The Voyager spacecraft have become popstars

Out of this world – The incredible Voyage of the Voyagers

The title of these columns is Attitude for Altitude – and this is nowhere better demonstrated than by two little spaceships that have real attitude – and altitude.

The two Voyager spacecraft are quietly getting on with the job of heading out of our solar system and into deep space. At over 61,000 km/h the two little Voyagers are right up there in the list of the top ten fastest objects, and they have been maintain that speed flying away from Earth for almost 50 years. Both carry the famous “Golden Record,” a 12-inch gold-plated disc containing sounds and images about life and culture on Earth.

The Voyagers unarguably own the record for the flying machines with the greatest range and endurance. Forty-six years ago, on 20 August 1977, NASA’s Voyager 2 launched from Cape Canaveral, Florida, on a Titan III-Centaur rocket. It embarked on a “grand tour” of the solar system that included visits to the Jupiter and Saturn systems and would make it the first spacecraft to visit the ice giants Uranus and Neptune and their moons. 

When they were launched, Jimmy Carter was in the first year of his presidency and Fleetwood Mac was in the charts with Don’t Stop. The two spacecraft took that song to heart and have not stopped ever since, travelling further from Earth than any other man-made object. Voyager 2 is now more 25 billion kilometres away and still they fly on, transmitting from the depths of interstellar space, rebuking every car and computer that profited from built-in obsolescence.

NASA’s rocket scientists are wondering how long they can keep going. There were glum faces at NASA in early August when the wrong command caused the transmission antenna of Voyager 2 to misalign with Earth – and the spacecraft went silent – possibly forever.

However, NASA said it wasn’t panicking. The mission’s scientists believed they had several options to restore communications with the half-century-old probe. And so they did. In an update in early August, NASA said all is now well once again with Voyager 2.

NASA’s Deep Space Network facility in Canberra, Australia, was able to “shout” a command to Voyager instructing the spacecraft to reorient itself into a proper position to facilitate communication with Earth.

It took 18.5 hours for the signal to reach the spacecraft, which is now 20 billion km from Earth. Finally, in the middle of the night, after an anxious wait of 37 hours, Voyager 2 once again started streaming back data.

Voyager 1 and 2 were launched to take advantage of a once-every-176-years alignment in the 1970s that made it possible for spacecraft to take gravity-assisted slingshots from planet to planet across the solar system.

Voyager 1 is currently the farthest spacecraft from Earth at about 24 billion kilometres, while Voyager 2 has travelled more than 20 billion kilometres. Both have now left the solar system and are in interstellar space, making them the only spacecraft to operate beyond the heliosphere, the sun’s bubble of magnetic fields and particles that extends well beyond the orbit of Pluto.

Though it launched second, Voyager 1 was so called because it was to reach Jupiter and Saturn first — in March 1979 and November 1980, respectively — before exiting the plane of the planets where it took the famous “Pale Blue Dot” photo.

Voyager 2 visited four planets: Jupiter in July 1979, Saturn in August 1981, Uranus in January 1986 and Neptune in August 1989.

Voyager’s discoveries are the stuff of legend among planetary scientists, many of whom still rely on the unique images from the spacecrafts’ now antiquated wide-angle and narrow-angle digital cameras.

The probes have taken photos of the volcanoes on Jupiter’s moon Io, and discovered that Jupiter’s Great Red Spot is an Earth-size storm. They studied Saturn’s rings; saw the giant moon Titan’s thick, Earth-like atmosphere; and revealed the tiny moon Enceladus to be geologically active.

Voyager 2 then set off by itself to check out Uranus and Neptune. The spacecraft’s first-ever images of Uranus revealed dark rings, the planet’s tilted magnetic field and its geologically active moon Miranda. Neptune, meanwhile, was also discovered to have rings and many more moons than scientists initially thought. We also got to see Triton, a geologically active moon that is orbiting “backward” and, like Pluto, is now believed to be a captured dwarf planet from the Kuiper Belt. 

