Aeronautics and astronautics – Aircraft propulsion – Fluid
Reexamination Certificate
1999-05-28
2001-05-08
Barefoot, Galen L. (Department: 3644)
Aeronautics and astronautics
Aircraft propulsion
Fluid
C244S074000, C244S172200, C060S224000, C060S226200
Reexamination Certificate
active
06227486
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to engines and propulsion techniques for earth-to orbit vehicles.
BACKGROUND OF THE INVENTION
As vehicles are propelled into earth orbit, their propulsion systems require engines which are driven with self contained oxidizers, i. e. rocket engines. Rocket engines are required for a number of reasons.
First of all, a vehicle entering earth orbit must be accelerated even after the vehicle leaves the atmosphere of the earth. Thus an engine driving such a vehicle must have a self-contained source of oxygen to facilitate combustion of its fuel.
Secondly, there is a need to provide a very high thrust to weight ratio for the vehicle in order to facilitate vertical liftoff and rapid acceleration. Rocket engines are well suited to this task.
However, a rocket propelled vehicle must have a large portion of its initial or take-off mass dedicated to fuel and on-board oxidizer. In other words, rocket engines have very low specific impulse, i.e., a low ratio of thrust to mass of on board oxidizer and fuel. A consequence of this inherently low specific impulse is that earth to orbit vehicles must be propelled into orbit using multiple stage rockets. Heretofore, there has been no practical way to propel a vehicle into earth orbit with a single stage launch vehicle. This need to use multiple stage rockets has, of course, precluded development of a reusable launch vehicle for earth orbit devices.
Development efforts have been directed to achieving a practical reusable launch vehicle for earth orbit devices. A number of prior art proposals have been made to utilize an air breathing engine to produce some of the needed thrust for an earth to orbit vehicle while the vehicle is still in the earth's atmosphere.
These prior art efforts have encountered one common difficulty. Turbojet engines are inherently heavy when compared to rocket engines. In other words, turbojet engines have a much lower thrust to weight ratio than rocket engines. As a result of this inherent feature of conventional turbojet engines, it is difficult to enhance payload performance of a launch vehicle by adding a turbojet engine to the vehicle. In many cases, the added weight of the turbojet engine exceeds any payload advantage which would result from reduction of weight derived from reducing on-board oxidizer.
There have been some prior art efforts directed to increasing the thrust to weight ratio of turbojet engines. Engines which operate with cryogenic fuels such as liquid hydrogen have been developed. These cryogenic engines utilize incoming-air pre-cooling as a mechanism to avoid overheating of engine components. If engine components can be operated at reduced temperature, they can be fabricated from relatively light alloys. Thus, a turbojet engine with effective pre-cooling can become an engine with an improved thrust to weight ratio.
In prior art turbojet engines, this pre-cooling is produced by a heat exchanger which employs the cooling effect of liquid hydrogen fuel as it passes from its on-board storage to a combustion chamber on the vehicle. While this system is somewhat effective in improving thrust-to-weight ratio, it does not improve this ratio sufficiently to add significantly to the payload performance of a launch vehicle. Some examples of these proposals are found in U.S. Pat. No. 5,101,622 (Bond) and an article entitled “Air Precooling for Aerospace Engine: Soviet Style”, A. Rudakov and V. Balepin, Aerospace Engineering, Aug. 1991, pp.29-30, (Ref. 2).
Other efforts have been made in the prior art to improve the thrust to weight ratio. Additional cooling is provided by overfueling the engine. The pre-cooled turbojet engine is driven with more hydrogen than is needed for stoichiometric operation. This passes more hydrogen through the pre-cooling system which produces greater cooling. This provides for somewhat higher thrust capability with light weight alloy engine components. But, this technique is subject to the rule of diminishing returns. Increased thrust is derived from use of excessive hydrogen. Excessive hydrogen use has its payload costs. More hydrogen must be put on board the vehicle and its storage tanks must be larger. Consequently, there is very little net improvement in thrust to weight ratio when the excess hydrogen cooling technique is employed.
Most of the prior art development efforts aimed at achieving a practical re-usable earth to orbit launch vehicle have focused on the use of air-breathing engines to augment rocket engines. These developments efforts have heretofore been frustrated because of the difficulties presented by the inherently low thrust to weight ratios of turbojet engines.
It is a goal of the present invention therefore to provide a practical propulsion system for re-usable earth to orbit vehicle which utilizes an air breathing engine combined with a rocket engine.
It is a further goal of the present invention to provide such a propulsion system by employing a unique set of operating techniques for combined turbojet and rocket engines.
SUMMARY OF THE INVENTION
The present invention is directed to a method of propelling a vehicle into earth orbit. The method comprises the steps of initiating acceleration of the vehicle with thrust provided from a combination of an air breathing engine and a rocket engine. Incoming air of the air breathing engine is cooled with fuel flow to both the air breathing engine and the rocket engine. The rocket engine is throttled when the vehicle reaches a first velocity. The vehicle is then accelerated to a second velocity using the turbojet engine as the principal source of thrust. The rocket engine is then returned to full operation to accelerate the vehicle to a third velocity sufficient to propel the vehicle into earth orbit.
Viewed from another aspect, the present invention is directed to an apparatus for conveying an optimum payload into earth orbit. The apparatus comprises a vehicle equipped with at least one turbojet engine and at least one rocket engine. Each of the engines is adapted to operate through oxidation of the same type of combustible fuel. The turbojet has an incoming-air cooling means which utilizes fuel flowing to both engines for cooling. The turbojet and rocket engines are adapted to operate simultaneously to produce take-off of the vehicle and to accelerate the vehicle to a first velocity. The turbojet is adapted to provide the principal source of thrust to accelerate the vehicle from the first velocity to a second velocity. The rocket engine is adapted to operate independently to accelerate the vehicle from the second velocity to a third velocity which is sufficient to place the vehicle into earth orbit.
Viewed for still another point of view, the present invention is directed to a low-mass apparatus for accelerating a vehicle. The apparatus comprises a rocket engine and a turbojet engine with a lightweight incoming-air cooler and lightweight engine components. The turbojet engine and the rocket engine are adapted to operate with the same type of combustible fuel. The incoming air cooler is adapted to utilize fuel flow to both of the engines whereby operating temperature of the turbojet is maintained below a critical temperature limit for the lightweight engine components.
The invention will be better understood from the following detailed description taken in consideration with the accompanying drawings and claims.
REFERENCES:
patent: 2531761 (1950-11-01), Zucrow
patent: 2679726 (1954-06-01), Moncrieff
patent: 3103102 (1963-09-01), Sargent et al.
patent: 3149461 (1964-09-01), Eichholtz
patent: 3261571 (1966-07-01), Pinnes
patent: 3285175 (1966-11-01), Keenan
patent: 3756024 (1973-09-01), Gay
patent: 5012640 (1991-05-01), Mirville
patent: 5740985 (1998-04-01), Scott et al.
Salkeld, “Mixed-Mode Propuslion for the Space Shuttle” Astronautics and Aeronautics,, pp 52-58, Aug. 1971.*
Scott, Space Acess launch System Based on Airbreathing Ejector Ramjet: Aviation Week and Space Tech, pp 75-77, Mar. 30, 1998.
Barefoot Galen L.
MSE Technology Applications, Inc.
Tribulski Peter
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