to know if the vehicle is damaged. I have zero doubt about that."

If damage crops up, then comes the hard part. Does NASA send out the astronauts to attempt a repair or order them into the space station to await rescue by Atlantis in a month's time?

Neither option is desirable. The space station is built for three occupants not nine, which would be the head count if Discovery's seven astronauts moved in. Besides, there's no guarantee Atlantis would arrive before the oxygen and other supplies ran out, especially since NASA would be trying to launch the rescue ship in the thick of hurricane season.

On the other hand, none of the five heat-shield repair kits aboard Discovery is certified. And none comes close to sealing a hole as big as the one that sank Columbia.

Among the repair tools, all of them rudimentary: caulking guns for dispensing pink-orange goo and gray paste, shoe polish-style applicators for dabbing on thick gray paint, bags of fluffy insulation to stuff into holes and overlaying covers, and mechanical plugs.

Three of the repair methods will be tested during the 12-day flight, two of them during a spacewalk by Robinson and Japanese astronaut Soichi Noguchi.

Coming up with reliable repairs has been the toughest part of returning to space. A patch that's just tenths of an inch too thick could disrupt the hot plasma flow surrounding a descending shuttle and increase the heating — destroying the repair, and the spacecraft.

The trouble is, the shuttle's glassy thermal tiles and carbon panels were never meant to be repaired in space.

"The tile, for example, is mostly air. That's why it's a good insulator. And how do you repair air?" asked former astronaut James Adamson, who served on NASA's return-to-flight oversight panel.

At this point, neither the Discovery crew nor the rest of NASA believes any more can be done anytime soon to significantly improve the odds. Patches for bigger holes are at least two years away. Some preventive measures are so far into the future that the shuttle's retirement almost certainly would come first.

For Collins, Discovery's commander, "The question comes down to, if we wait another two months or another six months, how much more will we learn to make us safer to fly?"

Everyone at NASA is painfully aware that even if the fuel tank lost no foam or other debris and the shuttle were impenetrable and the astronauts were armed with surefire repairs, any of the craft's 2 million working parts or 300 miles of wiring could still fail.

Former astronaut Richard Covey, chairman of the return-to-flight task force, said if he were climbing aboard Discovery this time around, he would be more worried about the main engines, auxiliary power units or booster rockets, than a stray piece of foam.

Covey rode Discovery into orbit in 1988 on the first shuttle flight after the Challenger explosion 2 1/2 years earlier. In that disaster 73 seconds after launch, it was cold-stiffened O-ring seals in a booster rocket and — just as it later was with Columbia — a flawed safety culture.

"I've always said that anyone who's not nervous during a space shuttle launch doesn't understand the physics of what's happening," Covey said.

The same holds true now for the landing.

"I could see another shuttle being lost because this is a dangerous business," said ex-astronaut Rick Hauck, commander of that first post-Challenger flight. "But you hope it's not lost for the wrong reasons."