Natural Nuclear Radiation Environments for the Grand Tour Missions

The solar flare, galactic, and magnetically trapped (Van Allen) nuclear particle radiation environments expected on three outer planet "Grand Tour" missions have been calculated. The missions are the 1977 4-planet mission (Jupiter - Saturn - Uranus - Neptune), the 1977 3-planet mission (Jupiter - Saturn - Pluto), and the 1979 3-planet mission (Jupiter - Uranus - Neptune). The planetary Van Allen belts contribute the largest doses behind 1 gm/cm2 shielding of aluminum. For the 1977 4-planet mission, which passes within 2.6 planet radii of Saturn, Saturn's Van Allen belts may contribute as much as 95% of the total dose of 5300 rads. For the 1977 3-planet mission, which passes within 4.3 planet radii of Jupiter, Jupiter's Van Allen belts contribute 90% of the calculated total dose of 1900 rads. The 1979 3-planet mission dose of 600 rads is due to approximately equal contributions of solar flare particles, galactic (cosmic ray) particles, and Jupiter's Van Allen belts (periapsis at 6.7 Jupiter radii).