Rockets, especially the faster ones, are very large and heavy due to the fuel needed to launch them. The Saturn V rocket that carried the Apollo 11 lander to the Moon was 363 feet tall and weighed 6.2 million pounds. Anything that would reduce this massive size of the equation would be a huge benefit to efficiency. This is where the X-43A comes in.
Instead of a rocket engine that uses liquid oxygen to aid fuel combustion, the X-43A’s scramjet (Supersonic Combustion Ramjet) uses air flowing through the engine at supersonic speeds to ignite the fuel. According to NASA, a scramjet-powered aircraft would not need heavy, expensive, and potentially dangerous liquid oxygen storage.
The X43-A itself is little more than a 12-foot-long aerodynamic wedge, much smaller and lighter than traditional rocket-propelled aircraft like the 50-foot-long X-15, a vehicle that itself reached speeds of Mach 6.7.
For its record flight, the X-43A was attached to a B-52B, an aircraft typically used for long-range strategic bombing, and carried aloft to its launch point. The unmanned X-43A relied on a launch vehicle – a Pegasus booster rocket – to bring it up to the supersonic speeds necessary for the scramjet to operate at full efficiency. It then flew to an altitude of 110,000 feet before safely descending 850 miles away to a designated point in the Sea Range of the Naval Air Warfare Center Weapons Division in California.