Design of a telescope-occulter system for THEIA

摘要

The Telescope for Habitable Exoplanets and Interstellar/IntergalacticAstronomy (THEIA) is a mission concept study for a flagship-classtelescope-occulter system to search for terrestrial planets and perform generalastrophysics with a space-based 4m telescope. A number of design options wereconsidered for the occulter and telescope optical systems; in this paper wediscuss the design of occulters and coronagraphs for THEIA and examine theirmerits. We present two optimized occulters: a 25.6m-radius occulter with 19mpetals that achieves 10^-12 suppression from 250-1000nm with a 75mas innerworking angle, and a 20.0m-radius occulter with 10m petals that achieves 10^-12suppression from 250-700nm with a 75mas inner working angle. For more widelyseparated planets (IWA > 108mas), this second occulter is designed to operateat a second closer distance where it provides 10^-12 suppression from700-1000nm. We have also explored occulter/coronagraph hybrid systems, andfound that an AIC coronagraph that exploits the symmetry of the PSF at theocculter can improve performance; however, it requires very accurate toleranceson the occulter manufacturing of the telescope/occulter system as the AIC doesnot cancel asymmetric terms. Other coronagraphs proved infeasible, primarilydue to the fact that the residual starlight from the occulter is not a planewave, and so is poorly suppressed by the coronagraph.