Nancy Grace Roman Space Telescope

The Nancy Grace Roman Space Telescope (shortened as Roman or the Roman Space Telescope, and formerly the Wide Field Infrared Survey Telescope or WFIRST) is a NASA infrared space telescope currently under development. Roman was recommended in 2010 by United States National Research Council Decadal Survey committee as the top priority for the next decade of astronomy. On 17 February 2016, Roman was approved for development and launch.[5] On 20 May 2020, NASA Administrator Jim Bridenstine announced that the mission would be named the Nancy Grace Roman Space Telescope in recognition of the former NASA Chief of Astronomy's foundational role in the field of space astronomy.[6]

Nancy Grace Roman Space Telescope
Rendered model of the Roman Space Telescope in May 2020.
NamesJoint Dark Energy Mission (JDEM)
Wide Field Infrared Survey Telescope (WFIRST)
Mission typeInfrared space telescope
OperatorNASA / JPL / GSFC
Websitehttp://roman.gsfc.nasa.gov/
Mission duration5 years (planned) [1]
Spacecraft properties
ManufacturerHarris Corporation
Launch mass4,166 kg (9,184 lb) [2]
Dry mass4,059 kg (8,949 lb)
Payload mass2,191 kg (4,830 lb)
Power2500 watts
Start of mission
Launch date2025 [3]
RocketCommercial launch vehicle [4]
Launch siteCape Canaveral
Orbital parameters
Reference systemSun–Earth L2 orbit
RegimeHalo orbit
Perigee altitude188,420 km (117,080 mi)
Apogee altitude806,756 km (501,295 mi)
Main telescope
TypeThree-mirror anastigmat
Diameter2.4 m (7 ft 10 in)
Focal ratiof/7.9
WavelengthsNear-infrared, visible light
Transponders
BandS-band (TT&C support)
Ka-band (data acquisition)
BandwidthFew kbit/s duplex (S-band)
290 Mbit/s (Ka-band)
Instruments
Wide-Field Instrument (WFI)
Coronagraph Instrument (CGI)
 

The Roman Space Telescope is based on an existing 2.4 m wide field-of-view primary mirror and will carry two scientific instruments. The Wide-Field Instrument is a 288-megapixel multi-band near-infrared camera, providing a sharpness of images comparable to that achieved by the Hubble Space Telescope (HST) over a 0.28 square degree field of view, 100 times larger than that of the HST. The Coronagraphic Instrument is a high-contrast, small field-of-view camera and spectrometer covering visible and near-infrared wavelengths using novel starlight-suppression technology.

The design of the Roman Space Telescope is based on one of the proposed designs for the Joint Dark Energy Mission (JDEM) between NASA and Department of Energy (DOE). Roman adds some extra capabilities to the original JDEM proposal, including a search for extra-solar planets using gravitational microlensing.[7] In its present incarnation (2015),[8] a large fraction of its primary mission will be focused on probing the expansion history of the Universe and the growth of cosmic structure with multiple methods in overlapping redshift ranges, with the goal of precisely measuring the effects of dark energy,[9] the consistency of general relativity, and the curvature of spacetime.

On 12 February 2018, President Trump's FY19 budget request proposed to terminate any development on the Roman (then called WFIRST) mission, due to a reduction in the overall NASA astrophysics budget and higher priorities elsewhere in the agency.[10][11][12] However, in March 2018, Congress approved funding to continue making progress on Roman until at least 30 September 2018,[13] in a bill stating that Congress "rejects the cancellation of scientific priorities recommended by the National Academy of Sciences decadal survey process".[14]

In testimony before Congress in July 2018, NASA administrator Jim Bridenstine proposed slowing down the development of Roman in order to accommodate a cost increase in the James Webb Space Telescope (JWST), which would result in decreased funding for Roman in 2020–2021.[15]

President Trump's FY2020 budget request, again, proposed termination of Roman (then called WFIRST) due to cost overruns and higher priority for JWST.[16] The telescope received US$511 million for FY2020.[17] On 2 March 2020, NASA announced that it had approved Roman to proceed to implementation, with an expected development cost of US$3.2 billion and a maximum total cost of US$3.934 billion including the coronagraph and five years of mission science operations.[18]

