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A program is being conducted for testing of slip rings for synchronous orbit application. Instrumentation systems necessary for monitoring electrical noise, friction, and brush wear at atmospheric pressure and at less than 5 x 10-8 torr have been developed. A multiplex scheme necessary for the simultaneous recording of brush displacement, friction, and electrical noise has also been developed. Composite brushes consisting of silver-molybdenum disulfidegraphite and silver-niobium diselenide-graphite have been employed on rings of coin silver and rhodium plate. Brush property measurements made included measurement of density, electrical resistivity, shear strength, and microstructure. Four contact combinations have been tested during an ambient condition run-in at 150 rev/min and a humidity sequence at 0.1 rev/min. The first six months of the two-year vacuum test at 0.1 rev/min have been completed. Electrical noise, friction, and brush wear data recorded during these periods have been analyzed and indicate the following. 1) MoS2 lubricated brushes gave lower noise values than those lubricated with NbSe2. 2) Friction coefficients are lower in vacuum than in air with MoS2 giving the lowest coefficient. 3) Low wear rate is the result of combination performance rather than a particular ring or brush material. 4) The best overall performance was obtained from Ag-MoS2-C/Ag combination.