Scramjet Engines

Scramjet engines are the newest form of propulsion from the jet propulsion family. They, like ramjets, use no moving parts to compress the air coming into the intake, but rather they use their speeds. They main difference between the ramjet and scramjet engine is their intake geometery, the Scramjet's intake will only compress the air at hypersonic speeds, whereas the ramjet engine will compress the air properly at supersonic speeds. You probably think the ramjet would obviously be better, except for the fact that at hypersonic speeds, it doesn't work, and the scramjet does. The scramjet will get a craft going mach 15, whereas the ramjet will get it going a maximum of mach 4.

The biggest problem (besides just designing one to work) is getting the craft going mach 5, at hypersonic speeds. There are a couple ways to do this, the easiest is also the most expensive. The easiest is using a rocket engine, but the whole point of the scramjet is to cut down on the use of rockets because normal rockets must carry an oxidizer and fuel, but scramjets must only carry fuel, so they weigh less, and cost less. The other option costs more to design and build, but in the long run the cost saved on the oxidizer overcomes this. This option uses a turbojet (with intake fans to compress the air at low speeds) which takes the craft to mach 1, then the engine turns into a ramjet (which provides more power, and reduces the need to use fuel to turn the fans, along with cutting out the risk of the fans getting destroyed at the high speeds) then the ramjet boosts the craft close enough to mach 5 for the scramjet to kick in. This idea completely erases the need for more weight and money to get the scramjet working

There is still one problem though. The scramjet will only get to mach 15, but to atain orbit mach 25 is needed. In one idea the scramjet will take the craft to the threshold of space, and then a small rocket will finish the job by speeding it to orbital velocity. This is a little more expensive than the other option, but it needs no oxidizer for 50-75% of the flight, depending on how hypersonic speeds are reached. This cuts the cost 25-35% over a completely re-usable one-stage-to-orbit vehicle like the venture star, and even more over the space shuttle, for which new fuel tanks and rocket boosters must be made each flight because it dumps them into the ocean. Anyway, the other option uses the scramjet to get as close to space as possible, then it ejects its orbital payload, and a smaller rocket than on the previous plan takes the payload alone into orbit. This is a cheaper option, but you couldn't get astronauts to the ISS this way.

In the long run though, no matter how you do it, the scramjet saves you some cost over using a normal rocket. Without oxidizer for a good part of the trip, this air breather saves weight (which means smaller engine which equals less money on its own) and also money on the oxidizer. The technology could also make a craft that flew to the threshold of space, then went from New York to Tokyo in a record amount of time just inside the atmosphere.


The ion drive
Fusion and antimatter drives
Other propulsions
Laser propelled light craft
Space Tethers
Ramjet/Scramjet engines
Other earth to orbit propulsion
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