Lockheed modified three F-104A Starfighter aircraft, Air Force serial numbers 56-0756, 56-0760, and 56-0762, to serve as Aero-Space Trainers (AST). They served with the Aerospace Research Pilot School (ARPS) at Edwards Air Force Base, California. Many astronaut candidates used the aircraft as part of their intensive training program. It gave them a low-cost trainer that provided flight experience at altitudes where conventional control surfaces would not be effective.

A Rocketdyne LR-121/AR-2 liquid-fuel rocket engine was added to the tail section of these aircraft just above the jet exhaust. It helped propel the NF-104A to altitudes in excess of 100,000 feet. The vertical stabilizer was enlarged, and the intake cones were also modified. A reaction control system (RCS) was added, consisting of hydrogen peroxide thrusters located in the nose and wingtips. The radar had to be removed to accommodate the pitch and yaw thrusters in the nose. Roll thrusters were placed in 24-inch wingtip extensions.