RECOMMENDATION: In exchange for this small, but crucial, contribution, NASA should secure through negotiation with the European Space Agency both a U.S. position on the Euclid Science Team with full data access and the inclusion of a team of U.S. scientists in the Euclid Consortium that would be selected by a peerreviewed process with full data access as well as authorship rights consistent with Euclid policies still to be formulated.

As with all NASA missions, the expectation is that NASA will ensure and support access to the Euclid data for the wider U.S. community once the proprietary data period has expired. This involvement is especially important for Euclid, whose survey data should enable significant legacy science. Through its direct involvement in Euclid, the U.S. science team will enhance not only the U.S. capabilities to study dark energy but also the broader use of the Euclid data by the U.S. community. If software developed by the U.S. Euclid team is made available to the community when the Euclid data become public, this step also will enhance the broader community’s ability to use the Euclid data. While the U.S. role on the EST should be more carefully delineated through negotiations with the European Space Agency, it could, for example, involve leadership in Euclid legacy science, defined as providing value-added data products to the community that combine relevant ground and space data sets (including those from WFIRST), given the importance of data dissemination to the U.S. community.

NASA and the European Space Agency are discussing several possible options for the U.S. hardware contribution. While the two agencies should determine the nature of the U.S. contribution, contributions with the maximum science benefit to the Euclid mission will benefit both the European and the U.S. communities.52 The reaction wheel could offer a significant improvement in mission efficiency. The filter wheel would also provide some benefit to the mission and would take advantage of U.S. expertise in designing filter wheels (e.g., for the Hubble Space Telescope). The near-infrared detectors, if characterized by U.S. instrumentalists who have expertise in this area, would be beneficial but would likely be the more expensive of the options.

The science goals of WFIRST go far beyond those of Euclid, and WFIRST is central to realizing those goals and to maintaining U.S. leadership in astronomy and astrophysics in the next decade and beyond. The committee notes that early expenditures on pre-phase A studies, particularly those that engage the community, often accelerate mission timelines and reduce costs.

Mission collaboration costs often grow, as demonstrated by the U.S. participation in the Planck mission discussed above. The committee recommends a tripwire for the hardware costs at 50 percent above the recommended value of $20 million.

RECOMMENDATION: NASA should seek independent community review of any financial commitment for hardware expenditures beyond $30 million for Euclid.

The committee recognizes that support for this science team will cost an additional ∼$2 million per year for about 10 years, for a total that is similar to the hardware investment. That is a necessary expense and not the kind of increase discussed herein. Given the constraints on the NASA budget it is crucial that the contribution to Euclid not grow and impact the rest of the space astrophysics program. The Decadal Survey Implementation Advisory Committee (DSIAC) proposed and described in NWNH would provide an appropriate mechanism for such a review.

CONCLUSION: The committee concludes that the combination of data from planned U.S.-led ground-based surveys with Euclid and WFIRST data will enhance the science return from both the ground- and space-based surveys, and that a coordinated, strategic approach to managing these joint data sets could position the U.S. community for a leadership role in their scientific exploitation.

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