Far Out: The Many Milestones of Voyager 2

Article August 22, 2023

An artist’s illustration of the Voyager 2 spacecraft. Credit: NASA/JPL-Caltech

It probably isn’t going to shock anyone that I, a planetarium educator and space news blogger, am also a Star Trek fan. I even like the super weird first movie, Star Trek: The Motion Picture, where the antagonist turns out to be (spoiler alert for a 44-year-old movie) V’ger, a sentient spacecraft that was built from a human space probe the movie calls Voyager 6.

In point of fact there was no Voyager 6—the Voyager mission consists of two spacecraft, the very creatively-named Voyagers 1 and 2. And Voyager 2 is both about to celebrate a whole series of anniversaries this week and was recently in the news, so let’s take a look at this very, very, very (very) long-lived spacecraft, its mission, and just what happened to it recently.

Where No Spacecraft Has Gone Before

A diagram showing the paths of Voyager 1 and Voyager 2 through the solar system. Credit: NASA/JPL-Caltech

In the mid-1960s an employee of the Jet Propulsion Laboratory noticed something interesting. In the late 1970s and going into the 1980s the solar systems’ outer gas giants were going to be very well-positioned for a single spacecraft to be able to visit all four of them. This was dubbed the “Grand Tour” and in 1969 NASA set to work making this ambitious mission a reality. Eventually NASA settled on two spacecraft, with an initial mission to have each fly past Jupiter and Saturn. If the first flybys went well, the second spacecraft could then be redirected to the Ice Giants, Uranus and Neptune.

It’s important to remember that in this era the outer solar system was not well-known. By the late ‘70s we had some up-close stuff of Jupiter and Saturn from Pioneer 10 and 11. Those images are...ooookay.

Jupiter and Saturn as seen by the Pioneer 11 spacecraft. Credit: NASA/JPL-Caltech

Better than nothing. The best you could hope for from a small thing built in the early 70s to be the first spacecraft to explore past Mars, where you weren’t even sure it would survive. And neither Pioneer spacecraft had gone anywhere near the Ice Giants.

The “Grand Tour” mission was going to change that. The spacecraft being designed for this journey had roughly three times the mass of Pioneer 11. That meant a lot more capacity for science instruments and a pair of nice cameras. Thanks to the Pioneers, we knew a spacecraft could survive the trip to the outer solar system, so we felt good about putting the good stuff on these new craft.

The twin spacecraft were ready for their “Grand Tour” launch windows in the second half of 1977 and by that point the mission had a new name: Voyager.

The Grand Tour

The launch of Voyager 2 on August 20, 1977. Credit: NASA/JPL-Caltech

You’d think, wouldn’t you, that if you have a pair of spacecraft named Voyager 1 and Voyager 2 that the first to launch would be Voyager 1? That would make sense. It would also be wrong. For orbital trajectory reasons, even though Voyager 1 would be the one to fly past Jupiter and Saturn first, Voyager 2 was the first off the launchpad.

On August 20, 1977 (so there’s the first of its anniversaries we’re celebrating), Voyager 2 set off on its long journey, followed a few weeks later, on September 5, by its twin.

By mid-December, Voyager 1 had overtaken Voyager 2. It flew through the Jupiter system in March 1979, and followed up with the flight through the Saturn system in November 1980. I could say a whole lot more about it but this blog post is about Voyager 2, so we’ll leave Voyager 1 here, heading perpetually outward, having successfully carried out its mission and paved the way for Voyager 2 to complete the Grand Tour.

Jupiter and Saturn as seen by Voyager 2. Credit: NASA/JPL-Caltech

Voyager 2 made it to Jupiter in July 1979. It saw volcanoes erupting on Io. It took detailed images of the surface of Europa, providing the first tantalizing evidence for the ocean we now believe rests underneath. It discovered the moon Thebe. It peered down on the Great Red Spot and took video footage of Jupiter’s atmosphere. The Saturn flyby, which occurred on August 26, 1981 (Anniversary #2!), allowed the spacecraft to map the rings and probe the atmosphere. It surveyed the moons Enceladus and Titan and revealed the details of Iapetus’s two-toned face. The images are light years (see what I did there?) better than the ones from Pioneer 10 and 11.

