Patent Publication Number: US-7210282-B1

Title: Case burning rocket

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
   This application is a Continuation-In-Part application which claims benefit of U.S. patent application Ser. No. 10/037,365 filed Jan. 4, 2002, now U.S. Pat. No. 6,782,693, entitled “Case Burning Rocket” which is hereby incorporated by reference, and benefit of co-pending, divisional U.S. patent application Ser. No. 10/910,400 to filed Aug. 3, 2004 entitled “Method of Making a Threaded Rod for a Case Burning Rocket” which is also hereby incorporated by reference. 

   BACKGROUND OF THE INVENTION 
   The present invention relates generally to solid rocket boosters. More particularly, this invention pertains to a case-burning solid rocket booster. 
   Core-burning solid rocket boosters are known in the art and are typically fast burning systems that produce large amounts of thrust. These systems burn solid rocket fuel from the inside of the solid rocket fuel core outward to the pressure containing case enclosing the core. This type of burn pattern is designed to minimize exposure of the case to the intense heat of combustion. 
   While this type of burn pattern produces high thrust, it also produces short burn times and, as a result, core-burning solid rocket boosters require multiple stages to reach orbit or to propel long-range missile systems. Examples of typical multiple-stage solid rocket boosters are described in U.S. Pat. No. 5,070,691, issued to Smith et al. on Dec. 10, 1991 and entitled “Solid Propellant Canister Loaded Multiple Pulsed or Staged Rocket,” and U.S. Pat. No. 4,956,971, issued to Smith on Sep. 18, 1990 and entitled “Solid Propellant Canister Loaded Multiple Pulsed Or Staged Rocket Motor.” Multiple-stage solid rocket boosters, however, are more complex than single-stage solid rocket boosters and are undesirable in some applications for this reason. 
   Core-burning solid rocket boosters also usually include a layer of insulation on the interior of the case in order to further protect the case from the heat of combustion. In some applications, however, this layer of insulation is undesirable because it adds weight and decreases overall rocket performance. 
   What is needed, then, is a solid rocket booster system that reduces to one stage or minimizes the number of stages required to reach orbit or to propel a long-range missile system and that does not require a layer of insulation to protect the case containing the solid rocket fuel from the heat of combustion. 
   SUMMARY OF THE INVENTION 
   Accordingly, one object of the present invention is to provide a solid rocket booster that requires fewer stages to reach orbit or to propel a long-range missile system. 
   Another object of the present invention is to provide a solid rocket booster that does not require a layer of insulation to protect the case containing the solid rocket fuel. 
   These objects, and other objects that will become apparent to someone practicing the present invention, are satisfied by a case-burning solid rocket booster that includes a case containing a solid rocket fuel, a combustion chamber connected to the case for burning the case and the solid rocket fuel, a nozzle connected to the combustion chamber for expelling the burned case and fuel to generate thrust, and a drive system for pulling the combustion chamber and nozzle up the case as the case and fuel burn. In an alternative embodiment, a hybrid version of the case-burning rocket includes an oxidizer supply system for supplying varying amounts of oxidizer to the combustion chamber to vary the thrust generated by burning the case and the fuel. In either embodiment, the booster of the present invention burns the case as well as the solid rocket fuel and thereby increases the amount of thrust produced by the booster. As a result, fewer stages are required to reach orbit or to propel a long-range missile system. In addition, no layer of insulation is required to protect the case containing the solid rocket fuel for the booster of the present invention because the case is actually consumed during the combustion process thereby increasing overall rocket performance. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of one embodiment of the present invention of a case-burning rocket booster. 
       FIG. 2  is a cross-sectional view of the embodiment shown in  FIG. 1 . 
       FIG. 3  is an enlarged cross-sectional view of the combustion chamber seal assembly of the embodiment shown in  FIGS. 1 and 2 . 
       FIG. 4  is an enlarged cross-sectional view of the seal assembly of the embodiment shown in  FIGS. 1 and 2  showing fluid flow into the combustion chamber. 
       FIG. 5  is a top view of the seal used with one embodiment of the present invention. 
