start in FY 2009. To accomplish this task, the committee assessed all five mission areas, using criteria that address both potential scientific impact and technical readiness. In addition, the report was to assess each mission in sufficient detail to provide input for decisions by NASA and for the NRC’s next astronomy and astrophysics decadal survey regarding both the ordering of the remaining missions and the investment strategy for future technology development within the Beyond Einstein Program. In responding to this latter charge, the committee has attempted to indicate what next steps each of the missions would need to take in order to prepare for future assessments.


The criteria adopted by the committee in assessing the missions fell into two general categories. First, the committee looked at the potential scientific impact within the context of other existing and planned space-based and ground-based missions. Here the committee considered how directly each assessed mission would address the research goals of the Beyond Einstein research program, likely contributions to the broader field of astrophysics, the potential for revolutionary scientific discovery, the scientific risks and readiness of the mission, and its competition from other ground- and space-based instruments.

Second, the committee considered the realism of preliminary technology and management plans and of cost estimates. Criteria used by the committee included plans for the maturity of critical mission technology, technical performance margins, schedule margins, risk-mitigation plans, and the proposal’s estimated costs versus independent probable cost estimates prepared by the committee.

The committee made its recommendations on the basis of the above criteria, but during its deliberations it identified several policy-related issues relevant to the Beyond Einstein Program. These issues included implications for U.S. science and technology leadership, program funding constraints, relationships in interagency and international partnerships, investments in underlying research and technology and supporting infrastructure, and the impact of International Traffic in Arms Regulations. The committee reviewed these issues in order to understand the broader context of the study.

Using the criteria described above, the committee performed extensive assessments for each mission. It is impossible to adequately summarize here all of the points that factored into the final mission selection. Rather, each of the missions reviewed by the committee is briefly described below, along with a summary of a few of the major points from the committee’s assessment.

Science Impact and Technology Readiness

Black Hole Finder Probe (BHFP)

The two Black Hole Finder Probe mission concepts presented to the committee are called EXIST (Energetic X-ray Imaging Survey Telescope) and CASTER (Coded Aperture Survey Telescope for Energetic Radiation). Both of these concepts use wide-field coded-aperture hard x-ray telescopes, divided into arrays of subtelescopes at two different energy bands. With their arrays of subtelescopes, either would survey the entire sky between a few kiloelectronvolts and 600 keV during the course of their 95 minute orbits, providing information about source variability on time scales ranging from milliseconds to many days.

Science Importance and Readiness BHFP is designed to find black holes on all scales, from one to billions of solar masses. It will observe high-energy x-ray emission from accreting black holes and explosive transients and will address the question of how black holes form and grow.

BHFP will be unique among current or planned missions in high-energy x-ray sensitivity combined with large field of view and frequent coverage of the sky. The resulting hard x-ray sky maps, temporal variability data, and the large number of short-lived transient detections will have a direct impact on a number of important astrophysical questions. BHFP will provide a unique window into the properties and evolution of astronomical objects whose physics is dominated by strong gravity.

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