Acquisition and control of a precision formation flying mission

Abstract

Using formation flying spacecraft as space-based interferometers will provide images of unprecedented resolution. Missions such as Stellar Imager plan to use multiple spacecraft in a formation instead of a typical monolithic space telescope, achieving a resolution up to 0.1 milliarcseconds. In order to assemble into a formation, these satellites must first locate each other using limited field-of-view sensors. Once the satellites are in a formation, the path length of the light going to the combiner satellite must be controlled to nanometer levels to produce an image of high quality. One solution to control to such precision is to use staged control methods, utilizing multiple actuators with overlapping strokes and bandwidths. This thesis first provides an algorithm for three satellites to initialize into a formation using relative measurements and limited field-of-view sensors. The satellites perform a search to locate each other, accurately point their transmitters at each other, and move into an equilateral triangle formation. This thesis also provides the framework for developing a staged pointing and phasing testbed using the Synchronized Position Hold Engage Reorient Experimental Satellites (SPHERES) as the coarse stage. The pointing actuation is provided by a fast steering mirror and a linear stage, and the phasing actuation is provided by an optical delay line consisting of a voice coil mirror and a piezo mirror.