       FIG. 6  is an enlarged cross-sectional view of the seal shown in  FIG. 5 . 
       FIG. 7  is a cross-sectional view of one embodiment of the present invention of a hybrid case-burning rocket booster. 
       FIG. 8  is an enlarged cross-sectional view of the assembly of the embodiment shown in  FIG. 7  showing fluid and oxidizer flow into the combustion chamber. 
       FIG. 9  is a perspective view of one embodiment of the composite steel rod of the present invention. 
       FIG. 10  is a partial cross-sectional view of composite steel rod of the present invention showing a mandrel being pulled through a collapsed sleeve disposed in the rod. 
       FIG. 11  is a view of the rod shown in  FIG. 10  taken along the  11 — 11  section line. 
       FIG. 12  is a view of the rod shown in  FIG. 11  taken along the  12 — 12  section line. 
       FIG. 13  is an enlarged drawing of one embodiment of the drive system of the present invention. 
       FIG. 14  is a view of the drive system shown in  FIG. 13  taken along the C—C section line. 
       FIG. 15  is a schematic view of sealing system of the embodiment shown in  FIGS. 1 and 2 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , one embodiment of the present invention of a case-burning rocket booster  10  includes a case  12  containing a solid rocket fuel  14  (see  FIGS. 3 and 4 ), a combustion chamber  16  connected to the case  12  for burning the case  12  and the fuel  14 , a nozzle  18  connected to the combustion chamber  16  for expelling the burned case and fuel to generate thrust, and a drive system  20  connected to the combustion chamber  16  for pulling the combustion chamber  16  and nozzle  18  up the case  12  as the case  12  and the fuel  14  burn. 
   The case  12  is made out of a structural but combustible material and is burned in the combustion chamber  16  along with the solid rocket fuel  14 . As the case burns, the overall thrust provided by the booster  10  increases because of the additional mass flow through the nozzle  18 . In one embodiment, the case is made out of a graphite epoxy composite and includes a combustion enhanced epoxy resin. This type of structural material is best suited for large-scale rocket motors because of its high strength to weight ratio, its smooth outer surface and its ease of fabrication. In other embodiments, however, the case can be made out of other combustible materials. In this embodiment, the case  12  includes a layer of oxidizer rich fuel next to the case wall (not shown) to enhance the burning of the case  12  in the combustion chamber  16 . 
   One advantage provided by the case-burning rocket booster  10  of the present invention is the fact that the case  12  is burned and then expelled through the nozzle  18  to produce a net gain in thrust. Another advantage is the fact that the booster  10  of the present invention does not require a layer of insulation inside the case  12  to protect the case from exposure to the heat of combustion. 
   The case  12  is designed to be combustible at a temperature generated in the combustion chamber, which is approximately 6,000 degrees Fahrenheit. In most applications, this temperature will provide sufficient heat to assure combustion of a graphite epoxy composite case. In applications where this temperature is insufficient to assure combustion, another material must be added to the composite case  12  to assure combustion of the case  12 . Finally, if necessary, combustible metallic powder, such as aluminum or magnesium powder, may be added to the epoxy resin, or combustible metallic threads, such as aluminum or magnesium threads, may be added to the graphite weave to enhance the combustion rate of the case  12 . 
   The case  12  is also designed to withstand the pressures generated by a conventional combustion chamber. While combustion pressures can vary depending on the application and the rocket size, most larger rocket boosters will have chamber pressures of approximately 500 pounds per square inch. Accordingly, in this embodiment, the case  12  has a case wall thickness of approximately 1.5 inches. In other applications, where the combustion chamber pressures are greater, the case  12  may require a wall thickness greater than 1.5 inches. 
