TABLE 7-11. DAMAGE RATES FROM COLLISIONS 7.1. 7.2 COMPONENT FAILURES The number of components involved in an operating SPS will demand sophisticated maintenance philosophies even if the components are designed for exceedingly long life. For analysis of maintenance, logistics, etc., some failure rates of components must be postulated, and these are given in Table 7-12. With a 30 year operational life, amplitrons present the greatest problem. Present similar devices have a life of slightly over 1000 h or one-eighth year. The 2. 5 million units of an SPS will have an expected failure rate of approximately 10 per hour. Other antenna and propulsion system elements have a lesser, but still quite significant, failure rate. If the assumed reliabilities cannot be achieved, maintenance requirements of the SPS will be more demanding. Automatic repair facilities are assumed. One concept for antenna maintenance would consist of an automated truck that would continuously drive over the back side of the antenna exchanging entire subarray wafers having failed components with spares. When a full load of failed subarrays has been gathered, they would be delivered to an automatic repair station, exchanged for repaired subarrays, and the route continued. The automatic repair stations would disassemble amplitrons, rebore, exchange conduction bands, recoat electrodes, etc., retaining 80 percent of the original component. Repair of the automatic repair facilities themselves would be handled by the crew if the failure rates of the 20 expected stations can be kept to approximately 20 failures per week. As shown in Table 7-13, the total crew per shift for operations and maintenance is approximately four.
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