The proposed Wide Field Infrared Survey Telescope
NASA
By Daniel CleryOct. 23, 2017 , 4:10 PM
NASA will have to scale back its next big orbiting observatory to avoid busting its budget and affecting other missions, an independent panel says. The Wide Field Infrared Survey Telescope (WFIRST) is due for launch in the mid-2020s. But 1 year after NASA gave the greenlight its projected cost is $3.6 billion, roughly 12% overbudget.
“I believe reductions in scope and complexity are needed,” Thomas Zurbuchen, head of NASA’s Science Mission Directorate in Washington, D.C., wrote in a memo that NASA released last Thursday.
Designed to investigate the nature of dark energy and study exoplanets, WFIRST was chosen by the astronomy community as its top space-based mission priority in the 2010 decadal survey entitled New Worlds, New Horizons in Astronomy and Astrophysics. But the start of the project was initially delayed by the huge overspend on its predecessor, the James Webb Space Telescope, which will be launched in 2019. Then last year, a midterm review of the 2010 decadal survey warned that WFIRST could go the same way and advised NASA to form a panel of independent experts to review the project.
NASA assembled that panel in April this year and it recently submitted its conclusions. The agency has not released its report, as it is due to be discussed by the Committee for Astronomy and Astrophysics of the National Academies of Sciences, Engineering, and Medicine this week, but it did release a memo from Zurbuchen to Christopher Scolese, director of the Goddard Space Flight Center in Greenbelt, Maryland, which is leading the project.
In it, Zurbuchen directs the lab “to study modifying the current WFIRST design … to reduce cost and complexity sufficient to have a cost estimate consistent with the $3.2 billion cost target [set last year].” Though the panel heaped praise on the WFIRST team for the work done so far, according to Zurbuchen’s memo, it faulted NASA managers for creating several challenges that have made the project “more complicated than originally anticipated.”
Paul Hertz, head of NASA’s astrophysics division, told ScienceInsider that one major demand was enlarging the spacecraft to accommodate a 2.4-meter mirror that the National Reconnaissance Agency donated in 2012. Another was adding an instrument called a coronagraph.
WFIRST, which will have the sensitivity of the Hubble Space Telescope but with 100 times its field of view, was originally designed to survey the sky for signs of cosmic acceleration caused by dark energy. But when exoplanet researchers realized it would also benefit their field they lobbied for the inclusion of a coronagraph. This device acts as a mask inside the telescope to block out the glaring brightness of a star and reveal any dim planets around it.
NASA also decided to split the ground segment for the mission between the Space Telescope Science Institute in Baltimore, Maryland, and the California Institute of Technology in Pasadena. And in an act of future-proofing, NASA wanted WFIRST to carry equipment making it compatible with a starshade, a proposed spacecraft that can be stationed at a distance to block out starlight and reveal exoplanets (more effectively than a coronagraph). “All these things added complexity,” Hertz says.
Zurbuchen’s memo to Scolese directs the lab to retain the basic elements of the mission—the 2.4-meter mirror, widefield camera, and coronagraph—but to seek cost-saving “reductions.” Hertz says this will require reducing the capabilities of instruments but ensuring they remain “above the science floor laid down by the decadal survey.” The coronagraph will be recategorized as a “technology demonstration instrument,” removing the burden of achieving a scientific target. The change will also save money, Hertz explains.
Hertz says exoplanet researchers shouldn’t worry about the proposed changes. “We know we’ll get good science out of the coronagraph. We’ll be able to see debris disks, zodiacal dust, and exoplanets in wide orbits,” he says. Astronomers wanting to see Earth twins in the habitable zone may be disappointed, however.
Zurbuchen also asked project managers to save money in the ground segment and by letting industry build some components or subsystems. The WFIRST team will need to submit a revised design by February 2018, before vendors are chosen, to begin building the hardware.
If costs continue to escalate, Zurbuchen says in his memo, NASA may need to abandon the 2.4-meter mirror and revert to the original, cheaper design using a 1.5-meter one. “That is plan B,” says Hertz, “but we very much like the 2.4-meter mirror.”
Source: Science Mag