Closed-loop operation of the dual-path Zernike wavefront sensor with LOWFS

Determine whether the Roman Coronagraph’s low-order wavefront sensor (LOWFS) can operate in closed loop when the dual-path Zernike wavefront sensor (ZWFS) is installed and being used for wavefront measurements.

Background

The Roman Coronagraph contains a dual-path ZWFS in the focal-plane alignment mechanism that can measure higher-spatial-frequency aberrations than the baseline LOWFS. The dual-path sensor is intended to operate alongside the LOWFS, but its reflected optical path has not been tested in the thermal-vacuum environment and is not definitively supported for in-space operations.

Closed-loop compatibility is important because the LOWFS maintains pointing and low-order wavefront stability during observations. Although unpublished JPL analyses suggest that closed-loop operation should be feasible, the absence of thermal-vacuum testing leaves the operational question unresolved.

References

One of the still open questions for the Roman dual-path ZWFS is whether the LOWFS will be able to work in closed-loop with the sensor in place.

— The Roman Coronagraph Community Participation Program: Using the Zernike wavefront sensor for a full characterisation of the Roman Space Telescope and the Coronagraph Instrument  (2608.17740 - Vigan et al., 18 Aug 2026) in Section 5, “Conclusions and perspectives”