By Irene Mona Klotz
at the Kennedy Space Center, Florida
Managers of the US space programme (Nasa) have honed in on a new launch date for shuttle Discovery, amidst growing confidence that its spaceships are ready to resume flights after more than two years of work to recover from the Columbia disaster.
Nasa officials say they are confident the shuttle is approaching readiness
Following a top-level meeting to review safety upgrades ordered after the fatal 2003 accident, the shuttle and its seven-member crew were retargeted for launch on 22 May - one week later than previously scheduled.
Although some work remains at the launch pad to prepare Discovery for flight - the payloads have yet to be loaded into the cargo hold and the ship still needs rocket fuels for its onboard steering systems - the postponement is primarily to give managers enough time to scrutinise engineering data on a handful of modifications that have not yet received official sanction.
"I'm very comfortable and very confident in all the changes we made to the vehicle," said shuttle programme manager Bill Parsons told reporters in a teleconference on Wednesday.
"We just weren't ready for a flight-readiness review. It was the amount of open paper."
Of the 20 major design modifications managers discussed at a critical meeting at the Florida spaceport, just one remains open for additional study.
Deputy programme manager Wayne Hale said engineers were working to understand how a new 15m (50ft) extension to the shuttle's robot arm would fare under the jostling and stresses of launch.
The boom, which is studded with sensors and imaging systems, was added to the shuttle's gear so that the crew can inspect the belly and wings of the ship after it is in space.
Columbia was destroyed because of damage to its left wing, the result of barrelling into a piece of foam insulation that had fallen off the shuttle's external fuel tank during launch.
The breach was a ticking time bomb that went off 16 days later as the ship sailed through the atmosphere at supersonic speeds, heading toward the landing strip in Florida.
Superheated gases blasted into the wing, which melted, triggering the shuttle's destruction and the deaths of seven astronauts.
The shuttle managers warned that additional delays were possible if anything unexpected arose as flight preparations ticked down toward the final weeks.
"We are aiming for a launch date based on our best knowledge, but if somebody comes in tomorrow and says, 'look, you forgot something', then we will give them serious consideration," Hale said.
The delay also will allow an independent panel headed by former astronauts Thomas Stafford and Richard Covey to review Nasa's fulfilment of 15 recommendations for the shuttle's safe return to flight made by Columbia accident investigators.
Eight recommendations are pending, including one Nasa is technically unable to complete, but appears comfortable enough with its efforts to proceed with launch.
The requirement was for shuttle astronauts to have the capability to repair the shuttle's heat-resistant tiles and carbon composite wing panels during flight in case of damage.
During Discovery's mission, as well as during the next flight aboard sistership Atlantis, currently targeted for launch in July, astronauts will test a variety of materials and techniques to patch holes and repair cracks in the shuttle's heat shield.
Managers say engineers have gone as far as they can without testing the procedures in orbit.
No 'voting matter'
On Monday, the new Nasa administrator laid to rest the whole issue of whether the technical fulfilment of the Columbia Accident Investigation Board's recommendations would force a launch postponement.
"If Wayne Hale, whom I highly respect, and others recommend that we should consider launching despite not having filled all the squares on Stafford-Covey, that is something I would consider, because I don't believe that engineers make blanket decisions in advance, and I don't believe the technical decisions are a voting matter," Mike Griffin said.
"I cannot begin at this time to say under what specific conditions that Nasa might elect to go ahead with the launch, given a disparity of opinions.
"That will depend on the technical details of the issue at hand, but that is precisely the point: we study those issues and we resolve them as they occur, and then we make our decision, and we hold ourselves responsible for it."
Nasa will set a firm date for liftoff at the conclusion of the flight-readiness review, now scheduled for 10 and 11 May.