Since the disintegration during reentry of its sister craft "Columbia" -- with the loss of all seven astronauts on board -- the "Discovery" has been much modified and improved. The liftoff has been set for 3:51 p.m. Eastern Daylight Time tomorrow.
The flight is risky but it has to be done, say the experts. Clive Simpson is the editor of the "Spaceflight" magazine of the British Interplanetary Society.
"One always has to recognize that flying in space, particularly with humans, is always going to be a risky business. And I think they will have done as many tests as they possibly can on the ground," Simpson said. "But, of course, the ultimate test is to fly the shuttle again actually into space. And I think all that you can do is to make sure that you've covered every area possible, and then you have to put the vehicle to the test at some point.”
America's space agency NASA is sure that all the redesigns, improvements, and testing are complete and that "Discovery" is going to lift off on schedule.
"NASA has been working tirelessly to bring the space shuttle fleet back into readiness to get ready to go fly," said Kelly Humphries, a manned space program spokesman for NASA. "All the preparations are leading up to our ability to make the upcoming launch window."
The "Columbia" disaster was caused by a piece of insulation foam falling from the external tank of the space shuttle and damaging one of the orbiter's wings. Later, when the shuttle returned to Earth at the end of its mission, the damaged wing was unable to withstand the heat of re-entry through the atmosphere and the craft broke to pieces.
NASA has worked on this and other problems ever since the disaster commission findings. Now, most experts are satisfied with the improvements, says Simpson.
"We can never be a 100 percent sure, but I think we can be pretty confident that they sorted that issue and that problem," Simpson said. "And we're not going to get any major sort of flight problem through that."
In command of "Discovery" will be an experienced astronaut, Eileen Collins, a veteran of several shuttle flights. And most of the other members of the crew have flown in space before, too. The STS 114 mission -- as it is officially designated -- is to last 13 days. The shuttle will dock with the space station in orbit and a series of special tests will take place.
Two astronauts, Stephen Robinson and the Japanese mission specialist Soichi Noguchi, will step out into space to test ways of repairing the outer skin of the shuttle in orbit.
A special 15-meter extension boom with cameras attached at the end of "Discovery"'s manipulator arm will check all the surfaces of the craft for any damage. "Discovery" will be also scrutinized by the two astronauts on board the space station.
And powerful ground telescopes, as well as spy satellites in orbit will be monitoring the mission during the ascent and in orbit. Simpson concludes that with all these precautions the astronauts should be safe.
"NASA is extremely sensitive now [about] having any kind of mishap in space," Simpson said. "So, I think they're putting so many measures in place, and they will be ultra-cautious on launch day. So, that is why I believe that it will in fact be one of the safest missions to be launched.”
And he points out that if some damage that would prevent "Discovery" from returning safely back to Earth is discovered, the shuttle could wait for rescue while attached to the space station.
Another shuttle, the "Atlantis," will be standing by, ready to fly from 19 July. And all the food, water and air "Discovery" is carrying in a special Italian supply module called "Raffaello" would comfortably last the crew for many weeks.