Sunday, February 1, 2004
The Columbia STS-107 Accident
In honor of seven heroes
NASA has finished its investigation of the Columbia tragedy and concluded that the shuttle’s left wing came apart in flight at something over 12,000 mph and caused the spacecraft to disintegrate 30 miles up. Columbia broke up only 16 minutes from touchdown.
The loss of the seven Columbia astronauts served to emphasize once again the risks of space flight and remind us all that no matter how remarkable our technology and how matter-of-factly we accept space flight, it’s still a very dangerous business.
Unfortunately, NASA’s fairly consistent successes over the last 106 launches have helped foster a blasé attitude on the part of many Americans. So it might be worthwhile to revisit the process of re-entry and examine what happened a year ago as the unpowered, 100-ton glider returned to Earth from 200 miles up.
Regular readers of this column may remember I interviewed shuttle astronaut Kent Rominger six years ago on a similar question. Rominger is a veteran space traveler with three shuttle trips and some 1,100 hours in space.
In the case of Columbia, the oldest shuttle’s fate apparently was sealed shortly after liftoff on January 16 when a piece of insulation separated from the huge external fuel tank and struck the shuttle’s left underwing. NASA officials saw the impact on video, but they’d witnessed similar incidents on other missions that resulted in little or no damage to the shuttle and, after three separate analyses, dismissed the impact as inconsequential.
When Columbia was ready for re-entry last February 1 over the Indian Ocean 12,000 miles from touchdown, a quartet of onboard computers positioned the shuttle so it was flying upside-down and backward. At the time, Columbia was orbiting roughly 1,000,000 feet above the Earth at 17,600 mph, about Mach 25.
As Rominger explained six years ago, “When we’re ready to return to Earth, we only need to slow 200 mph to drop out of orbit. We use the dual Orbital Maneuvering System engines to generate 1/4 G of deceleration in two to three minutes (depending upon weight), and that starts us downhill. If one OMS engine fails, we can deorbit with the other one, and if we absolutely had to, we could even use the maneuvering rockets for deceleration.” Rominger acknowledges there are plenty of real risks to space flight, but he comments, “Despite what Hollywood would have you believe, the chances of being stranded in space are essentially nil.”
When the critical deorbit burn is complete, the computers command the thrusters to pitch the nose down through vertical (remember, the shuttle is flying inverted and backward at this point) and gradually continue the pitch until the aircraft has passed level and is flying at an angle of attack of roughly 40 degrees nose up, now facing its direction of flight. There’s essentially no air to cause additional drag above 100 miles, so speed remains well over 16,500 mph as the shuttle descends toward the Earth at 20,000 fpm.
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