Plans for human spaceflight began in the US Armed Forces prior to NASA’s creation. The Air Force’s Man in Space Soonest project formed in 1956, coupled with the Army’s Project Adam, served as the foundation for Project Mercury. NASA established the Space Task Group to manage the program, which would conduct crewed sub-orbital flights with the Army’s Redstone rockets and orbital flights with the Air Force’s Atlas launch vehicles. While NASA intended for its first astronauts to be civilians, President Eisenhower directed that they be selected from the military. The Mercury 7 astronauts included three Air Force pilots, three Navy aviators, and one Marine Corps pilot.

On May 5, 1961, Alan Shepard became the first American to enter space, performing a suborbital spaceflight in the Freedom 7. This flight occurred 23 days after the Soviet Yuri Gagarin became the first human in space, executing a full orbital spaceflight. NASA’s first orbital spaceflight was conducted by John Glenn on February 20, 1962, in the Friendship 7, making three full orbits before reentering. Glenn had to fly parts of his final two orbits manually due to an autopilot malfunction. The sixth and final Mercury mission was flown by Gordon Cooper in May 1963, performing 22 orbits over 34 hours in the Faith 7. The Mercury program was widely recognized as a resounding success, achieving its objectives to orbit a human in space, develop tracking and control systems, and identify other issues associated with human spaceflight.

While much of NASA’s attention turned to space, it did not put aside its aeronautics mission. Early aeronautics research attempted to build upon the X-1’s supersonic flight to build an aircraft capable of hypersonic flight. The North American X-15 was a joint NASA–US Air Force program, with the hypersonic test aircraft becoming the first non-dedicated spacecraft to cross from the atmosphere to outer space. The X-15 also served as a testbed for Apollo program technologies, as well as ramjet and scramjet propulsion.