A little over 35 years ago, the NASA jet propulsion laboratory (JPL) launched the last two spacecraft of NASA’s Mariner series. Voyager 1 and 2 were the first in that series to be sent to explore the outer solar system. The Voyager spacecraft were launched 16 days apart, Voyager 2 being Launched first on August 20^th 1977, followed by Voyager 1 on September 5^th. Both crafts would take advantage of rare geometric alignment of the outer planets so that they could fly by their target planets, Jupiter and Saturn using the minimal energy and time. An option in Voyager 2′s trajectory, which was ultimately exercised, would also direct it toward Uranus and Neptune.

Both spacecraft carried onboard them a gold plated disc, in the event that either craft was found by intelligent life. The discs contain photos of Earth and scientific information along with greetings from the people of Earth and samples of music. They are both powered by three Radioisotope Thermal Generators that at launch would be able to produce 420 watts of electrical power. To communicate data back to earth the Voyager crafts had a 3.7m diameter dish high gain antenna and this would face Earth throughout its mission by means of 16 hydrazine thrusters and three-axis stabilization gyroscopes.

Although Launched later, Voyager 1′s trajectory was faster and it arrived at Jupiter first in March of 1979 and as Voyager 1 flew past the Jovian system we got to see Jupiter in detail like never before, but it was not until 4 months later in July when Voyager 2 arrived in the Jovian system that the greatest discoveries were made. It discovered rings around Jupiter and revealed the Great Red Spot to be a complex storm moving counterclockwise, along with many other smaller storms and eddies within the banded clouds, but maybe its greatest discovery was the volcanic activity on one of Jupiter’s satellites, Io.

Voyager 1 reached Saturn in November 1980 followed by Voyager 2 in August 1981 and this is where the two spacecraft parted company. This was to be the end of Voyager 1′s grand tour. A year earlier, Pioneer 11 had detected a thick gaseous atmosphere over Saturn’s moon Titan, and JPL elected for Voyager 1 to make a close flyby of Titan, before using its gravity to send Voyager 1 out of the plane of the solar system and off towards interstellar space.

Voyager 2 carried on with its grand tour visiting Uranus in January 1986, discovering 10 new moons and examining the planet’s rings along with its tilt before heading on to Neptune in August 1989. As this was the last planet Voyager 2 could visit it was of no matter what trajectory it left the system. But while it was there, it discovered Neptune’s Great Dark Spot, similar to the Great red spot on Jupiter.

Ever since the Grand Tour missions concluded, NASA has described them as interstellar missions to find out what the Solar System is like beyond the heliosphere, (a bubble of charged particles in the space surrounding the Solar System, “blown” into the interstellar medium (the hydrogen and helium gas that permeates the galaxy) by the solar wind.) On November 10^th 1997 Voyager 1 overtook Pioneer 10 as the most distant manmade object and it is still transmitting data, and scientists are using the plasma wave experiments onboard Voyager 1 to look for heliopause, the boundary where the solar wind fades into the interstellar medium.

Voyager 1 is believed to have entered the termination shock between February 2003 and December 2004.  This is the area where the solar wind slows to subsonic speeds.

And now 35 years on and at a distance from earth of over 11.3 billion miles, researchers may be seeing the first signs that Voyager 1 is nearing – or may have already crossed – the heliopause and has truly left our solar system; mankind’s first interstellar traveller.