2. Prior Art.

It is known in the prior art that rockets can be used to launch space vehicles and to place satellites into earth orbit. One of the most commonly used form of rockets is the"liquid fueled"rocket. In jet and rocket propelled engines, a fuel mixes with an oxidizer and burns to generate hot gases which exits the engine via a nozzle to provide thrust. All fuel must combine with an oxidizer in order to burn. At sea level, a separate oxidizer is not needed, as ambient air can serve as the oxidizer. At high altitudes (and in space), however, the air thins and there is no readily available oxidizer which allows the fuel to burn. It is therefore necessary for a spacecraft to carry its own oxidizer.

A common form of fuel is liquid hydrogen (referred to as LH2), and a common oxidizer is liquid oxygen (LOX). Both LH2 and LOX must be cooled to very low temperatures in order to maintain their liquid state. LOX is typically generated by first compressing air and then cooling it to a very low temperature, typically-300 degrees Fahrenheit. This supercold gas is then permitted to condense into a liquid. Because air is not pure oxygen, and includes other elements, the LOX is separated out of the liquid air using one of several known methods.

One of the drawbacks of the liquid fueled rocket is that a large mass

rocket, the ratio of oxidizer to fuel is typically 6 to 1. Thus, a typical rocket carries 35 pounds of oxidizer for every pound of payload. The extra weight of the LOX provides the largest penalty at lift-off, when the overall weight of the vehicle is the greatest The additional LOX also dictates the size of most of the structure and propulsion systems. If the weight of the oxidizer could be reduced before the spacecraft were to take off, it would greatly reduce the size of the system and increase the overall efficiency of the spacecraft operation.

In the prior art, it has been proposed that spacecraft might be able to generate LOX from ambient air while a the vehicle is flying. This type of system would be very advantageous because it would permit a spacecraft to take off without an initial supply of oxidizer. Such systems have not proved viable because they were too heavy, and too inefficient The major limitation with the prior art systems has been that the weight of the machinery to compress and cool the ambient air was too great to permit the spacecraft to get to orbit. Other prior art systems proposed a vehicle flying a supersonic speeds in order to compress air entering an inlet.

However, supersonic flight has many disadvantages and drawbacks. Among these are the fact that supersonic flight generates shock waves which disrupt the properties of the incoming ambient air. This make is much more difficult to cool the air and generate LOX.

The present invention overcomes the limitations of the prior art by providing a method and apparatus which permits a space vehicle to take off without an initial load of oxidizer. After take-off, the spacecraft cruises at a predetermined altitude at subsonic speed. The spacecraft carries an on-board liquid oxygen generator. The liquid hydrogen fuel for the rocket engine is stored in an internal tank. The LOX generator uses the liquid hydrogen fuel to cool incoming air, and liquefy the gaseous oxygen. Liquid hydrogen has an enormous heat capacity to cool the incoming air. The liquid

oxygen is then stored in a tank until it is needed to serve as an oxidizer in the rocket engine.

SUMMARY OF THE PRESENT INVENTION The present invention includes a method for placing satellites in low earth orbit. The method of the present invention is contemplated to be used on a spacecraft which includes turbofan engines and a rocket engine. The spacecraft carries a payload which is to be placed in orbit. In the method of the present invention the following steps are used. The spacecraft takes off from a runway like a traditional aircraft. At take-off, the spacecraft uses the turbofan engines for power. The spacecraft may then fly to a predetermined location at a predetermined time. The spacecraft then flies at a predetermined height at a subsonic speed. Compressed air from the turbofan engine is then used to generate liquid oxygen from the ambient air.

The liquid oxygen is stored in an oxidizer tank. When a sufficient amount of liquid oxygen has been generated, the liquid oxygen is used as an oxidizer to burn a fuel for the rocket engine. The rocket engine providing thrust to place the payload into earth orbit.

The present invention also includes a structure for generating liquid oxygen within an aircraft. The aircraft is powered by a turbofan engine and includes a storage tank containing liquefied hydrogen gas (LHz). The device for generating the liquid oxygen includes an extraction valve located downstream of a compressor stage of the turbofan engine. The extraction valve provides a stream of compressed air. This compressed air is fed into a heat exchanger and cooled. In the present invention, the heat exchanger consists of ducts which pass the compressed air near the skin of the aircraft. The temperature of the air at the aircraft surface is very cold, and acts as an extremely efficient cooling mechanism. The cooled air is then fed into a condenser. The generator condenses and liquefies the cooled air. A separator is then used to separate the liquid oxygen from the

constituent parts of the liquefied air. A storage tank in the aircraft is then used to store the liquid oxygen.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view showing a typical reusable space craft which employs the present invention.

Figure 2 is a diagram of a typical mission scenario of a spacecraft employing the method of the present invention.