In addition to making groundbreaking discoveries, the Voyager mission helped scientists determine what merited deeper exploration. The mission revealed Jupiter to be an incredibly complex planet, thus spurring NASA to launch the Galileo mission in 1989 and the Juno mission in 2011. The Voyager probes’ work also helped inspire the iconic Cassini mission to Saturn.

Voyager 1’s close flyby of Saturn’s largest moon Titan was the catalyst that justified the amazing Cassini mission. Cassini’s Huygens probe successfully parachuted onto the surface of Titan in 2005 and sent back an incredible video. This was the first landing ever accomplished in the outer Solar System and the first landing on a moon other than Earth’s Moon.

Voyager 2 has also been a catalyst for investigations into the role of the ice giant planets — not only in the solar system, but also in distant star systems, since most of the exoplanets found so far are roughly the size of Neptune and Uranus.

The big question is, how much longer will the Voyagers last?

Despite the recent communications near disaster, both the intrepid spaceships are still communicating with NASA’s Deep Space Network (which itself was created to communicate with Voyager 2 at Uranus and Neptune), receiving routine commands and occasionally beaming data and images back to Earth from its 1970s era computers. “We’re looking forward to getting data for probably another five or six years,” Stamatios Krimigis, principal investigator for the Voyager Interstellar Mission, said during a news conference held at COSPAR 22 in July.

To achieve the miracle of keeping these spacecraft alive in the frigid and far reaches of space, NASA is getting creative with the power supply and instruments. Over time, the Voyager team has commanded the probes to turn off instrument heaters and other nonessential systems.

Both Voyagers are nuclear powered, using radioisotope thermoelectric generators. The power pack loses 4 watts per year as the plutonium it relies on slowly decays and its heat is converted into electricity.

Each spacecraft’s power pack carries radioactive plutonium-238. As the isotope decays, it releases energy that is converted into electricity by three radioisotope thermoelectric generators (RTGs). At launch, the RTGs provided each spacecraft with 450 watts of power. Now, they’re producing less than half that amount and their electrical output is decaying by four watts each year. NASA says that it takes about 200 watts to send signals back to Earth, and they only have about five to six watts of power margin on each spacecraft.

In the deep cold soak of outer space, the key challenge is to keep the propellant lines warm above 2 degrees Celsius so the aiming system continues to work.

Voyager 2 has begun using a small backup power reserve, which will enable the spacecraft to keep from shutting down another science instrument until 2026. The power reserve was designed as a safety mechanism to protect the instruments in case the flow of electricity changes significantly on the spacecraft. Now that back-up power is being used to keep Voyager 2’s instruments up and running.

The rocket scientists were thrilled to discover that the instruments recalibrated to become more sensitive in their data collection because some of the detectors operate better when colder.

As the sole extensions of humanity outside the heliosphere’s protective bubble, the two probes are alone on their cosmic treks as they travel in different directions.

Given the age of the two spacecraft it is inevitable that a small failure could ultimately lead to losing communication completely, even if it still has power. But however long Voyager 1 and 2 continue to operate, the Voyager mission is already a massive success. The original mission was to perform flybys of the solar system’s gas planets and their moons and beam back data to Earth — tasks that both spacecraft had completed by 1989.

Now 35 years later, around the mid-to late 2020s, the probes’ scientific instruments will be shut down, and eventually, the spacecraft will go cold and silent — but their journeys into interstellar space will continue indefinitely.

In around 300 years, Voyager 1 and 2 will enter the Oort cloud, the sphere of comets surrounding the solar system. About 30,000 years later, they’ll exit the neighbourhood and silently orbit the centre of the Milky Way for millions of years.

Their scientific work may be almost over, but the Voyager spacecraft have only just begun their journeys into the cosmos. And who knows – maybe some clever lifeform will find and play Voyagers’ gold plated records and look back to where they came from.

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