5.3.10 Rotary Joint Technology Item — High-Power Slip Rings Criticality — Critical to program success SPS concepts transfer electrical power from the arrays or generators to the microwave by means of a slip ring. Slip ring performance is critical, since it represents a single-point failure on the vehicle. Present Capability: Slip rings are in common use in motors and generators. However, they are much smaller physically than the SPS slip rings and transmit less power. Required Capability: Large high-power slip rings are required for SPS. They must exhibit satisfactory mechanical and electrical stability in a GEO environment to last 30 years with minimal maintenance. Several megawatts of waste heat must be safely rejected to prevent overheating. Development Plans: Slip rings designs should be developed to meet SPS requirements. Subscale versions should be tested to verify their performance. Life prediction for rubbing surfaces should indicate 30-year life capacity. Item — Alternate Rotary Joint Concepts Criticality — Enhances probability of program success Brush-type rotary joints suffer from potential wear problems and high friction forces. These problems can be avoided if non-sliding joints can be developed to transfer the electrical power. Present Capability: Alternate concepts to sliding joints have been developed for small scale applications. One particular concept is rollamite, which consists of a set of rollers rolling on a continuous flexible band. Power transfer would occur at the point of contact between the band and the rollers. Required Capability: Large size, low friction rotary joints are required to transfer large amounts of power for SPS application. A life of 30 years in a GEO environment is required. Development Plan: Designs for alternative low friction concepts should be developed. Subscale models should be tested to verify their performance.
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