A. R. Frederickson

Characteristics of spontaneous electrical discharging of various insulators in space radiations

Sixteen samples of standard insulating materials with electrodes were exposed to the full variety of the earths space radiation belts on the CRRES (Combined Release and Radiation Effects Satellite) for 14 months. Spontaneous discharges were recorded for each sample and were compared to the radiation levels, which were simultaneously monitored. Samples with the most exposed insulator surface (not metallized) pulsed most frequently. Most of the pulses were less than 50 V on 50 Omega . Pulsing correlated weakly with electron flux, but no correlation with proton flux could be discerned. The pulse rate per unit electron flux was initially small, rose continuously for seven months, and then fell slightly during the last seven months. The pulsing rate decayed when the satellite left the electron belts. The decay became more rapid after seven months. There seem to be two kinds of pulses which exhibit differing statistics. One kind dominated during the first seven months, the other during the last seven months. This may be related to the fact that it took several months for electric fields in the samples to approach steady-state levels. A computer simulation predicts the temporal charging of the insulators by the high-energy electron flux. >

Upsets related to spacecraft charging

The charging of spacecraft components by high energy radiation can result in spontaneous pulsed discharges. The pulses can interrupt normal operations of spacecraft electronics. The 20-year history of ground studies and spacecraft studies of this phenomenon are reviewed. The data from space are not sufficient to unambiguously point to a few specific solutions. The ground based data continue to find more problem areas the longer one looks. As spacecraft become more complex and carry less radiation shielding, the charging and discharging of insulators is becoming a more critical problem area. Ground experiments indicate that solutions for spacecraft are multiple and diverse, and many technical details are reviewed or introduced here.

Spacecraft anomalies on the CRRES satellite correlated with the environment and insulator samples

The CRRES (Combined Release and Radiation Effects Satellite) has been extensively surveyed for the occurrence of onboard anomalies. CRRES system and instrument responses which were not programmed or commanded are classified as anomalies. The history of anomalies is correlated with the history of plasmas, high-energy particles, and electromagnetic fields as measured on CRRES. The anomalies for each instrument on CRRES are compared with those from other instruments. As a group, the 674 anomalies correlate well with high levels of high-energy electron flux and poorly with every other environmental parameter. >

Radiation-induced insulator discharge pulses in the CRRES internal discharge monitor satellite experiment

The internal discharge monitor (IDM) is designed to observe electrical pulses from common electrical insulators in space service. The IDM is flying on the combined release and radiation effects satellite (CRRES). The sixteen insulator samples include G10 circuit boards, FR4 and PTFE fiberglass circuit boards, FEP Teflon, alumina, and wires with common insulations. The samples are fully enclosed, mutually isolated, and space radiation penetrates 0.02 cm of aluminum before striking the samples. The IDM results indicate the rate at which insulator pulses occur. Pulsing began on the seventh orbit. The maximum pulse rate occurred near orbit 600 when over 50 pulses occurred. The average pulse rate is approximately two per orbit, but nearly half of the first 600 orbits experienced no pulses. The pulse rate per unit flux of high energy electrons has not changed dramatically over the first ten months in space. These pulse rates are in agreement with laboratory experience on shorter time scales. Several of the samples have never pulsed. IDM pulses are the seeds of larger satellite electrical anomalies. The pulse rates are compared with space radiation intensities, L shell location, and spectral distributions from the radiation spectrometers on CRRES. >

The radiation effects on Galileo spacecraft systems at Jupiter

The Galileo spacecraft has been subjected to the harsh charged-particle environment around Jupiter since 1995. As the spacecraft has far exceeded the radiation dose for which it was designed, there have been a number of system failures attributable to radiation effects. This paper is a summary of those failures, the evidence for their connection to radiation related causes, and the associated fixes the Galileo flight team has implemented.

Model for space charge evolution and dose in irradiated insulators at high electric fields

A method for calculating dose, charge deposition, current, and electric field profiles across a dielectric slab irradiated by 1-3 MeV electron beams has been developed. The model consists of following the electric field build-up with time. A sequence of Monte Carlo calculations for relativistic electrons moving in an electric field determines the motion of the high-energy electrons. This is coupled with electric field solutions using a 1-D electrostatic field code. As time proceeds, the profile of high-energy electron current changes as well as the dose deposition which affects the magnitude of the conduction currents. Several mechanisms for conduction in the dielectric are taken into account. The model predictions are compared with Kerr-effect electric field data on irradiated polymethylmethacrylate (PMMA) obtained by M. Hikita et al. (1988). >

The CRRES IDM spacecraft experiment for insulator discharge pulses

The internal discharge monitor (IDM), designed to observe electrical pulses from common electrical insulators in space service, is described. The IDM was flown on the Combined Release and Radiation Effects Satellites (CRRES). The 16 insulator samples included G10 circuit boards, FR4 and PTFE fiberglass circuit boards, FEP Teflon, alumina, and wires with common insulations. The samples were fully enclosed and mutually isolated, and space radiation generated 0.02 cm. >

Radiation-induced voltage on spacecraft internal surfaces

The charging of the surfaces of insulators beneath the thermal control blankets on spacecraft has been numerically simulated. Such insulators are found on wiring harnesses, bulkhead feed-throughs, component mounting hardware, tiewraps, thermal sensors, etc. These insulators are shielded from the low-energy space plasma by the grounded solar blankets. It is determined that the surfaces of these insulators rise to many tens of kV in the Earths electron belts unless sufficient conduction to the spacecraft frame is established. Secondary electron emission is not sufficient to hold the potential to low values. The dependence of charging on insulator thickness, electron energy spectra, and material properties is investigated. This phenomenon is posited as an explanation for the anomalies seen on many spacecraft, and on the CRRES (Combined Release and Radiation Effects Satellite) in particular. >

Analytic approximation for charge current and deposition by 0.1 to 100 MeV electrons in thick slabs

An analytic function is developed for approximation of current penetration and charge deposition as a function of depth with normal incidence high energy electrons on slabs. The slabs must be thicker than the electron penetration depth and be composed of one material. Six adjustable parameters are evaluated to fit the function to tabulated ITS monte carlo and experimental electron deposition data. The results were developed from data spanning the entire energy range in C, Al, Cu, Ag, and Au, but are assumed to apply to all atomic number materials at all energies in the range.

Radiation-induced defect introduction rates in semiconductors

The defect introduction rate at 295 K by 1-MeV electrons in the p-side of n/sup +/-p silicon junctions under various applied voltages was measured using both DLTS and C-V techniques. The introduction rate of most defects is a strong function of applied bias and distance from the junction. Open circuit irradiation produces the smallest introduction rate while reverse bias enhances the rate by a factor of five for most defects. The C-V technique finds three times the concentration of defects that the DLTS technique finds. The C-V technique cannot distinguish types of defects: it sums all defects. Heavy reverse bias irradiations produced unstable junctions that could be partially restabilized by further open circuit irradiations. The electron-hole pairs generated by the irradiation appear to play a major role in the development of the final defect population resulting from the same irradiation. Even in a short irradiation, defects initially created early in the irradiation are altered or annealed by continued irradiation Recombination-enhanced diffusion theory appears to explain some of the results and, therefore, may be an important factor in the defect introduction process in many semiconductors. >