The first untethered spacewalk was made by American Bruce McCandless II on February 7, 1984, during Challenger mission STS-41-B, utilizing the Manned Maneuvering Unit. He was subsequently joined by Robert L. Stewart during the 5 hour 55 minute spacewalk.
“Free of any lifeline and propelled into the dark void by tiny jets, they became, in effect, the first human satellites, ” reported the Feb. 8 New York Times.
The two astronauts used the extra-vehicular activity to simulate the procedures that were planned for the capture and repair of a malfunctioning satellite on a future mission. That objective was carried out in April 1984, when two astronauts successfully repaired the Solar Max satellite while using manned maneuvering units. In November of that same year, two STS-51A astronauts used their manned maneuvering units to retrieve two malfunctioning communications satellites, the Westar VI and Palapa B2.
The manned maneuvering units used by Captain McCandless and Colonel Stewart were not used again after 1984, as NASA 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.