Abstract:
A multiple stage orbital delivery vehicle that uses tractor propulsion to launch the vehicle into space. Only the upper stage of the vehicle includes an engine and avionics allowing the lower stages to be only liquid propellant tanks that may be dumped when empty. The liquid propellant may be either monopropellant or bi-propellant. The upper stage may include multiple nozzles that burn the propellant. Alternatively, the upper stage may include an aerospike engine instead of nozzles. The multiple stage orbital delivery vehicle may be air launched from an airborne aircraft or may be launched from the ground.

Description:
RELATED APPLICATION 
     This application is a divisional application of U.S. patent application Ser. No. 13/562,637 filed Jul. 31, 2012, and entitled “MULTIPLE STAGE TRACTOR PROPULSION VEHICLE,” the disclosure of which is hereby incorporated by referenced in its entirety. 
    
    
     BACKGROUND 
     1. Field of the Disclosure 
     The embodiments described herein relate to a multiple stage orbital delivery vehicle that uses tractor propulsion. 
     2. Description of the Related Art 
     Multiple stage rockets have been used to launch orbiting devices, such as satellites, in the past. These have included both ground and air launched systems. However, the multiple stage rockets are complex, requiring both engines and control actuation systems to steer each stage. These control systems typically utilize actuators in both the pitch and yaw control planes to point the engine nozzle in a method referred to as thrust vector control, and require either electrical or hydraulic power sources which are added cost and complexity. Each stage has to be ignited as the lower stage is dropped from the vehicle. If a stage fails to ignite, the vehicle may not be successful in delivering the satellite into orbit. Further, conventional small multiple stage rockets often use solid propellant stages, which are heavier, less efficient, and more expensive than liquid propellant. Once solid propellant has been ignited it is difficult to stop the combustion until the entire propellant has been consumed unless higher complexity pintle techniques are used. Varying thrust or throttling the thrust level is also a challenge for solid propellant rocket motors. 
     Further, launch vehicle overall reliability is a function of part count, and increasing the launch vehicle reliability needs to be addressed by either increasing the reliability of individual components with an associated expense, or else reducing the number of components. 
     SUMMARY 
     The present disclosure is directed to a multiple stage orbital delivery vehicle that uses tractor propulsion and overcomes some of the problems and disadvantages discussed above. The present disclosure is directed to the simplicity of a multi-stage launch vehicle employing only a single set of engines resulting in a lower overall part count, higher reliability, and lower cost compared to multiple stages each having separate engines and steering actuation systems. These advantages are magnified for smaller payload and air launched systems since the cost of engines, steering actuation, and support subsystems for each stage can dominate the total costs for smaller launch systems. The reliability of a simpler, lower part count implementation, particularly one employing monopropellant, is lower cost than multiple stages each with their own propulsion designed for the same level of reliability. 
     One embodiment of a multiple stage orbital delivery vehicle comprises a first stage releasably connected to the orbital delivery vehicle. The first stage includes a first fuel tank and first fuel system. The first fuel system may include a first fuel line. The orbital delivery vehicle includes a second stage including a second fuel tank and a second fuel system. The second fuel system may include second fuel line in releasable fluid communication with the first fuel line of the first fuel system. The second stage comprises one or more engines in fluid communication with the first and second fuel systems. The one or more engines use fuel from the first fuel tank or the second fuel tank. In an embodiment, only a single stage of the orbital delivery vehicle includes an engine. 
     The multiple stage orbital delivery vehicle may further comprise a payload bay that may be selectively opened. The multiple stage orbital delivery vehicle may further comprise a spacecraft positioned in the payload bay. The first fuel tank and the second fuel tank may be adapted to contain a liquid propellant, which may be a monopropellant or a bi-propellant. The second fuel line may include a valve to prevent leakage of fuel from the second fuel tank upon the disconnection of the first stage from the orbital delivery vehicle. The orbital delivery vehicle may include multiple engines each having a nozzle spaced around the exterior of the second stage. The orbital delivery vehicle may include a single engine having multiple nozzles spaced around the exterior of the second stage. The orbital delivery vehicle may include a guidance, navigation, and control system configured to control the operation of the engine(s). 
     The engine of the orbital delivery vehicle may be an altitude compensating nozzle engine, suitable engines may include a linear, curvilinear, annular, or toroidal aerospike engine. The engine of the orbital delivery vehicle may comprise an aerospike engine including an annular combustion chamber, throat, and nozzle. The nozzle of the aerospike engine being located around the exterior of the second stage. The nozzle of the aerospike engine may include multiple septums dividing the nozzle into multiple sections. 
