Abstract:
The present invention provides apparatus and methods for integrating structural members inside the body of a propulsion vehicle with tankage used to store fluid propellant and the like. Propulsion vehicles may be made lighter, more compact, cheaper, and easier to manufacture by using pressurized membranes of the tankage to accomplish other structural purposes. More specifically, tanks may be integrated with thrust structures to transfer thrust loads from the engine to the main body of the vehicle. Alternatively, the tanks may be integrated with the vehicle engine. Also, one tank may be integrated with one or more other tanks to form a single pressure vessel with multiple interior chambers. Tankage may additionally be combined with more than one of the foregoing to save additional weight and space. Methods of manufacturing a metallic integrated tank assembly include weld fabrication, machining, spinning, hydroforming, casting, forging, plating, metal deposition, or some combination thereof. Methods of manufacturing a composite integrated tank assembly include filament winding, fiber placement, hand-lay-up, or some combination. The methods listed above may be combined with other steps and tooling to create many different embodiments of the invention.

Description:
This application claims the benefit of provisional application 60/135,717 filed May 25, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. The Field of the Invention 
     The present invention relates to pressure vessels for carrying pressurized fluids. More specifically, the present invention relates to tanks designed to support an external, compressive load as well as the pressure of the fluid, for use in applications in which lightweight storage and structural members are desirable. 
     2. The Relevant Technology 
     Pressure vessels, or storage tanks, are commonly used to store fluids under pressure. Many types of propulsion vehicles require some type of fluid storage. For example, many types of launch vehicles, spacecraft, missiles, satellites, and rocket-propelled torpedoes all store a fluid propellant. Liquid fuel rocket motors typically require tanks of pressurized, combustible fluids that can be combusted and ejected from a nozzle to propel the rocket. Many forms of electric propulsion also require a pressurized fluid propellant. The term “fluid” includes both gases and liquids; many rockets store fuels in a substantially liquid form, with a component of combustible vapor. Additionally, rockets have a number of other structural features necessary for the rocket&#39;s operation. For example, rockets may have additional tanks, nozzles to direct exhaust gases, and thrust structures designed to convey force from the nozzle to the main body of the rocket. Typically, the inside of a rocket is a mass of tubes, tanks, wiring, and fixtures. 
     The cost and performance requirements that rockets typically operate under frequently dictate the use of lightweight, compact components. As a result, it is desirable to minimize mass and eliminate as much unnecessary structure as possible. Many vehicle applications are also volume sensitive and require that wasted space within the vehicle be minimized wherever possible. Tanks known in the art, however, are not well-suited to compact assembly, in part because they are often shaped with symmetrical, convex walls. Consequently, space between independent tanks and requisite inter-tank structure is typical. Furthermore, tanks known in the art create an enormous blockage through which it is difficult to route wiring, plumbing, conduits, and structural features necessary for operation of the rocket. The complexity of the rocket design is compounded because every other component of the rocket must be designed around the tank. 
     Furthermore, rockets often contain multiple tanks to hold different fluids, such as an oxidizer and a fuel. For example, oxygen may be stored in one tank, and a suitable liquid fuel in the other, so that the two may be combined to combust even in a vacuum. The use of multiple tanks adds additional complexity, volume, and weight to the rocket. A liquid-fueled rocket must typically carry two tanks, even though the fluids contained in the tanks are stored at similar pressures and will often be routed to the same location. 
     Consequently, there is a need, unfulfilled by the prior art, for part count reduction and for space and weight conserving tankage that can be effectively positioned within the body of a rocket or a similar propulsion vehicle, without hindering the placement of necessary equipment. There is a further need for space-saving configurations and structures that can be effectively used with tankage for the vehicle. The tankage and structures should be easily manufactured at low expense, and easy to assemble. Furthermore, the tankage and structures should be sturdy enough to tolerate the stresses created by high acceleration and vibration. 
     Similarly, there is a need for novel methods of manufacture, through which improved tankage and structures can be created, assembled, and installed in a propulsion vehicle. Such methods should be rapid, inexpensive, and preferably utilize available tooling with little modification. 
     The current invention discloses such an apparatus and method. 
     BRIEF SUMMARY OF THE INVENTION 
     The apparatus of the present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available tankage and propulsion vehicle structures. Thus, it is an overall objective of the present invention to provide tankage and propulsion vehicle structures that overcome the deficiencies in the prior art. 
     To achieve the foregoing objective, and in accordance with the invention as embodied and broadly described herein in the preferred embodiment, integrated tankage for propulsion vehicles and the like is provided. The integrated tankage comprises a wall, or pressurized membrane, at least a portion of which is specifically engineered to serve a function besides containment of the fluid within the tank. 
     For example, a thrust structure for a propulsion vehicle connects the engine to the main body of the rocket. When the rocket ignites, the engine pushes the rocket forward, and the thrust structure must bear the compressive stress induced by the force of the engine. The engine typically terminates, at its lower (aft) end, in an orifice, or nozzle, through which exhaust gases may pass to propel the rocket. The thrust structure connects the engine to the main body of the rocket, which is typically a cylindrical outer housing. The thrust structure is specially designed to support all engine loads while minimizing weight and bulk. 
     A tank may be properly situated and constructed to connect the nozzle with the main body of the rocket, such that a separate, thrust structure external to the tank is not necessary. The outer pressurized membrane of the tank may be configured so as to transfer the compressive force of the engine to the body, or an inner, tubular and/or conical structure within the tank may be connected to the nozzle to carry the compressive force. If a tank-internal structure penetrates the pressurized membrane of the tank, the two structures may be mechanically uncoupled, and a compliant liner or seal such as an O-ring seal or rod packing may be used at their juncture in such a way that the two structures may deform at different rates without leakage of internal fluid. 
