The Nancy Grace Roman Space Telescope, formerly the Wide Field InfraRed Survey Telescope (WFIRST), is a NASA observatory designed to settle essential questions in the areas of dark energy, exoplanets and infrared astrophysics. The telescope has a primary mirror that is 2.4 meters in diameter (7.9 feet), and is the same size as the Hubble Space Telescope's primary mirror. The Roman Space Telescope will have two instruments: the Wide Field Instrument and the Coronagraph Instrument.

The Wide Field Instrument will have a field of view that is 100 times greater than the Hubble infrared instrument, capturing more of the sky with less observing time. As the primary instrument, the Wide Field Instrument will measure light from a billion galaxies over the course of the mission lifetime. It will perform a microlensing survey of the inner Milky Way to find ~2,600 exoplanets. The Coronagraph Instrument will perform high-contrast imaging and spectroscopy of dozens of individual nearby exoplanets.

The Roman Space Telescope (NASA-led and managed by NASA's Goddard Space Flight Center) is designed for a five-year mission, and will launch on an EELV out of Cape Canaveral.

JPL is building the Roman Space Telescope's Coronographic Instrument (CGI) and is involved with detector validation and developing CGI's science capabilities. GSFC is responsible for the Roman Space Telescope Project. The Roman Space Telescope Science Center functions are the joint responsibility of the Infrared Processing and Analysis Center (IPAC), the Space Telescope Science Institute (STScI), and GSFC.

Overview of the Coronagraph Instrument (CGI)

The light from an exoplanet, as it would be seen in reflected starlight, is fainter than the host star by factors of 100,000,000 or more, and well beyond the reach of today's observatories on the ground or in space. The CGI is one of two instruments on board the Roman Space Telescope. The spacecraft is now in design Phase B and is scheduled for launch to L2 in 2025. the Roman Space Telescope CGI will demonstrate the first high-performance coronagraph system in space capable of direct imaging of mature exoplanet systems (such as our own) in reflected starlight, paving the way to a future possible NASA mission aimed at imaging and characterizing faint Earth-like planets.

Objectives of the CGI

Current ground-based and space-based instruments are limited to the detection of bright (self-luminous) young exoplanets, a million times fainter than their host star and located > 0.3 arc seconds away. A successful CGI technology demonstration, i.e., just meeting its baseline technical requirements (BTRs), will be capable of detecting planetary companions 20 million times fainter than their host star and located > 0.15 arc seconds away. Performance models based on current lab results predict the CGI would be capable of detecting planetary companions a billion times fainter than their host star and located > 0.15" away. CGI provides a crucial stepping stone in the preparation of future missions aiming to image and characterize Earth-like planets 10 billion times fainter than their host star and located 0.1 arc seconds away.

Critical CGI Technology Demonstrations

The Coronagraph Instrument on the Roman Space Telescope is an advanced technology demonstrator for future missions aiming to directly image Earth-like exoplanets. CGI will demonstrate for the first time in space the technologies for future missions needed to image and characterize rocky planets in the habitable zones of nearby stars. By demonstrating these tools in an integrated end-to-end system and enabling scientific observing operations, NASA will validate performance models and provide the pathway for potential future flagship missions.

Critical CGI Technology Demonstrations
CGI will premiere in space the technologies needed by future missions to image and characterize rocky planets in the habitable zones of nearby stars. By demonstrating these tools in a system with end-to-end, scientific observing operations, NASA will reduce the cost and risk of a potential future flagship mission.

CGI Science Capabilities

Direct Imaging of Exoplanets: 2020

Graph of direct imaging data
Direct imaging and spectroscopy of young self-luminous exoplanets have been achieved from ground and space observatories. Direct imaging of mature cool exoplanets in reflected starlight is currently beyond the reach of conventional techniques, as illustrated by the estimated brightness of a sample of known radial velocity exoplanets.

The Roman Space Telescope Coronagraph Instrument relies on the stability of a Space Observatory

Graph of direct stability data
Ground-based AO systems correct the rapid phase-dominated wavefront errors due to atmospheric turbulence. Freedom from atmospheric turbulence enables the iterative correction of both phase and amplitude wavefront aberrations and the suppression of scattered and diffracted light to levels limited only by telescope and instrument stability. The red dashed line is the approximate separation between Ground and Space-based sensitivity.

The Roman Space Telescope-CGI pioneers space coronagraph technologies

Graph of direct optical disturbances data
Best estimated CGI performance for three observing configurations (direct imaging at short and long wavelengths and spectroscopy) are based on currently demonstrated static and dynamic testbed performance and observatory optical disturbance models provided by the project.

The Roman Space Telescope-CGI provides guaranteed science return for circumstellar disks

Graph of sensitivity data
Early estimate of the CGI sensitivity for imaging of low-luminosity disks associated with a V=5 star. Surface brightness is represented in terms of flux ratios per imaging resolution element. Comparisons are made with previously-imaged disks in visible scattered light, and with HST instrument sensitivities. TW Hydra is a protoplanetary disk, while the rest of the dashed curves are debris disks. Credit: J. Debes.

Exoplanet Imaging

Following the recommendations of the Astro2010 decadal survey, the Roman Space Telescope Coronagraph Instrument (CGI) advances and demonstrates key technologies as enablers for the next generation of Earth-observing exoplanet observatories in space. The CGI is one of two instruments on the Wide Field Infrared Survey Telescope, a NASA project now in the design (Phase B) stage and scheduled for launch in 2025.

The CGI will demonstrate in space, for the first time, key enabling technologies for future Earth imaging missions, including precision optical wavefront control with deformable mirrors, sensitive photon-counting imaging detectors, selectable coronagraph observing modes, low-resolution spectroscopy, advanced algorithms for wavefront sensing and control, high-fidelity integrated spacecraft and coronagraph modeling, and post-processing methods to extract images and spectra. CGI is designed to demonstrate space coronagraphy at sensitivity levels of Jovian-mass planets and faint debris disks in reflected starlight.

Following initial commissioning and formal technology demonstrations in the first eighteen months of operations, NASA envisions a Participating Science Program to engage the exoplanet community. In these panels, we describe how CGI science will advance community goals in exoplanet astronomy and how it will validate key technologies for future exoplanet missions, now envisioned as HabEx and LUVOIR.

CGI Technologies

  • Two selectable coronagraph modes (HLC and SPC)
  • Pair of deformable mirrors for precision wavefront control
  • Photon-counting EMCCD imaging sensors
  • Single-slit spectrograph (R=50)
  • Autonomous operations on orbit
  • Data post-processing algorithms
  • Starshade compatibility
  • References to the recent CGI literature

Emulating the Roman Space Telescope data in the lab

JPL's Precision Projector Laboratory (PPL) uses a testbed designed to emulate astronomical data using real detectors in order to validate the Wide Field Instrument's strict requirements on photometry, astrometry, and especially galaxy shape measurement. The PPL testbed rapidly generates a range of customizable "scenes" (e.g. stars, galaxies, spectra) on large format detectors to uncover subtle systematic effects that can evade conventional detector testing and degrade science measurements. Once understood, detector issues may be mitigated via changes to hardware, calibration, mission operations, or data analysis. More information:

Field of Stars
A field of "stars" (point sources) emulated with an engineering grade infrared detector similar to those used by the Roman Space Telescope Wide Field Instrument.
Emulation system
The PPL testbed testing a near-IR detector in the gold cryostat.

Scientific Instrument(s)

- 2.4 m telescope used by both
- The Wide Field instrument
- The Coronagraph Instrument