WIKIARCHIVES.SPACE

The replacement of magnetic core with a well characterized semiconductor memory in the Space Shuttle orbiter general purpose computers (GPC's) has provided a wealth of on-orbit radiation effects data since 1991. The fault tolerant GPC's detect, correct, and downlink memory upset status and orbiter position information every few seconds, giving us the ability to correlate 1400 upsets to date with altitude, geomagnetic latitude, and solar conditions. The predicted upset rate was computed by a modified path-length distribution method. The modification accounts for the Weibull distribution cross-section (rather than a single upset threshold) and the device sensitive volume thickness. Device thickness was estimated by the method normally used to account for edge effects at the upset cross-section discontinuity that occurs at ion changes. A galactic cosmic ray environment model accurately models the average particle flux for each mission. The predicted and observed upset rates were found to be in good agreement for sensitive volume thicknesses consistent with the device's fabrication technology.