Astronaut Bruce McCandless II, STS 41-B mission specialist, participates in a historical spacewalk on February 7th, 1984. He is pictured a few meters away from the cabin of the Earth-orbiting Space Shuttle Challenger. This spacewalk represented the first use of a nitrogen-propelled, hand-controlled device called the Manned Maneuvering Unit (MMU), which allows for much greater mobility than that afforded previous space walkers who had to use restrictive tethers. McCandless, who helped design the MMU, was the first person to fly it, thus becoming the first "human satellite" in orbit around the Earth. Mission 41-B was the 10th space shuttle flight which launched from Kennedy Space Center on February 3rd, 1984 and returned on February 12th.