For Suzanne Dodd, Project Manager of NASA’s Voyager Interstellar Mission, the twin Voyager 1 and Voyager 2 spacecrafts are “sort of my first love – and true love.”
Her love for these vintage interstellar explorers, launched two weeks apart in 1977, has bloomed over many years. She began working on the Voyager mission in 1984, shortly after graduating from college, before leaving to work on other NASA projects, such as the Cassini-Huygens space research mission. Then, in 2010 she returned to where her career had started to take on her current role.
By then, the twin spacecrafts – each equipped with a range of instruments, including television cameras, infrared and ultraviolet sensors and cosmic-ray and charged-particle sensors, as well as a gold-plated record containing sounds and images selected to portray the diversity of life and culture on Earth to anyone or anything who might find them – had long completed their primary mission of conducting closeup studies of Jupiter and Saturn, and moved far beyond the outer planets.
On August 25, 2012, Voyager 1 made the historic entry into interstellar space – where the Sun’s constant flow of material and magnetic field stop affecting its surroundings. Six years later, Voyager 2 achieved the same milestone.
In the years since, the two spacecraft have continued exploring the universe and transmitting the information they collect about things, such as the interstellar magnetic field and cosmic rays, back to Earth via the Deep Space Network (DSN) – NASA’s trio of giant radio antennas located equidistant around the world, which support interplanetary spacecraft missions.
But on July 21, NASA suddenly lost contact with Voyager 2. “It was very distressing. And worrying and disheartening,” Dodd says.
The problem was quickly diagnosed.
To make a very fine adjustment to Voyager 2’s antenna so that it pointed more closely to Earth, flight controllers had built a precise command to send to the spacecraft. Upon review, they realised that the command had the wrong parameter in it.
“So, we rebuilt the command with the correct parameters,” Dodd explains. “But what happened is that we accidentally sent the earlier version of the command – not the updated one.”
This caused Voyager 2’s antennae to point two degrees away from Earth, severing all communication with flight controllers.
Although Dodd was confident that contact with Voyager 2 would have been restored in mid-October when the spacecraft was next due to automatically realign itself with Earth using the Sun and Canopus – the second brightest star in the night sky – she didn’t want to rely on this inbuilt protection feature. Nor did she want to wait three months to get the next batch of scientific data that the spacecraft had been collecting in the interim.
So, she and her colleagues – both in the United States and internationally – started doing everything they could, however low the probability of success, to manually restore contact with a spacecraft the size of an old Volkswagen beetle that was more than 19 billion kilometres from Earth and hurtling through deep space at a speed of over 56,000 kilometres per hour.
Critical to this very ambitious goal was the Canberra Deep Space Communication Complex, one of the three facilities that form the DSN.
Like the other two DSN facilities in Madrid and California, it is dominated by a giant antenna dish. Known as Deep Space Station 43, the dish in Canberra has a reflector surface made up of more than 1,200 aluminium panels and measures 70-metres in diameter, making it the largest steerable parabolic antenna in the Southern Hemisphere.
It is also now the only antenna in the DSN that is able to communicate with Voyager 2.
As Glen Nagle from the Canberra Deep Space Communication Complex explains: “After Voyager 2’s encounter with Neptune in 1989, it headed southward out of the planetary ecliptic. And it’s now so far south that our sister stations in the Northern Hemisphere can’t see it because Earth is in the way.
“So, since 2002, it’s kind of been exclusively ours,” Nagle laughs.
The first part of the grand plan to reconnect with Voyager 2 involved using Deep Space Station 43 to listen for any whisper of its carrier signal – “the heartbeat of the spacecraft”, according to Nagle.
Promisingly, scientists at the Canberra Deep Space Communication Complex detected a faint signal that resembled Voyager 2’s. To double-check, they listened deeply to the sounds of deep space a second time. They detected the same whisper as before.
After processing the data “to eliminate the junk mail of the universe” – as Nagle puts it – the scientists in Australia sent it to Dodd and her team in the United States for analysis, which confirmed that the signal had indeed come from Voyager 2.
Following this, scientists at the Canberra Deep Space Communication Complex transmitted what Nagle calls an “interstellar cooee” to Voyager 2. This transmission was approximately 250 percent stronger than normal ones to increase the chances of the spacecraft’s antennae detecting it.
“And that transmission contained a single command,” Nagle says. “‘which was: ‘reorientate your antennae back to Earth.’”
A long wait ensued: because of how far Voyager 2 is from Earth, it would take 18.5 hours for the transmission to reach it – and another 18.5 hours for scientists to know if it did. They weren’t confident.
But after thirty-seven nervous hours, a signal arrived. There was no doubt where it had come from. Contact with the lost spacecraft was restored.
“There were cheers and high-fives in the control room,” Nagle says. “And it was literally as if Voyager 2 had never been away. It was back to business as normal.”
Dodd says her team at NASA is conducting a thorough investigation into the incident to help ensure that something like it doesn’t happen again. But she knows that eventually the plutonium power source of the two twin spacecrafts that she loves so deeply will eventually run dry – and contact with them will be lost forever.
In order to delay the inevitable, NASA is progressively switching off instruments in both Voyager 1 and Voyager 2 in order to help them conserve power. “When we’re down to the last instrument, we’ll just let it run until we lose the signal, because the transmitter won’t have enough power to send the signal to us,” Dodd says.
She believes that moment will come “between 2027 and 2029 – possibly into 2030.”
But even after their onboard power runs out and they cease transmitting information about the universe back to Earth, the twin Voyager spacecrafts will continue their long, lonely journey through the cosmos, more or less intact, for millions – possibly billions – of years.
“If you want to think really long term,” Nagle says, “they will ultimately outlast the Earth and the Sun and be the last reminder that we ever existed in the universe.” And maybe – just maybe – they will prove to an alien civilisation that there is – or at least once was – other life out there. As Dodd says: “Perhaps in a few 100,000 years, somebody or something might find them and listen to the gold record that’s on board.”
Clarification: Initial story quoted Nagle as saying…”since 2022, it’s kind of been exclusively ours.” This was a typing error made in production and has been changed to 2002.