This stamp represents a real "first" for the country's stamps: It was the issued at the moment the flight was completed, the first time the United States honored a great event with a previously unannounced stamp issue. The Mercury program was the earliest U.S. project to put an astronaut into space. It used single-person, bell-shaped capsules that were placed into orbits above the Earth. Capsules re-entered the atmosphere ballistically, and parachutes were deployed on the final descent to ocean splashdown. Capsules were recovered by U.S. naval ships and helicopters. Project Mercury successfully flew two suborbital and four orbital manned missions.