Nancy Grace Roman Telescope

Quick facts

Overview

Summary

Mission Capabilities

Roman has two primary instruments, the Wide Field Instrument (WFI) and the Coronagraph Instrument (CGI). WFI is a powerful 300-megapixel infrared camera that contains 18 mercury cadmium telluride (HgCdTe) detectors that capture 16 million pixels each. The instrument will conduct extensive surveys of the sky and detect faint infrared light from distant galaxies, supernovae, and exoplanets, providing critical data on dark energy, galaxy evolution, and the discovery of new worlds.

CGI is an advanced technology demonstration instrument designed for imaging exoplanets and circumstellar disks. It employs a complex system of masks, prisms, and deformable mirrors to block out starlight, allowing it to detect and analyse faint objects close to stars. CGI is expected to achieve a contrast ratio 1,000 times better than previous space-based coronagraphs, making it a crucial tool for studying planetary systems beyond the solar system.

Performance Specifications

The Roman Space Telescope will operate in a quasi-halo orbit around the second Sun-Earth Lagrange point (L2), with a nominal mission duration of five years. WFI will offer the same resolution as Hubble, 0.1 arcsec/pixel, but over 200 times the field of view, 45 x 23 arcseconds. This spatial resolution is heavily dependent on wavelength with the highest resolution at the blue range of the prism wavelength coverage. It will have a spectral range from 0.48 to 2.3 micrometres, covering visible to near-infrared wavelengths. CGI, operating in visible light, will provide high-contrast imaging with the ability to detect exoplanets as close as 0.15 arcseconds to their host stars.

Space and Hardware Components

Roman features a 2.4 m primary mirror, and a spacecraft platform based on that of the James Webb Space Telescope (JWST). WFI includes a filter wheel with eight positions, enabling multi-band imaging across a wide spectral range. CGI incorporates two deformable mirrors, each with thousands of actuators to correct wavefront errors and achieve the required contrast for direct exoplanet imaging.

The spacecraft is equipped with advanced avionics, propulsion, and power systems to support its complex observational goals. It carries a sophisticated communication system to downlink the vast amounts of data generated by its instruments to ground stations on Earth.

Overview

The Nancy Grace Roman Space Telescope, named after NASA's first Chief of Astronomy, is designed to answer fundamental questions about the universe, particularly related to dark energy, exoplanets, and infrared astrophysics. This next-generation observatory will build on the legacy of the Hubble Space Telescope, offering a field of view 200 times larger, enabling it to survey the sky more efficiently and capture data that will deepen our understanding of the cosmos.

Roman is equipped with two primary instruments: the Wide Field Instrument (WFI) and the Coronagraph Instrument (CGI). WFI will conduct broad surveys to map the distribution of dark matter, study galaxy formation, and discover thousands of exoplanets. CGI, a cutting-edge technology demonstration, will directly image exoplanets and provide new insights into their atmospheres and the formation of planetary systems. 1) 3) 4)

Nancy Grace Roman, often referred to as the "Mother of the Hubble Space Telescope," was a pioneering American astronomer born on May 16, 1925 in Nashville, Tennessee, and passed away on December 25, 2018. From an early age, Roman showed a deep passion for astronomy, starting a club at age 11 where she and her classmates explored constellations and celestial objects. Despite facing gender barriers, she excelled academically, earning a Bachelor's degree in Astronomy from Swarthmore College in 1946 and a Ph.D. from the University of Chicago in 1949. Roman's career took her to NASA, where she became the first female executive and Chief of Astronomy, playing a crucial role in planning space-based observatories, including the Hubble Space Telescope. Her efforts in advocating for and securing funding for the Hubble project solidified her legacy as a trailblazer in space-based astronomy, ultimately leading to the dedication of NASA’s next major observatory in her honour. 14)

Roman Science Themes

The three primary science themes of Roman are dark energy, dark matter, and exoplanets.

The mission will attempt to unravel the mystery of dark energy through a High Latitude Wide-Area Survey (HLWAS), which will measure gravitational lensing and redshifts of hundreds of millions of galaxies. This survey will consist of imaging and grism spectroscopy. Dark energy will also be studied with data from the High Latitude Time Domain Survey (HLTDS), which aims to characterise supernovae light-curves of up to redshifts of 2. To study dark matter, Roman will gather an inventory of matter (both baryonic and dark) across a myriad of galaxies, providing insight into how it drives the formations of stars and galaxies. Stars in the Milky Way’s bulge will be studied through time-series microlensing imaging to look for exoplanets orbiting them. 18) 20)

Spacecraft

The Roman Space Telescope's spacecraft is built around a 2.4-metre primary mirror, which offers the same light-gathering power as Hubble with a much wider field of view. The spacecraft bus is based on the design used for the James Webb Space Telescope, ensuring high stability and precision in its operations. Roman is designed to operate in a quasi-halo orbit around the second Sun-Earth Lagrange point, providing a stable platform for its observations over its nominal five-year mission. 9)

