ExEP: Automated fine alignment and calibration of the Roman Coronagraph Instrument (paper)

The Decadal Survey on Astronomy and Astrophysics 2020 recommended that the next NASA flagship be a 6-meter telescope equipped with a coronagraph instrument to enable imaging and spectroscopy of earth-like exoplanets, which are on the order of 10−10 times fainter than their host stars in visible light. In preparation, the 2.4-meter Nancy Grace Roman Space Telescope (Roman) will launch by mid-2027 and its Coronagraph Instrument will demonstrate several key technologies at high contrast such as two different coronagraph types, high-actuator-count deformable mirrors, photon counting detectors, and low-order and high-order wavefront sensing and control (HOWFSC) loops. The performance of the model-based HOWFSC algorithms depends heavily on the accuracy of the calibrations and the alignments of the coronagraphic optical masks. For the Roman Coronagraph Instrument to achieve its desired performance of better than 10−8 contrast, the fine alignment and calibration routines must be both accurate and precise. The best way to guarantee such performance was to automate these routines. Due to the complexities of handshakes between ground and flight software and to monitor data quality, a person must still be part of the loop but does not perform any calculations manually. In this paper, we detail the strict requirements for fine alignment and calibration, the algorithms used, and the measured performance in thermal vacuum testing of the Roman Coronagraph Instrument.