As astronaut Bruce McCandless II flew the Manned Maneuvering Unit (MMU) out of the space shuttle Challenger's payload bay for the first time on February 7, 1984, many in the agency were fearful about the use of a self-propelled and untethered backpack in space. (Previous spacewalkers remained connected to the vehicle with tethers. This jet-pack allowed crews to move outside of the cargo bay and perform activities away from the safety of the spacecraft.) He remembered trying to ease the tension for his wife and the flight controllers in Mission Control, saying something similar to Neil Armstrong's declaration as he first stepped on the Moon in 1969. "It may have been one small step for Neil," he proclaimed, "but it's a heck of a big leap for me."
