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By Ashley Strickland, CNN
When the Voyager probes lifted off weeks apart in 1977, no one expected the twin spacecraft to have their missions extended from four years to 45 years and counting.
Now the mission team is getting creative with their strategies for the power supply and instruments on both Voyager 1 and 2 to allow both probes to continue collecting valuable data while exploring uncharted interstellar territory.
Voyager 1 is currently the furthest spacecraft from Earth at about 15 billion miles (24 billion kilometers) away, while Voyager 2 has traveled more than 12 billion miles (20 billion kilometers) from Earth. Both are in interstellar space and are the only spacecraft operating beyond the heliosphere, the sun’s bubble of magnetic fields and particles that extends well beyond Pluto’s orbit.
As the only extensions of humanity outside of the protective bubble of the heliosphere, the two probes are alone even in their cosmic journeys as they travel in different directions.
Think of the planets in the solar system as existing in a plane. Voyager 1’s trajectory lifted it up and out of the plane of the planets after passing Saturn, while Voyager 2 passed over Neptune and moved down and out of the plane of the planets, said Suzanne Dodd, manager of Voyager projects in NASA Jet Propulsion. Laboratory in Pasadena, California.
The information collected by these long-duration probes is helping scientists learn about the comet-like shape of the heliosphere and how it shields Earth from energized particles and radiation in interstellar space.
Voyager 2’s invaluable data is captured and returned to Earth via its five science instruments, while Voyager 1 still has four operational instruments after one failed earlier in the mission.
But a lot of care and monitoring has been needed to keep the “seniors” operating, Dodd said.
“I describe them as twin sisters,” Dodd told CNN. “One has lost his hearing and needs hearing aids, and another has lost some sense of touch. So they have failed differently over time. But in a general sense, they are very healthy for their age.”
Instruments designed to observe the planets as Voyager probes roamed the solar system in the 1980s were turned off to reuse memory for the interstellar mission that began in 1990, Dodd said. Voyager 1 reached the edge of the heliosphere in 2012, while the slower Voyager 2 crossed the edge in 2018.
Both Voyager probes are based on radioisotope thermoelectric generators. Nuclear power supply loses 4 watts per year as the plutonium on which it depends slowly decays and its heat is converted to electricity. Eventually, the Voyager team ordered the probes to turn off instrument heaters and other non-essential systems.
“But (Voyager) also gets very cold and we need to keep the propellant lines warm enough, around 2 degrees Celsius. (35.6 degrees Fahrenheit). If they freeze, we could lose our ability to target Earth. So it’s a balancing act between power and thermal and how we operate the spacecraft,” Dodd said.
a delicate balance
The team was pleasantly surprised that the instruments were recalibrated to become a bit more sensitive in data collection because some of Voyager’s detectors work better when they are colder.
“One way to look at it is to think of the two Voyagers as cabins on top of a mountain, and it’s very cold up there,” said Linda Spilker, Voyager project scientist at JPL. “Little by little you have to turn off the lights inside to conserve your energy. And you also have to turn down the thermostat, and yet you still perform well.”
Voyager 2 began using a small backup power reserve that was part of a safety mechanism, which will allow the spacecraft to avoid turning off another scientific instrument until 2026, instead of this year. The safety mechanism, which protects the instruments in case the flow of electricity changes significantly in the spacecraft, contained a small amount of power that acted as a backup circuit.
Now that power can be used to keep Voyager 2’s instruments running.
The spacecraft’s electrical systems are largely stable, so the team determined that it was a small risk for the big reward of being able to collect scientific data. The team will continue to monitor Voyager 2’s voltage and act accordingly if there are fluctuations.
If this strategy works for Voyager 2, it can be implemented on Voyager 1 as well, as the team will need to consider turning off another science instrument on the spacecraft in 2024.
“Instead of turning off a science instrument, maybe we’d like to do something very creative, engineering-wise, to get another year of science data,” Dodd said. “It’s operating the spacecraft in a way that it was never designed to do.”
Voyager 2’s plasma science instrument is still working, so it can take direct measurements of plasma density in interstellar space. Space plasma is matter made of charged particles, the movement of which is controlled by electrical and magnetic forces, according to POT.
“Imagine it as an ocean of space with waves, turbulence and activity, and Voyager’s instruments can measure what’s happening,” Spilker said. “Before you go to a new place, you make predictions of what you think you might find when you get there. With Voyager, we have learned to be surprised.”
Scientists expected the density of the plasma to decrease as Voyager moved further from the sun, but instead it increased. And the probes can measure and see the shocks as they propagate from the sun, Spilker said.
As long as Voyager 1 and 2 both stay healthy, the aging probes are likely to continue their unprecedented missions for years to come.
The CNN Wire
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