#NY Times: Six things that could have destroyed Columbia
The Axis of Weasel
By WILLIAM J. BROAD
http://www.nytimes.com/2003/02/02/national/02WRON.html
It could be days, weeks or even months before NASA has a clear idea of
what went wrong, if ever.
"There's a strong possibility they may never know," said John Tylko, a
space shuttle expert at the Massachusetts Institute of Technology.
"There are no on- board flight recorders that are recoverable."
Recorders are usually recovered in commercial airplane crashes.
Nor were scores of cameras recording Columbia's every move, as was the
case 17 years ago when the Challenger exploded.
Even so, experts listed six possible causes of the disaster, in order
of decreasing likelihood:
¶Problems with the shuttle's tile heat shield, which was apparently
damaged slightly at blastoff.
¶An explosion of some of the shuttle's fuels and oxidizers, which are
under high pressure.
¶The collapse of some part of the shuttle's structure, which is aged.
¶Faulty navigation for the fiery re-entry, possibly caused by a
computer problem.
¶The impact of a speeding rock or space debris.
¶Terrorism, perhaps by a technician at the launching site.
Eugene E. Covert, an aerospace expert who helped investigate the
Challenger disaster for the government, said it would be foolish to
speculate.
"Speculating at this point gives you a big opportunity to be wrong,"
Mr. Covert said. "It's better to wait and be right."
He said, however, that the forensic problem might be so hard that
engineers might never learn what went wrong. "It's a distinct
possibility."
NASA has a trove of data that it will carefully sift for clues in the
days and weeks ahead. In a way, Mr. Covert said, the flight data
recorded on NASA computers is "the biggest black box in the world."
But sorting through it could be an immense task. The final report on
what destroyed the Challenger, which exploded in flames minutes after
launching on Jan. 28, 1986, was issued nearly five months after the
disaster.
Even today, experts still debate details of how a leaky booster rocket
turned the Challenger into a ball of flame. With Columbia, a problem
for aerospace sleuths will be a lack of imagery in its last minutes.
Challenger blew up in sight of the Florida launching pad, where
long-range cameras recorded many details of its fiery demise.
By contrast, Columbia experienced its problem high in the atmosphere,
where no known cameras were tracking its descent.
Though he acknowledges photographs can be misleading, Dr. Covert said
the lack of photographs could be a severe problem.
Yesterday, the images of the Columbia descending that were played
repeatedly on national television were taken only after it became
clear that the shuttle was in trouble. They showed it breaking into
pieces.
NASA officials discounted reports that the Columbia was on an unusual
course during its descent for security reasons related to the presence
of an Israeli astronaut on board.
"There was nothing unusual about this trajectory at all," said Rob
Navias, a NASA spokesman at the Johnson Space Center in Houston.
One of the likeliest causes of the Columbia disaster is considered to
be faulty tiles, which cover the shuttle's lower side and repulse
intense heats during re- entry.
On Jan. 16, shortly after Columbia lifted off, a piece of insulating
foam on its external fuel tank came off and was believed to have hit
the left wing of the shuttle.
Leroy Cain, the lead flight director in mission control, assured
reporters on Friday that engineers had concluded that any damage to
the wing and tiles was minor and posed no safety hazard.
"We took a very thorough look at the situation with the tile on the
left wing, and we have no concerns, whatsoever," Mr. Cain said.
"Therefore, we haven't changed anything with respect to our trajectory
design."
Experts say a burn-through of a loose tile or protective surface could
trigger catastrophic failure in the fiery heat of re-entry. One way to
reduce that risk is to modify the shuttle's flight path.
In past shuttle missions, NASA has used long-range cameras on the
ground — and perhaps had spy agencies use cameras in space — to
examine the winged spaceships for signs of damage. NASA has not said
whether such precautions were taken on this mission.
Experts also said Columbia was not carrying one of NASA's robot arm in
its 60-foot payload bay. In the past, instruments on the payload arm
have been used to look for damage to tiles.
Another possibility is a chemical explosion, experts say. The shuttles
are loaded with tanks carrying hydrogen, oxygen and exotic fuels to
power its many engines. Just before descent, the shuttle starts three
extra power units, which run on hydrazine, a highly volatile fuel.
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