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entire airframe needs to be built around the intake design. Another problem is that the air thins out as the rocket climbs. Hence, the amount of additional thrust is limited by how fast the rocket climbs. Finally, the air ducting adds quite a bit of weight which slows the vehicle considerably towards the end of the burn.
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Another idea is to collect the working mass. With an air-augmented rocket, an otherwise conventional rocket engine is mounted in the center of a long tube, open at the front. As the rocket moves through the atmosphere the air enters the front of the tube, where it is compressed via the ram effect. As
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One potential method of increasing the overall performance of the system is to collect either the fuel or the oxidizer during flight. Fuel is hard to come by in the atmosphere, but oxidizer in the form of gaseous oxygen makes up to 20% of the air. There are a number of designs that take advantage of
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and energy source that accelerates it. It is easy to demonstrate that the best performance is had if the working mass has the lowest molecular weight possible. Hydrogen, by itself, is the theoretical best rocket fuel. Mixing this with oxygen in order to burn it lowers the overall performance of the
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in its fuselage. The chemical reaction between the fuel and the oxidizer produces reactant products which are nominally gasses at the pressures and temperatures in the rocket's combustion chamber. The reaction is also highly energetic (exothermic) releasing tremendous energy in the form of heat;
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The ejector ramjet is a more complex system with potentially higher performance. Like the shrouded and ducted rocket, the system begins with a rocket engine(s) in an air intake. It differs in that the mixed exhaust enters a diffuser, slowing the speed of the airflow to subsonic speeds. Additional
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It might be envisaged that such an increase in performance would be widely deployed, but various issues frequently preclude this. The intakes of high-speed engines are difficult to design, and require careful positioning on the airframe in order to achieve reasonable performance – in general, the
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The simplest version of an air-augmentation system is found in the shrouded rocket. This consists largely of a rocket motor or motors positioned in a duct. The rocket exhaust entrains the air, pulling it through the duct, while also mixing with it and heating it, causing the pressure to increase
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There are a wide variety of variations on the basic concept, and a wide variety of resulting names. Those that burn additional fuel downstream of the rocket are generally known as ramrockets, rocket-ejector, integral rocket/ramjets or ejector ramjets, whilst those that do not include additional
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of about 260 seconds (2.5 kN·s/kg), but using the same fuel in an air-augmented design can improve this to over 500 seconds (4.9 kN·s/kg), a figure unmatched even by high specific impulse hydrolox engines. This design can even be slightly more efficient than a
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as a longer, more efficient nozzle can be employed. Another advantage is that the rocket works even at zero forward speed, whereas a ramjet requires forward motion to feed air into the engine.
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fuel is then injected, burning in this expanded section. The exhaust of that combustion then enters a convergent-divergent nozzle as in a conventional ramjet, or the ducted rocket case.
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it travels down the tube it is further compressed and mixed with the fuel-rich exhaust from the rocket engine, which heats the air much as a combustor would in a
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system by raising the mass of the exhaust, as well as greatly increasing the mass that has to be carried aloft – oxygen is much heavier than hydrogen.
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is capable of producing very high exhaust velocities. The exhaust is directed rearward through the nozzle, thereby producing a thrust forward.
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that is imparted to the reactant products in the combustion chamber giving this mass enormous internal energy which, when expanded through a
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use the supersonic exhaust of some kind of rocket engine to further compress air collected by ram effect during flight to use as additional
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Brevig, Ola (April 1968). "A Simplified, Preliminary
Comparison between the Ejector Ramjet and the Shrouded Rocket".
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downstream of the rocket. The resulting hot gas is then further expanded through an expanding nozzle.
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burning are known as ducted rockets or shrouded rockets depending on the details of the expander.
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rocket design, implemented by Decree 708-336 of the Soviet
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The effectiveness of this simple method can be dramatic. Typical solid rockets have a
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In a conventional chemical rocket engine, the rocket carries both its fuel and
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The first serious attempt to make a production air-augmented rocket was the
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A slight variation on the shrouded rocket, the ducted rocket adds only a
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Air-augmented rockets finally entered mass production in 2016 when the
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Rockets that use supersonic exhaust to create additional acceleration
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It represents a hybrid class of rocket/ramjet engines, similar to a
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In this conventional design, the fuel/oxidizer mixture is both the
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not worse than both a comparable ramjet or rocket at every point.
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this fact. These sorts of systems have been explored in the
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Air-Breathing Launch
Vehicle Technology Being Developed
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73:Learn how and when to remove this message
345:"General Features of Rocket Propellants"
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271:Index of aviation articles
228:NASA GTX reference vehicle
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259:Meteor Air to Air Missile
276:Liquid air cycle engine
141:liquid air cycle engine
405:Spacecraft and Rockets
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211:Ejector ramjet (et al)
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170:combustion efficiency
89:Air-augmented rockets
417:1968JSpRo...5..444B
367:www.astronautix.com
351:. NASA. p. 42.
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283:References
185:Variations
155:Advantages
63:April 2009
47:improve it
288:Citations
114:Operation
51:verifying
437:NASA GTX
265:See also
143:(LACE).
120:oxidizer
413:Bibcode
220:History
45:Please
363:"Gnom"
234:Soviet
166:ramjet
149:ramjet
125:nozzle
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252:SSTO
244:NASA
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