taken from a ground-based Air Force tracking camera in the southwestern
U.S. show serious structural damage to the inboard leading edge of
Columbia's left wing, as the crippled orbiter flew overhead about 60
sec. before the vehicle broke up over Texas killing the seven astronauts
on board Feb. 1.
According to sources close to the investigation, the
images, under analysis at the Johnson Space Center in Houston, show a
jagged edge on the left inboard wing structure near where the wing
begins to intersect the fuselage. They also show the orbiter's right aft
yaw thrusters firing, trying to correct the vehicle's attitude that was
being adversely affected by the left wing damage. Columbia's fuselage
and right wing appear normal. Unlike the damaged and jagged left wing
section, the right wing appears smooth along its entire length. The
imagery is consistent with telemetry.
The ragged edge on the left leading edge, indicates
that either a small structural breach--such as a crack--occurred,
allowing the 2,500F reentry heating to erode additional structure there,
or that a small portion of the leading edge fell off at that location.
Either way, the damage affected the vehicle's flying
qualities as well as allowed hot gases to flow into critical wing
structure--a fatal combination.
It is possible, but yet not confirmed, that the
impact of foam debris from the shuttle's external tank during launch
could have played a role in damage to the wing leading edge, where the
deformity appears in USAF imagery.
If that is confirmed by the independent investigation
team, it would mean that, contrary to initial shuttle program analysis,
the tank debris event at launch played a key role in the root cause of
Another key factor is that the
leading edge of the shuttle wing, where the
jagged shape was photographed, transitions from black thermal protection
tiles to a much different mechanical system made of reinforced
carbon-carbon material that is bolted on, rather than glued on as the
This means that in addition to the possible failure
of black tile at the point where the wing joins the fuselage, a failure
involving the attachment mechanisms for the leading edge sections could
also be a factor, either related or not to the debris impact. The actual
front structure of a shuttle wing is flat. To provide aerodynamic shape
and heat protection, each wing is fitted with 22 U-shaped reinforced
carbon-carbon (RCC) leading-edge structures. The carbon material in the
leading edge, as well as the orbiter nose cap, is designed to protect
the shuttle from temperatures above 2,300F during reentry. Any breach of
this leading-edge material would have catastrophic consequences.
The U-shaped RCC sections are attached to the wing "with
a series of floating joints to reduce loading on the panels due to wing
deflections," according to Boeing data on the attachment mechanism.
"The [critical heat protection] seal between each
wing leading-edge panel is referred to as a 'tee' seal," according to
Boeing, and is also made of a carbon material.
The tee seals allow lateral motion and thermal
expansion differences between the carbon sections and sections of the
orbiter wing that remain much cooler during reentry.
In addition to debris impact issues, investigators
will likely examine whether any structural bending between the cooler
wing structure and the more-than-2,000F leading edge sections could have
played a role in the accident. There is insulation packed between the
cooler wing structure and the bowl-shaped cavity formed by the carbon
The RCC leading-edge structures are bolted to the
wing using Inconel fittings that attach to aluminum flanges on the front
of the wing.
The initial NASA Mission Management Team (MMT)
assessment of the debris impact--made on Jan. 18, two days after
launch--noted "The strike appears to have occurred on or relatively
close to the "wing glove" near the orbiter fuselage.
The term "wing glove" generally refers to the area
where the RCC bolt-on material is closest to the fuselage. This is also
the general area where USAF imagery shows structural damage.
The second MMT summary analyzing the debris hit was
made on Jan. 20 and had no mention of the leading-edge wing glove area.
That report was more focused on orbiter black tiles on the vehicle's
belly. The third and final summary issued on Jan. 27 discusses the black
tiles again, but also specifically says "Damage to the RCC [wing leading
edge] should be limited to [its] coating only and have no mission impact."
Investigators in Houston are trying to match the location of the debris
impact with the jagged edge shown in the Air Force imagery.
Columbia reentry accident investigators are also
trying to determine if, as in the case of Challenger's accident 17 years
ago, an undesirable materials characteristic noted on previous
flights--in this case the STS-112 separation of external tank insulation
foam debris--was misjudged by engineers as to its potential for harm,
possibly by using analytical tools and information inadequate to truly
identify and quantify the threat to the shuttle. As of late last week,
NASA strongly asserted this was not the case, but intense analysis on
that possibility continues.
The shuttle is now grounded indefinitely and the
impact on major crew resupply and assembly flights to the International
Space Station remains under intense review.
Killed in the accident were STS-107 mission commander
USAF Col. Rick Husband; copilot Navy Cdr. William McCool; flight
engineer Kalpana Chawla; payload commander USAF Lt. Col. Michael
Anderson; mission specialist physician astronauts Navy Capt. Laurel
Clark and Navy Capt. David Brown; and Israel Air Force Col. Ilan Ramon.
"We continue to recover crew remains and we are
handling that process with the utmost care, the utmost respect and
dignity," said Ronald Dittemore, shuttle program manager.
No matter what the investigations show, there are no
apparent credible crew survival options for the failure Columbia
experienced. With the ISS out of reach in a far different orbit, there
were no credible rescue options even if wing damage had been apparent
before reentry--which it was not.
If, in the midst of its 16-day flight, wing damage
had been found to be dire, the only potential--but still
unlikely--option would have been the formulation over several days by
Mission Control of a profile that could have, perhaps, reduced heating
on the damaged wing at the expense of the other wing for an unguided
reentry, with scant hope the vehicle would remain controllable to about
40,000 ft., allowing for crew bailout over an ocean.
Reentry is a starkly unforgiving environment where
three out of the four fatal manned space flight accidents during the
last 35 years have occurred.
