Review of the NASA Voyager Spacecraft Polycarbonate Capacitor Failure Incident

About six months before the second Voyager spacecraft was launched, a 75 ¿F polycarbonate capacitor used in its receiver tracking loop filter was found to be defective. This failure led to an investigation into the use of polycarbonate onate capacitors in high-impedance circuits. During the investigation, polycarbonate capacitor failures were induced by thermal cycling and extended periods at high temperature. The temperature coefficients of the leakage paths were measured and the results indicate that there are at least two separate types of leakage. The mechanism of the leakage paths are further complicated by what appears to be mechanical movement within the capacitor as its temperature is changed. The failure mechanism appears to be lot related and is believed to be associated with the polycarbonate material. Chemical tests on the material of capacitors from production runs that performed well and those that did not, have shown no detectable differences. A new system for pulse detecting during capacitor burn-in and during ramp testing has proven to be beneficial. Some parts that passed their conventional burn-in were subjected to an additional burn-in with pulse detection. Pulses were detected during the additional burn-in on parts that had been accepted by the conventional method of screening.