Lockheed Martin Skunk Works and Aerojet Rocketdyne have made a breakthrough in hypersonic propulsion technology, but the Mach 6.0-capable SR-72 remains more of aspiration than a real airplane.

Lockheed Martin Skunk Works and Aerojet Rocketdyne have made a breakthrough in hypersonic propulsion technology, but the Mach 6.0-capable SR-72 remains more of aspiration than a real airplane.