The 2.4 m primary mirror will have a temperature of 265 Kelvin with its roll angle being allowed to move from -15 degrees to +15 degrees to provide the maximum solar power to the spacecraft. The jitter, or pointing motion, of the telescope will be 12 milliarcseconds and the drift, or a motion in constant direction, will be 8 milliarcseconds. Above this mirror will be a Deployable Aperture Cover (DAC) that deploys once in orbit and is designed to keep light out of the telescope barrel along with a Solar Array Sun Shield (SASS) for solar power and an Outer Barrel Assembly (OBA). The OBA is there to provide structural support to the DAC and SASS as well as protecting the telescope from any stray light. 10) 11) 12)

Launch

Roman will be placed in a quasi-halo orbit around the second Sun-Earth Lagrange point (L2). It will be launched onboard the SpaceX Falcon Heavy rocket from NASA’s Kennedy Space Centre with a planned lifetime of five years.

Mission Status

• June 2024: WFI completed thermal vacuum tests, and the mission’s space operations centre  (SOC) began planning the community-led Roman Galactic Plane General Astrophysics Survey. 16)
• May 2024: Roman’s WFI entered its final integration and testing phase at BAE Systems in Boulder, US. This final stage of testing consists of electromagnetic interference and compatibility testing to ensure the spacecraft’s resilience to electrical disruptions. 15)
• June 2024: Completed key spacecraft assembly milestones.
• January 2024: Roman’s WFI began thermal vacuum testing at BAE Systems’ Tian test chamber. 17)

• September 2023: WFI was fully assembled at BAE Systems and began environmental testing, which included vibration and acoustic tests to simulate launch conditions, and thermal vacuum tests to simulate the space environment. 15) 17)

Sensor Complement

WFI is a highly sensitive infrared camera capable of capturing wide-field images with high resolution, thanks to its 18 HgCdTe detectors, each with 16 million pixels. CGI, on the other hand, is a sophisticated instrument designed for high-contrast imaging. It includes multiple optical elements, such as deformable mirrors and coronagraphic masks, to block out starlight and reveal faint exoplanets orbiting nearby stars. 2)

Wide Field Instrument

The Wide Field Instrument (WFI) on the Nancy Grace Roman Space Telescope is designed to capture a vast portion of the sky with unprecedented resolution and sensitivity in the infrared spectrum. WFI consists of 18 state-of-the-art HAWAII-4RG readout integrated circuits with mercury cadmium telluride (HgCdTe) detectors on each circuit, covering a field of view 200 times larger than Hubble’s infrared camera. The instrument has a filter wheel with eight positions, allowing it to image in various bands across the 0.48 to 2.3-micron range. WFI’s key capabilities include large-scale surveys to study dark energy, galaxy formation, and the discovery of new exoplanets through microlensing events. Its design supports a high level of photometric precision, essential for detecting subtle changes in brightness associated with distant supernovae or gravitational lensing effects. 13)

Each of WFI’s detectors is optimised for low noise and high quantum efficiency, ensuring that even faint infrared signals from distant objects are accurately captured. WFI will be used for a variety of scientific goals, including the study of the acceleration of the universe’s expansion (dark energy), the formation and growth of large-scale structures in the universe, and the discovery and characterization of exoplanets. 5) 6)

Coronagraph Instrument

The Coronagraph Instrument, designed for direct imaging of exoplanets, includes a complex system of masks, prisms, and deformable mirrors. These components block starlight and correct distortions to reveal faint objects close to stars, offering a glimpse into other planetary systems. The instrument operates in visible light and is a technology demonstration that aims to achieve 1000 times the contrast of existing space coronagraphs.

CGI is designed to achieve high-contrast imaging and spectroscopy of exoplanets and circumstellar disks, and incorporates several advanced components:

1. Deformable Mirrors: Two mirrors, each with 3,000 actuators, dynamically adjust their shape to correct for optical distortions caused by the spacecraft and space environment, achieving the high contrast needed to detect faint exoplanets near bright stars.
2. Coronagraphic Masks: These specialised masks block out the star’s light while allowing the light from nearby planets to pass through. CGI uses several types of masks, including hybrid Lyot, shaped pupil, and phase-induced amplitude apodization masks, each optimised for different observing conditions and scientific objectives.
3. Low-Order Wavefront Sensor (LOWFS): This system continuously monitors and corrects small misalignments and drifts in the optical system, ensuring that the high-contrast performance of the coronagraph is maintained over long observation periods.
4. Integral Field Spectrograph (IFS): The IFS allows CGI to perform spectroscopy on detected exoplanets, analysing their light to determine the composition of their atmospheres, search for biomarkers, and study their physical properties.
5. Performance Targets: CGI is expected to achieve a contrast ratio of at least 10-9, allowing it to detect planets as close as 0.15 arcseconds from their host stars. This capability will enable the direct imaging of gas giant exoplanets and potentially smaller, Earth-like planets in the habitable zones of nearby stars.

