Mission Specialist Bruce McCandless II ventured further away from the confines and safety of his ship than any previous astronaut ever has. This space first was made possible by the Manned Manuevering Unit or MMU, a nitrogen jet propelled backpack. After a series of test maneuvers inside and above Challenger's payload bay, McCandless went "free-flying" to a distance of 320 feet away from the Orbiter. The MMU is controlled by joy sticks positioned at the end of the arm rests. Moving the joy sticks left or right or by pulling them fires nitrogen jet thrusters propelling McCandless

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