|At about 100 meters from the cargo bay of the space shuttle Challenger, Bruce McCandless II was further out than anyone had ever been before.
Guided by a
Manned Maneuvering Unit (MMU), astronaut McCandless,
pictured above, was floating free in space.
McCandless and fellow
Robert Stewart were the first to
experience such an
"untethered space walk"
during Space Shuttle mission
The MMU works by shooting jets of
and has since been used to help deploy and retrieve satellites.
With a mass over 140 kilograms, an
MMU is heavy
but, like everything, is weightless when drifting in orbit.
The MMU was replaced with the
SAFER backpack propulsion unit.