No Answer Yet as to Why Shuttle Crashed

It has been eight days since the space shuttle Columbia disintegrated as it reentered Earth’s atmosphere. All seven astronauts aboard -- six Americans and one Israeli, five men and two women -- were killed.

Reminiscent of the Challenger explosion 17 years earlier, the loss of Columbia was a very public event. Scores of amateurs captured video of a single contrail splitting into multiple white streaks as pieces separated from the orbiter.

NASA’s quick -- and apparently candid -- release of information had slowed by week’s end. There is as yet no answer as to why the Columbia was lost.

Q: Where are officials focusing?

A: So far, three sets of clues have emerged -- all having to do with the shuttle’s wing. At 82 seconds into the flight, a chunk of foam insulation from the external liquid fuel tank broke off and hit the bottom of the left wing. NASA launch cameras captured a spray of debris from the incident, but video from the camera with the best view was out of focus and useless. Sixteen days later, in the last eight minutes of the flight, sensors at various points on the left wing recorded mild but unusual temperature increases -- or they failed altogether. Initially, Ron Dittemore, NASA’s shuttle program manager, said the insulation impact was the focus of the investigation, even though engineers already had examined it during Columbia’s flight and concluded that it could not have caused damage severe enough to destroy the spacecraft. Dittemore later said the episode was only one of many possible causes to be investigated. Then Friday, NASA announced that a piece of the leading edge of a shuttle wing had been found, possible providing a break in the investigation.

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Q: How is the disaster being investigated?

A: Within hours after the loss, NASA Administrator Sean O’Keefe appointed an eight-member panel to be headed by retired Navy Adm. Harold W. Gehman Jr. (Gehman previously led the investigation of the terrorist suicide bombing of the destroyer Cole in Yemen.) The board will use NASA personnel as its investigators, hold hearings, take testimony, determine the facts of the accident and make recommendations. In 1986, President Ronald Reagan appointed the commission that investigated the Challenger explosion. Beginning this week, the board will take over news briefings on the investigation’s status from NASA.

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Q: Dittemore talked of a “fault-tree” analysis. What is that?

A: Starting with the loss of Columbia as the event, a fault-tree analysis forces an examination of every aspect of the shuttle and its flight. A determination is made for each of the “branches” as to whether it could cause or contribute to the outcome. One way to think about it is that the most useful outcome would be a depiction of a tree that looked like a dead snag. The more limbs that remain on the tree when the investigation concludes, the more ambiguous the findings will be and the more difficult it will be to fix the problem.

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Q: Why isn’t the NTSB heading the investigation?

A: The National Transportation Safety Board has a reputation for solving mysteries of airplane crashes against all odds, even when the debris is on the ocean floor. But its role is to investigate accidents in public transportation systems, not crashes of military aircraft, which includes the shuttle. However, NASA has asked for assistance, and the NTSB is providing it.

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Q: The amateur videos seen on television show the shuttle disintegrating. Why doesn’t NASA see that in its data?

A: NASA lost communication with the shuttle at 7:59:22 a.m., about 16 minutes before it was to land. Up to that point, Columbia was intact and in controlled flight. Some problems were beginning to show, however: Signals from some sensors on the left wing were disappearing, including those registering tire pressure for the left main landing gear. Some sensors showed modest but unusual temperature increases. The computer-driven flight-control system was successfully correcting for an increased tendency to roll and turn to the left. There may be 32 seconds of additional, “fuzzy” data available after the last communication, if NASA engineers can extract it from their computers. Shuttles communicate with the ground through a system of multiple radio transmitters using several different frequency bands. Those signals are routed to a computer for processing into monitor displays and voices on speakers. The computer also checks whether the data is clean or full of errors. When there are too many errors for the computer to reliably interpret the signals, it stops forwarding the information to Mission Control but continues to store what it is receiving. The job for the engineers is to figure which information in those 32 seconds was received accurately and which is erroneous.

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Q: Will we ever know exactly what those amateur videos depict?

A: Eventually, NASA may be able to explain details of what the best quality videos show. None of the videos is time-synchronized with the data the shuttle was sending to NASA. Efforts to identify the exact space coordinates where visual events appear will be difficult because, as far as is publicly known, the location, angle, azimuth and times for each video are approximate at best. The shuttle disintegration depicted in the videos apparently occurred after NASA lost radio signals from the shuttle.

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Q: Where did the debris fall?

A: So far, it is known to have fallen only in Texas and Louisiana, in a swath southeasterly from the Dallas-Fort Worth area. Late last week, after a piece of one wing was found near Fort Worth, NASA officials ordered that the search be expanded 150 miles west of there. Examination of suspected debris in California, Arizona, Nevada and New Mexico was in its early stages, but so far none has proved to be from Columbia.

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Q: Two words used a lot last week were “plasma” and “drag”. What are they?

A: Plasma is what glows red as the shuttle reenters the atmosphere. It is the fourth state of matter. When energy (heat) is applied to a solid it becomes liquid. Add more energy and the liquid becomes a gas. Add more energy, in this case from the friction of the shuttle’s high speed as it plunges into the atmosphere, and the gas becomes plasma. On Earth, plasma is created for use in a number of industrial processes. And an ultra-thin layer of plasma created electrically between two glass panels is what enables the new generation of flat-panel television screens to entertain us.

Drag is an aerodynamic function of how smoothly air flows over a wing. The smoother the flow, the less thrust is required to move the wing forward. Drag increases as airflow becomes more disturbed. More thrust is then required to move forward at the same speed. Many factors can increase the drag of a wing. But in Columbia’s case, the suspected cause is damage to some insulating ceramic tiles under the wing or a structural failure.

When the wing on one side of an aircraft develops more drag than the wing on the other side, the aircraft rolls toward and turns in the direction of the wing with more drag, unless control surfaces are repositioned to compensate. If the drag imbalance is great enough, it cannot be compensated and the aircraft can no longer be controlled.

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Q: Could the astronauts have saved themselves or been saved by NASA?

A: No.

They didn’t carry any means of repairing tiles under the wing, if that was the problem, nor did they have any ability to do a space walk under the wing to find out. Since this was a science mission, the orbit was much lower than that of the international space station, and Columbia could not have reached it. The shuttle also lacked the equipment to dock with the station.

Sending another shuttle to the rescue also wouldn’t have helped. Shuttles can carry only seven people, and it takes two pilots to operate one. So a rescue orbiter could not have returned with all the astronauts on board. The only escape from Columbia was by parachute, which was possible only at low altitude in a controlled glide.

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Q: What about the crew aboard the international space station?

A: The two Americans and one Russian have supplies enough to remain there into June.

Then they can fly home in a Russian Soyuz module kept permanently docked at the station for emergencies.

The longer-term question is whether the space station can be completed with only the three remaining shuttles. NASA officials say it can and point out that most of the components were scheduled to be hauled into space on the other shuttles anyway. That assumes that the cause of Columbia’s loss is found and the remaining shuttles can be fixed to prevent recurrence.