CGI's capabilities represent a significant leap forward in direct exoplanet imaging, setting the stage for future missions that may one day image Earth-like planets around sun-like stars and search for signs of life. 7) 8)

Ground Segment

The Roman Space Telescope will downlink its data to Earth using X-band and Ka-band frequencies with a downlink rate of 250-500 Mbps and a data volume of 11 Tbits per day. The primary operations centre will be located at NASA's Goddard Space Flight Center, with additional support from ground stations worldwide. The mission's ground segment is designed to handle the vast amounts of data generated by Roman's instruments, ensuring that scientists have timely access to the information needed for their research.

All of Roman’s collected data will be non-proprietary, and will be openly available through the Mikulski Archive for Space Telescopes (MAST). 20) 21)

References  

1) “About Roman.” NASA Science, https://science.nasa.gov/mission/roman-space-telescope/introducing-the-roman-space-telescope/

2) “The Roman Coronagraph Instrument.” NASA Jet Propulsion Laboratory (JPL), https://www.jpl.nasa.gov/missions/the-roman-coronagraph-instrument

3) Lea, Robert. “What is the Nancy Grace Roman Space Telescope?” Space.com, 15 February 2023, https://www.space.com/nancy-grace-roman-space-telescope

4) “Nancy Grace Roman Space Telescope.” STScI, https://www.stsci.edu/roman

5) “Roman Space Telescope.” BAE Systems, https://www.baesystems.com/en-us/products/nancy-grace-roman-space-telescope

6) “Roman Space Telescope's Wide Field Instrument.” NASA Science, https://science.nasa.gov/mission/roman-space-telescope/wide-field-instrument/

7) “Roman Space Telescope.” Roman Space Telescope, https://roman.ipac.caltech.edu/mtgs/Roman_CGI_workshop.html

8) Cowing, Keith. “Nancy Grace Roman Space Telescope Coronagraph Instrument Overview and Status - Astrobiology.” the Astrobiology Web, 12 November 2023, https://astrobiology.com/2023/11/nancy-grace-roman-space-telescope-coronagraph-instrument-overview-and-status.html

9) “Frequently Asked Questions.” NASA Science, https://science.nasa.gov/mission/roman-space-telescope/frequently-asked-questions/

10) “Observatory - Technical - Roman Space Telescope/NASA.” Roman Space Telescope, https://roman.gsfc.nasa.gov/science/observatory_technical.html#spacecraft

11) “Spitzer: IRAC Instrument Handbook.” Spitzer: IRAC Instrument Handbook, https://irsa.ipac.caltech.edu/data/SPITZER/docs/irac/iracinstrumenthandbook/22/

12) “Telescope.” Roman Space Telescope, https://roman.gsfc.nasa.gov/interactive/parts/telescope/

13) “HAWAII-4RG.” Teledyne Imaging, https://www.teledyneimaging.com/en/aerospace-and-defense/products/sensors-overview/infrared-hgcdte-mct/hawaii-4rg/

14) “Who is Nancy Grace Roman?” NASA Science, https://science.nasa.gov/mission/roman-space-telescope/who-is-nancy-grace-roman/

15) “Testing of Roman Space Telescope’s primary instrument nearing completion at BAE Systems,” BAE Systems, May 21, 2024, URL: https://www.baesystems.com/en/article/testing-roman-space-telescope-primary-instrument-nearing-completion 

16) “Roman Science Operations Center Newsletter,” Space Telescope Science Institute, June 2024, URL: https://www.stsci.edu/contents/news/roman/2024/roman-science-operations-center-newsletter-june?filterUUID=a0520512-506c-4107-a9e6-8e1096de39e8 

17) “Roman Science Operations Center Newsletter, Space Telescope Science Institute, January 2024, URL: https://www.stsci.edu/contents/news/roman/2024/roman-science-operations-center-newsletter 

18) “Expanded Science Goals With Roman,” Space Telescope Science Institute, URL: https://www.stsci.edu/roman/about/science-themes 

19) “Observatory Overview,” Space Telescope Science Institute, URL: https://www.stsci.edu/roman/observatory 

20) “Nancy Grace Roman Space Telescope SCIENCE AND TECHNICAL OVERVIEW,” Space Telescope Science Institute, January 2024, URL: https://www.stsci.edu/files/live/sites/www/files/home/roman/documentation/technical-documentation/_documents/roman-science-technical-overview_trifold.pdf 

21) “Roman Space Telescope,” Mikulski Archive for Space Telescopes, URL: https://archive.stsci.edu/missions-and-data/roman