     The multiple stage orbital delivery vehicle may further comprise a third stage releasably connected to the orbital delivery vehicle below the first stage. The third stage may comprise a third fuel tank and a third fuel system. The engine(s) of the orbital delivery vehicle may use fuel from the third fuel tank when the third stage is connected to the orbital delivery vehicle, may use fuel from the first fuel tank when the third stage has been disconnected from the orbital delivery vehicle while the first stage is connected to the orbital delivery vehicle, and may use fuel from the second fuel tank when the first stage has been disconnected from the orbital delivery vehicle. The engine(s) of the orbital delivery vehicle may be adapted to use fuel from any fuel tank that is connected to the orbital delivery vehicle. The engine may be adapted to use fuel from fuel tanks in a specific order or may be adapted to use fuel simultaneously from any fuel tank connected to the orbital delivery vehicle. The guidance, navigation, and control system may control the use of fuel by the engine(s) from the fuel tanks connected to the multiple stage orbital delivery vehicle. 
     The multiple stage orbital delivery vehicle may further comprise a first oxidizer tank and first oxidizer system in the first stage and a second oxidizer tank and a second oxidizer system in the second stage. The first oxidizer system may comprise a first oxidizer line and the second oxidizer system may comprise a second oxidizer line. The second oxidizer line may be in releasable fluid communication with the first oxidizer line. The engine(s) of the multiple stage orbital delivery vehicle may use a combination of fuel and oxidizer from the first fuel tank and the first oxidizer tank or from the second fuel tank and the second oxidizer tank. In an embodiment, the engine(s) of the multiple stage orbital delivery vehicle may use a combination of fuel and oxidizer from the first fuel tank and the first oxidizer tank when the first stage is connected to the orbital delivery vehicle and use a combination of fuel and oxidizer from the second fuel tank and the second oxidizer tank when the first stage has been disconnected from the orbital delivery vehicle. 
     One embodiment is a method of launching a multiple stage orbital delivery vehicle. The method comprises using fuel from a first fuel tank of a lower stage of the orbital delivery vehicle in an engine connected to an upper stage of the orbital delivery vehicle. The lower stage is releasably connected to the orbital delivery vehicle. The method comprises disconnecting the lower stage from the orbital delivery vehicle and using fuel in the engine from a second fuel tank located in the upper stage of the orbital delivery vehicle. The lower stage may be disconnected from the multiple stage orbital delivery vehicle when the first fuel tank becomes empty of fuel. The lower stage may be disconnected from the multiple stage orbital delivery vehicle before it becomes empty of fuel. For example, the lower stage may be disconnected upon the vehicle reaching a predetermined altitude or after a predetermined amount of time has elapsed. 
     The method may further comprise dropping the orbital delivery vehicle from an airborne aircraft. The method may further comprise using fuel from a third fuel tank in the engine after disconnecting the lower stage with the third fuel tank being located in a middle stage between the lower stage and the upper stage of the orbital delivery vehicle. The engine may be adapted to use fuel from the third fuel tank prior to disconnecting the lower stage from the orbital delivery vehicle. The engine may be adapted to use fuel from any fuel tank that is connected to the orbital delivery vehicle. The method may include disconnecting the middle stage from the orbital delivery vehicle prior to using fuel from the second fuel tank in the upper stage of the orbital delivery vehicle. The middle stage may be disconnected from the multiple stage orbital delivery vehicle when the third fuel tank becomes empty of fuel. The middle stage may be disconnected from the multiple stage orbital delivery vehicle before it becomes empty of fuel. For example, the middle stage may be disconnected upon the vehicle reaching a predetermined altitude or after a predetermined amount of time has elapsed. 
     The method may include opening a payload bay of the upper stage and launching a spacecraft from the payload bay. The method may include flowing fuel through a first fuel line in the lower stage and through a second fuel line in the upper stage to the engine(s). The method may include flowing fuel through a first fuel line in the lower stage and through a second fuel line in the upper stage to the engine(s) and flowing an oxidizer through a first oxidizer line in the lower stage and a second oxidizer line in the upper stage to the engine(s). 