Development

The original design of Roman, called WFIRST Design Reference Mission 1, was studied in 2011–2012, featuring a 1.3 m (4 ft 3 in) diameter unobstructed three-mirror anastigmat telescope.[19] 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 telescope made by Harris Corporation to accomplish a mission like the one planned for Roman. 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.[20] 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 may 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;[21] this mission is now the only present NASA plan for the use of the NRO telescopes.[22] The Roman baseline design includes a coronagraph to enable the direct imaging of exoplanets.[23]

Several implementations Roman were studied (including the Joint Dark Energy Mission-Omega configuration, an Interim Design Reference Mission featuring a 1.3 m telescope,[24] Design Reference Mission 1 [25] with a 1.3 m telescope, Design Reference Mission 2,[26] with a 1.1 m telescope, and several iterations of the AFTA 2.4 m configuration). In the most recent report,[8] Roman was considered for both geosynchronous and L2 orbits. Appendix C documents the disadvantage of L2 versus geosynchronous in the data rate and propellant, but the advantages for improved observing constraints, better thermal stability, and more benign radiation environment at L2. Some science cases (such as exoplanet microlensing parallax) are improved at L2, and the possibility of robotic servicing at either of the locations requires further study.

The project is led by a team at NASA's Goddard Space Flight Center in Greenbelt, Maryland. The Project scientist for Roman from its inception until his death in 2017 was Neil Gehrels, who was succeeded by Jeffrey Kruk, followed in August 2020 by Julie McEnery. The Project manager is Jamie Dunn, who succeeded Kevin Grady in late 2018. The Program scientist is Dominic Benford, and the Program executive is John Gagosian. The Formulation Science Working Group is chaired by the Project scientist, along with Deputy chairs David Spergel and Jeremy Kasdin.[27]

On 30 November 2018, NASA announced it had awarded a contract for the telescope.[28] This was for a part called the Optical Telescope Assembly or OTA, and runs to 2025.[28] This is in conjunction with the Goddard Space Flight Center for which the OTA is planned for delivery as part of this contract.[28]

A February 2019 description of the mission's capabilities is available in a white paper issued by members of the Roman team.[29]

Science objectives
A Roman presentation by Jason Rhodes at the 2020 American Astronomical Society Conference

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, weak gravitational lensing.
  • Completing a census of exoplanets to help answer new questions about the potential for life in the universe: How common are solar systems like our own? 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 include also a sample of free-floating planets with masses likely down to the mass of Mars.[30]
  • Establishing a guest investigator mode, enabling survey investigations to answer diverse questions about our galaxy and the universe.
  • Providing a coronagraph for exoplanet direct imaging that will provide the first direct images and spectra of planets around our nearest neighbors similar to our own giant planets.

Roman will have two instruments. The Wide-Field Instrument (WFI) is a 300.8-megapixel camera providing multi-band visible to near-infrared (0.48 to 2.0 micrometers) imaging using one wideband and six narrowband filters. A HgCdTe-based focal-plane array captures a 0.28 square degree field of view with a pixel scale of 110 milliarcseconds. The detector array is composed of 18 H4RG-10 detectors provided by Teledyne.[31] It also carries both high-dispersion grism and low-dispersion prism assemblies for wide-field slitless spectroscopy. The second instrument is a high contrast coronagraph covering shorter wavelengths (0.5 to 0.8 micrometers) 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 as close as 0.15 arcseconds away from their host stars.

Funding history and status
Shawn Domagal-Goldman giving a presentation concerning Roman.

In the fiscal year 2014, Congress provided US$56 million for Roman, and in 2015 Congress provided US$50 million.[32] The fiscal year 2016 spending bill provided US$90 million for Roman, far above NASA's request of US$14 million, allowing the mission to enter the "formulation phase" in February 2016.[32] On 18 February 2016, NASA announced that Roman had formally become a project (as opposed to a study), meaning that the agency intends to carry out the mission as baselined;[5] at that time, the "AFTA" portion of the name was dropped as only that approach is being pursued. Roman is on a plan for a mid-2020s launch. The total cost of Roman at that point was expected at more than US$2 billion;[33] 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.[34] In April 2017, NASA commissioned an independent review of the project to ensure that the mission scope and cost were understood and aligned.[35] 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".[36] 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.[37] NASA confirmed 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 for begin on 11 April 2018.[38]

