Voyager 2 was one of a pair of spacecraft launched to explore the planets of the outer solar system and the interplanetary environment. Each Voyager had as its major objectives at each planet to: (1) ... investigate the circulation, dynamics, structure, and composition of the planet's atmosphere; (2) characterize the morphology, geology, and physical state of the satellites of the planet; (3) provide improved values for the mass, size, and shape of the planet, its satellites, and any rings; and, (4) determine the magnetic field structure and characterize the composition and distribution of energetic trapped particles and plasma therein.
Originally planned as a Grand Tour of the outer planets, including dual launches to Jupiter, Saturn, and Pluto in 1976-77 and dual launches to Jupiter, Uranus, and Neptune in 1979, budgetary constraints caused a dramatic rescoping of the project to two spacecraft, each of which would go to only Jupiter and Saturn. The new mission was called Mariner Jupiter/Saturn, or MJS. It was subsequently renamed Voyager about six months prior to launch. The rescoped mission was estimated to cost $250 million (through the end of Saturn operations), only a third of what the Grand Tour design would have cost.
Voyager 2 was the first of the two spacecraft to be launched, with liftoff occurring 20 Aug. 1977. What was at first an auspicious launch, however, proved to be the beginning of a number of problems. The primary cause of the initial problems were attributed to commanding by the AACS, including difficulty in determining the full deployment of the science boom. These problems resulted in a delay of four days in the launch of Voyager 1 to ensure they wouldn't occur for it.
Although launched sixteen days after Voyager 2, Voyager 1's trajectory was the quicker one to Jupiter. On 15 Dec. 1977, while both spacecraft were in the asteroid belt, Voyager 1 surpassed Voyager 2's distance from the Sun.
Several months after launch, in April 1978, Voyager 2's primary radio receiver failed, automatically kicking in the backup receiver which proved to be faulty. Attempts to recover the use of the primary receiver failed and the backup receiver was used for the remainder of the mission. Although use of the backup receiver made communication with the spacecraft more difficult, engineers were able to find workarounds.
Voyager 2 proceeded with its primary mission and flew by Jupiter (closest approach on 09 July 1979) and Saturn (05 Aug. 1981). During these flybys, Voyager 2 obtained images roughly equal in number to Voyager 1 (18,000 at Jupiter, 16,000 at Saturn).
Voyager 2's launch date had preserved one part of the original Grand Tour design, i.e. the possibility of an extended mission to Uranus and Neptune. Despite the difficulties encountered, scientists and engineers had been able to make Voyager enormously successful. As a result, approval was granted to extend the mission, first to Uranus, then to Neptune and later to continue observations well past Neptune. Voyager 2 made successful flybys of Uranus (24 Jan. 1986) and Neptune (25 Aug. 1989). Because of the additional distance of these two planets, adaptations had to made to accomodate the lower light levels and decreased communications. Voyager 2 was successfully able to obtain about 8,000 images of Uranus and its satellites. Additional improvements in the on-board software and use of image compression techniques allowed about 10,000 images of Neptune and its satellites to be taken.
All of the experiments on Voyager 2 have produced useful data.