May 31, 2023

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How Voyager Probes Keep Going Decades After Their Launch

Pasadena, California (CNN) When the Voyager probes were separated for weeks in 1977, no one expected that the twin spacecraft would stretch from four years to 45 years and still go.

Now, the mission team is innovating in its power supply and instrument strategies on both Voyager 1 and 2 to enable both probes to continue collecting valuable data as they explore uncharted interstellar territory.

Voyager 1 is currently almost the farthest spacecraft from Earth It is 15 billion miles (24 billion km) away, while Voyager 2 has traveled more than 12 billion miles (20 billion km) from Earth. Both are in interstellar space and are the only spacecraft to operate outside the heliosphere, the sun’s bubble of magnetic fields and particles that extends beyond Pluto’s orbit.

As the only extensions of humanity outside the protective bubble of the heliosphere, the two probes are alone even on their cosmic travels as they travel in different directions.

Think of the planets of the solar system as being on one plane. Voyager 1’s trajectory took it up and out of the planetary plane after passing Saturn, said Susan Dodd, Voyager project manager at NASA’s Jet Propulsion Plane, while Voyager 2 passed over the top of Neptune and moved down and out of the planetary plane. Laboratory in Pasadena, California.

Information gathered by these long-lived probes is helping scientists learn about the comet-like shape of the heliosphere and how it protects Earth from energetic particles and radiation in interstellar space.

Voyager 2’s invaluable data is being captured and returned to Earth by its five science instruments, while Voyager 1 still has four operational instruments after one of them failed in the mission earlier.

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But Dodd said it took a lot of care and monitoring to keep the “seniors” working.

“I kind of describe them as twin sisters,” Dowd told CNN. “One has lost his hearing and needs some hearing aids, and another has lost some sense of touch. So, they fail differently over time. But overall, they are pretty healthy for their age.”

Instruments designed to look at planets while the Voyager probe toured 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 atmospheric boundary in 2012, while the slower Voyager 2 crossed the boundary. in 2018.

Both Voyager probes rely on radioisotope thermoelectric generators. A nuclear power supply loses 4 watts per year because the plutonium it relies on slowly decays and its heat is converted into electricity. Over time, the Voyager team ordered the probes to turn off instrument heaters and other non-essential systems.

Each Voyager probe contains three radioisotope thermoelectric generators.

“But (Voyager) also gets very cold and we need to keep the fuel lines warm enough, about 2 degrees Celsius.” (35.6 degrees Fahrenheit). If they freeze, we may lose our ability to point to Earth. So it’s a balance between energy and heat and how we operate the spacecraft,” Dodd said.

delicate balance

The team was pleasantly surprised that the instruments were recalibrated to become a bit more sensitive in collecting data because some Voyager detectors work better when colder.

“One way to look at it,” said Linda Spilker, Voyager project scientist at the Jet Propulsion Laboratory, “is to think of Voyagers as cabins on top of a mountain, and it’s very cold out there. Turn off the lights inside to conserve your energy. You also have to lower the thermostat, and with It still works just fine.”

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Voyager 2 began using a small backup power reserve that was part of a safety mechanism, which will enable the spacecraft to turn off another science instrument until 2026, instead of this year. The safety mechanism, which protects the instruments if the electrical flow on the spacecraft changes drastically, contains a small amount of power that acts as a backup circuit.

Now, that power can be used to keep Voyager 2’s instruments running.

The spacecraft’s electrical systems are still largely stable, so the team decided it was a small risk for the larger reward of being able to collect science data. The team will continue to monitor the Voyager 2 effort and act accordingly if there are fluctuations.

The Voyager test model, shown here in 1976, contains a platform displaying several scientific instruments.

If this strategy works for Voyager 2, it could also be implemented on Voyager 1, where the team will have to consider shutting down another science instrument on the spacecraft in 2024.

“Instead of turning off a scientific instrument, we would probably want to do something very creative, engineering-wise, in order to get another year of science data,” Dodd said. “It powers the spacecraft in a way it was never designed to power.”

The Plasma Science instrument on Voyager 2 is still operational, so it can take direct measurements of the plasma density in interstellar space. Space plasma consists of charged particles, the motion of which is controlled by electric and magnetic forces NASA.

“Imagine it as an ocean of space with waves and turbulence and constant activity, and the Voyager instruments can measure what’s going on,” said Spilker. “Before you go to a new place, you predict what you think you might find when you get there. With Voyager, we’ve learned to be surprised.”

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Scientists expected the plasma density to decrease as Voyager got further from the Sun, but instead it increased. Spilker said the probes can measure and see the shocks as they propagate from the sun.

As long as both Voyager 1 and 2 remain healthy, the aging probes will likely continue their record-breaking missions for years to come.