WASHINGTON — An independent review board for NASA’s next flagship astronomy mission concluded in its final report that the project is “not executable” without additional funding or adjustments to the spacecraft.

NASA released the report, a 65-page document in the form of a PowerPoint presentation, Nov. 22, a month after the agency published its response calling for a reduction in the proposed cost of the Wide-Field Infrared Survey Telescope (WFIRST) and changes to its management.

The report, prepared by an outside committee established by NASA called the WFIRST Independent External Technical/Management/Cost Review (WIETR), found that various changes made to WFIRST since it was proposed as the top-ranking large, or flagship, mission in the 2010 astrophysics decadal survey created cost and technical difficulties.

“After multiple discussions that set the boundary conditions, NASA HQ made a series of decisions that set the stage for an approach and mission system concept that is more complex than probably anticipated from the point of view of scope, complexity, and the concomitant risks of implementation,” the report stated.

Those decisions include the use of a 2.4-meter telescope donated by the National Reconnaissance Office to NASA, larger than the one originally envisioned for WFIRST. Another factor is a decision to add an instrument called a coronagraph that is technically challenging but could support studies of extrasolar planets not possible with WFIRST’s other instrument, a wide-field imager.

Those changes, while increasing WFIRST’s capabilities, have also increased its costs. Initial concepts for WFIRST included in the decadal report had an estimated cost of less than $2 billion. The WIETR report concluded that, at a 70 percent confidence level, WFIRST would now cost $3.9 billion. An additional $250–300 million would also be needed if NASA changed the risk classification of the mission from Class B to Class A, which the report concluded would be consistent for missions of this caliber.

“The WIETR concludes therefore that although the scope is understood, as designed, the risks to the primary mission of WFIRST are significant and therefore the mission is not executable without adjustments and/or additional resources,” the report concluded.

Even before releasing the full report, NASA acted on its recommendations. In an Oct. 19 memo to Chris Scolese, director of the Goddard Space Flight Center, which hosts the WFIRST program, NASA Associate Administrator for Science Thomas Zurbuchen called for changes to the program to reduce its costs to an earlier target of $3.2 billion. He left open the door to more significant changes, including revisiting the use of the 2.4-meter telescope, if that cost target could not be achieved.

The report itemized the cost savings for a number of potential changes to WFIRST. The biggest would come from removing the coronagraph instrument from the mission, saving $400 million. Smaller reductions are possible with changes to the coronagraph or wide-field imager, as well as elimination of support for robotic servicing and compatibility with a potential future “starshade” spacecraft.

Zurbuchen, in his October letter, instructed that the coronagraph be reclassified as a technology demonstration instrument, one of the options considered by the report, to help reduce costs. However, the WIETR report concluded that if the $3.2 billion cost cap is required, as Zurbuchen indicated in his letter, it may require “descoping the [coronagraph] from the WFIRST mission, together with some of the other smaller-value descopes” to approach that figure.

That $3.2 billion cost cap, set by the program at a milestone known as Key Decision Point (KDP) A but not publicized prior to last month’s letter, may not be a realistic target at all, the WIETR team argued. “The expectation of a ‘$3.2B maximum’ management agreement cap set at KDP-A is not realistic for the scope, complexity, and expectations of the WFIRST mission,” it stated, citing the complexity created by the 2.4-meter telescope and the coronagraph.

NASA released the report with little fanfare Nov. 22, just before the Thanksgiving holiday, nearly a month after agency officials said it would wait until next year until doing so. At an Oct. 25 briefing about the report during a meeting of the Committee on Astronomy and Astrophysics of the National Academies’ Space Studies Board, Zurbuchen and others said they would wait until February, the deadline for completing proposed revisions to WFIRST, to release the report.

“The WIETR report has a lot of details in it, a lot of options that the WIETR panel laid out as possibilities for the team,” said Paul Hertz, director of NASA’s astrophysics division, at that meeting when asked why the release of the report would be delayed. “We want to give the project some space to make choices and come forward with a modified design without being second-guessed all the time in public.”

One committee member, though, pushed for an earlier release. “I think it was really a great job,” Thomas Young, a former NASA official and aerospace industry executive, said of the WIETR report. “Not releasing the report would take away from that. In other words, releasing the report shows that you’re transparent in what you’re doing.”

The cost growth of WFIRST could put pressure on other NASA astrophysics and broader science programs, something that a National Academies report that performed a midterm review of the 2010 astrophysics decadal warned about last year.

“WFIRST’s position as the number one recommendation from the 2010 Decadal Survey was predicated on it being low-risk technology and having a relatively short timescale. Circumstances accompanying the WFIRST implementation have dramatically altered the mission, increasing its cost and schedule,” the WIETR report stated.

“NASA HQ should be cognizant of community sensitivity regarding the perceived large and growing opportunity cost of WFIRST, relative to other compelling priorities for [NASA’s Science Mission Directorate], including other strategic missions,” the report continued. “This is especially important as preparations are being made for the 2020 Decadal Survey.”