Voyager 1: Earth's Most Distant Spacecraft

Voyager 1
The Voyager 1 spacecraft visited Jupiter and Saturn before heading out of the solar system. NASA

Today we're used to the ongoing missions of the Cassini spacecraft at Saturn and the Juno mission at Jupiter and the New Horizons mission to Pluto and beyond. However, they're just the latest in a long line of probes to the outer solar system. The first ones were the Pioneers 10 and 11, followed by the Voyager 1 and Voyager 2 missions. These were two spacecraft designed to explore the gas giant planets.

They each carried an array of cameras and instruments designed to record magnetic, atmospheric, lunar and other data about the planets images and data for further study back on Earth. 

Fast Facts

Voyager 1 is speeding along at about 57,600 kph (35,790 mph), which is fast enough to travel from Earth to the Sun three and a half times in one year.

Both spacecraft carry a gold record 'greeting to the universe' containing sounds and images selected to portray the diversity of life and culture on Earth.

The two-spacecraft Voyager missions were designed to replace original plans for a "Grand Tour" of the planets that would have used four complex spacecraft to explore the five outer planets during the late 1970s. NASA canceled the plan in 1972 and instead proposed to send two spacecraft to Jupiter and Saturn in 1977. They were designed to explore the two gas giants in more detail than the two Pioneers (Pioneers 10 and 11) that preceded them.

The Voyager Design and Trajectory

The original design of the two spacecraft was based on that of the older Mariners (such as Mariner 4, which went to Mars). Power was provided by three plutonium oxide radioisotope thermoelectric generators (RTGs) mounted at the end of a boom.

Voyager 1 was launched after Voyager 2, but because of a faster route, it exited the Asteroid Belt earlier than its twin.

It began its Jovian imaging mission in April 1978 at a range of 265 million kilometers from the planet; images sent back by January the following year indicated that Jupiter's atmosphere was more turbulent than during the Pioneer flybys in 1973 and 1974.

Voyager Studies Jupiter's Moons

On February 10, 1979, the spacecraft crossed into the Jovian moon system, and in early March, it had already discovered a thin (less than 30 kilometers thick) ring circling Jupiter. Flying past Amalthea, Io, Europa, Ganymede and Callisto (in that order) on March 5th, Voyager 1 returned spectacular photos of these worlds.

The more interesting find was on Io, where images showed a bizarre yellow, orange and brown world with a least eight active volcanoes spewing material into space, making it one of the most (if not the most) geologically active planetary bodies in the solar system. The spacecraft also discovered two new moons, Thebe and Metis. Voyager 1's closest encounter with Jupiter was at 12:05 UT on March 5,1979 at a range of 280,000 kilometers.

On to Saturn

Following the Jupiter encounter, Voyager 1 completed a single course correction on April 89 1979, in preparation for its rendezvous with Saturn.

A second correction on October 10, 1979 ensured that the spacecraft would not hit Saturn's moon Titan. Its flyby of the Saturn system in November 1979 was as spectacular as its previous encounter.

Exploring Saturn's Icy Moons

Voyager 1 found five new moons and a ring system consisting of thousands of bands, discovered a new ring (the 'G Ring'), and found 'shepherding' satellites on either side of the F-ring satellites that keep the rings well defined. During its flyby, the spacecraft photographed Saturn's moons Titan, Mimas, Enceladus, Tethys, Dione, and Rhea.

Based on incoming data, all the moons appeared to be largely composed of water ice. Perhaps the most interesting target was Titan, which Voyager 1 passed at 05:41 UT on November 12th at a range of 4,000 kilometers. Images showed a thick atmosphere that completely hid the surface.

The spacecraft found that the moon's atmosphere was composed on 90 percent nitrogen. Pressure and temperature at the surface was 1.6 atmospheres and -180° C, respectively. Voyager 1's closest approach to Saturn was at 23:45 UT on November 12, 1980 at a range of 124,000 kilometers.

Outward Bound

Because of the specific requirements for the Titan flyby, the spacecraft was not directed to Uranus and Neptune. Instead, following the encounter with Saturn, Voyager 1 headed on a trajectory out of the solar system at a speed of 3.5 AU per year. It is on a course 35° out of the ecliptic plane to the north, in the general direction of the Sun's motion relative to nearby stars. It is now in interstellar space, having passed through the heliopause boundary, the outer limit of the Sun's magnetic field, and the outward flow of the solar wind. It's the first spacecraft from Earth to travel into interstellar space.

On February 17, 1998, Voyager 1 became the most distant human-made object in existence when it surpassed Pioneer 10's range from Earth. In mid-2016, the Voyager 1 was more than 20 billion kilometers from Earth (135 times the Sun-Earth distance), and continuing to move away, while maintaining a tenuous radio link with Earth. Its power supply should last through 2025, allowing the transmitter to keep sending back information about the interstellar environment.

Edited and updated by Carolyn Collins Petersen.