The Martin X-23A PRIME (Precision Reentry Including Maneuvering reEntry) was a small lifting bodyre-entry vehicle tested by the United States Air Force in the mid-1960s. Unlike ASSET, primarily used for structural and heating research, the X-23 PRIME was developed to study the effects of maneuvering during re-entry of Earth's atmosphere, including cross-range maneuvers up to 710 statute miles (1143 km) off of the ballistic track.
The first PRIME vehicle was launched from Vandenberg AFB on 21 December 1966 atop an Atlaslaunch vehicle. This mission simulated a low Earth orbit reentry with a zero cross-range. The ballute deployed at 99,850 feet (30.43 km), though the recovery parachute failed to completely deploy. The vehicle crashed into the Pacific Ocean.
The second vehicle was launched on 5 March 1967. This flight simulated a 654-mile (1053-kilometre) cross-range reentry, and banking at hypersonic speeds. The recovery parachute deployed properly, and was located by two of the deployed recovery aircraft. During an inspection fly-by of the descending parachute system it was seen that reefing cutters on the harness suspending the vehicle from the parachute to insure stability of the vehicle behind the JC-130B recovery aircraft during reel-in, to permit safely boarding the vehicle, had failed to actuate. Perforce, the parachute and vehicle were allowed to descend to the sea. Subsequently, the vehicle separated from its flotation "ballloon" in the rough seas and, with the parachute, sank before a nearby range ship could arrive to retrieve it from the ocean.
The final PRIME mission was flown on 19 April 1967, and simulated reentry from low Earth orbit with a 710-mile (1143-kilometre) cross-range. This time, all systems performed perfectly, and the X-23 was successfully recovered. An inspection by a USAF-Martin team reported the craft "ready to fly again," although no later missions were carried out. The third X-23 is now on display at the National Museum of the United States Air Force at Wright-Patterson Air Force Base in Ohio.