The Voyager probes are the two furthest artificial objects ever, both now traveling in interstellar space after having been launched in 1977 just 16 days apart on a mission to fly by Jupiter and Saturn (as well as Uranus and Neptune for Voyager 2).
Despite having been in space for almost 42 years, the spacecraft continue to work. This is longer than any other spacecraft in history. And now, NASA has come up with a plan to squeeze as much science from them as possible before they stop operating.
The crafts are nuclear powered, which means they use a radioisotope thermoelectric generator to produce heat and electricity to power the instruments and keep them at a good operational temperature. There is enough radioactive juice left to run Voyager 1 until 2025 and Voyager 2 until at least next year. The discrepancy in end dates is because Voyager 2 has an extra instrument compared to its twin.
To save energy, the team has now decided to turn off the heating to the cosmic ray subsystem instrument (CRS) on Voyager 2. This is the instrument that confirmed last November the probe was no longer within the heliosphere and had finally crossed into interstellar space. The instrument is now at -59°C (-74°F) but it continues to work. That is well below the lowest tested temperature for the CRS, and it joins the ultraviolet spectrometer in being surprisingly resilient.
"It's incredible that Voyagers' instruments have proved so hardy," Voyager Project Manager Suzanne Dodd, from NASA's Jet Propulsion Laboratory, said in a statement. "We're proud they've withstood the test of time. The long lifetimes of the spacecraft mean we're dealing with scenarios we never thought we'd encounter. We will continue to explore every option we have in order to keep the Voyagers doing the best science possible."
The choices the team is making are not easy. To do the best they can to explore beyond the influence of the Sun, they have to decide for a longer lifespan with fewer instruments. Additional instruments will likely be switched off sooner rather than later.
"Both Voyager probes are exploring regions never before visited, so every day is a day of discovery," said Voyager Project Scientist Ed Stone, who is based at Caltech. "Voyager is going to keep surprising us with new insights about deep space."
It is crucial that the heater is kept on the fuel lines to the thrusters as those are key to keep maintaining the crafts’ antennae pointing at Earth. The data we get from Voyager 1 and Voyager 2 takes, respectively, 20 hours and 10 minutes and 16 hours and 40 minutes.