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| | Space on Aug 20, 2013

This date in science: NASA launched Voyager 2 space probe

Voyager 2 realized the vision of what was originally called a Grand Tour of the outer solar system. It remains the only craft to have visited all four outer planets.

August 20, 1977. NASA launched the phenomenal Voyager 2 space probe to the outer solar system on this date in 1977. They launched it some weeks before its twin craft, Voyager 1, which moved faster and eventually passed it to become the most distant human-made object from Earth, perhaps the first to leave the solar system. Voyager 2 has been operating for 35 years, 11 months, and 31 days as of August 20, 2013. Although its transmissions are faint, coming as they do from very far away, the craft still transmits data and receives messages via NASA’s Deep Space Network. Scientists believe it will be able to continue communications until around the year 2025.

As Voyager 2 sped away from Earth, it looked back and acquired this image of a crescent-shaped Earth and moon -- the first of its kind ever taken by a spacecraft -- on Sept. 18, 1977.  Voyager 2 was 7.25 million miles (11.66 million kilometers) from Earth at the time.  Image via NASA.

As Voyager 2 sped away from Earth, it looked back and acquired this image of a crescent-shaped Earth and moon — the first of its kind ever taken by a spacecraft — on Sept. 18, 1977. Voyager 2 was 7.25 million miles (11.66 million kilometers) from Earth at the time. Image via NASA.

This picture shows a region of the southern hemisphere extending from the Great Red Spot to the south pole. The white oval is seen beneath the Great Red Spot, and several small scale spots are visible farther to the south. Some of these organized cloud spots have similar morphologies, such as anticyclonic rotations and cyclonic regions to their west. The presence of the white oval causes the streamlines of the flow to bunch up between it and the Great Red Spot.

A region of Jupiter’s southern hemisphere extending from the Great Red Spot to the south pole. Before the Voyagers, we did not know Jupiter’s banded atmosphere, or Red Spot, contained so much detail. Image via JPL/Cal Tech.

Before the Voyagers, we did not know that Saturn's rings consisted of thousands of individual ringlets.  In this Voyager 2 image from 1981, you can also see the mysterious

Before the Voyagers, we did not know that Saturn’s rings consisted of thousands of individual ringlets. In this Voyager 2 image from 1981, you can also see the mysterious “spokes” in Saturn’s rings. Image via NASA.

Voyager 2 is still the only spacecraft to have visited the outer planets Uranus and Neptune.  Here is Uranus as seen by Voyager 2 in 1986.  To the spacecraft, the planet appeared as a featureless blue ball.  Image via NASA

Voyager 2 is still the only spacecraft to have visited the outer planets Uranus and Neptune. Here is Uranus as seen by Voyager 2 in 1986. To the spacecraft, the planet appeared as a featureless blue ball. Image via NASA

Voyager 2 passed Neptune in 1989.  It saw cloud features in Neptune's atmosphere, tracked by the Voyager cameras as the craft swept past.  Image via NASA.

Voyager 2 passed Neptune in 1989. It saw cloud features in Neptune’s atmosphere, tracked by the Voyager cameras as the craft swept past. Image via NASA.

Voyager project manager in 1977 was John Casani, shown here with small flag that was folded and sewed into the thermal blankets of the Voyager spacecraft before launch. Voyager 2 is behind him.  Also, shown are the famous gold records carried by the Voyager.  Read about the story of the records here.

Voyager project manager in 1977 was John Casani, shown here with small flag that was folded and sewed into the thermal blankets of the Voyager spacecraft before launch. Voyager 2 is behind him. Also shown is one of the famous gold records carried by the Voyagers. Read about the story of the records here.

NASA originally conceived of the Voyager mission in the 1960s as a planetary Grand Tour to study the outer planets. The fact that all four outer planets would be, temporarily, within one quadrant of the solar system around the decade of the 1980s inspired the idea. Inevitable funding difficulties intervened, and for a time it appeared the Grand Tour would never be realized. But Voyager 2′s launch took advantage not only of the particular configuration of planets – but also a new technique, called a gravity assist. This technique let the craft visit all four outer planets (Jupiter, Saturn, Uranus, Neptune), while requiring a minimal amount of propellant and a shorter transit duration between planets.

The plan hinged on whether Voyager 1 would be able to perform a successful flyby of Saturn’s large and intriguing moon Titan. It did, and Voyager 2 got the go-ahead to travel on toward Uranus and Neptune, ultimately realizing the vision of the planetary Grand Tour.

Voyager 2 remains the only craft from Earth to have visited Uranus and Neptune.

Bottom line: The phenomenal Voyager 2 spacecraft launched on August 20, 1977. It ultimately visited all four outer planets – Jupiter, Saturn, Uranus and Neptune – and remains the only craft from Earth to have done so.