The quest to fly faster and higher has characterized the history of airplane development. Developed in the late 1950's, the X-15 still holds the record for top speed and highest altitude attained by an airplane. When it ended after 199 test flights, piloted by 12 different test pilots, the X-15 program had produced test data in the hypersonic flight regime that would be indispensable to the later design of the space shuttle.