Satellite Bearing Torque Noise

Many spin-stabilized spacecraft use precision ball bearings to support and to align an antenna or instrument platform relative to the rotor. The pointing accuray of the instrument platform is affected by the dynamic fluctuations in running torque or torque noise of the bearings. Although many previous investigations have been concerned with average (or dc) torque, there is a lack of information on the spectral distribution of the torque noise of lightly loaded, large-diameter bearings at slow speeds. This paper summarizes experiments performed on seven pairs of bearings of two bore sizes. Limited measurements of bearings profilometry were made. A special fixture was used to measure torque noise over a range of preload, rotational speed, and temperature. The bearing torque noise was processed by a computer to obtain torque spectral density and rms. On the basis of this experimental data, an ad hoc model was developed to estimate torque spectral density for use in control system preliminary design and feasibility studies. Additional study is recommended to improve the modeling and to extend its applicability.