Continuation of Space-Array Program

Experiments were conducted to evaluate the coefficent of friction, mu sub s, in the PACSAT limited-motion joints and the resulting libration damping characteristics of the springs attached to the ends of the array. Measurements for mu sub s between surfaces burnished with pure molybdenum disulfide a solid- film lubricant show that this coefficient can be made independent of tension in the joints. Measurements made in a vacuum for the lubricated surfaces gave mu sub s 0.4. This value for the coefficient of friction in the PACSAT joints would result in no measurable degradation in the arrays radar cross section as a consequence of friction in the joints and in a geostationary array this friction gives rise to a damping of tip displacement, due to flexture, of about 2 cm per day. This damping of the primary flexural mode of oscillation for the array is adequate for future PACSAT applications. Experiments to measure the libration-damping characteristics of the springs to be attached to the ends of the array did not provide conclusive results, because a very large torsional pendulum was required to measure the damping coefficient of these springs when subjected to torsional strains with 6-hour periods as they would be for a PACSAT in a synchronous orbit. The size of this pendulum resulted in its being very sensitive to spurious perturbations. Although no quantitative data were obtained, it was observed that springs made from cadmium plated beryllium copper wire tend to damp torsional flexures with 6-hour periods more than do springs made of unplated wire.