Rendered model of the WFIRST spacecraft, July 2018
|Names||Joint Dark Energy Mission|
|Mission type||Infrared Space observatory|
|Operator||NASA / JPL / GSFC|
|Mission duration||5 years (planned)|
|Launch mass||4,166 kg (9,184 lb)|
|Dry mass||4,059 kg (8,949 lb)|
|Payload mass||2,191 kg (4,830 lb)|
|Start of mission|
|Rocket||Delta IV Heavy (proposed)|
|Contractor||United Launch Alliance (proposed)|
|Reference system||Sun–Earth L2|
|Periapsis||188,420 km (117,080 mi)|
|Apoapsis||806,756 km (501,295 mi)|
|Diameter||2.4 m (7 ft 10 in)|
|Wavelengths||Near-infrared, visible light|
|Band||S band (TT&C support)|
Ka band (data acquisition)
|Bandwidth||Few kbit/s duplex (S band)|
290 Mbit/s (Ka band)
Wide Field Instrument
The Wide Field Infrared Survey Telescope (WFIRST) is a NASA infrared space observatory currently under development. WFIRST was recommended in 2010 by United States National Research Council Decadal Survey committee as the top priority for the next decade of astronomy. On February 17, 2016, WFIRST was approved for development and launch.
WFIRST is based on an existing 2.4 m wide field-of-view telescope 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 WFIRST is based on one of the proposed designs for the Joint Dark Energy Mission between NASA and DOE. WFIRST adds some extra capabilities to the original JDEM proposal, including a search for extra-solar planets using gravitational microlensing. In its present incarnation (2015), 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, the consistency of general relativity, and the curvature of spacetime.
On February 12, 2018, development on the WFIRST mission was proposed to be terminated in the President's FY19 budget request, due to a reduction in the overall NASA astrophysics budget and higher priorities elsewhere in the agency. In March 2018 Congress approved funding to continue making progress on WFIRST until at least September 30, 2018, in a bill stating that Congress "rejects the cancellation of scientific priorities recommended by the National Academy of Sciences decadal survey process". In testimony before Congress in July 2018, NASA administrator Jim Bridenstine proposed slowing down the development of WFIRST in order to accommodate a cost increase in the James Webb Space Telescope, which would result in decreased funding for WFIRST in 2020/2021.
The original design of WFIRST (Design Reference Mission 1), studied in 2011–2012, featured a 1.3 m (4 ft 3 in) 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 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 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; this mission is now the only present NASA plan for the use of the NRO telescopes. The WFIRST baseline design includes a coronagraph to enable the direct imaging of exoplanets.
WFIRST has had a number of different implementations studied (including the Joint Dark Energy Mission-Omega configuration, an Interim Design Reference Mission featuring a 1.3m telescope, Design Reference Mission 1 with a 1.3m telescope, Design Reference Mission 2, with a 1.1m telescope, and several iterations of the AFTA 2.4m configuration). In the most recent report, WFIRST was considered for both geosynchronous and L2 orbits. Appendix C documents the disadvantage of L2 vs. 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 WFIRST from its inception until his death in 2017 was Neil Gehrels, who was succeeded by Jeffrey Kruk. 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.
On November 30, 2018 NASA announced it had awarded a contract for the telescope. This was for a part called the Optical Telescope Assembly or OTA, and runs to 2025. This is in conjunction with the Goddard Space Flight Center for which the OTA is planned for delivery as part of this contract.
An up-to-date description of the mission's capabilities (as of February 2019) is available in a recent white paper (https://arxiv.org/abs/1902.05569) issued by members of the WFIRST team.
- Answering basic questions about dark energy, complementary to the 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? WFIRST 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.
- 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.
WFIRST will have two instruments. The Wide-Field Instrument (WFI) is a 288-megapixel camera with a 0.28 square degree field of view providing multi-band near-infrared (0.7 to 2.0 micrometers) imaging using a HgCdTe focal-plane array with a pixel size of 110 milliarcseconds. The detector array will be composed of H4RG-10 detectors provided by Teledyne. It includes a grism for wide-field slitless spectroscopy and an integral field spectrograph for small-field spectroscopy. The second instrument is a high contrast coronagraph covering shorter wavelengths (0.4 to 1.0 micrometers) using novel starlight-suppression technology. It is intended to achieve a part-per-billion suppression of starlight to enable the detection of planets only 0.1 arcseconds away from their host stars.
Funding history and status
In fiscal year 2014, Congress provided $56 million for WFIRST, and in 2015 Congress provided $50 million. The fiscal year 2016 spending bill provided $90 million for WFIRST, far above NASA's request of $14 million, allowing the mission to enter the "formulation phase" in February 2016. On February 18, 2016, NASA announced that WFIRST had formally become a project (as opposed to a study), meaning that the agency intends to carry out the mission as baselined; at that time, the "AFTA" portion of the name was dropped as only that approach is being pursued. WFIRST is on a plan for a mid-2020s launch. The total cost of WFIRST is expected at more than $2 billion; NASA's 2015 budget estimate was around $2.0 billion in 2010 dollars, which corresponds to around $2.7 billion in real year (inflation-adjusted) dollars. 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 WFIRST 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 $3.2B cost target set at the beginning of Phase A." NASA announced the reductions taken in response to this recommendation, and that WFIRST would proceed to its mission design review in February 2018 and begin Phase B by April 2018. NASA confirmed that the changes made to the project had reduced its estimated life cycle cost to $3.2B and that the Phase B decision was on track for completion on April 11, 2018.
The Trump administration's proposed FY2019 budget would terminate WFIRST, citing higher priorities within NASA and the increasing cost of this telescope. The proposed cancellation of the project was met with criticism by professional astronomers, who noted that the American astronomical community had rated WFIRST the highest-priority space mission for the 2020s in the 2010 Decadal Survey. The American Astronomical Society expressed "grave concern" about the proposed cancellation, and noted that the estimated lifecycle cost for WFIRST had not changed over the previous two years. However, on March 22–23, Congress approved a FY18 WFIRST 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 WFIRST's total and annual development costs. Later, the President announced he had signed the bill March 23, 2018.
Institutions, partnerships, and contracts
The WFIRST project office is located at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and holds responsibility for overall project management. GSFC also leads 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 WFIRST 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. Further technical details of the mission are available at WFIRST specific web pages from NASA, GSFC, STScI, IPAC, and JPL.
Space agencies from four nations and regions, namely CNES, DLR, ESA, and JAXA are currently in discussion with NASA to provide various components and science support for WFIRST. NASA has expressed interest in ESA contributions to the spacecraft, coronagraph and ground station support. For the coronagraph instrument, contributions from Europe and Japan are being discussed. 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. The Japanese space agency JAXA is proposing to add a polarization module for the coronagraph, plus a polarization compensator. An accurate polarimetry capability on WFIRST may strengthen the science case for exoplanets and planetary disks, which shows polarization. In addition to these potential partnerships, Australia has offered ground station contributions for the mission.
In May 2018, NASA awarded a multi-year contract to Ball Aerospace to provide key components for the Wide Field Instrument on WFIRST. In June 2018, NASA awarded a contract to Teledyne Scientific and Imaging to provide the infrared detectors for the Wide Field Instrument. On November 30, 2018 NASA announced it had awarded the contract for Optical Telescope Assembly to the Harris Corporation of Rochester, New York.
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