Astronomy Picture of the Day

Explanation: At about 100 meters from the cargo bay of the space shuttle Challenger, Bruce McCandless II was farther 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 NASA astronaut Robert Stewart were the first to experience such an "untethered space walk" during Space Shuttle mission 41-B in 1984. The MMU works by shooting jets of nitrogen and has since been used to help deploy and retrieve satellites. With a mass over 140 kilograms, an MMU is heavy on Earth, but, like everything, is weightless when drifting in orbit. The MMU was replaced with the SAFER backpack propulsion unit.

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Web Site Statements, Warnings, and Disclaimers
NASA Official: Jay Norris. Specific rights apply.
A service of: LHEA at NASA / GSFC
& Michigan Tech. U.

Publications with keywords: space shuttle
Publications with words: space shuttle
See also:

• A Space Shuttle on the Streets of Los Angeles
• A Space Shuttle Over Los Angeles
• Shuttle Enterprise Over New York
• Discovery Departs
• The Flight Deck of Space Shuttle Endeavour
• Shuttle Plume Shadow Points to the Moon
• Atlantis Reflection

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