NASA’s Nancy Grace Roman Space Telescope (formerly known as WFIRST) is a flagship astrophysics mission planned for launch in 2025. The coronagraph instrument (CGI) on Roman will demonstrate the technology for direct imaging and spectroscopy of exoplanets around nearby stars. It will work with the 2.4-meter diameter telescope to achieve starlight suppression that is 2-3 orders of magnitude deeper than previous space-based and ground-based coronagraphs by using active wavefront control in space with deformable mirrors. CGI has passed its Preliminary Design Review (PDR) in September 2019 and is working toward the instrument Critical Design Review (CDR) in the spring of 2021. We describe the CGI engineering design going into CDR and the operational concept planned for CGI observations.
The WFIRST Coronagraph Instrument will perform direct imaging of exoplanets via coronagraphy of the host star. The Phase B optical design fits within a new allocated instrument enclosure and accommodates both Hybrid Lyot and Shaped Pupil coronagraphs. It provides optical path and space for accessible focal planes for occulting masks and field stops. It provides accessible pupil planes for shaped pupil and Lyot masks. It accommodates ten active optical assemblies, including one fast steering mirror, on focusing mirror, two deformable mirrors, and six precision alignment mechanisms. We present the optical design and analyses for the Direct Imaging channel, including polarization imaging. We also present the performance analysis of pupil imaging for starlight illumination and diffused light illumination of the pupil.