NASA has decided to shut down one of Voyager 2’s five remaining instruments — another sign that the spacecraft may be nearing the end of their historic missions. In one October 1 announcementthe agency explained that engineers waited as long as possible to collect valuable and unique data, but ultimately chose to turn off the spacecraft’s plasma science instrument to preserve Voyager 2’s remaining power supply.
The Voyager 1 and 2 probes are designed to travel further into space than any other man-made object, but keeping their systems functional requires a power source that is up to the task. To do that, both spacecraft rely on three radioisotope thermoelectric generators (RTGs) powered by decaying plutonium-238. Although this provided Voyager 1 and 2 with about 470 W at 30 volts at launch in 1977, the half-life of 87.74 years means the plutonium has lost about 0.79 percent of its power annually. More than 47 years later, the two now operate at an estimated two-thirds of their original capacity.
The plasma science instrument is designed to study the Sun’s particle emissions and uses four cup-shaped instruments. Three cups face the Sun to record the solar wind while in the heliosphere, while the fourth is placed at right angles to the others to capture information about various planetary magnetospheres, the heliosphere and the interstellar room. NASA explained that while crucial in determining the moment Voyager 2 left the heliosphere in 2018, its usefulness has significantly diminished since then. At the time it was turned off, the plasma science instrument only provided particularly useful data about once every three months as its slow 360-degree rotation pointed it back toward the sun.
[Related: Voyager 1 defies the odds yet again and is back online.]
Because of this inevitability, NASA decided it was time to scale back activities on Voyager 2 by discontinuing the plasma science instrument. However, this took much longer than leaving a computer program on Earth. More than 12 billion miles (20.9 billion kilometers) from its home planet, about 48 degrees south of the Sun’s ecliptic, NASA’s “shutdown” signal, sent on September 26, took 19 hours to reach Voyager 2, and again 19 hours before the confirmation signal returned.
This isn’t the first time engineers have pulled the plug on equipment aboard Voyager probes. After completing their first mission surveys of the solar system’s gas giants in the 1980s, NASA retired several instruments that were unusable for probes into interstellar space. All non-essential tools on both spacecraft have now also been taken offline, including some heaters. Voyager 1’s own plasma science instrument also stopped working in 1980, but engineers only turned it off in 2007 to save energy.
Despite some recent close calls, both Voyager spacecraft continue to make history every day by traveling further into space than any other man-made object in existence. Unless fatal problems arise, it is possible for Voyager 1 and 2 to continue transmitting data from at least one instrument until 2030. While this may be a long shot, NASA engineers are doing everything they can to increase those odds.
