Former astronaut Bruce McCandless II, a retired Navy captain and son of a Medal of Honor recipient who joined NASA during the buildup to the Apollo program, served as capsule communicator when Neil Armstrong took his historic first step on the moon and later flew in space twice during the shuttle program, died Thursday, NASA said Friday. He was 80. During his first space flight aboard the shuttle Challenger in February 1984, McCandless carried out the first untethered spacewalk, using a nitrogen gas-powered Manned Maneuvering Unit he helped design to fly well away from the orbiter for a series of tests. Photos of McCandless, floating alone in the deep black of space above the brilliant limb of Earth became iconic emblems of the space shuttle program and among the most widely reproduced. The Challenger crew also launched two communications satellites before returning to Earth, making the program's first shuttle landing at the Kennedy Space Center.