SPACE MISSIONS
The space age dawned in the outer solar system when the Pioneer 10 and 77 spacecraft flew a first reconnaissance by jupiter in December of 1973 and 1974. With gravitational assistance from jupiter Pioneer 77 went on to rendezvous with Saturn in September 1979, passing within about 21,400 kilometers of the planet. Pioneer 10 and 11 will cross the orbit of Pluto (but far from the planet) sometime between 1987 and 1990 on their way out of the solar system.
In the late summer of 1977 Voyager 1 and 2 were launched toward jupiter, Saturn, and their satellites. These spacecraft carried 11 different scientific instruments. For fear of radiation damage to measuring instruments, Voyager 1 was targeted to pass within about 5 Jupiter radii in its March 1979 encounter with the planet; and Voyager 2, no closer than about 10 Jupiter radii in july 1979. Besides studying Jupiter, both spacecraft "looked at" its innermost satellite Amalthea and the Galilean satellites (10, Europa, Ganymede, and Callisto). The Galilean satellites (shown in the photograph at the beginning of this chapter) were photographed with a resolution as good as that in Mariner 9's photographs of Mars.
After departing from jupiter, Voyager 1 and 2 headed for an encounter with Saturn, using the gravitational assist of Jupiter for their acceleration toward Saturn. Voyager 1 made its closest approach to Saturn in November 1980, Voyager 2 following some 10 months later, in August 1981. Voyager 2 also received a gravitational assist from Satu rn for a rendezvous with Uranus in January 1986 and if all goes well, with Neptune in August 1989.
The next space mission to the outer solar system, Project Calileo, is currently scheduled for launch sometime in the next decade. This mission will send to Jupiter a 2-ton orbiter with a detachable probe that will enter the planet's atmosphere on the sunlit side. The orbiter will then go into orbit about the planet.
