Voyager 1 runs on 69 KB of memory and an 8-track tape recorder

Fifteen billion miles from Earth, a 48-year-old spacecraft is transmitting scientific data using less memory than a single smartphone photo and the power of a refrigerator light bulb. Voyager 1, launched in 1977 for what was supposed to be a five-year mission, has become humanity's most improbable success story, now cruising through interstellar space at 38,000 miles per hour.

The spacecraft nearly went silent forever this year when its attitude control thrusters began clogging with debris after decades of use. Engineers at NASA's Jet Propulsion Laboratory faced a terrifying gamble: attempt to restart thrusters that had been dead since 2004, or watch Voyager drift away from Earth contact forever.

"It was such a glorious moment," said Todd Barber, the mission's propulsion lead, after the March revival succeeded. "These thrusters were considered dead. It was yet another miracle save for Voyager."

Built with 1970s technology, Voyager operates on 69 kilobytes of memory and transmits data at 160 bits per second. Yet it discovered active volcanoes on Jupiter's moon Io, revealed Saturn's moon Titan has a substantial atmosphere, and in 2012 became the first human-made object to enter interstellar space.

The spacecraft carries a golden record with Earth sounds and greetings in 55 languages, a cosmic message in a bottle that will outlast our planet itself.