On several occasions after the breakup of the Space Shuttle Columbia on February 1st, I found myself in conversations about the safety of the space program. Actually, my knowledge is limited to much lower altitudes and speeds and much more prosaic equipment. On a few occasions, nevertheless, I felt obliged to put in my two cents when someone commented that the Shuttle was obviously unsafe, given its record of one fatality for every 10 or so flights. It's hard to define an expected level of safety for something like the Space Shuttle. Considering the extreme difficulty of what it does, it has succeeded very well, though, like Concorde, it has been an economic failure. The appearance of safety depends a lot on the numbers that you select to represent it. The one-in-10 figure sounds awful; if you say one accident per 60 launches it sounds a bit better. But try putting it in terms of passenger miles. A week-long Shuttle flight with seven aboard racks up some 20 million passenger miles, and if you think of 1.2 billion passenger miles per disaster, it starts to sound almost good. That's the equivalent of 4,000 transcontinental flights of a half-empty 757.
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