Human missions beyond LEO, such as to the Moon, Mars, asteroids, or even to the moons of Jupiter and Saturn are considered as a natural extension of the current human activities in space. Such long journeys outside the protective umbrella of the geomagnetic field will expose both astronauts and equipment to the radiation environment found in the deep space (Horneck et al. 2003a). The lunar surface radiation environment is characterized by the GCR and SCR in the near Earth environment that impact the lunar surface thereby producing secondary particles which diffuse from the surface into the local environment. The mass shielding effect of the Moon itself is nearly a factor of two. On Mars which, like the Moon, lacks a magnetic field, GCR and SCR interact directly with the Martian atmosphere, whereby low energy charged particles are stopped and the composition of the particle fields penetrating to the surface of Mars is modified (Horneck et al. 2003b, Horneck et al. 2005). In the vicinity of Jupiter, the solar wind produces less deflecting effects on the GCR relative to the Earth. In addition, Jupiter's huge magnetic field traps electrons in a radiation belt extending up to large distances from Jupiter. The mechanism of magnetic trapping of radiation at Jupiter is the same that operates in the Earth's Van Allen belts. For a human mission to, e.g., Jupiter's moon Callisto, when crossing the jovian electron belts, peak radiation doses up to 3 mSv/day have been calculated for the habitat behind a 4 g/cm2 shielding of the spacecraft (De Angelis et al. 2004).
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