Figure 3 is a schematic diagram of the liquid oxygen generating apparatus of the present invention.

Figure 4 is a more detailed schematic diagram of the liquid oxygen generating apparatus of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An novel method and apparatus of using air liquefaction to provide oxidizer for use in placing satellites in low-earth orbit will be described.

In the following description, for the purposes of explanation, specific method steps, component arrangements and constructions and other details are set forth in order to provide a more thorough understanding of the present invention. It will be apparent to those skilled in the art, however, that the present invention may be practiced without these specific details. In other instances, well known manufacturing methods and structures have not been described in detail so as not to obscure the present invention unnecessarily.

The present invention allows a reusable space vehicle to attain low- earth orbit in a manner which requires the use of a minimum amount of fuel for a given amount of payload. Referring first to Figure 1, a general view of a typical reusable spacecraft 10 employing the present invention is shown. With the present invention, the spacecraft will take-off and land like a conventional airplane. The spacecraft therefore includes wings 12

and horizontal stabilizers 13 and a vertical stabilizer 14. The spacecraft will also include at least one turbofan engine 20. The turbofan engine is used to provide power to the spacecraft at take-off. The turbofan engine will be modified as described below in connection with Figure 3.

Referring again to Figure 1, the spacecraft of the preferred embodiment of the present invention is a two-stage craft. The second stage of the spacecraft includes at least one rocket engine 16. The second stage also includes the satellite or other payload which is to be placed in earth orbit. The rocket engine is used after take-off to provide power to insert the payload in orbit. The rocket engines are of the liquid fuel type which use liquid oxygen (LOX) as an oxidizer. The spacecraft will also include other elements which are not illustrated in Figure 1. Among such elements are fuel tank 18 which holds the fuel for the rocket engine 16. At the time of lift-off the fuel tank is substantially filled. The spacecraft also includes a oxidizer tank 19, which is substantially empty at the time that the spacecraft takes off. The fuel tank 18 and the oxidizer tank are connected by suitable pumps (not illustrated) to the rocket engines 16.

Referring again to Figure 1, it is to be understood that the configuration shown for the space vehicle 10 is for illustration and reference purposes only. Figure 1 is not meant to limit the type of vehicle that can be utilized with the present invention. In particular, the present invention can be used with a variety of different wing and fuselage configurations and with different arrangements of the flight control surfaces. The only limitation is that the spacecraft must include a wing with sufficient lift to permit take-off and cruise with a full payload. The preferred embodiment of the present invention also uses turbofan engines to provide thrust during take-off and the initial stages of a mission.

Referring next to figure 2, a typical mission profile of a space vehicle using the method of the present invention is shown. The typical

mission profile can be broken down into a number of different components, or stages. The various mission stages are indicated by the numbered diamonds on Figure 2. Figure 2 illustrates the typical stages of a mission which are included in the preferred embodiment of the method of the present invention.

These stages correspond to the steps that are employed in the method of the present invention.

At mission stage 1, the spacecraft takes off from a runway like a regular airplane. Power for take-off is supplied by the turbofan engines 20. At the time that the spacecraft takes off, it is carrying its payload, as well as liquid fuel for the rocket engines. The spacecraft does not, however, carry oxidizer for the rocket engine. The oxidizer will be generated during the third stage of the mission as described below. By not including the oxidizer in the take-off weight the spacecraft is able to lift a larger payload, and to transport that larger payload to earth orbit.

Referring again to Figure 2, the second mission stage is referred to as the"cruise and loiter' ! stage. This stage provides for a great amount of flexibility in mission planning and allows the spacecraft to be flown on a variety of different types of missions. During the second stage the spacecraft can fly to a predetermined location. This permits the spacecraft to place a satellite into orbit at a point which may be distant from the original take off location. For example, the spacecraft could take off, and then travel to a distant location over an ocean before the rocket engines are ignited. This type of mission could be useful in instances when a dangerous payload is being flown. Also, the spacecraft can loiter, or wait, until a specific time before launch. This permits the timing of the final orbit to be specifically adjusted.

Additionally, it is known that different types of earth orbits are easier to obtain when the satellite is launched from different locations.

For example, an equatorial orbit is most easily accomplished when the

spacecraft is launched from near the equator. This takes advantage of the speed of the earth's rotation. A polar orbit is most easily achieved if the spacecraft is launched from a higher latitude. The cruise and loiter step of the present invention therefore permits different types of orbits and missions to be achieved. This feature of the present invention is not available in the prior art, which uses rockets which launch from a fixed location.

Referring again to Figure 2, in the third stage of the mission, the spacecraft generates the oxidizer using an on-board LOX generator. The specific construction and operation of the LOX generator are described below with reference to Figure 3. In the preferred embodiment of the present invention, the spacecraft is flown at a subsonic speed. Compressed air is drawn from the turbofan engine. This air is then cooled using LH2 stored in the rocket fuel tank to create LOX. The generated LOX is stored in an oxidizer tank on the spacecraft.

