On Sat, 8 Feb 2003, Sander Pool wrote:
> Miles flown is indeed not a very good indication of stress on the system but
> hours spent in space is. The vehicle is under static stress because of the
> pressure difference between inside and out. Systems have to remain
> operational for a longer time etc.
However, static stresses are relatively predictable and seldom cause
failures. And systems seldom fail when they're just sitting there running
quietly; it's when you mess with them that bad things happen. :-) Space
itself is actually a fairly friendly environment in a lot of ways, because
it is so simple and predictable. Launch and reentry/landing are the
exciting bits, because of greater complexity and interactions with the
unpredictable atmosphere.
(The atmosphere in particular really likes being difficult. Les Hatton
pointed out that in one period of three months in 1987, there were *two*
"once in a hundred years" storms in the North Sea.)
Henry Spencer
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