where the astronaut is connected to the spacecraft with an umbilical cable for oxygen and power, or untethered. Untethered spacewalks were conducted on three missions in 1984 using the Manned Maneuvering Unit (MMU) and in a 1994 flight test of the Simplified Aid For EVA Rescue (SAFER) safety device worn on tethered U.S. EVAs.

Development history

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