NASA astronaut Bruce McCandless during the first untethered spacewalk in history. In this photograph taken on February 7, 1984 by his fellow crewmembers aboard the Earth-orbiting Space Shuttle Challenger on the STS-41B mission, McCandless II approaches his maximum distance (98 meters/320 feet) from the vehicle. McCandless became the first astronaut to maneuver about in space untethered, during this first “field” tryout of a nitrogen-propelled, hand-controlled backpack device called the Manned Maneuvering Unit (MMU).
Not long afterward, NASA discontinued such actions and decided to perform only tethered spacewalks for safety reasons. In 1994, NASA unveiled a new backpack called Simplified Aid for EVA Rescue, or Safer, and tested it with an untethered spacewalk, the fourth, and thus far last untethered extra-vehicular activity it has performed. Every astronaut at the International Space Station wears Safer, which is smaller and lighter than the manned maneuvering units, for use during an emergency.
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