ALMOST two weeks after the space shuttle Columbia broke up on re-entry, the investigation into what caused the tragedy is gathering momentum. An independent panel has taken over the inquiry to determine why seven astronauts lost their lives, and NASA is making an extraordinary effort to keep the public up to date. But despite this diligence, the likelihood of reaching a definitive answer any time soon seems remote.
More and more evidence continues to surface, including potentially crucial pieces of the shuttle itself, such as a 60centimetre section of the left wing鈥檚 leading edge and a wheel-well door, and images of the shuttle鈥檚 descent captured by an amateur astronomer and an advanced air force telescope. Military radar images even tracked what appears to be an object separating from the shuttle on its second day in orbit.
In a bid to streamline the daunting task, the panel鈥檚 nine members have split into three teams, departing Wednesday this week to the Michoud assembly plant in Louisiana where the shuttle鈥檚 huge external tanks are built, the Marshall Space Flight Center in Alabama where the main engines are tested, and to the Kennedy Space Center where orbiters are refurbished between missions. It was at Kennedy that a piece of falling insulation was seen striking the shuttle during lift-off on 16 January.
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Yet the number of possible explanations for the devastating accident seemed to be multiplying almost as fast as the evidence itself. NASA administrator Sean O鈥橩eefe continues to emphasise that no cause is being ruled out. But as 快猫短视频 went to press, nothing even close to a 鈥渟moking gun鈥� had emerged to explain the Columbia disaster. No one theory stands out, while some evidence only adds to the confusion by raising whole new scenarios.
Unlike the first weeks after Challenger exploded in 1986, this time NASA officials are bending over backwards to be open about every twist and turn of the investigation. Shuttle programme manager Ron Dittemore, who has earned universal praise for his candour, said as much to journalists: 鈥淎s we wade through these choppy waters of trying to gather all the relevant information, you have witnessed an inside view of our ups and downs as we have tried to steer a course throughout the week.鈥�
And yet, an explanation now seems even farther away than it appeared during the first few days. Four leading theories for Columbia鈥檚 demise have emerged from the wealth of new evidence and conjecture.
Radar at Eglin Air Force Base in Florida detected an object at least as large as a grapefruit moving away from the shuttle on the second day of its 16-day mission. Harold Gehman, head of the shuttle accident investigation board, says his team is looking for evidence that this object may have been a block of ice that formed on the shuttle鈥檚 waste-water vent tube, from which urine and excess water produced by the shuttle鈥檚 power units are periodically jettisoned into space.
The water is supposed to emerge as a fine mist, but at least once before it has formed a basketball-sized chunk of ice. That time, astronauts used the shuttle鈥檚 robotic armto knock it loose, but on Columbia鈥檚 ill-fated mission the arm had been left behind to make room for extra science payloads. On the earlier mission, NASA officials said they feared that if ice had remained in place during re-entry, it could have broken away when the retrorockets fired and damaged the wing 鈥� precisely what may have happened this time.
A second line of enquiry stems from photographs of the shuttle as it began its descent, taken by an amateur astronomer in California. One of these images, showing a mysterious purplish streak extending upwards from the shuttle, has now been turned over to the investigators. It has yet to be made public, but astronaut Tammy Jernigan has examined the photo and says it is credible evidence.
Some have suggested that the streak might be an instance of the upper-atmosphere electrical discharges known as sprites, elves or blue jets, which might have damaged the shuttle during re-entry. Ironically, a study of these phenomena had been one of the scientific projects carried out, with great success, by Columbia鈥檚 astronauts (快猫短视频, 1 February, p 10).
Investigators are also not ruling out the possibility that a chunk of space debris struck the shuttle鈥檚 wing at some time during the mission, although there is no evidence that this is what happened. Indeed, it could be impossible to ever know for sure. But studies indicate that of all the things that could go wrong during a shuttle mission, this is the one most likely to cause a catastrophic failure (see 鈥溾�楤lowtorch鈥� risk to shuttle鈥�). This scenario is also consistent with the Florida radar evidence, as it has not been determined yet whether the object it detected came from the shuttle or had been on a collision path with it.
A photograph taken by a powerful telescope at Kirtland Air Force Base in New Mexico, less than two minutes before contact was lost with Columbia, shows a jagged line on the leading edge of the shuttle鈥檚 left wing 鈥� the area where evidence of heat and aerodynamic drag was already showing up in telemetry data. This may add weight to the theory that a falling piece of foam insulation during lift-off damaged that part of the wing.
Engineers analysed the impact early on in the mission, and concluded it posed no danger. But The New York Times reported on 10 February that one engineer involved has said there is no data to support this conclusion, as comparative tests on the leading edge of the shuttle have never been done.
Despite Dittemore鈥檚 repeated assertions that such a light object could not have inflicted enough damage to cause the accident, NASA administrator Sean O鈥橩eefe admitted in a televised interview on Sunday that this is 鈥渟till a very current theory鈥�.
And it is still possible that something else altogether caused the accident. Examples include failure of the computers that control the orbiter鈥檚 descent or of the hydraulic systems or wiring that move the shuttle鈥檚 control surfaces. Investigators are especially interested in finding pieces of debris from any of these components that might reveal evidence of such failures.
Donald Kutyna, a member of the presidential commission that investigated the Challenger explosion and who has directed the investigation of various satellite failures, says that it is important to keep an open mind in the early stages of such an investigation and not to focus in on a particular theory until everything else can be ruled out. 鈥淵ou鈥檝e just got to look at everything,鈥� he told 快猫短视频 last weekend.
And so far at least, that is the approach the investigators are taking. At this point, O鈥橩eefe says: 鈥淣othing is off the table.鈥�
