GB2222635A - A propulsion system for an aerospace vehicle - Google Patents

Abstract

An oblique shock wave detonation ram jet engine has a slideable shock wave diffuser 18 to maintain and control the position of the shock wave within the ram jet engine duct 12 at airspeeds substantially in the range Mach 5 to Mach 16. The ram jet is retractable into the wing structure of the vehicle during re-entry into the atmosphere after space flight. The thrust of the ram jet engine is augmented by one or more rocket motors 16 located in an expansion surface in an exhaust portion of the engine which, when fired during the range of airspeeds mentioned above, increases the primary fluid throughput of the engine by entrainment. Two types of rocket motor may be so mounted, a liquid hydrazine burning type and a liquid hydrogen and oxygen burning type which may provide a main propulsion function in the airspeed range 0 to Mach 5 and Mach 5 to Orbital Velocity respectively. <IMAGE>

Description

PROPULSION UNITS FQR AERD5PACE VEHICLES The present invention relates to propulsion units and in particular to propulsion units for spacecraft launch vehicles capable of conventional horizontal take off and landing fran existing or extended runways at ground-based aerodrates.

There is a need for a new launch vehicle to supplement and eventually supercede the US Space Shuttle which has hitherto been the only re-useable spacecraft launch vehicle available to manufacturers and operators of satellites and other spacecraft. This need arises because of forecasts of the growth of the satellite market and the very high launch costs of the US space shuttle. Currently about 200-250 tonnes of spacecraft are put into orbit each year but by 1995 that will increase to about 500 tonnes, and to 1,000 tonnes per year by 2005. The current US Space Shuttle charges for satellite launch are $3 million per tonne for low earth orbit and $30 million per tonne for gecrstationary earth orbit.

A number of alternatives to the US Space Shuttle have been examined, including vertical take-off vehicles, air launched orbiters and various propulsion systems. The conclusion reached is that if US Space Shuttle launch costs are to be reduced to say 20% of current prices the launch vehicle must be totally recoverable, i.e., none of it should be thrown away into the sea, and that quick turn-around between launches is essential.

Quick turn-around may be most directly achieved by horizontal take-off and landing vehicles, avoiding the special installations necessary for vertical take-off operation of a rocket vehicle.

The major design feature, which will make a horizontal take-off and landing vehicle possible, is an air-breathing propulsion system capable of pooering the vehicle from take-off to altitudes in excess of 100,000 feet and to speeds in excess of Mach 16 combined with a conventional rocket propulsion system to take the vehicle into space at orbital speeds up to Mach 25.

Rockets are notoriously inefficient at low forward speeds and are hence unsuitable as a propulsion unit covering the complete flight envelope of the horizontal take-off and landing vehicle. By combining an air-breathing propulsion system and a rocket in one system, hereinafter referred to as an Orbital Air-Breathing Transport System (ORBS), that system might only use about 15% of its fuel reach the first 5% of its orbital energy compared with a rocket only system which would use about 50% of its fuel to get to reach energy level.

This is because OATS would use the unlimited free supplies of at spheric air in the lower levels of the atmosphere instead of using heavy on-board liquid oxygen.

one propulsion system proposal for ARTS processes the air in a novel fashion to use as the oxidant in a conventional rocket chamber to propel the vehicle from take-off to high level flight. In the upper levels of the atmosphere the system changes over to conventional liquid oxygen plus liquid hydrogen rocket propulsion. The full details of this system are not yet available.

would take-off from a conventional runway of suitable length and width, accelerate in a steady climb and turn onto track aimed at its initial orbital direction. It will go supersonic about 1d minutes after take-off at between five and six kilometers altitude and continue its climbing acceleration during the air-breathing part of the ascent up to Mach 5 at 25 kilometers. At this point, the power units will change over from air-breathing to liquid oxygen propulsion and the engine air intake will be closed down, the rocket ascent being continued at Mach 5 to minimise airframe temperatures during the ascent.As orbital energy is approached the main rocket engine will be cut off and the final orbital insertion manoeuvre will be made using the orbital manoeuvring system engines with fine thrust control.

For the de-orbital deceleration manoeuvre OWTS will be turned tail first and the orbital manoeuvre engines used to decelerate the vehicle for the initial stages of re-entry. During the early stages of re-entry attitude control will be maintained using reaction control thrusters but, as dynamic pressure builds up, the aerodynamic controls will became effective and the reaction controls may be dispensed with.

once past the maximum heating rate, as Mach number reduces, incidence will be progressively reduced and the trajectory controlled by a varying bank angle entering a hypersonic glide phase at 25 kilometers altitude aimed at the recovery point. As CAWS enters the lower levels of the atmosphere, speed will be progressively reduced to the subsonic range for the final glide recovery manoeuvre and entry into the landing pattern and landing on the conventional runway.

It has been sbown in studies undertaken in the USA (see for example, AIAA-86-1386 a paper delivered to the AIAAZASMESSAE/AS$E 22nd Joint Propulsion Conference on June 16th to the 18th 1986 by C J O'Brien and A C Kobayashi) that ceasing air-breathing at Mach 5 is inadequate and rmst be extended to much higher Mach numbers. It was proposed in the referenced paper to cambine an oblique detonation wave engine (ODE) with a dual expander rocket engine to provide a propulsion unit covering the entire flight envelope of a launch vehicle which would be known as an air augmented rocket vehicle.The dLial expander rocket engine provides both the boost phase fran vertical take-off to Mach 6 and 75,000 feet and the upper stage phase fran 144,000 feet to 230,000 feet in the speed range Mach 16-25.

Not only does the O'Brien/Robayashi proposal require a vertical launch with the special ground launch facilities that such a launch mode entails but a further disadvantage of their arrangement is that during re-entry into the Earths atmosphere ram air will pass through the CDWE's duct and cause excessive heating of the engine.

It is an object of this invention to provide an engine which is suitable for use on an tRIS vehicle which is relatively insensitive to heating effects caused by re-entry into the Earth's atmosphere. It is another object of this invention to provide a horizontal take off and landing ORlS vehicle which includes an improved dual mode engine.

According to the invention in one aspect thereof there is provided an oblique shock wave detonation ram jet engine comprising a duct portion, with an intake portion at one end and an exhaust portion at the other end, an upper wall, side walls and a lower wall, and a shock wave diffuser portion slidably mounted with respect to said upper wall.

Preferably said engine includes at least one rocket motor mounted in the exhaust portion of the duct and arranged to burn fuel with oxygen from a stored supply. Such a rocket motor, used for thrust augmentation of the ram jet, could also be used with a conventional ram jet with a fixed diffuser.

Preferably said shock wave diffuser portion comprises a retractable variable geometry shock wave diffuser portion integral with the lower wall of the duct and the engine may then include retractable fuel injection means pivotally mounted in the intake portion of the duct and hinged by one end thereto, and wherein said upper wall is provided with retraction means for retracting the said variable geometry shock wave diffuser portion and for retracting the retractable fuel injection means into a stored position in which they lie flush against the upper wall.

Advantageously there is provided an engine of any of the above types adopted so that at least a portion of the duct walls may be cooled by circulating fuel.

According to yet another aspect of this invention there is provided an oblique shock wave detonation ram jet engine of any of the above types which has aerodynamic control surfaces along at least one of its front or trailing edges.

According to the invention in a further aspect thereof there is provided an aerospace vehicle including an oblique shock wave detonation ram jet engine of any of the above types together with an air breathing engine.

According to yet another aspect of this invention there is provided an aerospace vehicle with one or more of the types of engine described above and wherein at least the upper walls thereof form an integral part of a wing or wings of said vehicle.

According to yet another aspect of this invention there is provided an aerospace vehicle with retractable propulsion engines and means to retract said engines into the structure of the vehicle for example to reduce aerodynamic drag during re-entry into the Earth's atmosphere following an orbital space flight.

