News Release

NASA Marshall Space Flight Center

Air-Breathing Technology

In conventional rocket engines, a liquid oxidizer (some form of oxygen) and a fuel are combined and burned to create a high-pressure, high-velocity stream of hot gases. These gases flow through a nozzle that accelerates them farther (8045 kilometers per hour [5,000 mph] is typical exit velocity), and then they leave the engine. This provides the thrust for the spacecraft.

Air-breathing rockets still use an oxidizer, but the source is oxygen from the atmosphere, rather than stored liquid oxygen onboard the craft. Intake vents allow the rocket to "breathe in" oxygen as the vehicle flies; this oxygen is combined with the rocket fuel, and combustion takes place. Current jet turbine engines use a similar process, but turbines have a compressor that generates pressure and can produce power even when stationary. Air-breathing rockets use rockets to provide the initial push to increase the speed of the vehicle until enough air is captured to provide adequate thrust for the vehicle. At that point, the rockets are turned off and the propulsion system uses the air to support the combustion process.

Why change the way a rocket is powered? If you don't have to carry the oxidizer on the rocket, you can reduce the weight by up to 50 percent. Lighter vehicles are both cheaper to operate and easier to launch. NASA's goal is to reduce the cost of space flights by a factor of 100, and this is a way to help achieve that goal.

It's a little more complicated than that, of course. Air-breathing rockets are more technically called combined cycle rocket engines because they employ both conventional rockets and air-breathing technology. The initial push comes from a rocket; then ramjets start the air-breathing process (visualize ramming the air through the vents into the combustor), and when the speed gets up to Mach 6, the scramjet takes over (scram jets use supersonic combustion; ram jets use subsonic combustion). Once the speed reaches Mach 15, the scramjets are turned off, the rockets go back on, and the vehicle goes into orbit.

Conventional rockets launch vertically- straight up- to exit the atmosphere as quickly as possible. Air-breathing rockets, because they need oxygen from the atmosphere, stay in the atmosphere as long as they can to inhale as much oxygen as possible. Rather than launching vertically, air-breathers can be launched either vertically or horizontally. They fly much like an airplane, cruising at high altitudes, taking in oxygen until the proper speed is reached for orbit.

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I read over the artical this sounds a lot like a type of ramjet to me. You know that there are such things as duel cycle ramjet/rocket hybreds. I found out about these years ago while trying to track down some information on the Aroura Project, but that's for another thread. Let's look into this a little deeper, it may not be as new as it sounds.

Tim

Wouldn't you need something to compress the air the higher altitude you go. I thought the higher you go the thinner thus less oxygen you have resulting in less fuel for the plane to burn. The greater the capacity the oxygen you can burn the bigger the explosion thus the faster you will go.

Originally posted by nepok
Wouldn't you need something to compress the air the higher altitude you go. I thought the higher you go the thinner thus less oxygen you have resulting in less fuel for the plane to burn. The greater the capacity the oxygen you can burn the bigger the explosion thus the faster you will go.

Well, if this engine work on the ramjet principle then it would use it's speed to achieve the compression. Ram jets use the principle of "shockwave compresion". Shockwave compression works by disrupting the airflow, setting up shockwaves. These shockwave slow the air down and compress it at the same time. this compression increases the amount of oxygen in a given volume of air. This principle was used in the Blackbird spyplane, that's why a blackbird has inlet spikes.

Tim

I read over the artical this sounds a lot like a type of ramjet to me.

yeah thats what it looks like