High-order wavefront sensing and control for the Roman Coronagraph Instrument (CGI): architecture and measured performance

TL;DR

This paper details the architecture and measured performance of high-order wavefront sensing and control for the Roman Space Telescope's CGI, demonstrating significant contrast achievements in space-like conditions.

Contribution

It introduces the system-level architecture and algorithms for high-order wavefront control in the Roman CGI, including ground-in-the-loop operations and performance validation.

Findings

Achieved better than 5×10⁻⁸ raw contrast in tests

Demonstrated two independent coronagraph architectures with dark holes

Performance limited by testing time, not by system capabilities

Abstract

The Nancy Grace Roman Space Telescope (``Roman'') is a 2.4m space telescope scheduled for a 2026 launch. The Coronagraph Instrument (CGI) on Roman is a technology-demonstration instrument with a coronagraph and, for the first time in space, deformable mirrors and active wavefront control. This paper walks through the algorithmic and system-level architecture of the HOWFSC implementation for CGI, including the use of ground-in-the-loop (GITL) operations to support computationally-expensive operations, and reports on instrument performance measured during thermal vacuum testing in instrument integration and test. CGI achieved better than $5\times10^{-8}$ total raw contrast with two independent coronagraph architectures covering 3-9 and 6-20 $\lambda/D$ between them and a $360^{\circ}$ dark hole on each. The contrast limits appear to be driven by time available for testing, and do not appear to represent a floor in the achievable performance of CGI in flight.