Martin Noecker/ Ball Aerospace & Technologies Corp.

Advanced Speckle Sensing for Internal Coronagraphs (ASSIC) is a study of two advanced methods for measuring residual wavefront errors in spaceborne internal coronagraphs. The coronagraph instrument suppresses starlight by a factor of about 10 billion, so that the starlight "speckles" from residual wavefront errors are as faint as the exoplanets we hope to see. These speckles are a significant threat to detection of Earth- sized exoplanets, particularly if they change with time. With current techniques, measuring these very faint speckles, to monitor and correct them, takes roughly as long as detecting the faint exoplanets, typically many hours or days. The prevailing strategy for managing these speckles has been to impose stringent thermal and mechanical stability requirements on the entire optical system, so that the speckles remain stable long enough to measure and correct them and then conduct a planet-search observation. The proposed advanced sensing methods are expected to improve the speed of speckle measurements, allowing frequent and accurate adjustments of the instrument to reduce them. This completely changes the technology landscape for such missions. It will dramatically reduce the time-scale for stability requirements on the telescope and instrument optical train. These methods appear to be applicable to all the leading candidates for coronagraph instrument: band-limited Lyot, shaped pupil, pupil remapping, and perhaps vortex and visible nulling coronagraphs.