According to yet another aspect of this invention a structural module, fram a plurality of which at least a part of an aerospace vehicle may be built, includes a torsion box structure at least one of the walls of which form part of an engine of one of the types described above. The e module may also include part of a wing for the aerospace vehicle, and/or it my include means for mounting an air-breathing engine, such as a gas turbine engine, in parallel with said engine of one of the types described above. The module may also include fuel and/or payload carrpartments and/or means to direct fuel over regions adjacent to said engine or engines for cooling purposes.

Embodiments of the invention will now be described by way of example only and with reference to the following drawings of which: Figure 1 is a schematic side view of an orbital air breathing transport system (aATS) vehicle; Figure 2 is a sectioned front view through an axis A-A of Figure 1; Figure 3 is a plan view of the aATS vehicle of Figure 1; Figure 4 is an enlarged detail fran Figure 3; Figure 5 is an end view in the direction of the line B on Figure 4; Figures 6 and 7 are sectioned side views through an engine, suitable for use with the vehicle shown in Figures 1 - 3 in deployed and stored configurations respectively; and, Figures 8 and 9 are sectioned side views of engines alternative to those of Figures 6 and 7.

Referring first to Figures 1 - 3 an orbital air breathing transport system aircraft 1 has retractable ram jet engines which can be stowed for re-entry into the Earths atmosphere. The e aircraft 1 has a retractable undercarriage 2, wings 3, trailing edge flaps 4, wing tip fin controllers 5 and optimally a central tail fin 6. The aircraft 1 has ccapertments 7 7 and 8 for carrying a payload and fuel respectively. The e wings and engines of the aircraft are of unitary construction and the wings are assembled fran modular wing/engine units 9. Each wing 3 comprises four such units each including an oblique shock wave engine 9 of identical configuration and each of which is separated from the other by side walls 10.Figures 6 and 7 show how each ram jet engine is integrated into a wing torsion box structure shown generally at 11.

Each engine comprises a duct 12 which has an intake 13 at one end and an exhaust 14 at the other end. The exhaust region 14 has an expansion surface 15 with a parallel set of rocket motors 16. Two types of rocket motor 16 are included in an array of motors mounted in the expansion surface 15. Both types are of similar construction but slightly modified to burn different types of fuel. One type of rocket motor is arranged to burn hydrazine and the other type is arranged to burn a mixture of liquid hydrogen and liquid oxygen. Both types of motor 16 are arranged alternately next to each other, in a linear array, spanwise across the expansion surface 15 so that whatever type of fuel is burned thrust is provided uniformly over the length of the expansion surface.In the embodiment of Figure 1 liquid hydrazine is burned in one set of motors 16 at take off and during the initial stages of flight until high enough speeds are reached for the ram jet engine to be used in an intermediate stage of propulsion. At the end of the ram jet stage of propulsion the second set of rocket motors 16 are used to burn liquid hydrogen and produce propulsion for the final orbital stage of flight. Although the two sets of rocket motors 16 are usually operated at these two different stages of flight both sets my be operated simultaneously at any time to provide a higher thrust impulse.

Figure 5 is a view fran the end of Figure 4 looking in the direction B and shows how the nozzles 13 are arranged next to each other, for clarity the nozzles which burn hydrazine are labelled as K and those which burn liquid hydrogen are labelled as L.

The duct 12 of the ram jet engine is defined between an upper surface 17, side walls 10 and a lower shock wave diffuser portion 18.

The e shock wave diffuser is slideably mounted between the side walls 10 so that it may be moved backwards and forward along an axis X-X and it is also slideably mounted between the walls 10 along an axis Y-Y. The torsion box is cambered to produce lift like an aircraft wing and is strengthened with struts 19. The e inside of each torsion box is divided into a series of canpartments each of which is accessible through inspection covers 20 in the upper surface of the torsion box.

A compartment 21 in the leading edge of the torsion box houses fuel pipes 22 and caiptment 23 houses actuators for moving shock wave diffuser portion 18. The rear catpartment 24 houses actuators 25 which are connected to an aerodynamic control flap 4 on the trailing edge of each torsion box, other carpartments are used for storing fuel. The upper wall 17 of the duct is provided with a cooling system which uses liquid fuel as a coolant. The wall 17 may either be a cavity wall or else it can be a solid wall with a matrix of pipes or ducts fixed immediately behind it inside the torsion box structure.

