The Nancy Grace Roman Space Telescope

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 Roman Space Telescope (NASA-led and managed by NASA's Goddard Space Flight Center; GSFC) is designed for a five-year mission, and will launch out of Cape Canaveral in the mid-2020s to L2. 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. In addition, it will perform a microlensing survey of the inner Milky Way to find ~2,600 exoplanets.

The Roman Space Telescope’s Coronagraph Instrument (Roman Coronagraph) will perform high-contrast imaging and spectroscopy of dozens of individual nearby exoplanets. NASA’s Jet Propulsion Laboratory (JPL) is building the Roman Coronagraph and is involved with detector validation and developing the Coronagraph’s observation 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 Roman Coronagraph Instrument

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 Roman Space Telescope Coronagraph Instrument will demonstrate the first high-performance coronagraph system in space capable of imaging directly mature gas giant exoplanet systems (similar to our own Jupiter) in reflected starlight, paving the way to a future possible NASA mission aimed at imaging and characterizing faint Earth-like planets.

Objectives of the Roman Coronagraph

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 Coronagraph technology demonstration, i.e., just meeting its threshold technical requirement (TTR), will be capable of detecting planetary companions 10 million times fainter than their host star and located >0.3 arcseconds away. Performance models based on current lab results predict the Coronagraph would be capable of detecting planetary companions a billion times fainter than their host star and located >0.15 arcseconds away. The Coronagraph 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 arcseconds away.

Critical Roman Coronagraph Technology Demonstrations

The Coronagraph Instrument on the Roman Space Telescope is an advanced technology demonstrator for future missions; for example, the Astro2020 Decadal Report has recommended a mission that will aim to directly image Earth-like exoplanets[MY1] . The Coronagraph 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.

Exoplanet Imaging

Following the recommendations of the Astro2010 and Astro2020 decadal surveys, the Roman Space Telescope Coronagraph Instrument advances and demonstrates key technologies in space to enable the next generation of Earth-observing exoplanet space-based observatories. Such technologies include 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. The Coronagraph 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 Coronagraph Community Participation Program to engage the exoplanet community. In this way, Coronagraph observations will advance community goals in exoplanet astronomy and how it will validate key technologies for future exoplanet missions, now envisioned as HabEx and LUVOIR.

Roman Coronagraph Technologies

• Direct imaging photometry centered at 573.8 nm (Band 1; 9.8% bandwidth) and 825.5 nm (Band 4; 11.7% bandwidth)
• Polarimetric observations centered at 573.8 nm (Band 1; 9.8% bandwidth) and 825.5 nm (Band 4; 11.7% bandwidth)
• Single-slit spectrograph (R=50) centered at 659.4 nm (Band 2; 16.8% bandwidth) and 729.3 nm (Band 3; 16.8% bandwidth)
• Pair of deformable mirrors for precision wavefront control
• Photon-counting EMCCD imaging sensors
• Autonomous operations on orbit

Data post-processing algorithms

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: https://arxiv.org/abs/1801.06599