Hypersonic Flight: 3,500-7,000 MPH (Mach 5 to Mach 10)
With the advent of rocketry, the first hypersonic vehicles were developed. Although they are not airplanes, rockets travel at these speeds as they accelerate into Earth orbit. Also, re-entry capsules such as those in the Apollo program travel at these speeds as they descend from orbit.
Once again, new technologies and new vehicle shapes had to be developed for hypersonic flight. In particular, new materials had to be developed to handle the intense heating caused by atmospheric friction.
The best known examples of hypersonic flight vehicles are the rocket-powered X-15 and the space shuttle which flies through all of the speed regimes when it re-enters the Earth's atmosphere. The space shuttle is coasting from a very high speed and high altitude when it flies hypersonically. It is decelerating the entire time. There are no aircraft today that can cruise at these speeds.
Research programs are underway to develop new engines that can operate at these speeds so that we can develop aircraft to cruise in this speed regime. Two such experimental aircraft currently being tested include the X-33 and the X-34. It is a tremendous challenge to design an airplane shape and an engine that can take off subsonically, accelerate through supersonic speeds, and cruise efficiently hypersonically.
What's faster than hypersonic" Hypersonic flight occurs at very high altitudes where the air is very thin. This helps reduce the drag and the heating due to friction. This thin air and high speed is part of what makes it so difficult to design an engine for these aircraft. To fly faster than hypersonic speed requires even thinner air at higher altitude. At these speeds and altitudes a vehicle is essentially outside our atmosphere and would more correctly be called a spacecraft. The space shuttle is both a spacecraft and aircraft
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