Design and Performance of Gas-Pressurized, Spherical, Space-Simulator Bearings

Abstract

Space-simulator bearings of the externally pressurized gas-lubricated type must meet a number of unusually stringent requirements. Of primary importance is that they contribute as nearly as possible zero error torque to the supported simulator structure, and that changes in this torque as the structure is rotated as desired about all three axes be extremely small. The bearing must be stable and free of vibration under all conditions; and in the more sophisticated simulators, the bearing must sustain lateral as well as vertical loads with close control of film thickness. Low-error torque requires first of all that the rotatable sphere be both geometrically perfect and flawless of surface. Errors in the bearing causing roll and pitch torques can be balanced out by the table balance weights; but azimuth torques cannot be counterbalanced. They are minimized by appropriate bearing design which places the gas-flow lines in planes passing through the azimuth axis. Bearing-design parameters and equations are established. A detailed computer analysis explains why these bearings cannot be operated below a certain minimum film thickness. Error torques resulting from flaws or scratches in the bearing and sphere surfaces are analyzed and found to increase with film thickness. Bearing-error torque is found to increase as the square of the load.