The Nancy Grace Roman Space Telescope is a NASA infrared space telescope that was launched on a trajectory toward a Sun–Earth L2 orbit on 30 August 2026. It is named after NASA's first chief of astronomy, Nancy Grace Roman.
The telescope is based on an existing primary mirror with a wide field of view that was donated by the National Reconnaissance Office and will carry two scientific instruments. The Wide-Field Instrument (WFI) is a 300.8-megapixel multi-band visible and near-infrared camera, providing image sharpness comparable to the Hubble Space Telescope over a 0.28-square-degree field of view, 100 times larger than imaging cameras on the Hubble. The Coronagraph Instrument (CGI) is a high-contrast, small-field-of-view camera and spectrometer covering visible and near-infrared wavelengths using novel starlight-suppression technology.
Its objectives include a search for exoplanets using gravitational microlensing, along with probing the chronology of the universe and growth of cosmic structure, with the end goal of measuring the effects of dark energy, the consistency of general relativity, and the curvature of spacetime. Roman was recommended in 2010 by the United States National Research Council Decadal Survey committee as the top priority for the next decade of astronomy. It was approved for development and launch on 17 February 2016. NASA expects to release Roman's first science images by early 2027.
Science objectives The science objectives of Roman aim to address cutting-edge questions in cosmology and exoplanet research, including:
Answering basic questions about dark energy, complementary to the European Space Agency (ESA) Euclid mission, and including: Is cosmic acceleration caused by a new energy component or by the breakdown of general relativity on cosmological scales? If the cause is a new energy component, is its energy density constant in space and time, or has it evolved over the history of the universe? Roman will use three independent techniques to probe dark energy: baryon acoustic oscillations, observations of distant supernovae, and weak gravitational lensing. Completing a census of exoplanets to help answer new questions about the potential for life in the universe: How common are star systems like the Solar System? What kinds of planets exist in the cold, outer regions of planetary systems? What determines the habitability of Earth-like worlds? This census makes use of a technique that can find exoplanets down to a mass only a few times that of the Moon: gravitational microlensing. The census would also include a sample of free-floating planets with masses likely down to the mass of Mars. Establishing a guest investigator mode, enabling survey investigations to answer diverse questions about the Milky Way Galaxy and the universe. Providing a coronagraph for exoplanet direct imaging that will provide the first direct images and spectra of planets around the Solar System's nearest neighbors, similar to giant planets. Detection of primordial black holes.
Instruments The telescope carries two instruments. Both were installed into the telescope in December 2024.
Wide-Field Instrument The Wide-Field Instrument (WFI) is the primary science instrument for the mission. It is a 300.8-megapixel camera, providing multiband imaging and spectroscopy from the visible to near-infrared (0.48 to 2.30 μm). Eight science filters, one wide band, and seven more narrow filters, provide high-quality images in subsets of the total spectral bandwidth of the instrument. It carries a high-dispersion grism and lower-dispersion prism assemblies for wide-field slitless spectroscopy.
A "dark element" made out of spectralon can block out the light from space and reflect calibration light onto the detector. The eight filters, two spectroscopy elements, and dark element are all attached to an Element Wheel Assembly (EWA) that rotates one element at a time into the active position.This enables the scientists to choose which colors of light are needed for each mission, or switch between imaging and spectroscopy modes.
A HgCdTe-based focal-plane array (FPA) captures a 0.28 square degree field of view with a resolution of 0.11 arcseconds. The detector array is composed of 18 H4RG-10 detectors provided by Teledyne. The instrument carries on-board calibration capability to help the scientists discern the subtle changes in images from their dark matter mission compared to ordinary distortions of the optics or of the FPA. The FPA is attached to a set of hexapod actuators that can reposition the focal plane into the best focus position based on analysis from the ground to ensure the captured images are always of high quality over the lifetime of the mission. WFI was completed and shipped to NASA in August 2024.
Coronagraph Instrument The Coronagraph Instrument (CGI) is a high-contrast coronagraph covering shorter wavelengths (575 nm to 825 nm) using dual deformable mirror starlight-suppression technology. It is intended to achieve a part-per-billion suppression of starlight to enable the detection and spectroscopy of planets with a visual separation of as little as 0.15 arcseconds from their host stars. CGI is intended as a technology demonstrator for an exoplanet imaging instrument on a future large space-based observatory, such as the Habitable Worlds Observatory (HWO).
History
Origins
The design of the Nancy Grace Roman Space Telescope shares a heritage with various proposed designs for the Joint Dark Energy Mission (JDEM) between NASA and the Department of Energy (DOE). The original design, called WFIRST (Wide-Field Infrared Survey Telescope) Design Reference Mission 1, was studied in 2011–2012, featuring a diameter unobstructed three-mirror anastigmat telescope. It contained a single instrument, a visible to near-infrared imager/slitless prism spectrometer.
