NASA is keeping Voyager 1 alive by switching off instruments and heaters one by one—but it cannot let the spacecraft become so cold that its fuel lines freeze. If those lines fail, Voyager could lose the thrusters that keep its antenna aimed at Earth, permanently silencing the most distant human-made object.

NASA is keeping Voyager 1 alive by switching off instruments and heaters one by one—but it cannot let the spacecraft become so cold that its fuel lines freeze. If those lines fail, Voyager could lose the thrusters that keep its antenna aimed at Earth, permanently silencing the most distant human-made object.

Nearly half a century after it left Earth, Voyager 1 is being kept alive one switch at a time. Its power supply fades a little every year, so mission engineers at NASA have been turning off instruments and heaters in a careful sequence, trading capability for time. But the trimming has a hard floor. If the spacecraft is allowed to grow too cold, the lines that carry its fuel could freeze, and that would threaten the small thrusters that keep its…