The five mission areas in NASA’s Beyond Einstein Program plan are in very different stages of technical development. Some of the mission candidates have been under study for more than 10 years, while others are at an early phase of conceptual design. Each mission candidate has its own balance of interest to the astronomy and physics research communities. The committee considered them all in as objective and transparent a way as possible, even if there is no perfectly commensurate basis for comparison. The committee recommends one mission area to be implemented first, but as noted in Chapter 2, each area makes an important contribution to Beyond Einstein research goals. Each mission area needs to receive appropriate support in order to prepare for consideration by NASA and the next astronomy and astrophysics decadal survey of the National Research Council. Some specific suggestions for providing such support are contained in the subsection below entitled “Beyond Einstein Cost Assessment Summary.”

The committee considered many ways to approach the intertwined scientific, engineering, and programmatic issues implied by its charge, and it has endeavored to respond to its entire charge as faithfully as possible. The committee firmly believes that, while the statement of task required it to recommend one mission area for a fiscal year (FY) 2009 new start, all of the Beyond Einstein mission areas address key scientific questions that take physics and astronomy beyond where the century of Einstein left them. Furthermore, the scientific issues are so compelling that Beyond Einstein research will be pursued for many years to come. Therefore, the committee responds to the task in the conviction that it is recommending the first element of an enduring program, and not the only and last mission in Beyond Einstein science.

How the Recommendations Evolved

The committee started with systematic consideration of each of the 11 mission candidates identified thus far in the five mission areas in the Beyond Einstein Program. Since the task of the committee was to select one of the five mission areas, rather than one of the 11 potential mission candidates, the mission candidates were considered only as representatives of the capabilities that could be provided by a mission area. The committee was aware that NASA typically makes a broad request for proposals in order to encourage the most up-to-date scientific strategies and technological approaches. The committee heard at least two presentations from each mission candidate team, in addition to presentations from individual scientific leaders, and had conversations with the broader scientific community in town hall meetings across the United States (see Appendixes C and D). Subsequently, the committee asked clarifying questions of each team and included the team’s written responses in the assessment process. Agency leaders in NASA, DOE, and the European Space Agency (ESA) provided additional presentations. Using these inputs, the committee assessed each mission candidate for its scientific excellence, its response to Beyond Einstein goals, its competition from other space- and ground-based projects in the United States and abroad, its scientific and engineering complexity, its cost and related programmatic implications, its stage of development and overall readiness, and pertinent individual factors. In making its recommendations, the committee considered the potential contribution of ground-based capabilities to address the scientific questions posed to the Beyond Einstein Program. The committee assumed that existing and proposed ground-based capabilities such as the Large Synoptic Survey Telescope and the Laser Interferometer Gravitational Wave Observatory (both supported by the National Science Foundation [NSF]) will be funded and operated as planned. While it is impossible to predict what discoveries will be made by ground-based systems, the projected performance of ground-based systems was compared with the expected performance of Beyond Einstein missions. This assessment culminated in draft individual write-ups for each mission candidate.

The committee carried out these steps before any formal discussion of the first part of its charge. The committee gave each mission candidate its full attention and developed a balanced view of the entire Beyond Einstein Program before addressing its main charge. Only after the drafting of the broad assessment of each mission as required in the second half of the charge did the committee start a comparative discussion to identify the main competitors for the FY 2009 start.

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