15bn miles from Earth — now power-saving may propel Voyagers to the 2030s

For nearly half a century they have been humankind’s most intrepid emissaries, pushing ever deeper into the cosmic unknown. Now, in an effort to keep the lights on for a little longer, Nasa is shutting down scientific instruments aboard its two venerable Voyager spacecraft.

The twin probes, launched in 1977, have spent the past 47 years travelling away from Earth, first making a grand tour of the outer planets before sailing beyond the influence of our sun into interstellar space. But time and physics are unrelenting: their power sources — radioisotope thermoelectric generators, which convert the heat from a decaying pellet of plutonium into electricity — are running low.

To extend the crafts’ operational lives, engineers at Nasa’s Jet Propulsion Laboratory (JPL) just north of Pasadena in California are now gradually switching off some of the instruments still gathering data.

Last month, Voyager 1’s cosmic ray detector subsystem — a suite of three telescopes designed to study cosmic rays, including protons from the galaxy and the sun — was powered down. Data from those instruments had helped show that in 2012 Voyager 1 became the first human-made object to exit the heliosphere — the region of space, where the solar wind, made up of particles that stream from the sun, has a significant influence.

On March 24, Voyager 2’s low-energy charged particle instrument, which detects ions, electrons, and cosmic rays, will follow suit. That will leave three active scientific instruments on each spacecraft, down from an original ten.

Suzanne Dodd, the Voyager project manager, said: “The Voyagers have been deep-space rock stars since launch, and we want to keep it that way as long as possible. But electrical power is running low. If we don’t turn off an instrument now, they’d probably have only a few more months before we’d have to call time on the mission.”

• Voyager 1 is finally contacting Earth again

In terms of space travel, the Voyagers remain unrivalled. No other spacecraft has ventured so far, and none are likely to match their achievements in the near future. Voyager 1 is more than 15 billion miles from Earth; Voyager 2 is trailing slightly behind at 13 billion miles. A radio signal from Earth takes more than 23 hours to reach Voyager 1.

The new plan should leave enough power for at least one instrument to stay running on each probe into the 2030s, Nasa said.

Linda Spilker, a JPL scientist, said: “Every minute of every day, the Voyagers explore a region where no spacecraft has gone before. That also means every day could be our last. But that day could also bring another interstellar revelation.”