The word 'hypersonic' refers to speeds faster than Mach 5, which is five times the speed of sound. Since the 1970s, the term has generally been assumed to refer to speeds of Mach 5 and above. Hypersonic vehicles, that is, those vehicles with speeds faster than Mach 5, produce extreme heat in flight. The parts of the vehicle that first contact the air cause air friction due to the speed. This friction can cause extreme heating temperatures on the surface of the vehicle and can reach 1,0000C. These temperatures cannot be sustained by most materials. The temperatures at higher speeds can be more extreme. For example, at Mach 8 temperatures can reach up to 30000C in the engine chamber. Extreme heating was the cause of the Space Shuttle Columbia accident during re-entry in 2003. To solve such problems, researchers are testing new materials to withstand the extreme heat experienced by hypersonic vehicles.