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. 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, and is intended for emergency use only.