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Space exploration is a risky enterprise. Rockets launch astronauts at enormous speeds into a harsh, unforgiving environment. Spacecraft must withstand the bitter cold of space and the blistering heat of reentry. Their skin must be strong enough to keep the inside comfortably pressurized and tough enough to resist damage from micrometeoroids. Spacecraft meant for lunar or planetary landings must survive the jar of landing, tolerate dust, and be able to take off again. For astronauts, however, there is one danger in space that does not end when they step out of their spacecraft. The radiation that permeates space-- unattenuated by Earth's atmosphere and magnetosphere--may damage or kill cells within astronauts' bodies, resulting in cancer or other health consequences years after a mission ends.

The National Aeronautics and Space Administration (NASA) has recently embarked on Project Constellation to implement the Vision for Space Exploration -- a program announced by President George W. Bush in 2004 with the goal of returning humans to the Moon and eventually transporting them to Mars. To adequately prepare for the safety of these future space explorers, NASA's Exploration Systems Mission Directorate requested that the Aeronautics and Space Engineering Board of the National Research Council establish a committee to evaluate the radiation shielding requirements for lunar missions and to recommend a strategic plan for developing the radiation mitigation capabilities needed to enable the planned lunar mission architecture. Specifically, the Committee on the Evaluation of Radiation Shielding for Space Exploration was asked to do the following:

1. Review and identify critical gaps in current knowledge of radiation environments on the surfaces of the Moon and Mars.

2. Assess and identify critical gaps in the current understanding of radiation health risks faced by astronauts during various surface activities.

3. Review current and projected approaches to and capabilities for radiation shielding, as well as other feasible strategies for mitigation of exposure to radiation.

4. Recommend a comprehensive strategy for mitigating the radiation risks for astronauts during lunar surface missions to levels consistent with NASA's radiation exposure guidelines.

5. Provide recommendations on what technology investments NASA should be making in preparation for lunar missions, and recommend development timelines to ensure that NASA has the appropriate level of radiation shielding in place to meet the planned schedules for keeping radiation exposures beneath their prescribed limits.

The committee was also asked to consider the likely radiation mitigation needs of future Mars missions and to give higher priority to research and development alternatives that would enhance NASA's ability to eventually meet those future needs. The complete statement of task appears in Appendix A.

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