Analysis hints at shuttle’s last seconds
Image: Flight Director Leroy Cain Seen On February 1
Entry flight director Leroy Cain holds his hand over his face as workers in Mission Control wait for a signal from the Columbia crew minutes before the scheduled landing in this image from Feb. 1.


Feb. 11 - NBC News' Robert Hager reports on the final minutes of Columbia's flight.

By James Oberg
  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.
   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.
       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.

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       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.

       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.
       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.



       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.

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 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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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.

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.
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.
       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.

       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.

       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.

  Procedures for shuttle bailout
      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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