The cavity wall or matrix of cooling pipes is connected between the fuel tanks and rocket motors by means of fuel pipes 22 so that when fuel is pumped from the fuel tanks into the rocket motors 16 and fuel injectors 27 it circulates through the cooling system to cool the upper wall 17 of the duct. Fuel injectors 27 are mounted across the intake 13 of the duct and are hinged at one end 28. Figure 8 is an alternative embodiment of the invention which shows the same basic arrangement of ram jet engine as Figure 6 but which also incorporates turbo props 29 to supply the rocket motors 16 with fuel. This embodiment also uses hydrazine rocket motors during the initial stages of flight, ram jet propulsion during an intermediate stage, and liquid hydrogen rocket propulsion during the orbital stage of flight.

Figure 9 shows a different embodiment of the invention compared to those shown in Figures 6, 7 and 8. The e embodiment has the additional feature of a hybrid propulsion unit 30. The e propulsion unit is mounted inside the torsion box so that when in its deployed position the inlet 31 protrudes from the top of the torsion box and into the airstream immediately in front of the fuel injectors 27 and so that its exhaust protrudes from the curved expansion surface 15 in the exhaust region 14 of the main wing/engine assembly. The e fuel injectors and variable shock wave diffuser portion can be retracted into a stowed position as with the previous embodiments.

The hybrid propulsion unit is used to propel the aircraft during the intial stages of flight fran Mach 0 to Mach 6 using atmospheric oxygen fran air drawn into the intake as one fuel element. At higher speeds the ram jet engine is used. The ram jet engine is used to propel the aircraft during the intermediate stage of flight until the aircraft flies beyond the atmosphere and ram air can no longer be used. The hybrid propulsion unit is then used to combust liquid hydrogen with liquid oxygen, from on board supplies, to propel the aircraft into the orbital stage of flight. The propulsion unit 30 is a hybrid between a conventional air breathing gas turbine engine and a conventional rocket motor and is used during the take off and orbital stages of flight.

Unlike the arrangements of Figures 7 and 8 which use rocket motors to burn liquid oxygen during both the initial and orbital stages of flight, the hybrid engine performs as an air breathing engine during the initial stage of flight and as a rocket motor for the orbital stages. Because air breathing is used during the initial stages of flight the engine does not require oxygen fran an on board supply consequently less liquid oxygen has to be carried on board the aircraft with further savings in weight and launching costs.

oration of the embodiment of Figure 1 will now be described with reference to that figure. Before take off the integrated wing/engine assemblies are opened into their deployed positions shown in Figure 6 along the aircraft wings and the liquid hydrazine rocket motors in the back of each ram engine are ignited to propel the aircraft along a runway. A jet propelled trolley of the type described in our co-pending patent application my be used to assist the aircraft during take off.The e aircraft is released fran the trolley and continues an accelerating flight until it reaches speeds in the order of Mach 5. During this initial stage of propulsion the aircraft is propelled by rocket motors 16 in the rear of the engine burning a mixture of Xydrazine and liquid oxygen to provide a propulsive force on the expansion surface at the rear of the rocket motor.

the the aircraft reaches speeds in the order of Mach 6, incident ram air forms an oblique shock wave inside the duct in a region 32. Liquid hydrazine fuel is then injected into the airstream from the fuel injectors at the front of the duct. The fuel mixes with ram air and the mixture flows into the shock wave region where it is compressed and heated until it detonates. Expanding gases which result fran the detonation are exhausted fran the expansion surface at the rear of the aircraft and provide forward propulsive force on the aircraft. Throughout this stage of propulsion efflux fran the rocket motor may be used to entrain and speed up the primary exhaust stream which in turn increases the flow of air into the duct 12. This technique further augments the thrust of the ram jet.

