Ramjets and Scramjets

Ramjets:

Ramjets work only at supersonic speeds; a ramjet would be useless in slow speeds. Unlike turbojets, ramjets have no moving parts. The air, which rushes in, is rammed into a space so quickly, that it compresses itself. This gives the ramjets a leap in speed to about Mach 6. (The diagram below shows the way the engine works.)However, since the air in the compressor rushes so fast, the temperature reaches 6,000ºF, which makes the aircraft slow down tremendously. To prevent that, engineers redesigned the engine, so the airflow speed would be less severe, and came up with a scramjet.

Scramjets:

A scramjet is an acronym for supersonic combustion ramjet. So, to solve the problem of overheating, they engineers created a scramjet. (A picture of the engine is below.) However, that created a whole 'nother problem-making the supersonic air mix with the fuel and combust within milliseconds, but they solved it, the details classified (as usual). So now the theoretic speed could be Mach 20-25, and the top speed is yet to be calculated. We still don't know if scramjets will actually fly, or if they will crash into somebody's backyard to make another false UFO story, because we can't test them completely. Sure, we can simulate the airspeed, but we can't simulate the 4,000 kelvins that will be at Mach 10. And computers are very limited in ability.

The Hyper-X Program

The Hyper-X program is the program whose engineers designed the ramjet and the scramjet. Their goal is to produce an aircraft, not a rocket, which will go into orbit cheaper than the conventional rocket (like the X-33's goal). They will see if a scramjet can fly when an unmanned prototype will have a go at Mach 7 in spring 2000. "The fuel for Hyper-X will be hydrogen. Rockets carry their own oxygen for combustion; an air-breathing scramjet engine burns oxygen scooped from the atmosphere. Scramjets therefore get their oxygen in the same manner as normal jet engines do. Because of this, air-breathing hypersonic vehicles should carry more cargo/payload than equivalent rocket-powered systems, due simply to having more weight and payload space available because of not having to carry its oxidizer on-board."