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By
James Oberg
NBC
NEWS SPACE ANALYST |
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Feb. 24 —
New analysis of the garbled last 32 seconds of radio signals from the
space shuttle Columbia has raised the possibility that the crew survived
up to a minute after the spaceship began tumbling out of control and
breaking up. This reconstruction of the tragic end of the mission on
Feb. 1 contrasts sharply with most preliminary assessments that the
craft disintegrated suddenly and totally. |
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IN THIS VIEW, the shuttle lost its
struggle to keep its nose pointed ahead, and began a flat spin to the
left. The airstream, though ferocious, was not powerful enough to tear
the vehicle apart immediately. The analysis indicates that Columbia
could have turned through at least one full tumble in about 20 seconds
while the cabin remained intact and pressurized. Following the breakup
of the vehicle, the cabin fell for tens of seconds before it was crushed
by the heat and deceleration.
For now, this scenario is only an analysis based on the assembly
of still-incomplete pieces of the Columbia puzzle. The scenario has not
been confirmed by senior officials at NASA or by members of the board
investigating the Columbia tragedy. But it is shared by a growing number
of space experts, inside and outside NASA, who have discussed their
views on condition of anonymity.
The image that emerges is of the shuttle turning end over end at
least once before the fuselage breaks apart. During the tumble, large
pieces of the wings, tail and engine nozzles would have been torn off.
But the crew cabin would survive for additional tens of seconds until
crushing deceleration finally tore it apart.
DECIPHERING THE DATA
The most persuasive evidence for this scenario comes from the 32
seconds of corrupted data that followed the last readable telemetry and
voice signals from the shuttle. The signals were unreadable in real time
because of massive “data dropouts” — and thus they did not appear on
Mission Control’s flight control screens. But the bitstream was recorded
at a ground station in White Sands, N.M., and it has slowly been
yielding its secrets to mathematical analysis. |
At the point when Mission Control’s readable data
stopped, Columbia was approaching the Dallas area at an altitude of
206,000 feet and a speed of 12,500 mph. With its nose pitched up by 40
degrees, the shuttle was in a steep left bank as part of a series of
“S-turn” maneuvers, aimed at bleeding off orbital energy and slowing
down for its planned landing at the Kennedy Space Center in Florida.
Although the shuttle was going Mach 16, the air was so thin that
the effective “dynamic pressure” on its structure was the equivalent of
a sea-level wind speed of 170 mph, or a Force 5 hurricane. If a space
shuttle were sitting on the Florida runway in such a storm, major damage
would be expected — but not instantaneous disintegration.
The re-entry heating reached as high as 3,000 degrees Fahrenheit,
but this was in the shock wave of squeezed air that was piling up a few
feet in front of the vehicle. This high temperature was not caused by
friction of the air moving across the shuttle’s skin itself — behind the
“shock front,” the air moved across the skin at only a few hundred miles
per hour. This hot air conveyed the tremendous heat of the re-entry
shock wave into the shuttle’s protective tiles. If those tiles were
damaged, as investigators suspect, the heat would have entered directly
into the shuttle’s metal structure. |
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According to several sources, the deciphered data show that for
several seconds after Houston Mission Control saw a loss of signal, the
flight continued much as it had up to that point, except that additional
steering rockets in the shuttle’s tail had turned on. This was
apparently the autopilot’s attempt to counter growing drag on the left
wing, which was pulling the shuttle’s nose to the left.
The origin of that drag remains unexplained, although most
analysts agree it was almost certainly the result of damage to the wing,
perhaps caused by debris that broke off the shuttle’s external fuel tank
shortly after liftoff 16 days earlier.
SILENCE, THEN A FINAL
BURST
After a few seconds of garbled data, the communication pathway —
leading from the shuttle to a satellite in space and then down to the
White Sands ground station — apparently went totally dead for about 20
seconds. Not even a garbled carrier signal came through.