     One embodiment of a multiple stage orbital delivery vehicle comprises a first stage comprising a first fuel tank and a first fuel system and a second stage comprising a second fuel tank and a second fuel system. The multiple stage orbital delivery vehicle comprises one or more engines in fluid communication with the first fuel tank and the second fuel tank. The one or more engines are adapted to be shared by the first stage and the second stage. The multiple stage orbital delivery vehicle may further comprise a third stage comprising a third fuel tank and a third fuel system. The third stage may be adapted to share one or more engines with the first stage or the second stage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an embodiment of a launch system for a two-stage orbital delivery vehicle. 
         FIG. 2  shows an embodiment of a two stage orbital delivery vehicle with the lower stage connected to the upper stage. 
         FIG. 3  shows an embodiment of a two stage orbital delivery vehicle with the lower stage disconnected from the upper stage. 
         FIG. 4  shows an embodiment of an upper stage of a two stage orbital delivery vehicle with the fairings being jettisons away to reveal the payload. 
         FIG. 5  shows an embodiment of an upper stage of a two stage orbital delivery vehicle with the payload being launched from the upper stage. 
         FIG. 6  shows a partial cross-section view of an embodiment of a two stage orbital delivery vehicle. 
         FIG. 7  shows a partial cross-section view of an embodiment of a multi-stage orbital delivery vehicle. 
         FIG. 8  shows a partial cross-section view of an embodiment of a multi-stage orbital delivery vehicle that includes an aerospike engine. 
         FIG. 9  shows a partial cross-section view of an embodiment of a two stage orbital delivery vehicle adapted to use a bi-propellant. 
     
    
    
     While the disclosure is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, it should be understood that the disclosure is not intended to be limited to the particular forms disclosed. Rather, the intention is to cover all modifications, equivalents and alternatives falling within the scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION 
       FIG. 1  shows one embodiment of a launch system  500  comprising an optional launch assist aircraft  510  carrying a multiple stage orbital delivery vehicle  100 . In the illustrated embodiment, the optional launch assist aircraft  510  comprises a Boeing F-15 Eagle fighter aircraft, although those of ordinary skill in the art will appreciate that the optional launch assist aircraft  510  may comprise a wide variety of other suitable aerial vehicles. In some embodiments, the multiple stage orbital delivery vehicle  100  is launched from the optional launch assist aircraft  510  after obtaining a predetermined altitude to assist in the launch of the multiple stage orbital delivery  100  into orbit. In other embodiments, the multiple stage orbital delivery vehicle  100  is adapted to launch off the ground and obtain orbit without the assistance of the optional launch assist aircraft  510 . 
       FIG. 2  shows an embodiment of a multiple stage orbital delivery vehicle  100  that includes a first or lower stage  10  connected to a second or upper stage  20 . The depiction of two stages is for illustrative purposes only, as the multiple stage orbital delivery vehicle  100  may include various number of stages necessary for the vehicle  100  to obtain orbit. The upper stage  20  includes one or more engines  25  that burn fuel to provide thrust in launching the multiple stage orbital delivery vehicle  100  into orbit. The multiple stage orbital delivery vehicle  100  may include a single engine having multiple nozzles around the perimeter of the vehicle. The engine(s)  25  may be located around the perimeter of the vehicle  100 . The number of engines  25  and the spacing around the perimeter of the vehicle  100  may be varied as would be appreciated by one or ordinary skill in the art having the benefit of this disclosure. 
     In one embodiment only a single stage of the multiple stage orbital vehicle  100  includes an engine  25  (or a plurality of engines  25 ). The single stage that includes an engine  25  is the upper stage  20 . In some embodiments (not shown), the upper stage  20  includes a single engine  25  with a plurality of nozzles connected to the single engine  25 . In some embodiments, two stages may share an engine or engines located on the upper stage. With only the upper stage  20  including an engine  25 , the design of the multiple stage orbital delivery vehicle  100  can advantageously be simplified. One or more lower stages  10  can simply comprise fuel tanks that are selectively connected to the upper stage  20  to provide fuel to the engine(s)  25  in the upper stage  20 . Once a lower stage  10  is empty of fuel, the lower stage  10  may be dropped from the multiple stage orbital delivery vehicle  100 . This configuration also permits the vehicle  100  to include only one vehicle attitude control system that is located in the upper stage  10  to control the operation of the engine(s)  25 . The vehicle axial and attitude control system controls a valve(s) in the engine(s)  25  to control the thrust from each individual engine. In operation, the guidance, navigation, and control system  130  (shown in  FIG. 6 ) controls the combustion of fuel in each engine  25  to adjust the thrust provided by each individual engine  25 , thereby controlling the flight of the multiple stage orbital delivery vehicle  100 . 
