The X-24 was one of a group of lifting bodies flown by the NASA Flight Research Center (now Dryden Flight Research Center) in a joint program with the U.S. Air Force at Edwards Air Force Base in California from 1963 to 1975. The lifting bodies were used to demonstrate the ability of pilots to maneuver and safely land wingless vehicles designed to fly back to Earth from space and be landed like an airplane at a predetermined site.
Lifting bodies’ aerodynamic lift, essential to flight in the atmosphere, was obtained from their shape. The addition of fins and control surfaces allowed the pilots to stabilize and control the vehicles and regulate their flight paths.
The X-24 (Model SV-5P) was built by Martin Marietta and flown from Edwards AFB, California. The X-24A was the fourth lifting body design to fly; it followed the NASA M2-F1 in 1964, the Northrop HL-10 in (1966), the Northrop M2-F2 in 1968 and preceded the Northrop M2-F3 (1970).
The X-24A was a fat, short teardrop shape with vertical fins for control. It made its first, unpowered, glide flight on April 17, 1969 with Air Force Maj. Jerauld R. Gentry at the controls. Gentry also piloted its first powered flight on March 19, 1970. The craft was taken to around 45,000 feet (13.7 km) by a modified B-52 and then drop launched, then either glided down or used its rocket engine to ascend to higher altitudes before gliding down. The X-24A was flown 28 times at speeds up to 1,036 mph (1,667 km/h) and altitudes up to 71,400 feet (21.8 km).
After learning about a remark by Chuck Yeager that he would like to have some jet-powered lifting bodies for training purposes, Martin designed and built two examples of the SV-5J on their own initiative, powered by a single Pratt & Whitney J60-PW-1 jet engine of 1360 kgf, in place of the X-24A's Reaction Motors XLR-11-RM-13 rocket engine. Martin also manufactured a full-scale, unflyable, mock-up of the SV-5J. (There is some confusion over the number built, which may be due to the mock-up being included in the production list.)
Both flyable examples built were never flown due to Martin being unable to convince Milt Thompson to fly the SV-5J, even after offering a $20,000 bonus. After the original X-24A was converted to X-24B, one of the SV-5Js was converted to represent the X-24A, for display at the National Museum of the United States Air Force, Wright-Patterson AFB, Ohio, beside the original X-24B. The unflyable mock-up ended up in Hollywood and was used in several movies as a space-ship prop.