NASA’s Voyager 1 is approaching an extraordinary milestone nearly 50 years after its launch, even as engineers battle dwindling power and mysterious technical problems. A clever energy-saving maneuver has extended the spacecraft’s scientific mission, while an unexplained 48-hour communications blackout recently gave NASA a scare. On November 18, Voyager 1 will reach a distance of one light-day from Earth, making even the simplest round-trip communication take 48 hours.