In 2012, another possibility emerged: NASA could use a second-hand National Reconnaissance Office (NRO) telescope made by Harris Corporation to accomplish a mission like the one planned for WFIRST. NRO offered to donate two telescopes, the same size as the Hubble Space Telescope but with a shorter focal length and hence a wider field of view. This provided important political momentum to the project, even though the telescope represents only a modest fraction of the cost of the mission and the boundary conditions from the NRO design had the potential to push the total cost over that of a fresh design. This mission concept, called WFIRST-AFTA (Astrophysics Focused Telescope Assets), was matured by a scientific and technical team; this mission is now the only present NASA plan for the use of the NRO telescopes. The Roman baseline design includes a coronagraph to enable the direct imaging of exoplanets.
Several implementations of WFIRST/Roman were studied. These included the Joint Dark Energy Mission-Omega configuration, an Interim Design Reference Mission and Design Reference Mission 1, both featuring a telescope, Design Reference Mission 2 with a telescope, and several iterations of the AFTA configuration.
Formulation In the fiscal year 2014, Congress provided US$56 million for Roman, followed by US$50 million in 2015. The fiscal year 2016 spending bill provided US$90 million for Roman, substantially more than NASA's request of US$14 million, allowing the mission to enter the "formulation phase" in February 2016. On 18 February 2016, NASA announced that Roman had formally transitioned from a study to a project, indicating its intent to proceed with the mission as baselined.
At that time, the "AFTA" portion of the mission concept name WFIRST-AFTA was dropped, as only that approach was being pursued with a plan for a mid-2020s launch. The total cost of Roman at that point was expected at more than US$2 billion. NASA's 2015 budget estimate was around US$2.0 billion in 2010 dollars, which corresponds to around US$2.7 billion in real year (inflation-adjusted) dollars.
In the 2015 final report, Roman was considered for both geosynchronous orbit and for an orbit around the Sun-Earth Lagrange point L2. L2 has disadvantages versus geosynchronous orbit in available data rate and propellant required, but advantages for improved observing constraints, better thermal stability, and more benign radiation environment. Some science cases (such as exoplanet microlensing parallax) are improved at L2, but the possibility of robotic servicing at either of the locations is currently unknown. By February 2016, it had been decided to use a halo orbit around L2.
Development
The mission began Phase A development in 2016 with Neil Gehrels, as project scientist, chairing the Formulation Science Working Group with co-chairs Jeremy Kasdin and David Spergel. In April 2017, NASA commissioned an independent review of the project to ensure that the mission scope and cost were understood and aligned. The review acknowledged that Roman offers "groundbreaking and unprecedented survey capabilities for dark energy, exoplanet, and general astrophysics", but directed the mission to "reduce cost and complexity sufficient to have a cost estimate consistent with the US$3.2 billion cost target set at the beginning of Phase B".
In January 2018, NASA announced the reductions taken in response to this recommendation, and that Roman would proceed to its mission design review in February 2018 and begin Phase B by April 2018. NASA confirmed (March 2018) that the changes made to the project had reduced its estimated life cycle cost to US$3.2 billion and that the Phase B decision was on track to begin on 11 April 2018.
In February 2018, the Trump administration proposed an FY2019 budget that would have delayed the funding of the Roman (then called WFIRST), citing higher priorities within NASA and the increasing cost of the telescope. The proposed defunding of the project was met with criticism by professional astronomers, who noted that the American astronomical community had rated Roman the highest-priority space mission for the 2020s in the 2010 Decadal Survey. The American Astronomical Society expressed "grave concern" about the proposed defunding, and noted that the estimated lifecycle cost for Roman had not changed over the previous two years.
In agreement, the United States Congress approved an FY2018 Roman budget on 22 and 23 March 2018 in excess of the administration's budget request for that year, stating that it "rejects the cancellation of scientific priorities recommended by the National Academy of Sciences decadal survey process", and directed NASA to develop new estimates of Roman's total and annual development costs. The President of the United States announced he had signed the bill on 23 March 2018.
In May 2018, NASA awarded a multi-year contract to Ball Aerospace (now called BAE Systems Space & Mission Systems) to provide key components (the Opto-Mechanical Assembly) for the Wide-Field Instrument on Roman. In June 2018, NASA awarded a contract to Teledyne Scientific and Imaging to provide the infrared detectors for the Wide-Field Instrument. On 30 November 2018, NASA announced it had awarded a contract for the telescope. This was for a part called the Optical Telescope Assembly (OTA), and ran to 2025. This was in conjunction with the Goddard Space Flight Center, for which the OTA was planned for delivery as part of the contract.
NASA was funded via a FY2019 appropriations bill on 15 February 2019, with US$312 million for Roman, rejecting the President's reduced Budget Request and reasserting the desire for completion of Roman with a planning budget of US$3.2 billion.