The first untethered spacewalk
Until 1984, every EVA was performed with a safety tether. That changed during the STS-41-B mission, when NASA astronaut Bruce McCandless achieved an untethered spacewalk while venturing outside the Space Shuttle Challenger. McCandless did so using the Manned Maneuvering Unit (MMU), which allowed him to drift more than 300 feet (91 meters) from the Shuttle. Two dozen small compressed nitrogen thrusters powered the unit, while a pair of motion-controlled handles on the armrest allowed McCandless to maneuver himself through space. This particular spacewalk, I have to say, took a lot of guts.
McCandless, along with crew member Robert Stewart, simply tested the new unit during the STS-41 mission, but it was put to good use during the STS-51-A mission in November 1984, when astronauts used the the propulsion device to capture two communication satellites that failed to reach their proper orbits.
