HabEx Telescope WFE stability specification derived from coronagraph starlight leakage

The Habitable Exoplanet Observatory Mission (HabEx) is one of four missions under study for the 2020 Astrophysics Decadal Survey. Its goal is to directly image and spectroscopically characterize planetary systems in the habitable zone around nearby sun-like. Additionally, HabEx will perform a broad range of general astrophysics science enabled by 100 to 2500 nm spectral range and 3 x 3 arc-minute FOV. To achieve its exoplanet science goals, HabEx is baselining both an internal coronagraph and a star-shade. But, an internal coronagraph requires an ultra-stable wavefront. Achieving this stability imposes never before required performance specifications upon the telescope and requires a new approach systems engineering. The telescope and coronagraph must be specified and designed as an integrated system. This paper describes a two-step systems engineering process that can be applied to any potential telescope/coronagraph combination. The first step is to determine the coronagraph's performance metrics of core throughput, raw contrast and stability of raw contrast. The second step is to calculate the sensitivity of the coronagraph's performance metric to its telescope's optical performance (e.g. wavefront stability). To illustrate the process, four representative architectures are evaluated: two vector-vortex and a hybrid Lyot coronagraph in combination with an off-axis monolithic telescope; and, an apodized pupil Lyot coronagraph with an on-axis hexagonal segment telescope (similar to the Webb Telescope aperture or the potential Large UV/Optical/IR Surveyor (LUVOIR) decadal mission).