During the third mission stage, the spacecraft travels at a subsonic speed. Subsonic flight is used in the preferred embodiment of the present invention, because it the most efficient. If an airplane flies at a supersonic speed, it generates shock waves. These shock waves are undesirable because they disrupt the flow of ambient air, and change its properties. With subsonic flight, the air is not disturbed by shockwaves.

Although the preferred embodiment of the present invention utilizes subsonic flight, it will be appreciated by those skilled in the art that the device of the present invention could be modified to be used at supersonic speeds.

After a sufficient amount of LOX has been generated, the rocket engines are ignited at mission stage 4. This places the spacecraft on a trajectory up and out of the atmosphere, and at mission stage 5, then the second stage of the spacecraft separates and continues on to orbit in mission stage 6a. The first stage re-enters the atmosphere at stage 6b, the

turbofan engines are re-started, and the spacecraft lands normally like a traditional airplane in mission stage 7.

Referring next to Figure 3, a schematic diagram showing the system which generates the oxidizer in the present invention is shown. The turbofan engine is referred to generally by reference numeral 20. The turbofan includes, in part, an inlet duct 22, a high bypass fan 24, a compressor stage 26, a burner stage 28, and a turbine and nozzle stage 29.

Ambient air enters through the inlet duct 22 and the fan 24, and is then split into two parts. The majority of the airflow goes into the bypass duct 27. The remainder of the air passes through the compressor stage 26.

In most modern jet engines, the bypass ration is 6 to 1. That is, six parts of air travel through the bypass duct 27 for each part of air that enters the compressor stage 26.

The purpose of the compressor 26 is to compress the incoming air for burning in the burner. Thus, the air downstream of the compressor 26 is of high pressure. Of the air leaving the compressor, normally twenty percent is injected directly into the fuel burner 28, and eighty percent bypasses the burner to be mixed downstream prior to the turbine stage 29. In the present invention, the high pressure air which bypasses the burner is extracted from the core of the turbofan through an extraction valve 32, and passed through tubing 33 to a heat exchanger 36. Figure 3 illustrates the heat exchanger in a schematic format.

The preferred embodiment of the present invention uses a heat exchanger with two stages. In the first stage, the compressed air from the extraction valve 32 is passed through ducts (not illustrated in Figure 3) next to the skin of the airplane. When the spacecraft is flying at altitude, the airplane skin is very cold, typically at a temperature near minus 30 degrees Fahrenheit. The ducts pass near the skin of the wings as well as the fuselage of the spacecraft. In the second stage of the heat

exchanger, liquid nitrogen (LN2) and liquid hydrogen are used to further cool the incoming air. LN2 has a temperature of minus 320 degrees Fahrenheit and liquid hydrogen has a temperature of minus 320 degrees Fahrenheit The LN2 is generated as described below.

From the heat exchanger 36, the compressed air (which has now been cooled to near minus 265 degrees Fahrenheit) passes through tubing 35 to a LOX generator/separator 38. The LOX generator/separator 38, expands and liquefies the incoming air, and separates it into LOX and LN2. LOX and LN2 are the primary chemical constituents of air. The newly-created LOX passes through tubing 41 to an oxidizer tank 42 where it is stored until used to ignite the rocket engines of the spacecraft.

As noted above, the LOX generator also produces LN2. The LN2 is routed back to the heat exchanger 36, and is used to pre-cool the incoming compressed air from tubing 33. After the nitrogen passes through the heat exchanger, it is in gaseous form. This gaseous nitrogen is injected under pressure back into the burner section of the engine where it is mixed with the combustion products and enters the turbine.

Referring again to Figure 3, the present invention makes use of the LH2 from the air liquefaction process to increase the operating efficiency of the turbofan engine 20. After the LH2 is used in the air heat exchanger, it has been heated, and expands into a gaseous form. This gaseous hydrogen (GH2) passes through tubing 45 and is directed back to the turbofan engine, where it is introduced into the burner stage 27 of the engine. The GH2 fuel combines with the twenty percent remaining air to burn and power the turbofan engine. In this way, the used hydrogen is not lost, and the overall operating efficiency of the turbofan engine 20, and the spacecraft overall is increased. Figure 4 illustrates a more detailed diagram of the structure of the present invention. The elements of the structure are shown in schematic format.

The description of the present invention has been made with respect to specific method steps, arrangements and constructions of a means for placing satellites in low earth orbit. It will be apparent to those skilled in the art that the foregoing description is for illustrative purposes only, and that various changes and modifications can be made to the present invention without departing from the overall spirit and scope of the present invention. The full extent of the present invention is defined and limited only by the following claims.