Alan Shepard: First American in SpaceU.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."Although it was referred to as a space suit by many at the time, it was actually a modified pressure suit," Ayrey said. "When they were looking for a space suit for Mercury, they were just looking for a suit that would hold pressure, in case they lost pressure aboard the capsule."Later space suits, intended to withstand life outside the spacecraft, also kept astronauts well ventilated and at a comfortable temperature as well as safe from radiation and micrometeorite impacts.—Ker Than

Photograph courtesy NASA