space walks were not until the Space Shuttle era began in the early 1980s. The Shuttle features cargo bay doors that allow astronauts easy access to the vacuum of space. The Gemini and Skylab research led to the development of a Manned Maneuvering Unit (MMU) for Space Shuttle astronauts. The nitrogen-jet-powered MMU was essentially a self-contained spacecraft that an astronaut wore like a backpack. The MMU was first used on the 10th flight of the Space Shuttle. Astronaut Bruce McCandless became the first person to fly freely, untethered in space in February 1984. The MMU was used a total of nine times on three Space Shuttle missions in 1984, but has not been used since. Tethers, grips, and other restraints proved more than adequate for space walks in a Shuttle cargo bay. The Canadarm robot arm proved itself ideal for recovery of satellites and other tasks outside the Shuttle. SAFER, which has been described as a simplified version of the MMU, has two advantages over the earlier system. It is a more convenient size and weight and ideal for an astronaut rescue device outside the Space Station.
SAFER is a rare type of technology—the kind that is built hoping that it won’t be used. So far, tethers, safety grips, and the robot arm have proved adequate to safely keep astronauts where they are supposed to be during space walks. But if they ever fail, SAFER will be ready.
