Among these deep space travelers, Pioneers 10 and 11 are appropriately named, for they truly are pioneering the exploration of the outer solar system. Launched in 1972 and in 1973, respectively, they were the first spacecraft to fly by Jupiter (in 1973 and 1974). At Jupiter, Pioneer 11’s trajectory was carefully targeted to swing it toward Saturn for an encounter in September 1979. We see some of the early results in this publication. Other spacecraft are following along the trail blazed by Pioneer Saturn. Voyager 1 passed by Jupiter in March 1979 and will reach Saturn in November 1980. Voyager 2 has also passed beyond Jupiter and will encounter Saturn in August 1981, with the further possibility of traveling on to Uranus (a 1986 encounter). Under development are the Galileo orbiter and atmospheric entry probe, destined to journey to Jupiter where the orbiter will return more detailed information, including high-resolution pictures of the Galilean satellites, and the probe will penetrate deep below the Jovian clouds. In the coming years, each of these follow-on missions will enrich our understanding of the solar system, greatly supplementing the observations of Pioneers 10 and 11. But one thing will never change. The Pioneers were first. Thomas A. Mutch Associate Administrator for Space Science National Aeronautics and Space Administration PIONEER SATURN [Illustration: Pioneer Saturn spacecraft.] Pioneer Saturn has given us our first close view of the spectacular ringed planet Saturn and its system of moons. The spacecraft began its journey to the giant planets Jupiter and Saturn on April 5, 1973, as Pioneer 11. It reached Jupiter on December 2, 1974, passing within 42,760 km of the Jovian cloud tops and taking the only existing pictures of Jupiter’s polar regions. Jupiter’s massive gravitational field was used to swing Pioneer 11 back across the solar system toward Saturn. Additional maneuvers were executed in 1975 and 1976 to place the spacecraft on a suitable trajectory, with the final aimpoint selected in 1977. From the many possible targeting options for the first Saturn flyby, two aimpoints were considered, both of which would result in a near-equatorial flyby that would give the best mapping of the high-energy particles and the magnetic field near the planet. The difference between these two aimpoints, which came to be known as the “inside” and “outside” options, was their relationship to Saturn’s unique ring system first discovered by Galileo in 1610. The “outside” option was finally selected because it was considered to be of less risk to the spacecraft and more valuable in planning the subsequent encounter of Saturn by Voyager 2, which will reach Saturn in 1981. Final targeting was completed during early 1978, when a series of timed rocket thrusts locked Pioneer into the desired trajectory. [Illustration: Pioneer Saturn voyage.] [Illustration: Encounter trajectory.]