CAPE CANAVERAL, Fla. (AP) -- Two years after Columbia's demise, excitement over the space shuttle fleet's return to the skies in just a few short months is finally overtaking the agony of the accident.

In the past few weeks, two special deliveries have boosted morale among shuttle workers and provided tangible evidence they are rounding the corner.

One is a special tool to inspect the next shuttle while in orbit for any damage to its thermal-protective skin. The other is a brand new fuel tank guaranteed by NASA not to shed big chunks of foam insulation that could harm the shuttle.

Those are two of the biggest technical changes resulting from a lengthy review of what destroyed Columbia and killed seven astronauts on that still painfully vivid Saturday morning, Feb. 1, 2003.

It's appropriate, workers say, that two of the most crucial items for safely going into space again are finally at Kennedy Space Center, just in time for the second anniversary of the tragedy.

"We won't ever forget that. But when we have something like this to work on, it gives us a lot of enthusiasm and pride to focus on the future," said payload operations manager David Schubert. He was standing next to a 50-foot inspection boom, the new tool astronauts will use to make sure the shuttle has reached space unscathed.

For the first time since Columbia went down, "we're in pretty much known territory," said NASA's top spaceflight official, Bill Readdy, a former space shuttle commander. "We know how to process vehicles. We know how to get to the launch pad from here."

"You can just feel it in the air," observed shuttle program manager Bill Parsons. Especially satisfying, he said, is knowing that this spring's flight will help the two men aboard the international space station. The shuttle Discovery will deliver much-needed groceries and replacement parts.

For virtually everyone, the next launch - possibly as early as May 12 - is deeply personal.

"We all want to do this in memory of the crew," said Sandy Coleman, project manager over the fuel tank. "This is for them and this is what they would have wanted us to do. We knew them. They knew the dangers of spaceflight, and if it had been reversed, they would have been doing it for us."

The fuel tank will be mounted to a pair of booster rockets in just over a week, and Discovery will be attached to the towering threesome in March for the long-awaited trip to the launch pad.

If Discovery is not flying by early June, NASA will have to wait until mid-July because of the unwavering requirement to launch the shuttle in daylight. That's to make sure NASA gets clear photos of the launch to make sure no damage occurred.

NASA guarantees that after two solid years of scrutiny and re-engineering, nothing bigger than a dinner roll will come off the fuel tank's foam exterior at liftoff, too small to do the kind of damage that brought down Columbia.

Compare that with the suitcase-size chunk of foam insulation that ripped away during Columbia's launch and gouged a sizable hole in the left wing. The hole was harmless in orbit, but during re-entry let in atmospheric gases hot enough to melt the wing from the inside out. The shuttle came apart over Texas, just 16 minutes from the Cape Canaveral landing strip where the astronauts' families and NASA hotshots - like Readdy - were waiting.

The bottom line, according to Readdy, is that even though a dinner roll is the maximum allowable size for flyaway foam, any pieces that do pop off will likely be more along the size of an inconsequential corn flake or two.

NASA is still trying to figure out just how small a piece of foam could cause catastrophic damage. It seems the shuttle is even more vulnerable than engineers thought. Mathematical models used to sort that out, however, tend to "pile worst upon worst upon worst," Readdy is quick to point out.

This time around, NASA has backup-upon-backup-upon-backup plans - just in case it's wrong about the fuel tank losing foam.

Discovery's seven astronauts will have a hole-repair kit, albeit rudimentary and not nearly as sophisticated as engineers had hoped. They also will have the option of moving into the space station to await rescue by shuttle Atlantis.

Most important, they will have the new fuel tank and the new laser-eyed inspection boom.

For Discovery's commander, Eileen Collins, it all comes down to this: "If it wasn't safe, I wouldn't get on it."

Unlike the Columbia astronauts, "we've got a lot of things going in our favor," said her co-pilot, James Kelly. "When you're on a crew, whether it's an airplane or on the space shuttle, if you know the health of your vehicle, then you can start making intelligent decisions about what you need to do."