the human exploration program and that it move quickly to give those areas careful attention in a process that emphasizes crosscutting reviews to reflect their interdisciplinary scope, generates rigorous priority setting like that achieved in the decadal science surveys, and utilizes input from a broad range of expertise in the scientific and technical community.

• NASA’s robotic science program has enjoyed remarkable success, and it provides lessons that are worth applying to the human spaceflight program. The committee recommends that successful aspects of the robotic science program—especially its emphasis on having a clear strategic plan that is executed so as to build on incremental successes to sustain momentum, use resources efficiently, enforce priorities, and enable future breakthroughs—should be applied in the human spaceflight program.

New opportunities for research will arise as a result of human space exploration, and other research efforts will facilitate its success, but these two categories of science need to be treated differently. Science that is enabled by human exploration is properly competed directly with “decadal-survey” science⁴ and then ranked and prioritized according to the same rigorous criteria. For science to enable human exploration, competitive choices will depend on the criticality of the problem the science addresses and the likelihood that it will resolve the problem. For the former kind of science, understanding is an end in itself. For the latter, understanding is a means to the goal of resolving an identified problem, and the degree of understanding needed depends on the problem at hand.

The presidential policy directive on exploration also provides the context for deciding on the future of the space shuttle and the mission of the International Space Station. NASA is directed to retire the shuttle as soon as the assembly of the ISS is complete, which is assumed to be by 2010, and to focus the use of the ISS on supporting the goals of long-duration, human space exploration. Doing this in the most cost-effective way possible is essential for achieving NASA’s goals for robotic and human exploration.