Development Testing of High Temperature Bearings for SP-100 Control Drive Assemblies

Initial preliminary development phases of two distinct SP-100 control drive assembly bearing test programs were successfully completed at elevated temperature in vacuum. The first was for the reflector drive line spherical self-aligning bearings. Each bearing consisted of a carbon-graphite ball mounted on an aluminum oxide-coated Ta-10%W shaft, captured by an aluminum oxide-coated Ta-10%W socket. One set of these bearings was exposed to temperatures up to 1180K (1665°F) at 1.33x10^-6 Pa (1x10^-8 torr) and subjected to 38000 cycles of motion. Friction coefficients were found to be between 0.11 and 0.25 over the full range of operation. Overall performance of the bearings was excellent, with only slight wear observed. The second test program was for the safety rod slider bearing. Zirconium carbide coated Nb-1%Zr bearing pads were stroked inside a molybdenum tube at temperatures up to 1422K (2100°F) at ∼1.33x10^-6 Pa with a normal load of 1.02 Kg between each sliding surface. Coefficients of sliding friction were found to increase from 0.90 at 293K to 1.20 at 1422K prior to high temperature dwells. Further testing identified areas for improvement in the next planned test series. Breakaway forces were well within the actuator design limits.