Originally Posted by
tdracer
Along that same line, when Patriot was first used in anger against Iraq, it didn't work very well against ballistic SCUD missiles (in spite of impressive looking TV footage).
We learned from that, and the current version of Patriot is far improved.
AFAIK Patriot was bad against the Scuds because of two problems - the first was that different modules used different time-bases that differed in the number of bits assigned to their clocks. The second was that the Patriots were kept running far longer without a reboot than ever before. This meant that the two modules had increasingly different notions of time. One module did the calculation of when to shoot and passed that time to the other, the other looked at a different clock as the basis for when to initiate the launch. Had the Patriots been rebooted several times a day they would likely have hit the incoming scuds. As it was they were firing way off schedule, where "way off" was some seconds or fractions of seconds. I think they were running continuously for days.
See also the Ariane flight V88 had a similar design problem that led to the loss of the launch vehicle and several satellites. "
The active module presented a diagnostic bit pattern to the On-Board Computer which was interpreted as flight data"
Edit to add why they were on line so long. In the anti-aircraft use, there would be long distance radar that would provide sufficient time to wake up the system and get it ready, but with missiles that time was reduced below what the system start took. I would be surprised if a reset would take as long as a startup, but they didn't know the source of the problem and thought it was because the missiles were too fast.