Phasing a deployable sparse telescope

Abstract

After launching and deploying a sparse space telescope, fine tuning is required to correct for inaccurate initial placement of its elements. We selected unique shapes and locations of these telescope aperture segments, to be able to distinguish between their diffraction patterns, while at the same time having a proper spatial frequency coverage. Then we improved the combined wave front, without measuring it directly: First we correlated each segment's focal image with its distinctive template, to correct its tilt. Next we interfered them with the other segments, pair by pair, using their limited coherence, to locate their mutual optical path differences. Finally, we optimized the combined focal image for fine alignment.