The Lockheed NF-104A was an American mixed power, high-performance, supersonic aerospace trainer that served as a low-cost astronaut training vehicle for the X-15 and projected X-20 Dyna-Soar programs.

Three aircraft were modified from existing Lockheed F-104A airframes and served with the Aerospace Research Pilots School between 1963 and 1971, the modifications included a small supplementary rocket engine and a reaction control system for flight in the upper atmosphere. During the test program the maximum altitude reached was over 120,000 ft (36,600 m). One of the aircraft was destroyed in an accident while being flown by Chuck Yeager. The accident was depicted in the book The Right Stuff and the film of the same name.

With the advent of manned spaceflight in the early 1960s, the United States Air Force Experimental Flight Test Pilot's School at Edwards Air Force Base was renamed the Aerospace Research Pilots School (ARPS), with the emphasis on training moving away from the traditional test pilot course to a more spaceflight oriented curriculum.

Charles Elwood "Chuck" Yeager ( /ˈjeɪɡər/; born February 13, 1923) is a retired major general in the United States Air Force and noted test pilot. He was the first pilot to travel faster than sound (1947). Originally retiring in 1975 as a brigadier general, Yeager was promoted to major general on the Air Force's retired list in 2005 for his military achievements.

His career began in World War II as a private in the United States Army Air Forces. After serving as an aircraft mechanic, in September 1942 he entered enlisted pilot training and upon graduation was promoted to the rank of flight officer (the World War II USAAF equivalent to warrant officer) and became a North American P-51 Mustang fighter pilot.

After the war he became a test pilot of many kinds of aircraft and rocket planes. Yeager was the first man to break the sound barrier on October 14, 1947, flying the experimental Bell X-1 at Mach 1 at an altitude of 45,000 ft (13,700 m). Although Scott Crossfield was the first man to fly faster than Mach 2 in 1953, Yeager shortly thereafter set a new record of Mach 2.44.