It’s been 47 years since the twin Voyager spacecraft started their historic mission. Having travelled through interstellar space, farther from Earth than any other human-made objects, their nuclear batteries are depleting — but NASA is taking measures to squeeze as much life out of the aging probes as possible.

Voyager 1 — launched in 1977 and now over 15.6 billion miles from Earth — started out with 10 science instruments, but now has just three running after NASA turned off another gadget to conserve its finite nuclear fuel supply. And later this month, the space agency's engineers will turn off another instrument on its exploration sibling, Voyager 2.

However, NASA isn’t ready to say goodbye just yet, and is taking measures to get as much life out of the pair as possible. On March 5, Voyager mission engineers at the Jet Propulsion Laboratory in southern California confirmed they have already turned off Voyager 1’s cosmic ray subsystem experiment.