Space Shuttle program: STS-41-B Mission: astronauts Bruce McCandless II and Robert L. Stewart make the first untethered space walk using the Manned Maneuvering Unit (MMU).

The Space Shuttle program was the fourth human spaceflight program carried out by the U.S. National Aeronautics and Space Administration (NASA), which accomplished routine transportation for Earth-to-orbit crew and cargo from 1981 to 2011. Its official program name was Space Transportation System (STS), taken from a 1969 plan for a system of reusable spacecraft where it was the only item funded for development, as a proposed nuclear shuttle in the plan was cancelled in 1972. It flew 135 missions and carried 355 astronauts from 16 countries, many on multiple trips.

STS-41-B was NASA's tenth Space Shuttle mission and the fourth flight of the Space Shuttle Challenger. It launched on February 3, 1984 and landed on February 11, 1984, after deploying two communications satellites. It was also notable for including the first untethered spacewalk.

Bruce McCandless II was an American Navy officer and aviator, electrical engineer, and NASA astronaut. In 1984, during the first of his two Space Shuttle missions, he completed the first untethered spacewalk by using the Manned Maneuvering Unit.

Robert Lee Stewart is an American retired military officer and NASA astronaut who was a brigadier general of the United States Army.

Extravehicular activity (EVA) is any activity done by an astronaut in outer space outside a spacecraft. In the absence of a breathable Earthlike atmosphere, the astronaut is completely reliant on a space suit for environmental support. EVA includes spacewalks and lunar or planetary surface exploration. In a stand-up EVA (SEVA), an astronaut stands through an open hatch but does not fully leave the spacecraft. EVAs have been conducted by the Soviet Union/Russia, the United States, and China; astronauts from Canada, Japan, Brazil, the United Arab Emirates, and the European Space Agency have also participated in EVAs conducted by those nations.