But then, a burst of three or four seconds of corrupted data was
received, followed by unbroken silence.
Some space engineers have interpreted this sequence as evidence
that the shuttle, succumbing to the growing leftward torque, had turned
away from pointing its antenna toward the relay satellite. The later
burst of data could have resulted from the antenna momentarily turning
again to face the satellite. The engineers surmised that a computer
program designed to select different antennas could not cope with the
fast turning. |
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Data from those final few seconds show a
spaceship that was mortally wounded, but still working. Power was still
being generated by the fuel cells under the payload bay, and signals
were being received all the way from the back end of the craft.
Although the crew cabin was still pressurized and the four
primary control computers were still functioning, other systems were in
terminal distress. The three redundant hydraulic pressure generators —
needed to control the shuttle’s aerosurfaces — were still functioning.
But hydraulic pressure on the left side of the shuttle was zero in all
three lines. The thruster system in the tail was reporting massive
leakage of propellant.
These failures would have filled the cabin with the noise of
alarms. Indicator lights would have been ablaze. The crew on the flight
deck would have responded to these alarms in accordance with their
training, if they were able. Those seated on the middeck would have
prepared for emergency bailout once they got low enough in the
atmosphere.
Based on the still-fragmentary readings, some engineers believe
the shuttle was in a flat left spin. Others have suggested that the left
wing was totally torn off, or was bent up against the side, causing the
vehicle to roll left. In either scenario, the vehicle would have turned
its back end into the wind. Parts of the tail (including, apparently,
the drag chute package) would have torn off first, along with the
bell-shaped rocket nozzles for the main engines and the orbital
maneuvering engines. Damage there would explain the propellant leak
alarms, which would have been followed by fiery detonation of the mixing
chemicals. |
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Interpretation of the videotapes of the disintegration over
Dallas remains unclear. Some smaller pieces are seen coming off a main
body, followed by flashes of light that could indicate the detonation of
propellant in the leaking tanks. A much larger scatter of large and
small objects then can be seen. Heavier objects — three in particular,
possibly the main engine blocks — forge ahead. Lighter tumbling objects,
likely wing segments, slow and fall more quickly.
THE CREW’S FATE
The path of the crew cabin can only be guessed, once it tore
loose from the rest of the fuselage and electrical power ceased.
Buffeted and braked by air drag, it would have been heated by the
surrounding shock-induced plasma. Falling deeper into the atmosphere,
G-forces would have built up to the point that the heat-weakened
aluminum frame collapsed in on itself. Some pieces broke loose and were
carried away by the aerodynamic forces.
A more precise analysis depends on the scatter of impact points
of the cabin and its contents — information that is still being analyzed
by the accident team.
This analysis follows in the footseteps of the investigation into
the 1986 Challenger tragedy. In Challenger’s case, the initial
impressions were that the crew had perished instantly when the shuttle
came apart, a minute after its launch from Kennedy Space Center. Only
months later did it become clear that the crew cabin had separated
cleanly and had risen to an altitude of 65,000 feet before falling back
to impact the ocean with a force of 200 G’s.
Equipment recovered from the wreck showed that at least some of
the crew had survived the initial breakup and had activated their safety
equipment. Medical specialists later concluded that they soon lost
consciousness but were not killed until the impact with the ocean, two
minutes after the explosion.
Columbia’s crew had better survival gear, including pressure
suits and personal parachutes. Assuming they were conscious of the
emergency, they would have closed their visors when cabin pressure was
lost. Their suits would have automatically pressurized. It would then be
only a question of hoping that the cabin held together until it fell low
enough — below 40,000 feet or so — for them to blow the escape hatch and
jump free. This would not have seemed an entirely hopeless situation,
until the cabin’s own structure began to fail.
No one can know what Columbia’s seven astronauts were actually
experiencing and doing in the final seconds of their flight, but the
engineers who discussed the possible scenarios were deeply shaken by the
implications. The overwhelming consensus is that the lack of knowledge
is probably the merciful way it should be.