       FIGS. 3-5  show the multiple stage orbital delivery vehicle  100  dropping the lower stage  10  and launching a payload  40 . The lower stage  10  is typically dropped after the tank in the lower stage  10  has become empty, as shown in  FIG. 3 . Although only one lower stage  10  is shown in the illustrated embodiment, the multiple stage orbital delivery vehicle  100  could include multiple lower stages  10  that could also be dropped during the flight of the vehicle  100 . To launch the payload  40 , which may be an orbiting device such as a satellite, from the upper stage  20 , the upper stage  20  may include fairings  30  that are jettisoned away from the upper stage  20  to reveal the payload, as shown in  FIG. 4 . The payload  40  may then be deployed from the upper stage  20 , as shown in  FIG. 5 . 
       FIG. 6  shows a cross-section of an embodiment of a multiple stage orbital delivery vehicle  100  that uses a liquid monopropellant fuel. The lower stage  10  comprises a fuel tank  11  and a fuel line  15  that connects to a fuel line  21  in the upper stage  20  to provide fuel to the engine(s)  25  via lines  22 . Once the fuel tank  11  in the lower stage  10  is dropped from the multiple stage orbital delivery vehicle  100 , the engine(s)  25  will begin to burn fuel from the fuel tank  24  in the upper stage  20  delivered via fuel lines  21  and  22 . The lower stage  10  may be dropped when the fuel tank  11  has become substantially empty. However, the lower stage  10  may be selectively dropped from the multiple stage orbital delivery vehicle  100  prior to the fuel tank  11  becoming substantially empty. The lower end of the fuel line  21  of the upper stage  20  may include a valve  23 , such as a check valve, that prevents downward flow of fuel out of line  21  after the lower stage  10  has been dropped from the multiple stage orbital delivery vehicle  100 . 
     The upper stage  20  includes one or more engines  25  that burn fuel from the fuel tanks  11 ,  24  in each stage to produce the thrust to launch the multiple stage orbital delivery vehicle  100  into orbit. As discussed above, a guidance, navigation, and control system  130  may be used to control the thrust provided by each individual engine  25  to control the vehicle  100  during flight. The engine(s)  25  may be moved to change the thrust vector. The movement of the each individual engine  25  may also be controlled by the guidance, navigation, and control system  130 . 
     The upper stage  20  includes a payload  40 , which may comprise an orbital device such as a satellite, located in a cavity in the upper stage  20 . The upper stage  20  could include a nose cap that is jettisoned away with the fairings  30  to expose the payload  40 . In one embodiment, the guidance, navigation, and control system  130  may be integral with the payload  40  and used to control both the payload  40  after deployment from the upper stage  20 , as well as the operation of the engine(s)  25  during the launch of the vehicle  100 . 
       FIG. 7  shows an embodiment of a multiple stage orbital delivery vehicle  200  that includes a first or lower stage  210 , a second or middle stage  270 , and a third or upper stage  220 . The multiple stage orbital delivery vehicle  200  comprises one or more engines  225  located in the upper stage  220  only. The lower stage  210  and middle stage  270  do not include any engines. In the embodiment illustrated in  FIG. 7 , the lower stage  210  includes a fuel tank  211  and a fuel line  215  that is connected to a fuel line  275  in the middle stage  270 , which is in turn connected to a fuel line  221  in the upper stage  220 . Fuel lines  222  connect fuel line  221  with the engines  225  of the upper stage  220 . 
     In operation, fuel can be delivered from the fuel tank  211  in the lower stage  210  to the engine(s)  225  located on the upper stage  220  via fuel lines  211 ,  275 ,  221 , and  222 . Once the fuel tank  211  of the lower stage  210  is empty, the lower stage  210  will be dropped from the multiple stage orbital delivery vehicle  200 . The engine(s)  225  of the vehicle  200  will then begin to burn fuel from the fuel tank  271  of the middle stage  270 . Fuel from the fuel tank  271  in the middle stage  270  will be delivered to the engine(s)  225  via fuel lines  275 ,  221 , and  222 . Fuel line  275  may include a valve  276 , such as a check valve, at the lower end that prevents the downward flow of fuel out of the end of fuel line  275  after the lower stage  210  has been disconnected from the multiple stage orbital delivery vehicle  200 . Once the fuel tank  271  of the middle stage  270  is empty, the middle stage  270  may be dropped from the vehicle  200 . The engine(s)  225  will then burn fuel from the fuel tank  224  in the upper stage  220 , with the fuel being delivered to the engine(s)  225  via fuel lines  222  and  223 . Fuel line  222  may include a valve  226  that prevents the downward flow of fuel out of the end of fuel line  222 . The upper stage  220  may then launch a payload device in the same manner as discussed above. The multiple stage orbital delivery vehicle  200  may include more stages than three stages as depicted, as would be recognized by one of ordinary skill in the art having the benefit of this disclosure. 
