HOUSTON - An object seen floating near shuttle Columbia on its second day in space is almost certainly a tile-covered panel that somehow came dislodged from the edge of the ship's left wing, investigators said yesterday.
Tests show that the so-called "carrier panel" most closely matches the object tracked by radar while the shuttle was in orbit, said Maj. Gen. John Barry, a member of the Columbia Accident Investigation Board overseeing the inquiry into the ship's breakup on Feb. 1.
A missing panel might have created a vulnerable spot on the wing where hot gases could get inside as the ship slid through the atmosphere on its landing attempt. But investigators cautioned that more analysis is needed, and it's too early to pin the accident on a lost panel.
"You're way ahead of us if you blame the carrier panel," said board Chairman Harold Gehman Jr., a retired Navy admiral. "We would in no way conclude that we've found the initiating event here."
The object was discovered after the accident, when officials at U.S. Space Command began reviewing 3,100 routine radar observations that were taken of the ship during its 16 days in space. The object eventually was tracked re-entering the atmosphere, where it presumably burned up over the Pacific Ocean.
The left wing may have been damaged by debris during Columbia's Jan. 16 launch, when a large piece of foam insulation came loose from the shuttle's external tank and slammed into the left wing.
NASA studied the foam incident during the mission and found that it presented no safety risk. But continuing analysis since the accident has refined both the size of the foam and the likely area where it struck the spaceship.
Board members said the latest footprint of the debris strike is focused on a 2-foot-wide area near reinforced carbon-carbon panel No. 6 - one of the 22 panels that cover the edge of the left wing. Two nearby carrier panels also may have been hit. This area was not part of the analysis done during the mission.
In addition, board member Roger Tetrault said the foam is now estimated to be about 24-by-15-by-5 inches, which varies slightly from earlier estimates. In coming weeks, researchers plan to start shooting foam at reinforced carbon-carbon panels, carrier panels and other objects to see how they are damaged on impact.
Barry said a close examination of the remaining three orbiters' carbon-carbon panels has found that tiny holes often pit the surface. The "pinholes" are repaired if they get bigger than .04 inches, but the minuscule imperfections might weaken the panels.
He said the holes possibly are created when zinc - leaching from unpainted parts of the launch complex while the shuttle sits on its launch pad - eats into the carbon-carbon.
Barry said NASA was aware of this problem, but added, "I don't think it quite got the attention maybe that it has now, obviously, with the mishap."
Robyn Suriano writes for the Orlando Sentinel, a Tribune Publishing newspaper. Sentinel staff writer Gwyneth K. Shaw contributed to this article.