1113. Instrumented Gas Bearings Provide a Test Bed for High Accuracy Inertia (Moments & Products) Measurements

Paper

Abstract

This paper discusses the techniques employed in configuring and instrumenting a gas bearing system to provide a sensitive and accurate means of measuring the inertial properties of bodies. The subject system is designed for a single degree of freedom about Z (vertical) axis. Instrumentation is required to provide projected x-x and y-y axis moments and z axis period, speed, and position readouts. Moment data is derived from a single load cell that monitors stabilizing bearing forces in a single plane. A photoelectric pickup system creates the required Z axis data.
To aid in understanding the mechanical bearing restraints a series of graphs and explanations are presented in this text. Considerations overall stiffness and the influence on accuracy will be briefly discussed. Presented, also, are instrumentation and hardware techniques that take advantage of the high resolution and low noise profile characteristic of properly configured gas bearing test beds. In summary the combination of low noise and high resolution spells wide dynamic range thus allowing large CG offsets while preserving product of inertia capability at very low rotational speeds.
Increasingly, spacecraft construction has moved away from a ‘rigidbody’ approach to construction. Current trends are toward vehicles that display long appendages such as antennas and solar panels. Such a system has a static or quiescent mass distribution and a very different dynamic characteristic. Future facilities designed for complete operation in a vacuum or helium environment will have controlled tensional acceleration and readout capabilities that will provide dynamic as well as static inertial profiles of these difficult to measure payloads. Gas bearing systems easily adapt to these new requirements of the future.