Study of radiation shielding requirements for n-MOS devices on the Exosat spacecraft. Final report

The device-degradation and radiation-shielding problems presented by the probable use of an n-channel microprocessor integrated circuit of the 8080 type on the Exosat spacecraft of the European Space Agency, was studied. The radiation exposure likely for this device was calculated, using various assumptions for the amount of surrounding absorber, some being intentional shielding others being normal structure elements and device encapsulation. The conclusion was that this type of device could be used if careful engineering design and quality control were used. Mission doses vary between 5000 and 800 rads for various configurations and some patterns of MOS device will tolerate these doses. The use of specially thickened module covers was not recommended, a better method being upgrading device quality and applying internal (local) shielding when necessary and possibly modular addition of external plates in specific directions only. The result of this shielding philosophy would be much greater efficiency in weight use. The further development of a rads (reduction) per gram philosophy was strongly recommended. Throughout, the strong link between mission success and the choice (and control) of the correct MOS manufacturing technology is emphasized and some guidelines on control of manufactured MOS parts (n-channel and complementary type) with respect to tolerance to radiation are given