supersonic planes like the SR-71 Blackbird pictured above, which managed to fly at over three times the speed of sound, but imagine this: NASA set aside $15 million to develop a hypersonic plane that could exit our atmosphere at speeds between Mach 5 and Mach 20. The US space agency's not expecting to build it quite that cheaply, of course, and it's not holding out hope for a contractor to build the entire plane just yet -- the organization intends to fund some sixteen smaller science and engineering projects (ranging from "how to build a Mach 8+ engine" to "predicting hypersonic fluid dynamics") and letting would-be government contractors pick and choose. Know how to quantify baseline turbulent aeroheating uncertainty in a hypersonic environment? You've got until November 23rd to get your proposal in.
Update: As some have pointed out in comments, hypersonic flight isn't unprecedented -- NASA spent eighteen years developing and testing the X-15 space plane starting in 1951, which reached Mach 6.7 using a rocket engine.