U.S. astronaut Alan Shepard poses in his silver pressure suit in a 1963 picture from the early days of NASA's Mercury space program. Thursday marks the 50th anniversary of Shepard becoming the first American in space, when he completed a short suborbital voyage aboard the Freedom 7 spacecraft. Less than a month before, Soviet cosmonaut Yuri Gagarin had become the first human in space with his successful orbital flight aboard the Vostok 1 spacecraft. (See "Yuri Gagarin: First Human Space Flight in Pictures.") Over the decades, the U.S. space suit has evolved as astronauts' duties have become more complicated. The suit Shepard wore during his 16-minute flight was designed by aerospace manufacturer B.F. Goodrich. Called the Mark-IV, it was essentially a converted Navy-pilot suit, said Bill Ayrey, a space suit historian with ILC Dover in Delaware.