   Referring to  FIGS. 13 and 14 , the drive system  20  includes a series of metal threaded rods  22  and a motor or engine  75 , which is enclosed in a base  26 . The motor or engine  75  is connected to the threaded rods  22  and is operable to turn the threaded rods  22  as the case  12  and fuel  14  are burned in the combustion chamber  16 , thereby pulling the combustion chamber  16  and nozzle  18  up the case  12 . In the embodiment shown in  FIGS. 13 and 14 , the turbine engine  75  burns tanked liquid fuel and oxidizer  77 , which is supplied to the engine  75  through an inlet  79 , located in the base  26 . Engine exhaust is directed away from the system  20  through an exhaust port  80 . The amount of fuel  77  supplied to the engine  75  is determined by the required speed for the threaded rods  22 . The required speed of the threaded rods is, in turn, determined by the rate at which the case  12  and fuel  14  burn. The case and fuel burn rate is determined by either a direct feed back system (not shown), such as thermal couples (not shown), that measures the rate of solid fuel and case combustion or a pre-programmed drive rate that matches the predicted burn rates of the solid fuel  14  and case  12 . 
   The turbine engine  75  drives a high reduction gear train  78  in a self-contained housing. The gear train  78  includes an output shaft  70  and an output gear  71  that is supported by a bearing  74 . The output gear  71  meshes with the main rod drive gears  72  located on each of the threaded rods  22 . The drive gears  72  are held in place by nuts  73  attached to the threaded rod  22  and supported by a thrust bearing  76 . In this embodiment, a ring gear  81  mechanically equalizes the position of all the gears  72  in the drive system  20 . 
   In an alternative embodiment, the metal threaded rods  22  are replaced with a composite/steel threaded tension rod  21  (See  FIG. 9 ). The rod  21  is fabricated by pulling epoxy resin saturated graphite yarn  61  wrapped around a metal collapsed sleeve  63  through a hardened steel outer tube  62 . A mandrel  64  is then pulled through the collapsed sleeve  63  using a pull rod or cable  67 , thereby expanding the sleeve  63  and compressing the mix of graphite yarn  61  and epoxy resin  65  against the outer tube  62 . As a result, excess epoxy resin  65  and air bubbles  66  are forced out of the tube  62 . This method of fabrication provides the same compression effect as an auto-clave. A conventional auto-clave, however, can only be used to provide external pressure. The graphite/epoxy mix, the expansion sleeve, and the outer threaded shell are bonded together as the resin cures to form a lightweight completed assembly 
   The combustion chamber  16  is cylindrical in shape and includes a series of flanges  28  having threaded openings  29  so that the combustion chamber  16  is pulled up the case  12  toward the base  26  when the motor or engine rotates the threaded rods  22 . In one embodiment, the combustion chamber  16  also includes a layer of insulation  23  (see  FIG. 3 ) for protecting the interior of cavity  24  of combustion chamber  16  from the heat of combustion. In an alternative embodiment, the threaded rods  22  are designed to be broken apart using explosive cutting charges (not shown) as the rods  22  pass through the threaded openings  29 , thereby reducing the weight of the booster  10  and preventing portions of the threaded rods  22  from extending into the rocket exhaust as the fuel  14  burns. In another alternative embodiment, the drive system  20  includes cables and spools instead of threaded rods to move the combustion chamber  16  and nozzle  18  up the case  12 . 
   Referring to  FIGS. 2 and 3 , the combustion chamber  16  is sealed to the case  12  using a unique sealing systems  29  (see  FIG. 15 ), which prevents high temperature gasses from escaping from the combustion chamber  16 . The system  29  includes a pair of seals,  30  and  32 , with fluid trapped between the two seals in a fluid compartment  48 , to prevent combustion leaks. In one embodiment, seal  30  includes two heat-resistant metal rings,  34  and  36 , and seal  32  includes an elastomer ring  38  to prevent fluid from passing by seal  38  and a backing ring  40  (see  FIGS. 4–6 ). The rings,  34  and  36 , include a series of notches  35 , which allow some fluid to flow past the rings. When in use, the rings,  34  and  36 , are oriented so that the notches  35  of each ring are misaligned. As a result, while the rings,  34  and  36 , prevent a substantial portion of any fluid from passing the rings, some fluid can pass through the notches  35  of one ring and then through the notches  35  of the other ring into the combustion chamber  16 . 
