Astronauts Fly Free: First Untethered Spacewalk

Astronaut Bruce McCandless floated 320 feet from the Space Shuttle Challenger on February 7, 1984, farther from any spacecraft than any human had ever been, with nothing connecting him to the ship except a radio signal. He was propelled by the Manned Maneuvering Unit, a nitrogen-gas-powered jetpack strapped to his spacesuit, moving through the void at 17,500 miles per hour relative to Earth’s surface. If the MMU failed, he would drift away and die. The photograph of his solitary figure against the blue curve of the planet became one of NASA’s most recognized images. McCandless had waited twenty years for this moment. He joined the astronaut corps in 1966 and served as capsule communicator for Apollo 11, relaying messages between Houston and the lunar surface. He was then assigned to help develop the MMU, a backpack-sized propulsion system that would allow astronauts to maneuver independently in space without tethers. The device used twenty-four nitrogen-gas thrusters controlled by joysticks on each armrest, with enough fuel for approximately six hours of operation. The STS-41-B mission launched on February 3, 1984, with McCandless and fellow astronaut Robert L. Stewart scheduled to test the MMU on separate spacewalks. McCandless went first. He backed away from the shuttle bay slowly, testing the thrusters in small increments, then flew out to a distance of 320 feet. The shuttle crew, commanded by Vance Brand, watched from the flight deck. Mission Control monitored his vital signs and fuel consumption. Stewart performed his own MMU flight the following day. The untethered spacewalk demonstrated that astronauts could work freely in space, a capability NASA considered essential for satellite repair, construction of space stations, and eventually assembling large structures in orbit. The MMU was used on three shuttle missions before being retired after the Challenger disaster in 1986 prompted a reassessment of acceptable risk. No astronaut has performed a fully untethered spacewalk since. McCandless’s photograph endures as the defining image of human freedom in space.