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NASA’s Racing Against the Clock to Keep Voyager Alive in Interstellar Space
The clock is ticking...
A century from now, a brave but desperate collection of humans will embark upon a journey to another world. Fleeing an Earth in decline, the crew of the Ark One will settle into stasis pods on a years-long trip to Proxima Centauri b, humanity’s future home. That is, if they can get there alive. Alas, the events of The Ark (now streaming on Peacock!) notwithstanding, humanity isn’t yet ready to send people beyond the solar system.
We may not be ready for interstellar travel even a century from now, but when we do finally cross that boundary, we’ll be greeted by the machines we sent in advance. Humanity’s oldest running and farthest flung machines are the Voyager spacecraft (1 and 2) and despite being nearly old enough to collect a pension, they’re still going strong, thanks to the ingenuity of the scientists operating them from the ground.
THE SOLAR SYSTEM’S OUTER LIMITS
There’s no sign that reads “Now Leaving the Solar System” once you reach a certain distance from the Sun. Instead, scientists have debated over the location of the solar system’s furthest edge and landed on the heliosphere.
We think of the Sun as being a finite object, bounded by roiling plasma and solar flares, but its influence stretches much further. While the visible parts of the Sun may be confined to a relatively small portion of the solar system, the Sun dominates activity in the solar system in a number of invisible ways. Within the solar system, the Sun’s gravity dominates, keeping everything in its designated place, and its electromagnetic field overwhelms anything from outside the solar system.
Beyond the heliosphere, you’ve entered into a new type of space, beyond the domineering influence of the Sun’s electromagnetic field. Voyager 1 crossed that boundary more than a decade ago, in August of 2012, and Voyager 2 followed in December of 2018.
Getting to their distant locales meant flying in more or less a straight line away from the Sun for 46 years and counting. Pulling that off meant designing spacecraft robust enough to withstand decades of cosmic punishment and a power system which would keep them operational for as long as possible.
WHAT POWERS VOYAGER?
When we want to put a satellite in orbit around the Earth or a spacecraft in orbit around another planet, we typically take advantage of the free energy coming from the Sun. Everything from small probes to the International Space Station gathers solar energy using immense solar panels. But the scientists and engineers responsible for the Voyager craft knew they would go farther than anything before (or since) and that they couldn’t rely on solar power.
Instead, both of the Voyager craft were equipped with Radioisotope Thermoelectric Generators (RTGs). Each RTG holds a small amount of Plutonium-238 in its guts. As the radioactive fuel decays, it sheds alpha particles which hit the unit’s interior and generate heat. That heat then feeds through a thermoelectric converter which transforms it into electrical power the spacecraft can use.
Plutonium-238 has a half-life of 88 years. In simple terms, that means that every 88 years, roughly half of the material you start with will have decayed away. The Voyager craft have only been running for 46 years, but that’s long enough for a significant portion of their fuel to have decayed. They are generating less heat, and therefore, less energy. As available power declines, NASA scientists have had to come up with creative solutions to keep Voyager 1 and 2 in action.
HOW SCIENTISTS ARE KEEPING VOYAGER ALIVE
The Voyager craft don’t need power for propulsion. Their racing days are over and now they’re riding through space on their own steam, roughly 35,000 miles every hour, with no friction to slow them down. But they do need power to take measurements and make observations, and then beam that information approximately 15 billion miles back to Earth.
In 2019, energy production had declined enough that scientists cut power to Voyagers’ heating systems. The heaters were intended to keep the scientific instruments warm, but the big brains at NASA were betting that they would still operate in the -50 Celsius temperatures of deep space.
They were right, and it bought the Voyager a few more years, but they need another boost. In March 2023, scientists took the next energy conservation step for Voyager 2. They’ve allowed the craft to dip into reserve power meant to protect it from voltage spikes. Using the reserve power will make the craft more susceptible to damage, but authorities believe the risk is minimal. Besides, the alternative is Voyager starving to death.
NASA is keeping an eye on Voyager 2 over the next several months. If nothing goes wrong, they’ll make the same move on Voyager 1. NASA has a pretty good track record of building machines that outlive their initial mission timelines. The Curiosity Rover, for instance, landed on Mars in 2012 with a planned mission of a little less than two years. That was more than a decade ago and it’s still going strong.
If Curiosity, or any other spacecraft wants to knock Voyager off the number one spot, they’re going to have to wait a while. If these measures are successful, scientists are hopeful Voyager 1 and 2 will keep sending back valuable scientific data well beyond their 50th birthdays. And what we learn in the meantime will not only help to refine our understanding of the universe but will also lay the first bricks on the road which will eventually take humanity to the stars.
Get a preview of humanity’s cosmic exodus in The Ark, streaming now on Peacock!