James Oberg, space analyst for NBC News, spent 22 years at the
Johnson Space Center as a Mission Control operator and an orbital
designer.
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Shuttle probe poses orbital puzzle |
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Investigators say
mysterious object,
wing damage may point
to problems in orbit |
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Feb. 25 — A close-up view of a shuttle tile recovered west
of Fort Worth, Texas, shows an unusual burn pattern on the
tile's underside. Click on the video button for an update on
the Columbia investigation from NBC News' Robert Hager. |
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MSNBC STAFF AND WIRE REPORTS |
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Feb. 25 — Investigators
combing through debris from the shuttle Columbia have
discovered what is believed to be a penetration of
Columbia’s left wing from the top, NBC News reported
Tuesday. This could suggest that a piece of the shuttle came
off during orbital flight, setting the stage for its doom.
Also Tuesday, NASA confirmed that it had recovered cockpit
videotape taken by the shuttle astronauts, but said it ended
several minutes before the accident. |
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THE VIDEO
starts at about 8:35 a.m. ET Feb. 1, about nine minutes before
the shuttle began entering the upper layers of Earth’s
atmosphere, and continues for four minutes after the start of
re-entry. Four of the Columbia astronauts can be seen performing
routine activities, NASA said.
The tape ends at about 8:48 a.m., roughly 12 minutes
before the breakup, while the shuttle was still over the Pacific
and flying normally. The rest of the tape was burned, and
investigators told NBC News that the surviving footage provided
no new leads.
The tape was recovered several days ago, but its release
was delayed to give NASA time to show it to the families of the
astronauts. NASA was expected to release the video to the public
later this week.
Columbia disintegrated Feb. 1 over Texas during re-entry
at the end of a 16-day science mission, killing all seven
astronauts aboard. The remaining three space shuttles have been
grounded until an investigation into the tragedy is completed.
Much of the speculation about the cause of the breakup
has centered on damage that might have been done to
heat-shielding tiles on the bottom of the left wing just after
Columbia’s Jan. 16 liftoff, by chunks of foam insulation flying
off from the shuttle’s external fuel tank. According to the
foam-damage theory, the impact might have opened enough of a
breach in the shuttle’s underside to let in the hot gases built
up during the shuttle’s descent.
However, reports from investigators on Tuesday pointed in
a different direction, to events that may have occurred the day
after launch.
MYSTERY OBJECT
Military radar-tracking data indicate that on Jan. 17, a
1-foot square (30-by-40-centimeter) object separated from the
shuttle, trailed it in orbit for a couple of days, then
re-entered Earth’s atmosphere and burned up on Jan. 20. The
mystery object was not noticed until the data were reviewed in
the wake of the Columbia breakup.
Initially,
NASA said it suspected the object might be frozen wastewater
dumped overboard or an orbiting piece of space junk that the
shuttle happened to encounter. But on Tuesday, Air Force Brig.
Gen. Duane Deal, a member of the board investigating the
Columbia accident, discounted both possibilities and said the
object almost had to have been a piece of the shuttle itself.
“It was something that more than likely came loose,” Deal
said. He said the composition of the object was unknown, but it
was lightweight and not dense.
Columbia had just gone through a major maneuver in orbit,
about 24 hours into its flight, when the object popped out of
nowhere, Deal said. That suggests it could have broken loose
from the shuttle during the maneuver.
“You or I could invent a dozen scenarios,” Deal said. “It
could have been something loose that separated, it could have
been something inside the payload bay.”
It also could have been part of the left wing, where all
of the overheating and other troubles developed during re-entry.
Wing Damage
That
would mesh with reports from engineers at Kennedy Space Center,
where recovered fragments of the shuttle are being reassembled
for analysis. NBC News’ Jay Barbree quoted engineers as saying
the wreckage indicated that there was a hole in the top of the
left wing, near the fuselage and above the area of the wing’s
wheel well.
