On-orbit insulator charge storage and partial discharge in the space radiation belts

The internal discharge monitor (IDM) has been flying on the CRRES spacecraft and sampling insulator discharge pulses from 16 samples for 14 months. The instrument has worked nearly flawlessly and has recorded a total of approximately 4300 electric pulses from the 16 samples. The time of occurrence of each pulse is known within 32 seconds and can be compared to the space radiation spectra which are being simultaneously recorded by several radiation spectrometers on the same satellite. An experiment was performed to determine how often radiation-induced pulsing occurs on unbiased insulators in space. It was found that dark conductivity in the insulators is so small that there is no clear evidence of a strong roll-off in the pulsing rate at the low radiation fluxes in space. The results may also be interpreted to mean that dark conductivity has decayed in space, resulting in the pulse rate per unit electron flux increasing over time