On the tenth shuttle mission, STS-41-B, McCandless tested the Manned Maneuvering Unit, a hand-controlled backpack that fired jets of nitrogen gas. With no line connecting him to Challenger, he moved as far as 320 feet from the orbiter, 170 miles above Earth, and stayed outside for about an hour and a half. Later that day Army Lieutenant Colonel Robert Stewart flew the unit too. NASA hoped the device would let astronauts repair satellites and assemble space stations.
At 7:25 on a Tuesday morning, Houston time, McCandless fired his thrusters, rose slowly out of Challenger's cargo bay and cleared the spacecraft. He was travelling at more than 17,500 miles per hour, the same speed as the shuttle, so to the crew watching through the windows he seemed to hang in place against the curve of the Earth. Neil Armstrong had made history on the Moon fifteen years earlier, and McCandless nodded to him on the way out: "It may have been one small step for Neil, but it's a heck of a big leap for me."
He was 46, a third-generation Navy officer whose father and grandfather had both received the Medal of Honor. He had also spent years working on the backpack's development, and History.com describes it as a jet pack of his own design. As well as flying the unit, he tried out a pair of bifocals meant to help him focus inside his helmet, and a foot-restraint platform for working outside the spacecraft.
NASA's photograph of McCandless floating alone above a blue Earth, with nothing holding him to anything, became one of the best-known pictures of the space age.
Key people: Bruce McCandless II, Robert L. Stewart, Vance D. Brand