Occasionally, peculiar features show up in otherwise reliable data sets. These features can almost invariably be explained as the result of adverse effects on spacecraft and instrumentation by the environment external to the sensor itself. For example, within weeks after the Applications Technology Satellite 5 (ATS 5) was launched into geosynchronous orbit in August 1969, a strange pattern was observed in the behavior of the 50-eV to 50-keV particles near local midnight (see the article “Spacecraft Charging at Synchronous Orbit,” by S. E. DeForest, Journal of Geophysical Research, vol. 77, p. 651, 1972). After careful analysis, it was found that ATS 5 was charging to potentials as high as 10,000 volts during spacecraft eclipse. DeForest notes that the effects of local charging near particle detectors could “snarl the particle optics in an indecipherable manner that probably would resemble interesting new physical phenomena.” Other diverse reasons for unusual effects in data and systems are cosmic ray hits on imaging electronics, “glinting” from adjacent spacecraft, physical contamination from spacecraft outgassing or debris, offsets caused by improperly shielded electronics, and simple instrument degradation caused by age and/or radiation dose.