Astronaut Bruce McCandless flying through space free and untethered in one of the most iconic space photos of all time. The Manned Maneuvering Unit (MMU) is an astronaut propulsion unit that was used by NASA on three Space Shuttle missions in 1984. The MMU allowed the astronauts to perform untethered EVA spacewalks at a distance from the shuttle. #nasa #science #technology #space #shuttle