Flight designs and pupil error mitigation for the bowtie shaped pupil coronagraph on the Nancy Grace Roman Space Telescope

Abstract

The Nancy Grace Roman Space Telescope will carry a coronagraph instrument (CGI) that will serve as a demonstrator for technologies needed for future high-contrast imaging missions in space, including deformable mirrors (DMs) to correct high-order wavefront errors that would otherwise limit the achievable contrast. The CGI has three baselined interchangeable observing configurations, one of which is a bowtie shaped pupil coronagraph for high-contrast spectroscopy. We present the flight designs for two closely related mask configurations of the bowtie shaped pupil coronagraph: a baseline 0-deg mask configuration for the technology demonstration and a 60-deg mask configuration contributed by the NASA Exoplanet Exploration Program. The shaped pupil mask and Lyot stop for each mask configuration result from an iterative process that maximizes the core throughput subject to constraints on other performance metrics, such as the contrast: a linear program optimizes the shaped pupil mask for a given Lyot stop, and the optimization repeats for various Lyot stops until the highest-throughput combination is identifiable. The flight designs for the baseline and rotated mask configurations have core throughputs of 4.50% and 3.89%, respectively, at 4 λD and are robust to conservative estimates of potential pupil errors such as misalignments and manufacturing errors. If these estimates are exceeded in flight, the DMs can be used to mitigate the effects of the excess error.