This Week in NASA History: Voyagers 1 and 2 Embark on Planetary Grand Tour

ASK OCE — August 17, 2006 — Vol. 1, Issue 1

On August 20, 1977, NASA launched Voyager 2 aboard a Titan Centaur expendable rocket on the first leg of a “Grand Tour” of the outer solar system.

Voyager 2 was joined weeks later when Voyager 1 was launched on September 5, 1977 on a faster, shorter trajectory.

The concept for the so-called “Grand Tour” resulted from a discovery by NASA scientists in the late 1960s that once every 176 years, the Earth and all the major planets of the solar system cluster on one side of the sun. This unique planetary grouping made it feasible to undertake close up observation it of all the planets in the outer solar system except Pluto in a single expedition.

Eighteen months after launch, in February of 1979 Voyager 1 achieved its primary mission objective by entering the Jovian system. It took another month to reach the point where it could explore the moons Io and Europa.

Voyager 1 and 2 explored Jupiter’s moons in July 1979. Two years later, Voyager 2 reached the vicinity of Saturn and began returning data from the planet. A critical part of this mission occurred on August 21, 1981 when Voyager 2 emerged from behind Saturn with its focusing instruments pointed the wrong direction out into space due to a jammed aiming mechanism. This problem was soon remedied, and Voyager 2 remained responsive to its Earth-bound controller.

Voyager 1 was not quite as fortunate. The spacecraft went up over Saturn’s orbital plane and was never seen or heard from again. In September 1981, Voyager 2 left Saturn behind. With the successful achievement of all its mission objectives at Jupiter and Saturn, Voyager 2 executed additional flybys of the two outermost giant planets, Uranus and Neptune in December of 1980. In January 1986, Voyager 2 passed near Uranus and in 1989 it encountered Neptune.

The “Grand Tour” proved a resounding success, with the two space probes exploring all the giant outer planets, 48 of their moons, and the unique systems of rings and magnetic fields those planets possess. In 1993, Voyager 2 also provided the first direct evidence of the heliopause the boundary between our solar system and interstellar space.