Roman Space Telescope Wide Field Instrument Design Evolution

The Nancy Grace Roman Space Telescope will enable advances in astrophysics by providing a large-scale survey capability in infrared wavelengths. The observatory is designed to provide data that will allow astronomers to unlock mysteries of the universe, answering high-priority scientific questions related to the evolution of the universe and the habitability of exoplanets. Using a 2.4 m (7.9 ft) primary mirror, Roman will capture comparable quality images to Hubble, but with more than 200 times the field of view of Hubble’s near-infrared channel, enabling the observatory to conduct comprehensive and efficient surveys. The Wide Field Instrument (WFI) features a 300-megapixel mosaic focal plane assembly with 18 H4RG detectors. WFI includes filters that provide an imaging mode covering 0.48 - 2.0 μm and two slitless spectroscopy modes. To meet scientific objectives, WFI requires a stable structural and cryogenic environment. NASA designs and develops the WFI science data signal chain and selected Ball Aerospace as their partner to design and develop the WFI Opto-Mechanical Assembly. In this paper, we present a WFI design evolution overview from early phases of the project through the critical design review. Innovations that increased performance, improved testability, and reduced mass and power will be discussed. Moving the third telescope mirror from the instrument to the heritage telescope assembly, eliminating the cryocooler by converting from an active to passive thermal design, unfolding the optical path to eliminate the mirror in the instrument design, and changing the plane of the serviceable latch configuration to ensure a kinematic mount are presented.