During science operations, JWST’s wavefront is measured regularly and the telescope’s mirror alignment is corrected via commanding as needed to reduce wavefront error and maintain the observatory’s excellent optical performance (see additional details on this JWST NASA Blog article).

The measured wavefronts typically vary at a low level and over a range of timescales; see Optical Telescope Element (OTE) Science Performance Memo 2 for a description over the first year of science operations. On rare occasions, relatively large mirror shifts can occur, such as the event in February 2024 (described in OTE Science Performance Memo 3). Such large mirror shifts are thought to be caused by the release of stored mechanical stresses. After the correction made following this event, the JWST OTE has exhibited unprecedented levels of wavefront stability. On October 3rd, 2024 the team applied a mirror control update after a record of 186 days of telescope stability (see Figure 1).

JWST users can access archived wavefront maps and utilize STScI tools to visualize and trend JWST wavefront error, and to create high-fidelity modeled Point Spread Functions (PSFs) corresponding to measured wavefronts at particular points in time. Information on generating simulated PSFs using wavefront measurements can be found in the WebbPSF documentation. Best practices for generating PSFs to use with science data are captured on this WebbPSF reference page. 

Users with questions about these resources should contact the  JWST Help Desk using the WebbPSF/JWST Telescope card.