The Manned Maneuvering Unit (MMU) is an astronaut propulsion unit that was used by NASA on three Space Shuttle missions in 1984. The MMU allowed the astronauts to perform untethered extravehicular spacewalks at a distance from the shuttle. The MMU was used in practice to retrieve a pair of faulty communications satellites, Westar VI and Palapa B2. Following the third mission the unit was retired from use. A smaller successor, the Simplified Aid For EVA Rescue (SAFER), was first flown in 1994, and is intended for emergency use only.
U.S. astronaut Bruce McCandless uses a Manned Maneuvering Unit during the 1984 STS-41-B mission
Robert L. Stewart
SMM being captured, 1984
Dale Gardner retrieves Westar 6.
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, Canada, the European Space Agency and China.
Cosmonaut Sergey Volkov works outside the International Space Station on August 3, 2011.
Stephen Robinson riding the Canadarm2 during STS-114 on August 3, 2005. The first in-flight repair of the Space Shuttle. The landmass in the backdrop is the Bari region of Somalia.
Ed White performs the first American spacewalk during Gemini IV.
Buzz Aldrin walks on the Moon during the pioneering Apollo 11 mission in 1969.