NASA - National Aeronautics and Space Administration

The distinguished Langley aeronautical researcher John Becker, who was an early advocate of the X-15 program, identified 25 specific accomplishments of the program, including:

• First application of hypersonic theory and wind tunnel work to an actual flight vehicle.
• First use of reaction controls for attitude control in space.
• First reusable super alloy structure capable of withstanding the temperatures and thermal gradients of hypersonic reentry.
• Development of a servo-actuated-ball nose flow direction sensor for operation over an extreme range of dynamic pressure and a stagnation air temperature of 1,900° F (for accurate measurement of air speed and flow angle at supersonic and hypersonic speeds).
• Development of the first practical full pressure suit for pilot protection in space.
• Development of inertial flight data systems capable of functioning in a high dynamic pressure and space environment.
• Discovery that hypersonic boundary layer flow is turbulent and not laminar.
• Discovery that turbulent heating rates are significantly lower than had been predicted by theory.
• First direct measurement of hypersonic aircraft skin friction and discovery that skin friction is lower than had been predicted.
• Discovery of hot spots generated by surface irregularities.

(These last few discoveries including the Space Shuttle.)

• Discovery of methods to correlate base drag measurements with tunnel test results so as to correct wind tunnel data (and thereby improve design criteria for future air- and spacecraft).
• Demonstration of a pilot's ability to control a rocketboosted aerospace vehicle through atmospheric exit.
• Successful transition from aerodynamic controls to reaction controls and back again.
• First application of energy-management techniques (for the positioning of the vehicle for all future reusable launch vehicles following their reentry from space).
• Use of the three X-15 aircraft as test beds to carry a wide variety of experimental packages.

The experiments included tests of horizon definition and proposed insulation that bore fruit in the navigation equipment and thermal protection used on the Saturn launch vehicles in the Apollo program, which dispatched 12 astronauts to the moon and back. Among the 12 was Neil Armstrong, the first human to step on the moon's surface and a former X-15 pilot.

Image above: Pilot and NASA technician talk post-flight. Credit: NASA

In the area of physiology, researchers learned that the heart rates of X-15 pilots ranged from 145 to 185 beats per minute during flight. This greatly exceeded the normal 70 to 80 beats per minute experienced on test missions for other aircraft. The cause of the difference proved to be the stress X-15 pilots encountered during prelaunch in anticipation of each mission. As it turned out, the higher rates proved typical for the future physiological behavior of pilot-astronauts.

More intangibly but no less importantly, in the words of John Becker, the X-15 project led to "the acquisition of new piloted aerospace flight know how by many teams in government and industry. They had to learn to work together, face up to unprecedented problems, develop solutions, and make this first manned aerospace project work. These teams were important national assets in the ensuing space programs."

As the partial list of accomplishments suggests, the X-15 brilliantly achieved its basic purpose of supporting piloted hypersonic flight within and outside the Earth's atmosphere. In addition, it carried out the "explorations to separate the real from the imagined problems and to make known the overlooked and the unexpected problems."

More information about NASA aeronautics research programs is available at aeronautics.nasa.gov. More information about NASA Langley Research Center is available at www.nasa.gov/centers/langley/home/index.html. More information about NASA Dryden Flight Research Center is available at www.nasa.gov/dryden.

More about the X-15 program:
+ Overview
+ X-15 Test Pilots
+ X-15 Aircaft
+ X-15 Accomplishments

FS-2006-03-119-LaRC
NASA Langley Research Center