Since Saturday, there has been a lot of talk about Columbia being the second Shuttle that has been destroyed, as if two accidents in 113 missions suggest an unusual pattern. Years ago, NASA's risk assessment pegged the expected Shuttle success rate at 99 percent; higher than any US, Soviet, Chinese, French, Japanese space program ever. But this doesn't mean the expected accidents will come exactly on each 100th mission. If they did, nobody would fly that one.
The last Space Shuttle accident was 17 years ago, before many Americans living today were even born. And despite
the terrible losses of Challenger and Columbia, this is still the safest, most successful long-term space program ever.
Photo right, John Taylor.
There have also been some references to the Columbia being aged, tired or even antiquated. That's a lot like saying Britney Spears is showing her age because she's no longer 16. Old compared to what? At age 22 the Columbia was younger than many planes in the commercial airlines fleet. And how many 747s are out there with only 27 landings in their logbooks? None.
Granted the Columbia's 28 flights took it around the world hundreds, perhaps even thousands of times. But once outside the atmosphere the stresses were slight. The takeoffs and re-entries are what count. Which is why NASA inspects every inch of its orbiters between each mission, and why Columbia was given a complete overhaul just a couple of years ago. In 1999 it came out of the factory in Palmdale, California, largely rebuilt.
So what went wrong? We may not know for a time. That's because NASA's accident process starts by trying to rule out what didn't cause the accident. The "fault-tree" to which several TV commentators have already made reference, is a process that calls for investigators to begin by thinking up every conceivable situation that could have caused an in-flight breakup. Those possibilities--all of them--get written down on the fault tree form in boxes along a horizontal line.
Then engineers look for strong evidence that proves some of these fault modes can be absolutely ruled out. The items that remain get moved to the next, shorter line and the process starts over. More investigation rules out more possibilities. The fault tree ends up looking like an inverted pyramid. When everything else has been ruled out, the one possibility left at the bottom of the pyramid is the one on which they can finally focus.
NASA has seen over time that no other method works as well. If you instead start with only the most likely cause, such as ice or insulation from the External Tank that apparently hit the Columbia's nose and wing after launch, you could end up fixing the wrong problem. Since that in turn could bring about another accident, fixing the wrong problem just isn't an option.
And we don't have four years to do it this time. Not only does the International Space Station depend on the Space Shuttle, so does NASA itself. NASA doesn't mark time well. The US space program either moves forward or it withers. Given that the Space Shuttle and International Space Station represent the high water mark of American technology to the rest of the world, we can't afford to let these efforts die. The US space program costs a tiny fraction of the federal budget, but serves as a potent force in our economy. Beyond the dollars it puts into the pockets of American workers, it is a huge symbol of America's superiority in technology and aerospace. Those just happen to be our leading exports. In a weak economy that sector must remain strong.
Here are my predictions: Watch for NASA to find the cause of the accident and to spell out the fixes. Watch for the President and Congress to support NASA in getting those fixes made. And watch for the Shuttle to be back operating in space far sooner than after Challenger.
John Taylor,
Logan, Utah
2/7/03
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