On February 7, 1984, Bruce McCandless became the first human to float free from any earthly anchor when he stepped out of the space shuttle Challenger and flew away from the ship. In a still-startling NASA image from that mission, untethered McCandless hangs 320 feet from Challenger, suspended above our impossibly blue planet and appearing paradoxically powerful and fragile against the yawning vastness of the cosmos.

But McCandless’s most memorable spacewalks, immortalized by a photo taken later during the mission, took place on his very first spaceflight. He’d been asked to test a new 300-pound Manned Maneuvering Unit, or MMU, which is basically a nitrogen-powered jetpack that allows astronauts to twist and turn through space as George Clooney’s character did in the movie Gravity. But this was no feature film, and to say that people were nervous about an unrecoverable malfunction is no overstatement.