Launched in 1977, Voyagers 1 and 2 are the longest-running spacecraft, still operating at more than 11 billion miles from home, decades after the end of their nominal goal of exploring the outer solar system planets. They still get their power from the same three radioisotope thermoelectric generators, or RTGs, that have served them for years. But with these generators yielding less power every year, the spacecraft have started to flag.

Mission controllers have had to make some tough calls about which instruments to prioritize, and recently made the call to turn off heating for Voyager 2’s cosmic ray instrument. The instrument itself is still functioning for now, despite operating at conditions of negative 74 degrees Fahrenheit, when it was only tested down to negative 49 degrees.

The craft has five functioning instruments remaining, which it still uses to collect data and send back to Earth on its long journey into deep space.

After all these years

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The Voyager spacecraft launched in 1977 as twin spacecraft, each with ten instruments to explore space and tour the solar system, sending back humanity’s first close-up look at most of the outer planets.

Voyager 1 visited Jupiter and Saturn before heading for deep space, while Voyager 2 swung by those planets plus Uranus and Neptune, its trajectory carrying it off at a slower pace. But since 1989, both have been exploring the empty space beyond the planets, and returning priceless information about how far the solar atmosphere extends its influence. It was only in 2018 that Voyager 2 officially entered interstellar space, returning information on how the space environment changed as it finally left the Sun’s sphere of influence.

Voyager 2 has five working instruments compared with Voyager 1’s four. Most of them have been switched off intentionally, as the imaging cameras, for instance, are not useful so far from any sunlight or photographical objects. But they are still measuring cosmic rays, magnetic fields and other charged particles that fill interstellar space far beyond the worldly realm of the planets.

By measuring these particles, astronomers are learning just how far the Sun’s energy extends, and how those fields interact with the interstellar medium beyond the solar system’s edges.