Spacewalk. Astronaut Bruce McCandless floats free above the Earth in his manned maneuvering unit (MMU). This is a composite image showing the Earth photographed during another shuttle mission. Bruce McCandless conducted this spacewalk on February 7, 1984, during shuttle mission 41B. McCandless helped design the MMU and was the first person to fly it, thus becoming the first "human satellite" in orbit around the Earth. The MMU is propelled by nitrogen thrusters controlled by the astronaut's hands. Because no umbilical cord attaches the astronaut to the spacecraft, it gives much greater mobility than was available to previous spacewalkers. Storm clouds are seen over the Earth.