NASA's Voyager 1 mysteriously lost touch with Earth

Voyager 1, the most distant human-made spacecraft, unexpectedly stopped communicating with Earth for two days, missing scheduled check-ins on October 18 and 19. It resumed contact on October 20, before NASA engineers needed to send repair commands, and has remained in touch since. Investigators have not determined what caused the outage, but found that one set of thrusters had shut down and a backup set took over. These small engines help point and steady the craft; its onboard systems automatically switch to backups when they detect a problem. NASA says the incident is unprecedented for the mission, though the spacecraft’s age makes further surprises likely.

The episode adds to signs that Voyager 1’s decades-long mission is nearing its limits. Launched in 1977, it explored the outer planets before entering interstellar space in 2012, and now travels about 38,000 miles per hour. Its plutonium power supply loses roughly four watts each year, so NASA has switched off instruments and recently replaced three power-hungry devices on each Voyager with lower-power alternatives to preserve key science measurements. On November 18, Voyager 1 is expected to reach one light-day from Earth, about 16.09 billion miles away. At that distance, a signal will take 24 hours to arrive and another 24 hours for a reply to return, making even routine communication a two-day exchange.