CAPE CANAVERAL, Fla. (Reuters) - NASA managers cleared the shuttle Discovery for launch on July 1, over the objections of the agency's top safety officer and its lead engineer, officials said on Saturday.
"There were very different viewpoints on the issue of whether we were ready to fly or not," NASA Administrator Michael Griffin told a news conference. "I can't possibly accept every recommendation given to me by every member of my staff, especially when they all don't agree."
The crux of the debate was whether additional modifications to the shuttle's fuel tank were necessary before flights resume. NASA redesigned the tank after the 2003 Columbia accident and then again following the first post-Columbia mission last July. Both times, large pieces of insulating foam fell off the tank.
Columbia was hit and damaged by the falling debris, triggering the ship's breakup as it flew through the atmosphere for landing. Seven astronauts aboard died in the accident.
Discovery escaped impact from falling foam debris during its launch last July, but NASA suspended flights for additional modifications. Some engineers say the agency has not gone far enough.
Griffin and other top managers acknowledge the risk of potentially dangerous debris impacts on the shuttle and have appointed a special team to redesign the most troublesome areas, known as ice frost ramps. These hand-sprayed chunks of foam cover metal brackets on the outside of the tank. The foam keeps ice from forming, which could break off and strike the shuttle during liftoff.
Although smaller than the debris chunks that downed Columbia and flew off during Discovery's July 2005 launch, in a worst-case scenario ice frost ramp foam could strike a shuttle and damage its heat shield.
Even if that were to occur, said Griffin, the shuttle crew would not be threatened. Since the Columbia accident, NASA has set up a safe haven for shuttle astronauts aboard the International Space Station should their vehicle become too damaged to safely return to Earth. In addition, shuttle crews now scrupulously inspect their ship for heat shield damage with a new sensor-laden boom after reaching orbit.
"We're not in the situation that we were in with during Columbia," Griffin said.
What was at risk, he added, was the ability to finish building the space station if NASA did not get on with flights. The shuttle fleet is to be retired in 2010. Sixteen more missions to finish station assembly are planned, plus a possible final servicing call to the Hubble Space Telescope.
Delaying Discovery's launch until a new ice frost ramp design is ready would put more pressure on the shuttle program during the final years of station assembly, Griffin said.
While the loss of another vehicle likely would end the shuttle program, Griffin said he was willing to accept that risk in order to complete the station before the fleet is retired.
"If we're going to fly, we need to accept some programmatic risks -- not crew risks -- and get on with it," Griffin said.