Uranus and Neptune as seen by Voyager 2. Credit: NASA/JPL-Caltech

Having made it past the Big Guys intact, Voyager 2 was given the go-ahead to make the flybys past Uranus and Neptune. It reached Uranus in January 1984 and quickly discovered 11 previously unknown moons and two previously unknown planetary rings, among a host of other things. It reached Neptune on August 25, 1989 (anniversary #3! August is a big month for this spacecraft). While there it discovered six moons, two rings, and the Great Dark Spot. To this day, the only close-up images we have of the Ice Giants and their moons are those taken by Voyager 2. We’ve never gone back. (Yet.)

To Infinity And Beyond

A diagram showing the Sun’s heliosphere and where Voyager 1 and Voyager 2 are relative to it. Credit: NASA/JPL-Caltech

With all its planetary flybys done, there was nothing to stop Voyager 2 from just…continuing. Like its twin, it just kept going outward. It’s still going outward. It completely exited the bubble of space exposed to the Sun’s solar wind, the heliosphere, in 2018. This means that, while it’s still in our solar system, in the realm of space controlled by the Sun’s gravity, it’s feeling the winds from other stars. It’s in interstellar space.

Just a month ago, on July 18, Voyager 2 passed the distance traveled by the long-dead Pioneer 10 to become the second farthest thing humans have ever sent out into space, topped only by Voyager 1. As of mid-August 2023, after 46 years in space, Voyager 2 is 12.3 billion miles from its starting point. Over the years it’s shut down a number of bits of equipment, including the cameras, to supply the remaining science instruments with the power they need to operate. Even with its reduced circumstances, Voyager 2 is still considered an active mission.

Please Phone Home

What put Voyager into the news earlier this summer was, shall we say, a failure to communicate. On July 21, NASA mistakenly sent a signal to the spacecraft that caused it to point its big antenna near Earth, about 2 degrees away, but not at Earth. This configuration did nobody any good. None of the data or telemetry Voyager 2 was sending us was being received, and it was believed that nothing we sent was going to be able to reach the spacecraft. NASA was concerned but not panicky, as Voyager 2 has it written into its code that it should re-orient itself with respect to Earth a few times a year. The next re-orientation date was October 15. The spacecraft would be shouting into the void until then, but there was no reason to believe it would suffer harm.

On August 1, the Deep Space Network, an array of huge radio antennas around the globe that we use to talk to interplanetary spacecraft, detected Voyager 2’s carrier signal. This signal doesn’t really carry any information, beyond the fact that the spacecraft was transmitting and therefore functional, but it was good to know the old ship was still sailing. It also meant that there was a chance that a strong enough signal emitted by the Deep Space Network could reach Voyager 2, even with the misaligned antenna. NASA wasn’t hopeful, but it was worth a shot.

On August 4, the Deep Space Network dish in Canberra, Australia, shouted loudly at Voyager 2. The team on Earth then waited in suspense as the shout traveled the 18.5 light hour distance out to Voyager 2, followed by another 18.5 hour wait for any potential return signal. 37 hours after Earth yelled at Voyager 2, science and telemetry data from the spacecraft began pouring back into the Deep Space Network. Unexpectedly, Voyager 2 had heard the signal and turned its antenna back to Earth.

Into The Void

How long Voyager 2 (or Voyager 1, for that matter) will last is anyone’s guess at this point. Nobody seriously thought they would last this long back in 1977. Their nuclear power sources are running down, though, and it’s suspected that they’ll only make it a few more years at most. Of course, once they no longer have power, they’ll still be heading outward—their flights past the gas giants gained them enough momentum to leave the solar system entirely.

An image of the Golden Record carried aboard both Voyager 1 and Voyager 2. Credit: NASA/JPL-Caltech

Voyager 2 isn’t heading anywhere in particular. There are no stars that we can see closer than a few light years to its path. But it is carrying a message. Both Voyagers carry a golden record (a project spear-headed by the late great science education god Carl Sagan), which carries photos, a number of spoken greetings, music, and various sounds from Earth. You know, just in case someone, somewhere, sometime should happen to stumble across it and wonder where it came from.

(And then maybe supe it up into a super craft and send it back to Earth like V’ger. I’m not saying it’s likely, I’m just saying it would be very hilarious if Star Trek: The Motion Picture turned out to be right.)