Robert Kimball

For two full days in mid-October, Earth’s most distant machine simply vanished. Sixteen billion miles out, in the cold dark beyond the solar system, Voyager 1’s faint radio whisper stopped arriving. On October 18 and again on the 19th, the giant dishes of NASA’s Deep Space Network pointed themselves at the probe’s expected position and heard nothing. For a spacecraft that has been answering for nearly half a century, the silence was unnerving. Then, on October 20, the signal was simply back. No commands had been sent. No one on Earth had fixed anything. Voyager had repaired itself. Engineers later pieced together what had happened. One set of thrusters—the tiny engines that keep the spacecraft’s big dish pointed precisely at Earth—had shut down. Backup thrusters automatically took over. This is the spacecraft’s built-in “fault protection,” a decades-old safety routine that drops everything non-essential and locks the probe into a stable configuration so ground teams have time to figure out what went wrong. It worked exactly as designed. The exact trigger is still under investigation. “This is the first time we’ve seen the spacecraft do something like this,” said Voyager mission manager Kareem Badaruddin, “but we are also at a point in the mission where we have to expect the unexpected.” The scare came on the heels of a carefully planned victory. In September, engineers executed a high-stakes maneuver they nicknamed the “Big Bang”: they simultaneously powered down three aging heaters and switched on lower-power replacements. Voyager’s electricity comes from the slow decay of plutonium, and it loses about 4 watts every year. Without the swap, the team would have been forced to shut off another science instrument by the summer of 2027. The simultaneous switch was the only way to save power while still keeping critical parts warm enough to function. Launched in 1977, Voyager 1 is now roughly 16 billion miles from home. On November 18 it will cross a quiet but profound milestone: one light-day from Earth. From that moment on, any message sent to the spacecraft will take a full day to arrive, and any reply will take another day to come back. The machine is old. The power is dwindling. The thrusters are cranky. And yet, somewhere in the interstellar dark, Voyager 1 is still listening, still pointing itself home, and still, when it has to, fixing itself.