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. Several stringers on the main parachute failed to cut, preventing a successful recovery. It too was lost in the Pacific.
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.