Analysis of information sources in references of the Wikipedia article "Lockheed Martin X-33" in English language version.
Flight tests would involve speeds of up to Mach 15 and altitudes up to approximately 75,800 meters... The test program was baselined for a combined total of 15 flights.
Flight tests would involve speeds of up to Mach 15 and altitudes up to approximately 75,800 meters... The test program was baselined for a combined total of 15 flights.