131:, at which point the liquid oxygen can be fed into the engine as usual. It will be seen that heat-exchanger limitations always cause this system to run with a hydrogen/air ratio much richer than stoichiometric with a consequent penalty in performance and thus some hydrogen is dumped overboard.
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In order to appreciably reduce the mass of the oxygen carried at launch, a LACE vehicle needs to spend more time in the lower atmosphere to collect enough oxygen to supply the engines during the remainder of the launch. This leads to greatly increased vehicle heating and drag losses, which therefore
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while the engine was running on air and the liquid oxygen was being stored. As the aircraft climbed and the atmosphere thinned, the lack of air was offset by increasing the flow of oxygen from the tanks. This makes ACES an ejector ramjet (or ramrocket) as opposed to the pure rocket LACE design.
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compared to rockets), and the performance of launch vehicles of all types is particularly affected by increases in vehicle dry mass (such as engines) that must be carried all the way to orbit, as opposed to oxidizer mass that would be burnt off over the course of the flight. Moreover, the lower
65:(LOX) needed for combustion is the majority of the weight of the spacecraft on lift-off, so if some of this can be collected from the air on the way, it might dramatically lower the take-off weight of the spacecraft.
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fuel is flowing. This rapidly cools the air, and the various constituents quickly liquefy. By careful mechanical arrangement the liquid oxygen can be removed from the other parts of the air, notably
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Conceptually, LACE works by compressing and then quickly liquefying the air. Compression is achieved through the ram-air effect in an intake similar to that found on a high-speed aircraft like
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When it was demonstrated that it was relatively easy to separate the oxygen from the other components of air, mostly nitrogen and carbon dioxide, a new concept emerged as ACES for
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has a very low density (0.0678 kg/L) and is therefore very bulky. (The extreme bulkiness of the LH2 tankage tends to increase vehicle drag by increasing the vehicle's
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thrust-to-weight ratio of an air-breathing engine as compared to a rocket significantly decreases the launch vehicle's maximum possible acceleration, and increases
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as a propellant and air-liquefaction coolant in LACE may well outweigh the benefits gained by not needing to carry as much LOx on board.
208:.) Finally, LOx tanks are relatively lightweight and fairly cheap, while the deep cryogenic nature and extreme physical properties of LH
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tanks and plumbing must be large and use heavy, expensive, exotic materials and insulation. Hence, much as the costs of using LH
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Most significantly, the LACE system is far heavier than a pure rocket engine having the same thrust (air-breathing engines of
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during the late 1950s and early 1960s, where it was seen as a "natural" fit for a winged spacecraft project known as the
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Thus, the advantages, or disadvantages, of the LACE design continue to be a matter of some debate.
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due to the need to stay much deeper within the atmosphere than a pure rocket would during the
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is nearly two orders of magnitude more expensive. LOx is dense (1.141 kg/L), whereas LH
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of a lifting, air-breathing vehicle launch trajectory as compared to a pure rocket on a
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increases fuel consumption to offset the drag losses and the additional mass of the
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since more time must be spent to accelerate to orbital velocity. Also, the higher
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Other issues are introduced by the relative material and logistical properties of
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A Comparative
Analysis of Singe-State-To-Orbit Rocket and Air-Breathing Vehicles
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On the other hand, the reduced gravity losses come at the price of much higher
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that compress the air. The LACE design then blows the compressed air over a
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of the air-breathing engine and the savings in LOx mass are largely lost.
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engine that attempts to increase its efficiency by gathering part of its
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Rockets, not air-breathing planes, will be tomorrow's spaceships
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design of the 1980s, but this did not progress beyond studies.
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For jet engines that cool but do not liquefy the air, see
555:"Liquid Air Cycle Rocket Equation, Henry Spencer Comment"
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during the late 1950s and early 1960s, and by late 1960
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Liquid Air Cycle Rocket
Equation, Henry Spencer Comment
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air-breathing vehicle, the advantages of the higher
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408:were involved in the LACES research. However, as
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139:The use of a winged launch vehicle allows using
312:{\displaystyle {\frac {1}{1+{\frac {gD}{aL}}}}}
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87:LACE was also the basis of the engines on the
147:to overcome gravity, which greatly reduces
76:had a testbed system running. However, as
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611:Rocket engines using hydrogen propellant
16:Concept of hybrid atmospheric jet engine
442:that cools but does not liquefy the air
369:LACE was studied to some extent in the
68:LACE was studied to some extent in the
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494:: CS1 maint: archived copy as title (
267:introduces an additional penalty term
386:Air Collection and Enrichment System
327:. This term implies that unless the
412:moved to ballistic capsules during
379:Liquid Air Collection Engine System
347:) are both implausibly large for a
80:moved to ballistic capsules during
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525:from the original on June 4, 2011.
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46:. A liquid air cycle engine uses
571:Liquid Air Cycle Rocket Equation
537:"LOX/LH2: Properties and Prices"
392:engine, using it as additional
50:(LH2) fuel to liquefy the air.
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261:inlet and airframe drag losses
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239:, the costs of using more LH
237:single-stage-to-orbit rocket
135:Advantages and disadvantages
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265:ballistic launch trajectory
250:types have relatively poor
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169:thermal protection system
371:United States of America
196:. LOx is quite cheap; LH
518:. AFIT/GAE/ENY/06-J13.
252:thrust-to-weight ratios
89:British Aerospace HOTOL
28:liquid air cycle engine
436:Reaction Engines SABRE
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224:may well outweigh the
95:Principle of operation
606:Single-stage-to-orbit
601:Spacecraft propulsion
402:Marquardt Corporation
325:air-breather's burden
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36:spacecraft propulsion
440:precooled jet engine
426:Air-augmented rocket
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21:Precooled jet engine
231:benefit of using LH
157:aerodynamic heating
543:on March 13, 2002.
509:Orloff, Benjamin.
329:lift-to-drag ratio
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539:. Archived from
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222:hydrocarbon fuel
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541:the original
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479:. Retrieved
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206:frontal area
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143:rather than
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105:intake ramps
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31:
27:
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161:boost phase
109:shock waves
595:Categories
481:2019-05-27
452:References
349:hypersonic
248:almost all
44:atmosphere
319:into the
74:Marquardt
42:from the
520:Archived
490:cite web
446:Scramjet
420:See also
125:nitrogen
103:, where
101:Concorde
40:oxidizer
365:History
189:versus
107:create
390:ramjet
145:thrust
61:, the
59:rocket
576:HOTOL
523:(PDF)
516:(PDF)
475:(PDF)
468:(PDF)
431:RB545
400:Both
235:in a
121:water
53:In a
496:link
438:- a
410:NASA
404:and
155:and
141:lift
127:and
78:NASA
32:LACE
187:LOx
70:USA
597::
492:}}
488:{{
355:sp
229:sp
191:LH
180:sp
175:,
163:.
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345:g
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341:a
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290:g
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281:1
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