These include the Soyuz 1 reentry accident that
killed cosmonaut Vladimir Komarov in 1967 and the 1971 Soyuz 11 reentry
accident that killed three cosmonauts returning after the first
long-duration stay on the Salyut 1 space station.
The only fatal launch accident has been Challenger in
1986, although Apollo astronauts Gus Grissom, Ed White and Roger Chaffee
were killed when fire developed in their spacecraft during a launch pad
test not involving launch.
No other accident in aviation history has been seen
by so many eyewitnesses than the loss of Columbia--visible in five
Telemetry and photographic analysis indicate the
breakup of the historic orbiter took place as she slowed from Mach
20-to-18 across California, Nevada, Arizona and New Mexico with the loss
of structural integrity 205,000 ft. over north-central Texas where most
of the debris fell.
The science-driven STS-107 crew was completing 16
days of complex work in their Spacehab Research Double module and were
16 min. from landing at Kennedy when lost. Landing was scheduled for
8:16 a.m. CST.
Abnormal telemetry events in the reentry began at
7:52 a.m. CST as the vehicle was crossing the coast north of San
Francisco at 43 mi. alt., about Mach 20.
The orbiter at this time was in a 43-deg. right bank
completing its initial bank maneuver to the south for initial energy
dissipation and ranging toward the Kennedy runway still nearly 3,000 mi.
That initial bank had been as steep as about 80 deg.
between Hawaii and the California coast, a normal flight path angle for
the early part of the reentry. The abnormal events seen on orbiter
telemetry in Houston indicate a slow penetration of reentry heat into
the orbiter and damage on the wing, overpowering the flight control
system. Key events were:
* 7:52 a.m. CST: Three left main landing gear
brakeline temperatures show an unusual rise. "This was the first
occurrence of a significant thermal event in the left wheel well,"
Dittemore said. Engineers do not believe the left wheel well was
breached, but rather that hot gases were somehow finding a flow path
within the wing to reach the wheel well.
* 7:53 a.m. CST: A fourth left brakeline strut
temperature measurement rose significantly--about 30-40 deg. in 5 min.
* 7:54 a.m. CST: With the orbiter over eastern
California and western Nevada, the mid-fuselage mold line where the left
wing meets the fuselage showed an unusual temperature rise. The 60F rise
over 5 min. was not dramatic, but showed that something was heating the
wing fuselage interface area at this time. Wing leading edge and belly
temperatures were over 2,000F. While the outside fuselage wall was
heating, the inside wall remained cool as normal.
* 7:55 a.m. CST: A fifth left main gear temperature
sensor showed an unusual rise.
* 7:57 a.m. CST: As Columbia was passing over Arizona
and New Mexico, the orbiter's upper and lower left wing temperature
sensors failed, probably indicating their lines had been cut. The
orbiter was also rolling back to the left into about a 75-deg. left bank
angle, again to dissipate energy and for navigation and guidance toward
Runway 33 at Kennedy, then about 1,800 mi. away.
* 7:58 a.m. CST: Still over New Mexico, the elevons
began to move to adjust orbiter roll axis trim, indicating an increase
in drag on the left side of the vehicle. That could be indicative of "rough
tile or missing tile but we are not sure," Dittemore said. At the same
time, the elevons were reacting to increased drag on the left side of
the vehicle, the left main landing gear tire pressures and wheel
temperature measurements failed. This was indicative of a loss of the
sensor, not the explosion or failure of the left main gear tires,
Dittemore believes. The sensors were lost in a staggered fashion.
* 7:59 a.m. CST: Additional elevon motion is
commanded by the flight control system to counteract left side drag. The
drag was trying to roll the vehicle to the left, while the flight
control system was commanding the elevons to roll it back to the right.
But the rate of left roll was beginning to overpower
the elevons, so the control system fired two 870-lb.-thrust right yaw
thrusters to help maintain the proper flight path angle. The firing
lasted 1.5 sec. and, along with the tire pressure data and elevon data,
would have been noted by the pilots.
At about this time, the pilots made a short
transmission that was clipped and essentially unintelligible.
In Mission Control, astronaut Marine Lt. Col. Charles
Hobaugh, the spacecraft communicator on reentry flight director Leroy
Cain's team, radioed "Columbia, we see your tire pressure [telemetry]
messages and we did not copy your last transmission."
One of the pilots then radioed "Roger," but appeared
to be cut off in mid-transmission by static. For a moment there were
additional static and sounds similar to an open microphone on Columbia
but no transmissions from the crew.
All data from the orbiter then stopped and the
position plot display in Mission Control froze over Texas, although an
additional 30 sec. of poor data may have been captured.
Controllers in Mission Control thought they were
experiencing an unusual but non-critical data drop-out. But they had
also taken notice of the unusual buildup of sensor telemetry in the
preceding few minutes.
About 3 min. after all data flow stopped, Hobaugh in
Mission Control began transmitting in the blind to Columbia on the UHF
backup radio system. "Columbia, Houston, UHF comm. check" he repeated
every 15-30 sec., but to no avail. In central Texas, thousands of people
at that moment were observing the orbiter break up at Mach 18.3 and
Milt Heflin, chief of the flight director's office,
said he looked at the frozen data plots. "I and others stared at that
for a long time because the tracking ended over Texas. It just stopped.
It was then that I reflected back on what I saw [in Mission Control]
The loss of Challenger occurred 17 years and four
days before the loss of Columbia.
"Our landscape has changed," Heflin said. "The space
flight business today is going to be much different than yesterday.
"It was different after the Apollo fire, it was
different after Challenger."
Columbia, the first winged reusable manned spacecraft
first launched in April 1981, was lost on her 28th mission on the 113th