   Referring to  FIG. 15 , the sealing system  29  also includes a fluid supply system  43  that includes a fluid container  44 , a fluid channel  46 , and a pump  45 , and a fluid pressure control system  47 , which includes a pressure control valve  49 , a pressure modulator  51 , and a pressure transducer  53  to measure combustion chamber pressure. 
   To prevent super hot rocket gasses from blowing past the seals, fluid  42  is pumped, using the pump  45 , from the fluid container  44  ( FIG. 2 ) into the combustion chamber  16  through the fluid channel  46  and into fluid compartment  48  located between seal  30  and seal  32 . The pressure of the fluid  42  between the seals (hereinafter referred to as the “seal pressure”) is maintained above the pressure in the combustion chamber  16  using the fluid pressure control system  47 . 
   At rocket booster start up, the pump  45  pressurizes the fluid compartment  48  to a seal pressure that is a preset differential pressure above the anticipated start up combustion chamber pressure. In one embodiment, a start up algorithm contained in the pressure modulator  51  selects a preset differential pressure of approximately 50 pounds per square inch (PSI) and maintains seal pressure approximately 50 PSI above the anticipated start up combustion chamber pressure. As soon as the seal pressure reaches the preset differential pressure above the combustion chamber pressure, the pressure modulator  51  provides a data signal to a rocket control circuitry (not shown) to ignite the rocket fuel  14 . Once the fuel  14  is ignited, the pressure transducer  53  provides a combustion chamber pressure data signal to the fluid pressure control system  51 . Based on the combustion chamber pressure data signal, the pressure modulators  51  directs the pressure control valve  49  to incidentally open or close in order to maintain seal pressure between 20 to 70 PSI above the combustion chamber  16  pressure through out the rocket burn cycle. The pressure modulator  51  contains an algorithm that assures that sufficient fluid  42  flows through the fluid compartment  48  to prevent over heating of the seals  19 ,  20 ,  38  and  40 . The pressure control valve  49  provides fluid pressure data back to the pressure modulator  51  during all operations. 
   As a result of the pressure differential between the seal pressure and the combustion chamber pressure, some fluid  42  leaks past seal  30  and is burned in the combustion chamber  16 . This leakage prevents overheating of the fluid  42  between the seals,  30  and  32 . Furthermore, as the leakage fluid vaporizes in the combustion chamber  16 , it absorbs heat and prevents the seal  30  and case  12  from being exposed to excessive heat in the low temperature volume area  15  (see  FIG. 15 ) in the combustion chamber. The combustion chamber insulation liner  23  is profiled in a manner that causes this low temperature volume area to be created. In one alternative embodiment, the fluid  42  is flammable to facilitate case combustion and provides initial burning and heating of the case  12 . 
   Referring to  FIGS. 7 and 8 , one embodiment of the present invention of a hybrid case-burning rocket booster  50  is shown. The hybrid booster  50  is identical to the booster  10  discussed above with the exception of an oxidizer supply system  52 . In addition, in some alternative embodiments, the drive system  20  and the combustion chamber  16  can be reduced in size. This hybrid concept provides the ability to throttle the rocket during ascent as well as provides a way to terminate combustion, and restart combustion if necessary. More specifically, the hybrid booster  50  includes the case  12 , combustion chamber  16 , nozzle  18 , and drive system  20  of the booster  10  described in detail above. The oxidizer supply system  52  includes a liquid oxidizer tank  54  and an oxidizer channel  56  for supplying liquid oxidizer  58  to the combustion chamber  16 , which increases the amount of thrust generated by the booster  50  when compared to the thrust generated by burning only the case  12  and fuel  14 . In addition, the oxidizer supply system  52  also includes a throttle assembly (not shown) for controlling the amount of liquid oxidizer  58  supplied to the combustion chamber  16  and thereby controlling the amount of thrust generated by the booster  50 . Using the oxidizer supply system  52 , the hybrid booster  50  can be throttled in a manner that is similar to a liquid rocket without the need for cryogenic storage of hydrogen. 
   Thus, although there have been described particular embodiments of the present invention of a new and useful Case Burning Rocket, it is not intended that such references be construed as limitations upon the scope of this invention except as set forth in the following claims.