Eileen Collins (search) is a veteran of three space shuttle missions and on Wednesday, she hopes to add one more trip to her resume.

"People ask me what's going to be the hardest day of the mission? Flight day one, flight day two, flight day three ... the mission is packed," she said. "The world is watching but I'm not focused on the world watching. I'm focused on the priorities: Getting things done on time but doing them safely."

Collins is the crew commander on the shuttle Discovery, which is scheduled to lift off on Wednesday on a mission NASA (search) is calling "Return to Flight." In NASA-speak, the mission is also known as STS-114.

The Risks in Space

Discovery will carry seven astronauts to the International Space Station (search), along with needed supplies and replacement parts. If the shuttle suffers irreparable damage en route, the astronauts will move into the station and await a rescue by the shuttle Atlantis.

With more than 2 million parts to the shuttle, some former astronauts say there are 2 million different ways things could go wrong.

"NASA's tried to kill me for 30 years if you get right down to it, with all the various devices and all the things I went through," said Story Musgrave (search), who flew into space six times aboard a NASA shuttle. "The shuttle has, to give it credit, opened up space. It has done its job and it's fantastically vulnerable, very difficult, it's the most dangerous vehicle we've ever come up with."

NASA officials acknowledge the risks taken with each mission.

"Just think about it for a second. We put seven people on top of 4.5 million pounds of high explosives and accelerate them to a speed seven times faster than a rifle bullet in just a few minutes. Now if that doesn't put the risk in perspective!" said Wayne Hale, deputy manager for NASA's space shuttle program.

The first shuttle flew to orbit in 1981. Since then, the vehicle has proved to be risky to operate and expensive to maintain. But from the beginning, NASA management told the world the shuttle was perfect — an operational vehicle as safe as an airplane.

"I think one place where NASA went wrong was losing sight twice of the fact that this was not an operational technology but remained an experimental technology," said Diane Vaughan, author of "The Challenger Launch Decision."

The notion of the shuttle being safe was shattered in January 1986 when the shuttle Challenger exploded 73 seconds after launch, killing all seven people aboard. The ensuing investigation revealed a culture at NASA that had gradually begun to accept escalating risk and was full of flawed decision-making. But what wasn't fully addressed was how operating on a shoestring budget was a real threat to safety.

After Challenger, 88 missions launched and landed; NASA thought the new system for assessing risk was serving them well. But that system proved it had its own flaws and analysts cited it as one of the factors that destroyed Columbia on Feb. 1, 2003, when the shuttle exploded upon re-entry.

In the Columbia disaster, a briefcase-size chunk of foam broke apart from the external fuel tank about 81 seconds after liftoff. The foam hit the shuttle's wing at 500 mph. NASA veterans like Musgrave said the foam coming off "becomes normal" because it kept happening and it was like playing "Russian Roulette." Some requests for more images of the orbiter were denied because of "in-family" classification by NASA. Many called for a culture change within the space agency.

Discovery's Mission

The major focus of the STS-114 mission will be testing and evaluating space shuttle flight safety, which includes new inspection and repair techniques.

At the International Space Station, crew members will replace one of the orbital outpost's control moment gyroscopes. The crew also will conduct at least three spacewalks while at the ISS. The first spacewalk will demonstrate repair techniques of the shuttle's thermal protection system. During the second, the spacewalkers will replace the failed CMG with one delivered by the shuttle. On the third, they will install the external stowage platform.

In preparation for the "Return to Flight" mission, there was the usual rigorous NASA training. What's new on the shuttle's plan, however, is testing the ability of it to repair itself. Astronauts practice working with an expandable goo as a quick fix, for example, for filling in small damaged areas.

"I kind of likened it a little bit to trying to spackle your wall while standing on a roller-skate kind of thing. You're kind of unstable," said Lora Bailey, project leader at NASA in charge of tile repair. "Some of the things that we're asking the crew to do here is require some level of precision, you know, pointing the applicator that dispenses material very precisely in a certain damaged area, so it would be a challenge for him to do that."

To comply with the Columbia Accident Investigation Board's recommendations, NASA engineers developed ways for astronauts to inspect and repair damage to their ship's outer thermal layer while in orbit.

On the second day of the flight, Discovery's crew is going to use two lasers and a camera at the end of the shuttle's 50-foot arm and 50-foot extension, to scan both the left and right wing, as well as the nose of the orbiter, to look for damage. On the third day, the crew will rendezvous with the space station, where the space station crew will take pictures of the Discovery's tiles with a digital camera, so the pictures can be linked to NASA crew on the ground.

Future of Space Exploration

NASA chief scientist James Garvin (search) stressed the importance of future space exploration.

"[Space expert] Carl Sagan once said, 'why would not this miracle that we have here on Earth not be everywhere?' It's just like, imagine living in North Africa. If all you knew was your one little oasis, you might think most of the Earth was bland," Garvin said.

Added Collins, "As humans, it's part of our desire to explore and go to new places and learn new things."

Apollo astronaut Gene Cernan not only had the opportunity to go into space but also the privilege of leaving the last footprints on the moon.

"What a human being feels at that point in time cannot be explained by science. I can only imagine stretching it way out, what it would be like to stand on Mars," Cernan said.

"Why space? I got my sewing machine. I got my computer. I got my automobile. I got my telephone. What else do I need? I'm glad someone didn't say that 50 or 100 years ago, or even 30 years ago because we wouldn't be enjoying the lifestyle that we enjoy on this planet today. We can't afford not to go."

Added Musgrave: "The deeper you go into space and the things you find out can become a mirror to look at the human species."

"Today a student can pick up and see the universe unfolding in front of her or him, see the surface of Mars as if you were standing there," added NASA's Garvin. "They can see the surface of Titan, a world 2 billion kilometers from Earth. They can imagine a mission to Pluto."

Collins, who knew the Columbia crew members who perished in that accident, said she will remember the sacrifices they made for the program. "They believed in space exploration as we do, and we want to continue with their mission," she said.

"Maybe in your lifetime we will have people living on the moon, traveling to the moon and eventually going to Mars and doing that," she said. "Even more exciting than that, we'll have the opportunity to travel in space on a vacation."

Added Cernan: "Dreams are what makes reality. Dreams are what make the future come true."

FOX News' Peter Russo, Melanie Dadourian and Iraida O'Callaghan contributed to this report.