From: National Research Council
Posted: Tuesday, March 18, 2014
WASHINGTON -- The opportunity to increase the aperture and resolution on NASA’s planned Wide-Field Infrared Survey Telescope (WFIRST) would significantly expand the scientific capabilities of the mission, but the risk of cost growth is significantly higher than for NASA’s original design, says a new report from the National Research Council.
WFIRST was ranked the top-priority large space mission in the National Research Council’s 2010 decadal survey of astronomy and astrophysics research. WFIRST would probe the nature of dark energy – the as yet unexplained driver behind the accelerating expansion of the universe; study the architecture of other solar systems; and advance understanding of how galaxies, stars, and black holes evolve. This science program, together with the mission’s moderate cost, low technical risk, and mature design were key factors in its top ranking among large space missions.
NASA initially considered a design of WFIRST with a 1.3-meter aperture. In 2012, the National Reconnaissance Office gave NASA hardware for two 2.4-meter telescopes -- the same size as the currently operating Hubble Space Telescope. NASA dubbed these the Astrophysics Focused Telescope Assets (AFTA) and began to study an alternative to the original telescope design. After the NRO telescopes were acquired, NASA also began to consider the addition of a coronagraph, an instrument that would advance goals in the study of exoplanets.
The new Research Council report compares the WFIRST/AFTA design both with and without a coronagraph to the original mission concept, on the basis of their science objectives, technical complexity, and programmatic rationale, including projected cost. The report does not recommend which design NASA should adopt.
The committee that wrote the report found that the larger aperture provided by the 2.4-meter design “will significantly enhance the scientific power of the mission” for cosmology, exoplanet surveys, and general infrared survey science, such that the mission is consistent with the scientific goals described in the decadal survey. This new design also makes inclusion of a coronagraph attractive.
However, the inherited hardware was designed for another purpose, and the degree to which changes to the hardware must be made to accommodate a different launch vehicle and scientific requirements is uncertain at this time. This uncertainty contributes to higher technical risk and a greater likelihood that costs will increase beyond current estimates, the report says. The WFIRST/AFTA without the coronagraph was estimated to cost $2.1 billion, up from an estimate of $1.8 billion for an earlier design which was more similar to the mission recommended in the 2010 survey report.
A coronagraph was not envisioned by the 2010 Research Council report as being a part of WFIRST, but it has the potential to advance objectives aimed at the eventual realization of a future Earth-like planet imaging mission. However, the coronagraph design is immature, and there has been limited study of accommodating the instrument on the mission, the report says. Recognizing the scientific importance and public excitement surrounding exoplanet science, the committee recommended that NASA move aggressively to mature the coronagraph design and develop a credible cost, schedule, performance, and observing program so that the coronograph’s impact on the WFIRST mission can be determined.
Subsequently, an independent cost and technical evaluation of WFIRST/AFTA with a coronagraph should be conducted to determine whether the instrument’s impact on the mission and the NASA astrophysics program is acceptable or if the coronagraph should be removed from the mission. The report says that if pursuing the WFIRST/AFTA with the coronagraph compromises the overall balance of the NASA astrophysics program, then it is inconsistent with the 2010 survey’s guidance.
The report was sponsored by NASA. The National Academy of Sciences, National Academy of Engineering, Institute of Medicine, and National Research Council make up the National Academies. They are private, independent nonprofit institutions that provide science, technology, and health policy advice under a congressional charter granted to NAS in 1863. The National Research Council is the principal operating arm of the National Academy of Sciences and the National Academy of Engineering. For more information, visit http://national-academies.org. A committee roster follows.
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Pre-publication copies of Evaluation of the Implementation of WFIRST/AFTA in the Context of New Worlds, New Horizons in Astronomy and Astrophysics are available from the National Academies Press on the Internet at http://www.nap.edu or by calling 202-334-3313 or 1-800-624-6242. Reporters may obtain a copy from the Office of News and Public Information (contacts listed above).
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