Shuttle launch moved to May 22
NASA: More analysis needed on new damage inspection system
Discovery has had 286 modifications, including 41 recommended by the Columbia Accident Investigation Board.
After a three-year hiatus, NASA plans a launch this May.
Shuttle Discovery moved to assembly building.
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(CNN) -- NASA announced Wednesday it had moved the launch date for the space shuttle Discovery to May 22, a week later than previously scheduled.
The space agency had targeted Discovery for a May 15 launch date.
"The 15th was always just a target," said shuttle program manager Bill Parsons. "We always knew we would evaluate that as we got closer."
Parsons and his deputy, Wayne Hale, made the announcement on a conference call with reporters.
They cited paperwork delays and the need for more time to analyze test results on the new orbital boom sensor system -- a robotic arm mounted in the shuttle's payload bay that is tipped with a suite of cameras and other instruments.
Astronauts will use the boom to inspect tiles on an orbiter's wings and nose cone for any damage that might have occurred during launch.
The shuttle fleet has been grounded since the Columbia broke apart February 1, 2003, over Texas while on approach to Kennedy Space Center in Florida.
NASA has a window from May 15 to June 3 in which to launch the shuttle on a rendezvous trajectory with the international space station.
The window is limited because the agency has committed to daytime launches for the next two missions to provide ideal lighting conditions for upgraded cameras that will image the shuttle as it climbs into orbit.
If NASA does not launch in the window that closes June 3, it would have to wait until mid-July for conditions to be acceptable again.
In August 2003, the independent Columbia Accident Investigation Board concluded that insulating foam flew off the shuttle's external fuel tank during lift off, striking and cracking a panel on the orbiter's wing.
When the shuttle re-entered the atmosphere, searing hot gases seeped into the wing and incinerated the spacecraft.
The underside of a space shuttle is covered with insulating tiles. The cone and edges of the wings are clad with reinforced carbon-carbon panels.
They make up the thermal protection system designed to protect the shuttle during the heat of re-entry.
Before the Columbia accident, astronauts had no way to inspect the thermal protection system and repair damage in orbit.
Development of such capability was one of 15 recommendations the CAIB laid out for NASA to complete before returning the shuttle fleet to service.
According to Wayne Hale, NASA scientists are still wrapping up certification tests on the orbiter boom sensor system and that was one reason the launch date has been delayed.
Developing effective repair techniques has been particularly vexing to NASA. Two methods will undergo limited testing by Discovery astronauts, but mission managers admit they will likely need to be modified before they can be certified.
Virtually everyone at NASA agrees astronauts would never be able to repair a hole the size of the one that doomed Columbia.
But NASA has made what its engineers believe is good progress toward eliminating the possibility that large debris would be shed from the shuttle's external tank.
And the agency has developed a plan to use the space station as a "safe haven" for astronauts in the event of an in-orbit emergency.
In such a scenario, a shuttle crew would live aboard the station for six to eight weeks while another orbiter was prepped for a rescue mission.
Return to flight
After the Columbia disaster, NASA was castigated for safety lapses and complacency about risks to the shuttle.
NASA was forced to change its safety culture and re-evaluate the shuttle's flight worthiness after Columbia burned up.
Since then, Discovery has had 286 modifications, including 41 recommended by the CAIB.
The Stafford-Covey Return to Flight Task Group, the independent oversight group chartered by NASA to certify the agency has met all CAIB recommendations, has yet to issue its final report.
A meeting to draw up the report had been scheduled for late March, but was postponed to allow NASA to finish paperwork the task group had requested.
Parsons said he expects a Stafford-Covey meeting to be scheduled the first week in May.
NASA's new chief, Michael Griffin, said Monday he might let the space shuttle return to flight even if the independent panel had not signed-off on some safety improvements, Reuters reported. (Full story)
"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 opinion between various interested parties as to whether we should or shouldn't," Griffin said.
Earlier this month, Discovery reached a major milestone when it was rolled out to the launch pad at Kennedy Space Center on Cape Canaveral.
"We feel very comfortable that this will be a very safe mission, and we would not launch if we didn't feel this would be a very safe launch," NASA spokeswoman Jessica Rye told CNN.com at the time.
The Discovery crew continues to prepare for the flight and is confident the mission will be safe.
"We have come a long way, and in that respect, we are ready to fly this mission," said shuttle commander Eileen Collins the day after the rollout.
CNN's Kate Tobin and Michael Coren contributed to this report