More Than One Piece of Debris Hit Shuttle at Liftoff
By WILLIAM J. BROAD and KENNETH CHANG
uring Columbia's liftoff, not one but three chunks of debris flew off the 15-story external fuel tank and hit the shuttle's left wing, according to a
document NASA made public yesterday. Previously, the public inquiry into what caused the craft to break up on re-entry focused only on the largest
chunk.
The document, dated Jan. 24, is the third in a series of reports that analysts at Boeing, a major shuttle contractor, prepared to help NASA judge if the debris
had endangered the shuttle and its crew of seven astronauts. The first report talked of "a large piece of debris," not three. All three reports, completed while
Columbia was in orbit, reassured NASA that any damage from the debris would not threaten the flight.
Officials of the space agency initially discounted speculation that debris damage could have been responsible for the shuttle's disintegration on Feb. 1. But the
theory regained prominence this week as a panel independent of NASA has looked into possible causes of the disaster.
NASA officials said yesterday that the new Boeing report was part of a number of documents being released slowly in response to Freedom of Information Act
requests from journalists and others. NASA previously released the two other Boeing reports, dated Jan. 21 and Jan. 23, as early damage assessments.
The increase to three chunks of debris in the Jan. 24 report, officials said, grew out of an evolution in the team's analysis and understanding of the liftoff
videos.
The cameras showed that some 80 seconds after Columbia blasted off on Jan. 16, debris struck the orbiter's left wing. Small teams of NASA engineers and the
shuttle program's contractors calculated that the debris hit the wing's underside at about 500 miles an hour, smashing into fragile tiles that protected Columbia
from searing heat.
A small team of Boeing engineers in Houston was formed to evaluate the danger, using computer models to predict where the debris hit and the possible
damage to thousands of tiles meant to shield the shuttle's belly from fiery heat during re-entry to the earth's atmosphere.
The newly released report was by Carlos Ortiz, leader of the Jan. 21 analysis by five Boeing experts. It said the debris originated from the area of the fuel tank
known as the bipod, where two large struts connect the shuttle and its external tank, or E.T.
"Multiple pieces of debris were seen emanating from the E.T. bipod area and later seen impacting the orbiter lower surface," Mr. Ortiz said in the report. "Three
pieces of debris were observed."
The document, "Debris Transport Assessment of Debris Impacting Orbiter Lower Surface in STS-107 Mission," focused on just one chunk, the largest. It
gave three estimates for its size — 20 by 16 by 6 inches, 20 by 10 by 6 inches, and 20 by 10 by 2 inches.
Hinting at the continuing nature of the analysis, the report noted, "Film review continuing to better define impact area."
Yesterday, James Hartsfield, a spokesman for the Johnson Space Center in Houston, said NASA officials had earlier suggested that numerous debris pieces
might have been involved at Columbia's liftoff and defended how Boeing focused only on the largest piece.
"You have to do some limiting in your analysis," he said in an interview, and that is acceptable if "you've narrowed it down to the worst-case piece that we
thought possible."
He said it was unclear whether three pieces came off the bipod region, or one came off and broke into three pieces. Mr. Hartsfield said he had no information
on the size of the two smaller pieces. "The most important thing is the worst case," he said, "and its worst-case velocity and place to strike the orbiter."
Dr. Paul S. Fischbeck of Carnegie Mellon, a co-author of a 1990 report warning NASA of debris damage, said the Boeing analysis was a reasonable step but
too limited. "You might want to look at the possibility that all three hit in the same place," he said in an interview. "But it's not a bad first pass."
However, the three Boeing reports, taken together, he said, fall short of adequately judging the overall risks to the orbiter. "This new report does nothing to
answer this question," Dr. Fischbeck said.
In another development, NASA officials confirmed yesterday that a piece of tile from Columbia was found near Lubbock, Tex. The site is 270 miles from the
previous westernmost point for shuttle debris, near Fort Worth.
Meanwhile, NASA yesterday released more concerned e-mail messages sent by engineers at Langley Research Center in Virginia. One e-mail message sent after
the accident warned that if the large piece of debris was pure ice — a theory that had been proposed — it would weigh more than 60 pounds and because of
its speed "would be the equivalent of a 500 pound safe hitting the wing at 365 miles per hour."
NASA had previously released an e-mail message that Robert H. Daugherty, an engineer at Langley, sent on Jan. 31 warning that if the damaged area was near
the wheel well, the heating could cause the tires to explode.
In the new e-mail message, dated Jan. 28, Mr. Daugherty did not anticipate that the damage would destroy Columbia. He described the likelihood of a breach in
the wheel well as "arguably very unlikely" but expressed frustration that ground controllers were not doing more to assess possible dangers. "Getting
information is being treated like the plague," he wrote on Jan. 29.
Some mission analysts, he added, "have used words like they think things are `survivable,' but `marginal,' " apparently alluding to failures that would not
endanger the crew.
The magazine Aviation Week & Space Technology reports in its coming issue that as far back as 1988, NASA engineers worried that a gouge in the shuttle's
tiles could leave it vulnerable to a turbulent flow of gases hot enough to melt the tiles and burn through the aluminum skin beneath.
When a shuttle re-enters the atmosphere, the first tenuous wisps of air flow smoothly past the wings. As the shuttle descends, the air becomes denser, and at
some point, usually when the shuttle has slowed to about nine times the speed of sound, the smooth air flow turns turbulent, almost instantaneously.
On several Columbia flights, the smooth-to-turbulent transition occurred unusually early in its re-entry, causing hotter-than-normal heating. Columbia's wings
were known to be considerably "rougher" than those of the other shuttles.
In its Feb. 24 issue, Aviation Week reproduces a diagram that it says came from NASA's flight readiness review before a flight of Atlantis in December 1988.
The diagram marks a spot on the left wing, eerily close to where a piece of debris may have struck Columbia on liftoff.
The 1988 analysis indicated that on a rough wing, the gouged tile would heat to temperatures of 3,150 degrees Fahrenheit, 1,000 degrees hotter than normal.
The document notes that tiles experience "massive shrinkage" at temperatures of 2,900 degrees Fahrenheit, opening gaps, and melt at 3,200 degrees.
Aluminum, which the underlying wing structure is made of, melts at 1,010 degrees.
The document concluded, "Aluminum burn-through might have resulted" in such a situation.
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