development effort which also started in 1984 has analytically and experimentally screened all possible insulator materials and has resulted in selecting single crystal alumina as the high voltage insulator. Accelerated tests of the alumina insulator are being conducted to verify the analytical prediction of the insulator lifetime in the space reactor power system operating environment. The lifetime degradation mechanism is ionic conduction of aluminum and oxygen in opposite direction and eventually loss of bonding between the insulator and the niobium refractory metal. The insulator ionic
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