Roman Space Telescope Primary Mirror Delivers 30% Better Performance Than Requirements

Engineers completed the final round of cryogenic vacuum tests on the mirror assembly in 2024. The measured surface figure and mid-spatial-frequency errors came in at roughly 70% of the maximum allowed values, giving the mission extra margin for the Wide Field Instrument's high-contrast imaging goals. These results build directly on polishing processes refined for Hubble servicing and JWST, but applied here at lower cost and risk because the Roman design reuses an existing on-orbit proven aperture.

The performance gain matters for the mission's core objectives: detecting and characterizing exoplanets via microlensing and direct imaging, plus measuring the acceleration of the universe with weak lensing. Extra margin reduces the chance that on-orbit thermal drifts or launch-induced figure changes will eat into science return, a lesson learned from earlier flagship telescopes.

Next steps include integrating the mirror with the instrument suite and spacecraft for system-level thermal-vacuum testing scheduled through mid-2025. If the 30% margin holds through those campaigns, NASA will have quantitative evidence that the telescope can deliver its highest-priority observations even under conservative degradation assumptions.