highest speed rocket
A scramjet (supersonic-combustion ramjet) is a ramjet engine in which the airflow through the whole engine remains supersonic. The highest speed attained by a rocket-powered airplane, NASA's X-15 aircraft, was Mach 6.7. The fastest air-breathing, manned vehicle, the SR-71, achieved slightly more than Mach 3. The X-43A more than doubled the top speed of the jet-powered SR-71.