HOUSTON - The astronauts aboard the space shuttle Discovery are again scanning their orbiter's heat shield to get a second look at slightly damaged areas seen in a previous sweep.
The crew is using Discovery's camera and laser-tipped orbital boom sensor system (OBSS) to study at least nine parts of the shuttle's thermal protection system before the end of the day. The operation is part of a six-day heat shield verification plan, though shuttle managers and Discovery's crew have both expressed confidence that the orbiter is fit for reentry and landing.
"Right now, the indications are very good," Wayne Hale, NASA's deputy shuttle program manager, said Thursday. "We don't see anything major."
After studying images from Thursday's docking and Wednesday's OBSS survey of the nose cap and reinforced carbon carbon (RCC) panels along Discovery's wing leading edges, shuttle engineers picked out 11 specific sites where they found interesting nicks, scuffs or blemishes in the orbiter's heat shield.
Two of those sites will be inspected in tandem with Saturday's spacewalk activities, during which STS-114 mission specialists Soichi Noguchi and Stephen Robinson will test out tile and RCC repair methods on intentionally damaged samples in the payload bay, NASA officials said.
The spacewalk is the first of three for Noguchi and Robinson to install a spare parts platform outside the ISS, replace one broken gyroscope and repair the power system of among other tasks.
STS-114 pilot James Kelly and mission specialist Charles Camarda are steering the orbital boom system, with help from flight controllers. They began today's inspection at about 8:44 a.m. EDT (1244 GMT).
Today's OBSS look at Discovery's underside will yield much more information about the tiles there than traditional, two-dimensional images. A boom-mounted laser can generate three-dimensional views of tiles.
"What you don't see is depth," said John Shannon, NASA's manager of flight operations and integration for the shuttle program, of traditional imagery Thursday. "If you had a gouged tile, we don't think we have but if you did, you'd only see the white area."
Evaluating damage to the shuttle's heat shield is a major goal for Discovery's STS-114 mission. NASA's last orbiter flight, Columbia's STS-107 mission, ended in tragedy two weeks after a piece of external tank foam pierced a heat-resistant panel on its left wing. The damage allowed hot gases into the wing during reentry, which destroyed the orbiter on Feb. 1, 2003. Columbia's STS-107 crew did not survive.
NASA officials said Thursday that a small piece of foam may have struck Discovery, but was not large enough to be a concern and no damage has turned up from wing-mounted sensors and the initial OBSS inspection. That foam shedding, and a larger piece which clearly missed the orbiter, prompted NASA officials to hold off on future shuttle flights until the problem is solved.
Meanwhile, Discovery's crew is in the middle of their fourth day in space. Robinson and Noguchi are spending the bulk of the day going through the tools they will need for tomorrow's spacewalk.
Earlier today, Kelly and mission specialist Wendy Lawrence installed the Raffaello cargo pod at a port along the station's Unity module. That cargo shipment is expected to be opened at about 10:49 a.m. EDT (1439 GMT).
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