       FIG. 8  shows an embodiment of a multiple stage orbital delivery vehicle  300  that includes a lower stage  310  having a fuel tank  311  and fuel line  315  that is connected to a fuel line  321  of the upper stage  320 . In the embodiment shown in  FIG. 8 , the upper stage  320  includes an aerospike engine  325  comprising a combustion chamber  323 , throat  324 , and nozzle  326 . Fuel line  321  may be connected directly to the combustion chamber  323 . Alternatively, an additional fuel line may connect fuel line  321  to the combustion chamber  323 . The throat  324  connects the nozzle  326  to the combustion chamber  323 . The nozzle  326  encircles the entire perimeter of the upper stage  320 . The aerospike engine  325  may include a plurality of septums  327  that divide the nozzle  326  into a plurality of sections. The plurality of sections can be controlled by a navigation and guidance system to adjust the thrust of each section controlling the flight of the multiple stage orbital delivery vehicle  300 . As described above, the lower stage  310  of the multiple stage orbital delivery vehicle  300  may be dropped after the fuel tank  311  becomes empty. The fuel line  321  may include a valve  328  to prevent leakage of fuel after the lower stage  310  has been disconnected. 
       FIG. 9  shows an embodiment of a multiple stage orbital delivery vehicle  400  that uses a bi-propellant fuel. The multiple stage orbital delivery vehicle  400  includes a lower stage  410  connected to an upper stage  420 . Additional stages could be connected to the multiple stage orbital delivery vehicle  400 , as would be appreciated by one of ordinary skill in the art. The multiple stage orbital delivery vehicle  400  comprises one or more engines  425  located in the upper stage  420  only. The lower stage  410  does not include any engines. 
     The lower stage  410  includes an oxidizer tank  411  with an oxidizer line  413  connected to a manifold  431  in the upper stage  420 . The lower stage  410  also includes a fuel tank  412  with a fuel line  414  connected to a the manifold  431  in the upper stage  420 . A bulkhead or wall  415  divides the lower stage into an oxidizer tank  411  and a fuel tank  412 . In operation, the oxidizer in the oxidizer tank  411  is delivered to the engine(s)  425  on the upper stage  420  via oxidizer line  413 , manifold  431 , and lines  432  and the fuel in the fuel tank  412  is delivered to the engine(s)  425  on the upper stage  420  via fuel line  414 , manifold  431 , and lines  432 . 
     Thrust is provided by the combination of the oxidizer and the fuel at the engine(s)  425  of the upper stage  420 . The thrust of each engine  425  may be controlled by the guidance, navigation, and control system  430 , which may comprise a conventional navigation and guidance system that may be incorporated into a payload device in the upper stage  420 . Once the oxidizer tank  411  and fuel tank  412  are empty, the lower stage  410  will be dropped from the upper stage  420 . Oxidizer line  413  and fuel line  414  are adapted to break apart when the lower stage  410  is dropped from the upper stage  410  with a portion of the lines remaining in the upper stage  410 . The upper portion of lines  413  and  414  may include valves  426  and  427  that prevent the downward flow of oxidizer and fuel out of tanks  421  and  422  upon the separation of the lower stage  410  from the upper stage  420 . After the lower stage  410  is disconnected from the upper stage  420 , oxidizer will be delivered to the engine(s)  425  from oxidizer tank  421  via oxidizer line  423 , manifold  433 , and lines  434 . Likewise, fuel will be delivered to the engine(s)  425  from fuel tank  422  via fuel line  424 , manifold  433 , and lines  434 . A bulk head or wall  428  divides the upper stage into an oxidizer tank  421  and a fuel tank  422 . The configuration of the oxidizer and fuel tanks is for illustrative purposes and may be varied. 
     Although this invention has been described in terms of certain preferred embodiments, other embodiments that are apparent to those of ordinary skill in the art, including embodiments that do not provide all of the features and advantages set forth herein, are also within the scope of this invention. Accordingly, the scope of the present invention is defined only by reference to the appended claims and equivalents thereof.