The liquid fuel is circulated through the fuel pipes 22 and a cooling system to cool the wall surface 17 before it is burned in the rocket motors 16. The circulation of cold liquid/gas fuels through the cooled surface 17 protects the engine/wing structure fran the heat of combustion and ram air. Throughout the ram jet propulsion stage the shock wave is maintained in region 32 of the duct by moving the shock wave diffuser portion backwards and forwards along an axis X-X on the underside of the duct. This is necessary to prevent the shock wave froml oscillating inside the duct as the aircraft accelerates. If the intake and duct were of fixed geometry the position of the shock wave inside the duct would vary with different airspeed and aircraft attitude.If the shock wave were to move too far forward along the duct it could block off the flow of air through the duct and prevent costustion, causing the engine to stall. The shock wave is maintained at a constant optiltuin position inside the duct throughout a wide range of aircraft speeds, by moving the shock wave diffuser, by means of remotely controlled actuators, to different pre-determined positions inside the duct each of which is calculated to match the airspeed of the aircraft.

The aircraft continues to use ram air until it leaves the Earth's at sphere. The e second set of rocket motors 16 burning liquid hydrogen and liquid oxygen is then used to propel the aircraft until it reaches orbital velocity.

Shen the aircraft has completed its mission in orbit and shortly before it is due to re-enter the Earth's atztsphere the ram air engine is retracted into the stowed configuration of Figure 7. Remotely controlled actuators are used to move the fuel injectors 27 about their hinged end 28 until they lie flush against the cooled surface 17 of the torsion box. The variable geometry shock wave diffuser 18 is then moved by remotely controlled actuators along a Y axis until it makes flush contact with the cooled surface 17 of the torsion box.

In its stowed position the cowl portion no longer defines a duct 12 and air passes over the outside surface of the wing reducing kinetic heating of the aircraft when it re-enters the Earth's atmosphere and establishing aerodynamic lift forces. During re-entry aerodynamic control surfaces such as the flaps 4, tail fin 6 or wing tip controllers 5 are used to steer the aircraft and control its attitude as it glides, unpowered, back to Earth.

Although only one specific embodiment of the invention has been described other embodiments are possible without departing fran the scope of the invention for example the engines might be externally mounted in retractable pods on the CATS and need not necessarily be integrated into the wing design. Although the engine is described burning a fuel mixture of one type in one set of rocket motors during the initial stage of flight, and a fuel mixture of another type in another set of rocket motors during the final acceleration into space and orbit, both motors may be operated simultaneously at any time during the flight to provide a higher thrust impulse.

Claims (8)

1. An oblique shock wave detonation ram jet engine comprising a duct portion with an intake portion at one end and an exhaust portion at the other end, an upper wall, side walls and a lower wall and a shock wave diffuser portion slideably mounted with respect to said upper wall.

2. A ram jet according to Claim 1 in which at least one rocket motor is mounted in the exhaust portion of the duct and arranged to burn fuel with oxygen fran a stored supply.

3. A ram jet engine according to Claims 1 or 2 in which said shock wave diffuser portion comprises a retractable variable geometry shock wave diffuser portion integral with the lower wall of the duct.

4. A ram jet engine as claimed in Claim 3 and further including retractable fuel injection means pivotally mounted in the intake portion of the duct and hinged by one end thereto, and wherein said upper wall is provided with retracting for retracting the said variable geometry shock wave diffuser and for retracting the retractable fuel injection means into a stored position in which they lie flush against the upper wall.

5. A ram jet engine according to any of the preceding clams adapted so that at least a portion of the duct walls may be cooled by circulating fuel.

6. A ram jet engine according to any of the preceding claims and which has aeroiynamic control surfaces along at least one of its front or trailing edges.

7. A structural module, fran a plurality of which at least a part of an aerospace vehicle may be built, including a torsion box structure at least one of the walls of which form part of a ram jet engine as claimed in any preceding claim.

8. An aerospace vehicle including at least one oblique sbock wave detonation ram jet engine of a type according to any of claims 1 to 6 above.