3. X43A Scramjet Cont’d 7,500mph
Photo: nasa
The “scramjet” aspect fo the jet only works at speeds above 3,400mph which meant that engineers had to use other forms of propulsion to reach that speed before engaging the scramjet, for that they used a high-speed Pegasus Rocket. Only three examples of this vehicle were built and intended for one use only. The scramjet would only fire for 10 seconds and then the aircraft would glide for about 10 minutes before intentionally crashing into the ocean.