The Wide Field Instrument (WFI) is the main instrument on the Roman Space Telescope, offering imaging and spectroscopic capabilities in the near infrared (NIR) from 0.5 to 2.3 microns. WFI produces images that match the resolution of the Hubble Space Telescope NIR capabilities, but with a field of view 200 times larger.

The Wide Field Instrument (WFI) is the primary instrument of the Roman Space Telescope and it is central role to enabling its survey capabilities. A concise summary of Roman and WFI performance is provided in the Table of Key Parameters for Roman's WFI, with additional details available throughout the WFI Handbook. The WFI Quick Reference provides more details of the topics introduced below. 

The Roman operates in a Sun-Earth L2 orbit, with observing constraints designed to maximize power generation and avoid the Earth and the Moon. The resulting Field of Regard (FOR) provides access to 59% of the sky at any given time, with full sky coverage achieved over the 5-year primary mission. Efficient slew and settle performance supports wide-area and time-domain surveys, such as the Roman Community Defined Surveys.

The WFI provides a large field-of-view (FOV) with an active area on the sky of 0.281 deg², roughly 100 times the area covered by HST/ACS or JWST/NIRCam, and 200 times that of WFC3/IR on HST. The WFI FOV is populated by eighteen H4RG-10 (HgCdTe) detectors (over 300 million pixels) with a plate scale of 0.11 arcsec pix^-1, comparable to HST/WFC3-IR. The Figure of the WFI Focal Plane in Context shows the focal plan and the FOV against the Andromeda galaxy and the View of the Roman Focal Plane Array provides a sense of the physical size of the focal plane.

The WFI supports both imaging and slitless spectroscopy. The WFI is sensitive to wavelengths from 0.5 to 2.3 microns, with eight filters, including wide filter (F146), and two dispersive elements (a prism and a grism) for slitless spectroscopy. Details of the focal plane and optical elements are provided in the Description of the WFI and  WFI Optical Elements articles. 

Roman’s mission-level science requirements drive stringent calibration of WFI data. The instrument includes an internal Relative Calibration System (RCS) and a dark element within the optical assembly (see Description of the WFI). The WFI Perfomance section provides a description of the known instrumental effects in the data and how these effects will be corrected or mitigated through data processing. Ground characterization and planned on-orbit calibration activities are described in the WFI Characterization Activities section. 

WFI science data are acquired with interleaved fine guiding for precise pointing control and use data compression and multi-accumulation (MA) readouts to manage data volume. Information on WFI data products and access is provided in the Data Handbook, while observation-planning guidance is available in the Observing with the WFI section of the WFI Handbook.

The WFI Documentation Ecosystem

While the Roman Documentation (RDox) on the WFI is still under construction, users may find additional relevant information in content held outside of RDox, as shown in the WFI Documentation Ecosystem Table below.

References

• Scientific Visualization Studio at NASA Goddard, "NASA's Nancy Grace Roman Space Telescope's Wide Field Instrument" Visualization ID: 13235, Created June 29, 2019 and Updated May 3, 2023
• Nancy Grace Roman Space Telescope at STScI

For additional questions not answered in this article, please contact the Roman Help Desk.