Manned Maneuvering Unit

The Manned Maneuvering Unit, or MMU, was a nitrogen-propelled backpack that let a NASA astronaut fly untethered outside the Space Shuttle. It was designed to fit over the life-support backpack of the shuttle spacesuit and was stowed on the payload bay wall near the airlock. The MMU was used on three Space Shuttle missions in 1984, STS-41-B, STS-41-C and STS-51-A. Its flights included the first untethered spacewalks and the retrieval of two faulty communications satellites, Westar VI and Palapa B2. NASA awarded the fabrication contract to Martin Marietta of Denver in 1980. After the third mission the unit was retired, because the shuttle and its robotic arm proved able to do most of the planned work, and a smaller successor, the Simplified Aid For EVA Rescue (SAFER), first flew in 1994 for emergency use only.