You're floating in the cargo bay of the Space Shuttle Discovery, 365 miles above the Earth. Before you, anchored in a special mounting, is the Hubble Space Telescope. Your mission, simply stated, is to fix it. In other words, you have been assigned one of the most demanding jobs ever given to an astronaut.

"Suits are hard," Musgrave says. "They're just miserable. Because they're so stiff." Shuttle space suits are filled with oxygen at a pressure of 4.3 pounds per square inch. That gives the spacewalker enough oxygen to breathe -- but it also makes the suit about as flexible as a balloon in a Thanksgiving-day parade.

For that reason, Musgrave was fussier than the finest tailor about the fit of his space suit. To bend at the waist, for example, he would need as much leverage as possible. To achieve this, Musgrave knew, his feet and shoulders would have to make firm contact with the suit itself. He also knew that during a six-hour spacewalk, being inside a tight-fitting suit would compress his spine -- which meant the suit had to be even tighter at the start of the day. "I wear a very, very, very tight suit," Musgrave says.

Musgrave paid special attention to the fit of his gloves. Before the flight, he says, "I spent two hours 'tuning' my gloves. I tune every finger." That meant having more pressure on his fingertips and less at the places between the fingers. It meant precisely adjusting the length of each finger of each glove, so that the glove's joints would coincide with those of his fingers.

Even after you have your space suit perfectly adjusted, Musgrave says, don't expect it to feel like a second skin. "You learn a new body. You acquire a new arm. It's not your arm. It's not the suit arm. It's the combination of your arm and the suit arm. The suit does not have the same joints you have, and so you have to learn appropriately."

Musgrave says a prospective spacewalker has to relearn even simple motions -- for example, grabbing a floating tool. "If you think you're going to get into a suit and reach out for something, you're going to miss it," he says, unless you practice it beforehand.

That's just what Musgrave did -- hour upon hour of practice, using a number of methods. First, he did "walk-throughs", wearing normal clothes, with engineers who helped design the Hubble instruments right there, to answer any questions.

Musgrave also practiced on something called the air-bearing table: picture him perched a special platform that rides across an ultra-smooth surface, cushioned by a thin film of pressurized air. Working in weightlessness is like being on a three-dimensional ice-skating rink, and the air-bearing table is designed to show an astronaut how tricky that can be. However, it only allows freedom of motion in two dimensions at once.

Then there was the "Neutral Buoyancy Laboratory", actually the world's largest swimming pool, containing mockups of the shuttle cargo bay and Hubble telescope. Underwater, wearing a pressurized space suit, an astronaut can practice working in three-dimensions. But there are drawbacks. Unlike the vacuum of space, water creates resistance whenever you try to move through it. And of course, a space-suited astronaut in the "water tank" doesn't enjoy the weightless conditions of a real space walk. Being upside down, for example, feels more like standing on your head -- and you're likely to feel your shoulders digging into the metal bearings inside your space suit. "The water is no darn good," Musgrave says. "Even NASA doesn't really know about all the weaknesses [of practicing] in the water."

"We never used a checklist. Because ... a ballerina doesn't have a checklist and neither does an opera singer ... We learned it by visualization."

Nevertheless, Musgrave had spent countless hours rehearsing for the Hubble repairs by the time he and his crewmates left Earth. And most of all, Musgrave had spent a lot of time thinking about everything he would do during the Hubble repair. In fact, he'd been thinking about how to repair a space telescope for about 20 years -- most of his astronaut career.

So, how did he feel, as he awoke on launch morning, with one of NASA's most important missions ahead of him?

"It's just like going to the Olympics. You are totally trained. You are honed to the edge. You've done what you can do. That's it." Even so, Musgrave says, he could never be sure of success. "You don't know whether you're going to win the Olympics. How could you know?" In the end, he says, he looked at the challenge the way a high-jumper does: "It's you and the bar."

When Musgrave finally emerged from the Space Shuttle's cabin into the vacuum of space, there was a sense of familiarity about it all. Not just because he'd trained so hard, but because he'd walked in space before: Musgrave had made the first walk of the shuttle program, in 1982. And months of practicing for the repair had given him an extraordinary familiarity with the Hubble's components.

For example, if Musgrave's job was to install a new high-resolution camera, he made sure he could visualize exactly what was going on inside the instrument with every turn of every screw. If that sounds like the ultimate nuts-and-bolts experience, then Musgrave has a surprising description of the repair:

"It was a ballet."

A ballet? Two figures in bulky space suits and massive backpacks aren't exactly the picture of grace. And yet, Musgrave strove for dancer's grace in his movements. "You have to worry about every finger and toe. If you've got a hand out of place in the ballet you're going to lose style."

During training, he says, "I would go through ballet books page after page," studying the dancer's version of perfection, and translating it in his mind to perfect space-walking technique.

What does that perfect technique look like?

During a Hubble repair, it often means working in confined areas, like the access doorway leading to a delicate scientific instrument, without moving your body. In such situations, Musgrave says, "The ideal form for a space walker is to see a lot of motion at the wrist level, less at the elbow and almost none at the shoulders."

There's another aspect of a dancer's method that the astronauts used: Visualization. "We never used a checklist. Because, you know, a ballerina doesn't have a checklist and neither does an opera singer... We learned it by visualization." The same technique let Musgrave keep track of some three hundred separate tools. He and his fellow spacewalkers had tools to handle every possible contingency. And yet, even in weightlessness, in the shuttle's cavernous cargo bay, Musgrave says he never lost track of them. "You could ask me halfway into [any spacewalk] where all three hundred tools were, and I could rattle them off."

If keeping track of the tools sounds tough, try using them. The hardest part of any spacewalk, Musgrave says, is working with your hands in pressurized gloves. If you want to understand why, try squeezing a tennis ball, repeatedly, for hours on end. Opening and closing your hand inside a space-suit glove is just as tiring. For that reason, Musgrave says he tried to avoid clutching objects. "Any time I see myself grabbing I say, 'Is there another way to do it?' I don't grab things. I push and I touch." To use a power tool, for example, he cradled it between his two gloves, without actually holding on.

Still, some jobs required an almost impossible level of dexterity. Musgrave remembers that in order to install one component, he had to undo ten sets of connectors, which were secured by tiny screws -- and he had to do it while his feet were anchored on the shuttle's sixty-foot robotic arm.

"There were little connections in the back of this box, the size of what's in the back of your PC. And they had little screws that are only about three millimeters long. I had a wrench that was about three feet long, and I was on the end of a sixty foot arm, and I had to drive these little screws three-and-a-half turns."

That was hard enough with space suit gloves. But keeping the screws from floating away -- possibly inside the telescope's delicate mechanisms -- made it even tougher.

"That was the most demanding job I had ever done," Musgrave says. "I was on the edge of my ability."

Musgrave made three of the mission's five spacewalks. When it was all over, Musgrave knew he had done his job well. But he didn't share his crewmates' jubliation at a successful mission. "I put on a smile for people," he remembers. "I felt humble and quiet." The reason, Musgrave says, is that he couldn't be sure, even then, that the telescope was fixed. He didn't know that until the repaired Hubble sent back its first new images.

By that time, Musgrave was back home, in Houston. He remembers the thrill of seeing Hubble's magnificent face-on image of the spiral galaxy called M-100. Even then, Musgrave says, he didn't think about what he and his crewmates -- along with dozens of flight controllers, mission planners, and engineers -- had helped to accomplish.