HOUSTON – With the Discovery orbiter sitting atop its launch pad and a potential liftoff date five weeks away, seven astronauts are looking toward a mission they hope will mark NASA’s return to shuttle flight.

“It’s time to go back to fly,” said veteran astronaut Eileen Collins, commander of Discovery’s STS-114 mission. “We’re 95 percent complete with our training.”

The STS-114 spaceflight would cap more than two years of work by NASA mission managers and engineers to boost shuttle safety and prevent another accident like that which resulted in the loss of the Columbia orbiter and its seven-astronaut crew in 2003.

The Columbia orbiter was struck by external tank foam insulation during launch which damaged its wing and caused it to break up over Texas during reentry.

“We miss the Columbia crew and we miss our fellow astronauts,” Collins said. “We will be remembering them on our spaceflight.”

Collins and her STS-114 crewmates are currently set to launch no earlier than May 15 on a mission bound for the International Space Station (ISS). Discovery rolled up to its launch pad early Thursday.

A busy schedule

NASA and the STS-114 crew still face some much-needed tasks before Discovery can lift off its launch pad and return to space.

On Friday, the crew will undergo a 12-hour simulation spanning two days of their spaceflight, Collins said, adding that next week STS-114 mission specialists Soichi Noguchi and Stephen Robinson will once again don spacesuits and plunge into a giant pool to rehearse the three spacewalks they will conduct during Discovery’s spaceflight.

Shuttle mission managers are also planning a test later this month to check the integrity of Discovery’s redesigned external fuel tank by pumping it with the liquid oxygen/liquid hydrogen fuel the shuttle burns during launch. A terminal countdown test is slated for the end of the month, Collins said.

Meanwhile, an independent oversight group charged with evaluating NASA’s return to flight effort is still waiting on additional data before it can sign off on the space agency’s launch plans.

The Stafford-Covey Return to Flight Task Force has passed NASA on seven of the 15 recommendations submitted by Columbia accident investigators as imperative issues to be addressed before the next launch. Of the eight remaining, several hover near closure.

Collins said her crew has met with the Stafford-Covey group several times to brief its members on NASA’s return to flight work.

“Their work is not done yet, in fact, our work is not done yet,” said Collins, adding that NASA still must complete debris and design verification reviews for Discovery’s flight. “If we ever get to the point where a recommendation is not filled in anyone’s mind, we are not going to fly until we are ready to fly.”

Shuttle safety

NASA officials have repeatedly said Discovery’s flight will be among, if not the, safest mission ever to fly.

Engineers have redesigned portions of shuttle external fuel tanks to prevent the type of foam shedding that doomed Columbia. An emergency plan to house the crew aboard the International Space Station has been sketched out in the off chance Discovery suffers critical damage during the mission.

The STS-114 flight will carry a 50-foot (15-meter) orbital boom tipped with instruments to scan sensitive areas of Discovery’s thermal protection system for damage. Astronauts aboard the space station will also photograph the thermal protection tiles and panels as the orbiter flips around, exposing its belly to the ISS during approach.

Meanwhile, Noguchi and Robinson will test two methods of repairing the tiles and reinforced carbon carbon (RCC) panels that protect orbiters from the searing heat of reentry as part of their first spacewalk. A third repair technique to plug small holes in RCC panels will be demonstrated inside Discovery, while the two men wear spacesuit gloves.

Those tests, and others, are required before NASA can be sure its thermal protection repair methods will be effective in an emergency, STS-114 astronauts said.

“I believe we still need to wait and do more testing to get more data on some repair techniques,” Collins said.

However, STS-114 flight director Paul Hill told reporters that the location of a particular damage point could govern whether mission managers would consider using one of the current repair methods.

“I do see a scenario where we could make a repair,” Hill said.

For example, a small knick in an area where damage may not be critical could be repaired as a measure to boost mission safety, he added.

“We never thought it would be possible to repair this vehicle in space,” said STS-114 mission specialist Charlie Camarda. “But yet I still feel, and I’m very hopeful, that these systems will be mature and beyond mature in the not too distant future.”

Collins said she and her crew plan to enter quarantine about seven days before their flight and fly to Kennedy Space Center about four days before launch.

“We have got to get this shuttle to fly again and complete this major goal of completing the space station,” Collins said.

• Special Report: NASA's Return to Flight