A laser metrology system for precision pointing

Abstract

Precision spacecraft payloads are driving the need for fine pointing control and vibration cancellation. One implementation that provides pointing and disturbance control is the Stewart-Gough platform equipped with active sensing and actuating elements. The Precision Pointing Hexapod (PPH) at Naval Postgraduate School (NPS) is exactly such a platform initially installed with voice coil actuators and accelerometers on each strut by CSA Engineering Inc. High pointing accuracy, however, requires an additional external sensing system that feeds back the accurate location and orientation information of the moving platform for control. The first implementation by NPS of such sensing system is the eddy current metrology system. Currently, that system only provides measurement of the two degrees of motion that define the pointing direction and has issues such as questionable absolute pointing accuracy and lower resolution. This thesis seeks to develop a new laser metrology system, utilizing diode lasers and position sensing detectors, to provide all six degree of freedom information of the platform motion at higher precision and accuracy. The tasks of developing the laser metrology system from theory to design, fabrication, implementation, and verification are documented in this thesis. Recommendations for future work and lessons learned are also captured.