"Ever since I've been an astronaut I knew I wanted to do a spacewalk."
John L. Phillips, astronaut
The advent of the Space Shuttle and space stations made it obvious to the National Aeronautics and Space Administration (NASA) that some method of extravehicular space locomotion was needed. The space agency called on the Lockheed Corporation (now Lockheed Martin) to build a device that would allow astronauts to manipulate satellites, repair and build structures, and perhaps even rescue colleagues engaged in extravehicular activities (EVAs).
In 1984 the Manned Maneuvering Unit (MMU) became reality. The backpack-like unit was designed to work alongside the life-support systems already in place on a space suit. It was stowed in the payload bay of the Space Shuttle when not in use and simply attached to the standard Extravehicular Maneuvering Unit (EMU) spacesuit when astronauts needed to work on a part of the space station or ship that they could not easily access when walking with a tether. The unit used twenty-four different thrusters to allow astronauts to maneuver with some degree of agility, but it was still small enough to allow precision work. Astronauts moved using a handheld control unit, and an autopilot could hold them at a constant attitude.
The MMU was deployed on three separate Space Shuttle missions, but it has not been used since the explosion of Space Shuttle Challenger. For the most part, tethered space walks have proved adeguate to replace the device, but a Simplified Aide For EVA Rescue (SAFER) unit is present on the International Space Station; its primary function is to assist in the rescue of an accidentally untethered astronaut.
