Humans have left a lot of stuff in space. There is so much stuff that space junk has become a serious problem. Much of it is defunct satellites in orbits high enough that they can’t simply fall back down to Earth. But just because a satellite has died, don’t think it’s all over. Six of them have demonstrated that, sometimes, satellites can spontaneously and unexpectedly come back to life. These revenant spacecraft orbiting our planet are known as zombie satellites.

A zombie satellite can be any satellite that begins to communicate again after an extended period of inactivity. Usually, these devices lose their orbit or can’t power themselves up, getting to a point where the ground can no longer contact them. And then, spontaneously, they begin to operate again, or clever people on earth manage to find new ways to establish contact.

Let’s start with the veteran of these zombie satellites. Transit 5B-5 was launched back in 1965. Transit was a precursor to GPS, one of the first satellite navigation systems. To increase its longevity, the satellite is nuclear-powered and in a stable polar orbit, meaning its orbit is between 60 to 90 degrees with respect to the equator. Operators are unable to control it, but its communications were heard long after Transit was retired in 1996.

Zombie might not be the exact term for Galaxy 15, a telecommunications satellite operated by Intelsat. Launched in 2005 with a 15-year mission, it drifted out of its orbital slot after the operator lost control of it in April 2010. Galaxy 15 seemed like a goner, but by December 2010, the satellite rebooted itself and Intelsat was able to place it back into its original slot. So, it was fully brought back to life.

Among the record-holders for the longest gap between communications, there’s AMSAT-OSCAR 7. Launched in November 1974, this was an amateur radio satellite that operated for 7 years. In 1981, a battery failure put an end to its mission – but 21 years later, on June 21, 2002, the satellite started communicating again.

Amateur radio operators have actually played a big role in all this, and one among them, Scott Tilley, in particular. He’s responsible for receiving communications from the Lincoln Experimental Satellite, LES-5, originally launched in 1967 by the US Air Force, back in 2020. It only works when the solar panels are getting sunlight. A couple of years before that, he was able to find the IMAGE satellite, another zombie satellite that had been “lost” by NASA in 2005.

Tilley was actually looking for a completely different satellite, a secret US satellite known as USA-280 or Zuma. The satellite was probably lost during a SpaceX launch in 2018. The mishap brought down the anger of far-right commentators on Elon Musk’s SpaceX, long before the billionaire publicly embraced them on Twitter.

Last, but certainly not least, is another of the Lincoln Experimental Satellites: LES-1. It was launched in 1965, but it never achieved optimal orbit to test the use of Super High Frequency radio transmission, instead tumbling out of control in space. So, imagine the surprise of hearing back from it in 2012, 47 years after it was lost. Even in the signals, it is possible to hear that the satellite is tumbling.