NASA’s Nancy Grace Roman Space Telescope has exceeded expectations following extensive instrument testing and precise optical adjustments. Its main camera system, the Wide Field Instrument, is delivering optical performance nearly 30% better than predicted. Launched on August 30, Roman will survey vast regions of the sky to investigate dark matter, dark energy, and other cosmic mysteries.
After activating the Wide Field Instrument in September, engineers examined its 18 detectors and associated electronics, tested its rotating wheel of optical components, and checked its thermal controls. Adjustable internal LEDs provided controlled signals for measuring detector sensitivity. Although launch forces and differences between ground and orbital conditions can affect alignment, Roman required only minor corrections. Engineers shifted its secondary mirror by approximately one-sixteenth of a human hair’s diameter. The resulting optical error measured just 63 nanometers RMS, compared with a prelaunch image-quality requirement of approximately 90 nanometers RMS. This measurement describes how far incoming light deviates from an ideally focused wavefront.
The telescope’s Coronagraph Instrument, initially slightly out of focus, now meets the team’s performance expectations. Further work will refine its camera settings and the configurations of its deformable mirrors, which change shape to correct incoming light. Engineers also plan to test its ability to suppress unwanted light, a capability essential for detecting faint objects close to brighter ones. With both scientific instruments meeting or exceeding expectations, Roman has passed another milestone toward routine observations, with sharper survey images anticipated.