The Trump administration's proposed FY2019 budget would terminate Roman (then called WFIRST), citing higher priorities within NASA and the increasing cost of this telescope.[10] The proposed cancellation 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.[11][12] The American Astronomical Society expressed "grave concern" about the proposed cancellation, and noted that the estimated lifecycle cost for Roman had not changed over the previous two years.[39] However, on 22–23 March 2018, Congress approved a FY18 Roman budget in excess of the administration's budget request for that year and stated that Congress "rejects the cancellation of scientific priorities recommended by the National Academy of Sciences decadal survey process", and further directed NASA to develop new estimates of Roman's total and annual development costs.[13][38] Later, the President announced he had signed the bill 23 March 2018.[40] NASA was funded via a FY2019 appropriations bill on 15 February 2019 with US$312 million for Roman, rejecting the President's Budget Request and reasserting the desire for completion of Roman with a planning budget of US$3.2 billion.[41]

Again the Trump administration proposed to terminate Roman (then called WFIRST) in its FY2020 budget proposal to Congress.[42] In testimony on 27 March 2019, NASA Administrator Jim Bridenstine hinted that NASA would continue Roman after the James Webb Space Telescope, stating "WFIRST will be a critical mission when James Webb is on orbit".[43] In a 26 March 2019 presentation to the National Academies' Committee on Astronomy and Astrophysics, NASA Astrophysics Division Director Paul Hertz stated that Roman "is maintaining its US$3.2 billion cost for now... We need US$542 million in FY2020 to stay on track". At that time, it was stated that Roman would hold its Preliminary Design Review (PDR) for the overall mission in October 2019 followed by a formal mission confirmation in early 2020. NASA announced the completion of the Preliminary Design Review (PDR) on 1 November 2019, but warned that though the mission remained on track for a 2025 launch date, shortfalls in the Senate's FY2020 budget proposal for Roman threatened to delay it further.[3]

Institutions, partnerships, and contracts

The Roman project office is located at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and holds responsibility for overall project management. GSFC also leads the development of the Wide-Field Instrument, the spacecraft, and the telescope. The Coronagraphic Instrument is being developed at NASA's Jet Propulsion Laboratory in Pasadena, California. Science support activities for Roman are shared among Space Telescope Science Institute (Baltimore, Maryland), which is the Science Operations Center; the Infrared Processing and Analysis Center, Pasadena, California; and GSFC.

Four international space agencies, namely Centre National d'Études Spatiales (CNES), German Aerospace Center (DLR), European Space Agency (ESA), and Japan Aerospace Exploration Agency (JAXA) are currently in discussion with NASA to provide various components and science support for Roman.[44][45] NASA has expressed interest in ESA contributions to the spacecraft, coronagraph and ground station support.[46] For the coronagraph instrument, contributions from Europe and Japan are being discussed.[46] A contribution from Germany's Max Planck Institute for Astronomy is under consideration, namely the filter wheels for the star-blocking mask inside the coronagraph.[47] The Japanese space agency JAXA is proposing to add a polarization module for the coronagraph, plus a polarization compensator. An accurate polarimetry capability on Roman may strengthen the science case for exoplanets and planetary disks, which shows polarization.[48][49] In addition to these potential partnerships, Australia has offered ground station contributions for the mission.[50]

In 2012, the U.S. National Reconnaissance Office (NRO) donated two space telescopes that it did not need anymore.[51] These telescopes are 2.4 meters across, about twice as large as the telescope that had been planned for Roman. As a result, the mission had been rebranded as WFIRST-AFTA, "AFTA" standing for Astrophysics Focused Telescope Assets.[52]

In May 2018, NASA awarded a multi-year contract to Ball Aerospace to provide key components for the Wide Field Instrument on Roman.[53] In June 2018, NASA awarded a contract to Teledyne Scientific and Imaging to provide the infrared detectors for the Wide Field Instrument.[54] On 30 November 2018, NASA announced it had awarded the contract for Optical Telescope Assembly to the Harris Corporation of Rochester, New York.[28]

See also

References
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