Manned Maneuvering Unit

The Manned Maneuvering Unit (MMU) is an astronaut propulsion unit that was used by NASA on three Space Shuttle missions in 1984, STS-41-B, STS-41-C, and STS-51-A. The MMU allowed the astronauts to perform untethered extravehicular spacewalks at a distance from the shuttle. The MMU was used in practice to retrieve a pair of faulty communications satellites, Westar VI and Palapa B2. Following the third mission the unit was retired from use. A smaller successor, the Simplified Aid For EVA Rescue (SAFER), was first flown in 1994; it is intended for emergency use only.