The Patriot system was originally designed to operate in Europe against Soviet medium- to high-altitude aircraft and cruise missiles traveling at speeds up to about MACH 2 (1500 mph). To avoid detection it was designed to be mobile and operate for only a few hours at one location.
Right, but it didn't say that it was a cap on how long it should work correctly, rather it's a lower bound and also sets the maximum they tested it to. This is a design feature, but not a requirements feature, then, that it required a reboot after less than 8 hours of operations.
http://archive.gao.gov/t2pbat6/145960.pdf
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I never did embedded programming or government programming, so what your saying make sense from a spec perspective.