PROJECT VOYAGER - A GRAND TOUR TO THE GIANT PLANETS JUPITER, SATURN, URANUS AND NEPTUNE

Once every 150-175 years, the heliocentric positions of Jupiter, Saturn, Uranus and Neptune (J, S, U and N) permit an earth-launched spacecraft (chemically propelled) to sequentially pass by these four planets, using a series of successive gravity-assist maneuvers at each. The twin-VOYAGER spacecraft (800 kg) were launched on August 20 and September 5, 1977 and have had six close encounters with these four planets during the decade 1979-1989. Both V1 and V2 studied Jupiter and Saturn and their complex systems of Moons, rings and magnetospheres in great detail in 1979-1981,. Only V2 encountered Uranus and Neptune in 1986 and 1989, respectively. Remarkable discoveries by the scientific instruments on V1 and V2 include active volcanos on the Jovian Moon Io and radiation belts in the previously unknown global magnetic fields of Uranus and Neptune. During cruise between planetary encounters, V1 and V2 collected significant data on the energetic particles (cosmic rays), solar wind plasma and interplanetary magnetic fields (IMF) which fill the heliosphere. The spacecraft are exiting the solar system and expect to encounter the boundary with the interstellar medium within the next decade. This paper surveys certain of the results relevant to magnetized plasmas and energetic particles. It should be noted that the density of these astrophysical plasmas is so small (n<102/cc), that they are qualified to be legitimately described as collisonless-plasmas.