The engine of the second X-15 rocket plane ignites moments after launch from its NB-52A mothership on a research flight in the early 1960s. Many research results from the X-15 program at NASA's Flight Research Center contributed directly to the success of the Apollo lunar landing missions. (NASA photo) The North American Aviation X-15 rocket planes – designed to explore the problems of atmospheric and space flight at supersonic and hypersonic speeds – served as flying laboratories, carrying scientific experiments above the reaches of the atmosphere. Many research results from the X-15 program at NASA's (Dryden) Flight Research Center contributed directly to the success of the Apollo lunar missions, now being celebrated on the 40th anniversary of the first moon landing on July 20, 1969. North American – later North American Rockwell, then Rockwell International – served as prime contractor for both the X-15 and Apollo Command/Service Module spacecraft.
Designers of the Apollo CSM drew upon experience from the X-15 program, and even used the X-15 as a test bed for new materials. Advanced titanium and nickel-steel alloys developed for the X-15 were found to be applicable to Apollo and later spacecraft designs. The discovery of localized hot spots on the X-15, for example, led to development of a bi-metallic "floating retainer" concept to dissipate stresses in the X-15's windshield. This technology was subsequently applied to the Apollo and space shuttle orbiter windshields.
The X-15's performance allowed researchers to accurately simulate the aerodynamic heating conditions that the Apollo Saturn rocket would face, and allowed full recovery of test equipment, calibration of results, and repeated testing where necessary. In 1967, technicians applied samples of cryogenic insulation – designed for use on the Apollo Saturn V second stage – to the X-15's speed brakes to test the material's adhesive characteristics and response to high temperatures.
X-15 re-entry experience and heat-transfer data were also valuable, and led to design of a computerized mathematical model for aerodynamic heating that was used in the initial Apollo design study. Lessons learned from X-15 turbulent heat-transfer studies contributed to the design of the Apollo CSM because designers found that they could build lighter-weight vehicles using less thermal protection than was previously thought possible.