NASA’s Nancy Grace Roman Space Telescope has achieved image quality nearly 30% better than predicted for its main camera, following extensive testing and precision adjustments. Launched on 30 August, the observatory will investigate dark matter, dark energy and other cosmic mysteries through sweeping surveys that depend on its Wide Field Instrument. Both scientific instruments now meet or exceed their anticipated performance.
After activating the Wide Field Instrument in September, engineers checked its 18 detectors, associated electronics and rotating assembly of filters and other optical components. They also tested internal calibration lights, which allow differences in detector sensitivity to be identified and corrected, along with alignment and temperature-control systems. The telescope’s optics were already remarkably well aligned: its secondary mirror required a movement equivalent to roughly one-sixteenth of a human hair’s diameter. Such precision is challenging because launch forces can shift equipment, while conditions in orbit cannot be reproduced exactly on Earth.
The final measurements showed an optical error of 63 nanometres RMS, compared with a pre-launch image-quality requirement of approximately 90 nanometres RMS. This measure describes how far incoming light deviates from an ideally focused wavefront; a lower value indicates less error. Engineers also corrected a slight focus problem in the Coronagraph Instrument. Further work will refine its camera settings and the configurations of its deformable mirrors. In the coming weeks, tests will assess its ability to suppress unwanted light, an essential capability for observing faint objects close to much brighter ones.