“Now if, as they believe, this occurred in orbit,
Columbia could have been hit by something coming off the shuttle
or even space junk,” Barbree reported.
NASA officials and investigators cautioned, however, that
there was not yet a leading theory on what caused Columbia’s
breakup, and that it could take months to come to a conclusion.
The investigative board’s chairman, retired Navy Adm. Harold
Gehman, indicated that he was not familiar with the condition of
wing debris at Kennedy Space Center.
Conceivably, the damage to the top surface of the wing
could have been done during the breakup, or even as the debris
was falling to earth.
WESTERNMOST PIECES
OF TILE
During Tuesday’s news briefing, Gehman showed pictures of
a tile that was recovered west of Fort Worth, Texas, one of the
westernmost pieces of confirmed Columbia debris. He said the
tile showed signs of heat damage on its underside, as well as an
unusual pattern of burn damage on its top side, with flecks of
orange material visible. “I am told that this is not typical of
a re-entry tile,” he said. “This is very unusual.”
Gehman said another tile fragment, found 300 miles (500
kilometers) west of Fort Worth, is thought to have come from
from the upper surface of the left wing near the fuselage — the
same area noted by the engineers in Florida.
Since the shuttle was flying from west to east when it
broke up, the westernmost pieces of debris could hint at the
location of the heat-shield breach that investigators believe
led to Columbia’s destruction. The tile fragment from the top of
the left wing could have been one of the earliest pieces shed
during the breakup.
Search teams have been looking for fragments from the
shuttle even farther west, in the Nevada desert, but so far
there has been no confirmation that any of the bits turned in
for analysis actually came from the shuttle.
COMPUTER ANALYSIS
Board member Scott Hubbard, director of NASA’s Ames
Research Center, said computer analyses show that a hole of 20
square inches (129 square centimeters) would account for the
rapid temperature rise of 60 degrees Fahrenheit (33 degrees
Celsius) detected in Columbia’s left landing gear compartment
during the final few minutes of flight.
What needs to be done next is a more sophisticated and
complex analysis in which the hole is moved to various wing
locations, he said.
Among the early tentative findings:
The tires in the left landing gear compartment likely did
not explode, though there was some disturbance going on in that
area.
The ship’s hydraulic systems failed in the final seconds
of the doomed flight and the hydraulic fluid dumped out
somewhere.
Even though the power and guidance systems were still
working up until the total loss of data and the fuselage was
still intact, there were no signals from the left wing.
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Procedures
for shuttle bailout |
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This excerpt from the Shuttle Crew Operations Manual, a
4-inch-thick "user's manual" published by Johnson Space Center's
Flight Crew Operations Directorate, describes how shuttle crew
members can use their emergency equipment to bail out of a
tumbling shuttle crew module:
Although no formal requirements or plans exist for
crewmembers to bail out of the orbiter during uncontrolled
flight, they may be able to do so under certain circumstances.
The hatch jettison pyrotechnics do not require orbiter power to
function and can be activated even if orbiter power is lost.
Each crewmember is wearing his or her own emergency oxygen
bottles and parachute, and if the crew cabin were not spinning
rapidly, at least some of the crewmembers should be able to get
to the side hatch and get out.
In the case involving loss of orbiter control, the
crewmembers should activate their emergency oxygen as soon as
possible and then evaluate the situation. The crew should remain
within [the crew module] until it passes through 40,000 feet....
If the cabin is depressurized, the partial pressure bladders in
the Launch/Entry Suit will be inflated above 35,000 to 38,000
feet, so the crewmembers can judge altitude in that way.
Once out of the orbiter, crewmembers should pull their
parachute D-rings to activate the automatic opening sequence for
their parachutes. ... The 18-inch pilot chute is deployed 1.5
seconds later and immediately deploys the 4.5-foot drogue chute.
The drogue chute stabilizes the crewmember down to an altitude
of 14,000 feet, then deploys the main canopy. |
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