Astronaut Bruce McCandless becomes the first untethered human spacewalker when he leaves the cargo bay of Space Shuttle Challenger aboard a Manned Maneuvering Unit, a jetpack-like device allowing him to maneuver freely with no hoses or cables connecting him to the shuttle. In development since the Gemini era, and tested briefly aboard Skylab in prototype form, the MMU will see use on only three missions before NASA puts it in mothballs.
