In the three and a half years since the release of the 2010 decadal survey in astronomy and astrophysics, New Worlds, New Horizons in Astronomy and Astrophysics1 (NWNH), NASA has studied several approaches to realizing the Wide-Field Infrared Survey Telescope (WFIRST), NWNH’s first priority for a large space mission for the decade 2010-2020. Two of these approaches, the 1.3-m aperture WFIRST/Interim Design Reference Mission (IDRM), based on the implementation considered by NWNH, and the WFIRST/Astrophysics Focused Telescope Assets (AFTA), a configuration with a 2.4-m telescope utilizing hardware made available to NASA by the National Reconnaissance Office, would enable a mission of the scientific scope envisioned for WFIRST. The larger aperture of WFIRST/AFTA offers the potential of substantially greater scientific reach than is possible with WFIRST/IDRM. The large aperture also makes inclusion of a coronagraph attractive. This addition was not envisioned by NWNH as part of WFIRST, but it has the potential to advance NWNH objectives aimed at the eventual realization of a future Earth-like-planet imaging mission that was a high priority of the NWNH survey.
This report of the National Research Council’s Committee on an Assessment of the Astrophysics Focused Telescope Assets (AFTA) Mission Concepts responds to a request from NASA to compare the WFIRST mission described in NWNH to the WFIRST/AFTA design reference mission, with and without a coronagraph, on the basis of scientific objectives, technical complexity, and programmatic ra-
1 National Research Council, New Worlds, New Horizons in Astronomy and Astrophysics, The National Academies Press, Washington, D.C., 2010.
tionale, including projected cost. The committee was also charged with assessing the responsiveness of the WFIRST/AFTA mission to the overall strategy to pursue the NWNH science objectives and, in particular, those articulated for WFIRST. In addition, NASA requested an assessment of the responsiveness of the coronagraph, if added, to the exoplanet technology development and scientific objectives identified by NWNH.
After considering the scientific reach of WFIRST/AFTA compared to the primary goals described in NWNH, the committee offers the following finding:
Finding 3-2: The opportunity to increase the telescope aperture and resolution by employing the 2.4-m AFTA mirror will significantly enhance the scientific power of the mission, primarily for cosmology and general survey science, and will also positively impact the exoplanet microlensing survey. WFIRST/AFTA’s planned observing program is responsive to all the scientific goals described in NWNH.
The coronagraph design is currently immature, with two very different options being considered, and within those, several implementations are possible. All of these designs would demonstrate advanced techniques likely to be directly applicable to any future Earth-like-planet imaging mission.
Finding 1-7: The WFIRST/AFTA coronagraph satisfies some aspects of the broader exoplanet technology program recommended by NWNH by developing and demonstrating advanced coronagraph starlight suppression techniques in space.
In the programmatic context, the committee emphasizes that the maturity of the WFIRST design and technologies and the relatively low technical, cost, and schedule risks associated with the implementation considered by NWNH were central to the mission’s top ranking in the large category. NWNH also placed strong emphasis on a balanced program of activities with significantly increased investment in the Explorer and research and analysis (R&A) programs. NWNH noted that cost growth in large missions has resulted in a serious imbalance in the program that continues to jeopardize its overall scientific return.
Finding 3-3: If implementing WFIRST/AFTA compromises the program balance, then it is inconsistent with the rationale that led to the high-priority ranking in NWNH.
The committee’s evaluation notes that there are risks as well as benefits of utilizing inherited hardware designed for another purpose. Informed by this and the Aerospace Corporation’s cost and technical evaluation (CATE), the committee offers the following finding:
Finding 2-4: The risk of cost growth is significantly higher for WFIRST/AFTA without the coronagraph than for WFIRST/IDRM.2
Because of the immature design and because there has been very limited study of the coronagraph’s accommodation on the mission, the committee could not quantitatively assess the cost and risk impact to the WFIRST/AFTA program.3 However, the committee found the following:
Finding 2-6: Introducing a technology development program onto a flagship mission creates significant mission risks resulting from the schedule uncertainties inherent in advancing low technical readiness level (TRL) hardware to flight readiness.
Finding 2-7: WFIRST’s moderate cost, low technical risk, and mature design were important to its ranking as the top priority for a large space mission in NWNH. The inclusion of the coronagraph compromises this rationale.
Finding 2-8: Without corresponding augmentation to other NASA programs accompanying funding to include the coronagraph on WFIRST, the inclusion of the coronagraph is not consistent with stated priorities in NWNH. In a time of reduced budgets, the first priority in NWNH is “to develop, launch, and operate WFIRST and to implement the Explorer program and core research program recommended augmentations.” Implementing the coronagraph would address some aspects of the exoplanet technology development; the exoplanet technology development program was considered a lower priority by NWNH.
WFIRST/AFTA is a highly compelling scientific mission addressing head-on some of the most exciting and fundamental questions in astrophysics today. The committee also recognizes the high scientific importance of, and public excitement surrounding, a future mission that could image Earth-like planets. However, because of the priority NWNH placed on the WFIRST primary science and the implementation of a balanced program, the committee makes the following recommendation:
Recommendation 2-1: NASA should move aggressively to mature the coronagraph design and develop a credible cost, schedule, performance, and observing program so that its impact on the WFIRST mission can be determined. Upon completion of this activity, and a cost and technical evaluation of WFIRST/AFTA with the coronagraph, an independent review focused
2 See also Finding 2-2.
3 See Finding 2-5.
on the coronagraph should be convened to determine whether the impact on WFIRST and on the NASA astrophysics program is acceptable or if the coronagraph should be removed from the mission.
After a decision has been made on the mission implementation, in order to ensure that budget plans and contingencies are adequate to ensure that WFIRST’s implementation is consistent within the context of all of the NWNH priority recommendations, the committee makes the following recommendation:
Recommendation 3-1: NASA should sponsor an external technical and cost review of the WFIRST/AFTA mission that NASA plans to propose as a new start. This review should be independent of NASA’s internal process. The objective of the review should be to ensure that the proposed mission cost and technical risk are consistent with available resources and do not significantly compromise the astrophysics balance defined in the 2010 National Research Council report New Worlds, New Horizons in Astronomy and Astrophysics. This review should occur early enough to influence the exercising of a re-scoping of the mission if required.