Along the Tracks

Monday, February 03, 2003

Space shuttle fatality rates

There seems to be a lot of mistaken impressions over how “dangerous” a vehicle the space shuttle is. Many are calling for an end to the program, based on these impressions. Gregg Easterbrook’s column on Time Magazine’s web site is just the most noted of these “throw in the towel” opinions. But let’s look more closely.

The space shuttle has now lost 14 astronauts in two accidents - painful, tragic losses, each one. If we can set emotions aside for a moment, however, we might note that the shuttle fleet has traveled 375,203,627 miles (as off last April - the latest precise figures I could find). It has been surprisingly difficult to track down how many astronauts have ridden on shuttles (I’ll keep trying and update once I find the numbers) but, for argument purposes, lets just say an average of five astronauts per flight (most likely a low-ball estimate).

When comparing transportation system fatalities, one of the commonly-used statistics is “fatalities per 100 million passenger miles.” For the space shuttle program, there have been 14 fatalities over approximately 200,733,940,445 passenger miles. (Again, this is a rough estimate - but remember, automobile traffic fatalities per passenger mile are also by necessity based on estimates.)

That breaks down to one fatality per 14,338,138,603 passenger miles - or about 0.007 fatalities per 100 million passenger miles traveled. By comparison, the automobile fatality rate for 1999 was approximately 1.5 fatalities per 100 million passenger miles - far higher than that of the space shuttles.

There are a few caveats, not the least of which is the fact each astronaut racks up an incredible number of miles on a single mission, greatly increasing the odds of an accident for that astronaut - just as long-haul truckers and commercial passenger plane pilots increase their individual odds of fatal accidents by traveling greater miles. And again, let me say every loss of these pioneering heroes is a sobering tragedy. Still, this statistical breakdown is a great credit to NASA and its efforts at safety, and should be a clear rebuttal to those who think the space shuttle program is “too dangerous” to continue.

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