At this speed - more than 4,300mph (6,900km/h) - it could travel from London to New York in about an hour.
WaveRider is one of several projects currently under way to create an aeroplane able to reach much higher speeds than today's jets, after Concorde was decommissioned in 2003.
During a test in June 2011, WaveRider failed to reach the target speed.
A B-52 bomber will lift the wingless unmanned jet from US Edwards Air Force Base in California to 50,000 feet (15,250m).
We covered the previous 2011 test last year.
Mach 6 is six times the speed of sound. Concorde's cruising speed was was Mach 2 - it flew from London to New York in just over three hours.
The WaveRider test flight is expected to last for about five minutes. At the end of it, the aircraft will break into pieces and fall into the Pacific.
The test is essentially a repeat of last summer's attempt, when the hypersonic aircraft reached Mach 5, but the engine failed to attain full power.
In August 2011, US military scientists attempted to get another unmanned hypersonic experimental aircraft to reach Mach 20 - 20 times the speed of sound.
However, they lost contact with the Falcon Hypersonic Test Vehicle 2 (HTV-2) after it had separated from its rocket.
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