Metrology for spatial interferometry V

The proposed Space Interferometry Mission (SIM) spacecraft designs include high resolution stellar interferometers for micro-arc-second accuracy astrometric measurements. The stellar interferometers require picometer accuracy 1D metrology gauges, surface metrology gauges and 3D metrology gauges to measure the required distances or to calibrate the fiducials that define the end points of the interferometric paths. The absolute metrology gauges required by these interferometers can be considerably less accurate due to the careful design of the astrometric interferometers and the fiducials on the spacecraft. An auto-aligning, 3D metrology gauge constructed using the sub-picosecond linear metrology gauges was described in earlier papers. The sub-nanometer, in-vacuum tracking result from this 3D metrology gauge are presented. The resulting jitter is analyzed and is shown to be caused by thermal drift in the alignment of the gauge heads, warpage of the base table and the time-dependent tilt of the experiment as a whole. The aberrations in the light beams of the laser distance gauges can result in errors in the distance measurements performed using these gauges. Simulations using spot shapes and aberrations present in a realistic measurement system used in a stellar interferometer is space are performed to quantify the amount of expected errors. The results of these simulations are presented.