The X-15 had a thick wedge tail for stability at hypersonic speeds.

The first stage is then jettisoned and the vehicle re-enters the atmosphere at hypersonic speed.

Even at hypersonic speeds, that would take some time.

That helps the internal parts withstand the hypersonic speeds over Mach five.

Most of the jet travels at hypersonic speed.

The vehicle is at over 200,000 feet (61 km) in altitude and hypersonic speed.

The goal is realistic mimicry of hypersonic speeds, more than five times the speed of sound.

If successful, the flight will be the first of an air-breathing, nonrocket plane at hypersonic speeds.

Therefore time in the atmosphere at hypersonic speed would be considerable, possibly 15-30 minutes.

However, at hypersonic speeds, this model becomes applicable.