By Paul Rincon
BBC News science reporter, at Kennedy Space Center
The US space agency's administrator Dr Mike Griffin told a Discovery pre-flight news conference that the space shuttle was ready to go back into orbit.
Dr Griffin wants to see a shuttle replacement as soon as possible
Dr Griffin said a safe flight was crucial to the future of Nasa and to the nation.
In a frank press conference, he said that spaceflight was a dangerous business and always would be.
He added that Nasa had done everything it could to make the shuttle as safe as possible.
"There is no recovery from the mistakes we've made, whether it's going back to the Apollo fire, the loss of Challenger, or the loss of Columbia, going back to go through 100 years of flight, the lessons that we who fly have learned and know are written in other people's blood," he told reporters at Nasa's Kennedy Space Center in Florida.
"Obviously, it is utterly crucial for Nasa, for the nation, for our space programme, to fly a safe mission," Dr Griffin said at the Tuesday briefing.
"We have done everything that we know to do."
Discovery's launch is the culmination of two-and-a-half years of work to make the shuttle as safe as possible for human spaceflight.
The Columbia accident was triggered by a suitcase-sized piece of foam insulation that broke off the external fuel tank during lift-off, damaging the vehicle's left wing.
When the crew attempted to return through the atmosphere on 1 February 2003, super-heated gases entered the wing and tore the orbiter apart.
Dr Griffin told reporters: "Is there anything we don't know about that can bite us? Yeah. This is a very tough business - a very tough business."
SHUTTLE RETURN TO FLIGHT
Mission known as STS-114
Discovery's 31st flight
17th orbiter flight to ISS
Payload: Raffaello Multi-Purpose Logistics Module
Lift-off: To be determined
Location: Kennedy Space Center, Launch Pad 39B
Discovery crew: Collins, Kelly, Noguchi, Robinson, Thomas, Lawrence and Camarda
By its retirement in 2010, the shuttle will have been in use for three decades. Dr Griffin said this was "enough". "It's time to take what we have learned and move on," he added.
Dr Griffin has speeded up development of a replacement for the shuttle, to be known as the Crew Exploration Vehicle.
"Even with 113 launches under its belt, [the shuttle] is still an experimental test-flight programme," he explained.
He said he wanted the US to be the major space-faring nation of the 21st Century and beyond.
He said the return to flight represented the first step in Nasa's fulfilment of President Bush's vision for space exploration, to take astronauts back to the Moon and on to Mars.
Discovery's mission will last 12 days. The orbiter will carry spare parts and other equipment to the International Space Station (ISS).