Space weather challenges intrinsic to the human exploration of space

There is renewed emphasis on human exploration of the solar system, starting with a US. initiative to return to the Moon in the 2015-to-2020 timeframe and subsequent human missions to Mars and beyond. Exposure to radiation is one of the primary threats to the health of the astronauts who embark on exploration missions. While the steady exposure to galactic cosmic radiation provides the largest contribution to the cumulative mission dose for long-duration missions, the threat posed by solar particle events (SPEs), particularly for missions to the Moon, can be severe. This paper provides an overview of the impact of SPEs on human missions and emphasizes the multidisciplinary character of research needed to reduce the threat that SPEs pose. Predicting an SPE involves the solar physics community (predicting the eruption and character of a sufficiently large coronal mass ejection), the plasma/particle community (determining the time evolution of the event and its energy spectrum) and the heliospheric physics community (characterizing the propagation of emerging particles through the ambient solar wind background).