Shuttle fleet grounded indefinitely

Discovery arrives at space station with supplies, prepares to do repairs.

SPACE CENTER, Houston - The crew of Discovery arrived at the International Space Station Thursday to deliver supplies and begin several days of repair work while mission managers back on Earth vowed not to launch another shuttle until they are sure it is safe.

Their confidence has been shaken by the loss of a large chunk of insulating foam from Discovery's external fuel tank during the ship's flight from Florida on Tuesday. Just such an incident brought down the space shuttle Columbia in February 2003, killing seven astronauts, and NASA has spent the past two years redesigning the fuel tank to keep it from happening again.

Space shuttle program director Bill Parsons Wednesday grounded the shuttle fleet while engineers tackle the problem anew. "Obviously, we've got more work to," Parsons told reporters in a news conference at Mission Control Wednesday evening.

Flight director Paul Hill said Thursday that the seven astronauts aboard Discovery and their two Russian and American counterparts on the space station were informed of Parsons' decision but were too busy to react.

Shuttle commander Eileen Collins docked Discovery at the space station at 6:18 a.m. CDT. Station crewmen John Phillips and Sergei Krikalev photographed the approach and beamed the images to the ground for analysis. The pictures joined a suite of photos, videos, and radar and laser scans that engineers are using to ensure that Discovery does not suffer the same fate as its sister ship.

Discovery carried up an Italian-built cargo module which the astronauts will attach to the station and begin unloading on Friday. The day also will be filled with preparations for a Saturday spacewalk, the first in a planned series of three.

The imagery analysis by a team of almost 200 people is expected to conclude in a few days with a decision about whether Discovery's heat shield does or does not need repairs before the orbiter returns to Earth on Aug. 7.

Engineers have particular interest in two chipped heat-resisting tiles on the shuttle's underbelly and four divots in the insulating foam on the external fuel tank. At mid-day Thursday, mission managers still believed the tile damage was insignificant. They were more alarmed by four divots in the insulation on the fuel tank. The largest hole measures about a foot wide and two or three feet long, indicating the loss of an eight-inch-thick chunk of foam that weighed almost a pound.

NASA officials said they are reasonably sure from looking at video recordings that the largest chunk and two others did not strike the orbiter, but they lacked sufficient data Thursday to reach a conclusion about the fourth piece.

The biggest chunk came from alongside some pipes and a cable tray that run vertically up one side of the rust-colored fuel tank. When the tank was redesigned, NASA changed the way insulating foam is sprayed on this area, known as the PAL Ramp (Protuberance Air Load Ramp), in hopes of keeping the foam from coming loose. NASA considered removing the insulation altogether, but tests indicated that it provided some aerodynamic protection for the pipes and tray.

No debris shedding from that region of the fuel tank is acceptable, shuttle operations manager John Shannon told reporters Thursday. "It doesn't matter how close it came to Discovery," he said. "We're treating this extremely seriously. We're going to fix this before we go fly."

Officials stressed that they consider Discovery's mission a test flight to gather knowledge about technical changes made in the name of safety since the Columbia disaster. "We're in a learning curve here," said mission management team chairman Wayne Hale. "We're seeing things that we have never seen before."

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