The U.S. space program began with the Jan. 31, 1958, launch of the unmanned satellite Explorer 1. The same year, the National Aeronautics and Space Association embarked on Project Mercury, the first American program to carry humans into space. Mercury astronaut Alan Shepard became the first American to achieve suborbital flight on Feb. 20, 1962.
Project Mercury concluded in 1963 and was the first of three major manned missions. The second, Project Gemini, was announced in 1962 and featured 10 manned, and two unmanned, orbital flights. Following President Kennedy's imperative to reach the moon, NASA launched Project Apollo. Apollo 11 successfully landed on the moon on July 20, 1969. The Apollo project ran for several more missions, and the Saturn V rocket it used was later adapted to carry the Skylab space station into low Earth orbit. Beginning with the April 1981 launch of the space shuttle Columbia, NASA focused on developing reusable vehicles for routine spaceflight. The shuttle program was discontinued early in the 21st century.
NASA has also managed a number of successful uncrewed missions. The Pioneer program lasted between 1958 and 1978, and two of the craft, Pioneers 10 and 11, were the first to explore the outer planets. NASA later sent Viking probes to Mars and Voyager probes to the outer reaches of the solar system. As of 2015, NASA continues to operate multiple unmanned robotic probes as well as a large number of orbiting satellites.