     In the alternative, the engine itself may be integrated with the tank, such that the lower (aft) end of the tank is shaped to form a nozzle. In such a configuration, the pressure of expanding exhaust gases in the nozzle would impinge directly on the aft pressurized membrane of the tank, so that the tank supports the nozzle. A separate thrust structure may then be provided to connect the engine to the main body of the rocket, or the tank may also transmit the force of the engine directly, thus enabling integration of both the engine and the thrust structure into the tank. The nozzle may be of a conventional type, or may have an annular, “aerospike” design. A compliant liner or seal between the engine or thrust structure and outer pressurized membrane may be employed to permit varying rates of strain, as described above. 
     As a further alternative, a tank may have an internal wall adapted to form a bulkhead between nested internal chambers, thereby merging abutting pressure vessels to form a single lighter, simpler structure. Since pressures on either side of the bulkhead will be typically closer to each other than to the ambient pressure outside the tank, the bulkhead can be made thinner than the outer vessel wall. The weight associated with two abutting domes and associated inter-tank structure may be largely eliminated. A tube or other extension of one chamber may pass through a second chamber so as to allow access to both fluids from one end of the common-bulkhead tank. This tube or extension may be an integral part of the bulkhead. Again, the internal bulkhead or bulkhead extension tube and tank wall may be mechanically uncoupled at one end, and a compliant liner or sealing member may be used at their juncture, allowing the two structures to deform or translate with respect to each other without leakage of internal fluid. Furthermore, the fluid-separating bulkhead and extension tube may also be configured as tank-integral, engine thrust structure. 
     These and other objects, features, and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the manner in which the above-recited and other advantages and objects of the invention are obtained will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
     FIGS.  1 ( a ) through ( h ) are sectional views of various embodiments of a portion of a vehicle incorporating an integrated tank and thrust structure according to the invention, 
     FIGS.  2 ( a ) through ( c ) are sectional views of a tank and polar fitting with ( a ) a compliant liner, ( b ) an O-ring type seal, and ( c ) rod packing internal structural seals; 
     FIGS.  3 ( a ) through ( d ) are sectional views of a portion of a vehicle incorporating an integrated tank and thrust structure, wherein the thrust structure is an internal feature of the tank; 
     FIG. 4 is a sectional view of an aft portion of a vehicle incorporating an integrated tank and a conventional engine, according to the invention; 
     FIG. 5 is a sectional view of an aft portion of a vehicle incorporating an integrated tank and an aerospike engine, according to the invention; 
     FIGS.  6 ( a ) through ( e ) are sectional views of various embodiments of an aft portion of a vehicle or vehicle stage incorporating an integrated tank, pressurized thrust structure, and conventional engine according to the invention; 
     FIGS.  7 ( a ) through ( c ) are sectional views of various embodiments of vehicle tankage and structure incorporating an integrated tank, thrust structure, and conventional engine, wherein the thrust structure is an internal feature of the tank. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The presently preferred embodiments of the present invention will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. It will be readily understood that the components of the present invention, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the apparatus, system, and method of the present invention, as represented in FIGS. 1 through 7, is not intended to limit the scope of the invention, as claimed, but is merely representative of presently preferred embodiments of the invention. 
     The present invention includes novel configurations and methods for using pressure vessels to perform structural, load-bearing functions. More specifically, propellant tanks in rockets are integrated with interior structural features of a rocket, including but not limited to thrust structures, engines, and bulkheads. 
     Pressure vessels, or tanks, designed to hold a fluid under high pressure are subject to unique stresses. Axial and “hoop,” or circumferential, tensile stresses build in the walls, or pressurized membranes, as the fluid presses outward. Consequently, pressure vessels are already preloaded with a considerable tensile stress. Placing a compressive load on them does not increase the total stress level if the load is properly applied. Rather, external, distributed compressive loads applied to a pressure vessel tend to negate the tensile stresses caused by the pressure of fluid within the tank. 
     As a result, pressurized tanks are well suited for bearing such distributed compressive loads because the pressurized membranes need not be made any thicker or stronger to withstand the additional load. This makes them good candidates for performing additional structural functions, especially in space-limited applications such as propulsion vehicles. The following figures illustrate how pressure vessels can be integrated with internal structural features of a propulsion vehicle. 
     “Internal structural features” includes thrust structures, engines, bulkheads, and other members within the main body of the vehicle that bear an additional substantial load besides that induced by the pressure of the fluid within the tank. “Thrust structure” refers to one or more members that transmit thrust from the engine to the main body of the vehicle. “Pressurized membrane” refers to any fluid pressure-bearing portion of the wall of a pressure vessel or tank. “Dome” refers to the structure that forms either end of a tank, regardless of its shape or method of fabrication. “Integrated” components need not be integrally fabricated or unitary; they must simply abut each other in at least one surface of substantial size. “Main body” refers to a casing substantially enclosing all of the internal components of a rocket, or, in the event that the casing is unitary with propellant tanks, all parts of the casing located forward of the tanks. “Polar fitting” refers to a connection located at either a forward or an aft dome of the tank designed to convey a load to the tank or receive a load from the tank. The polar fitting may connect to an exterior feature, such as a dome, or an interior feature such as an interior passageway or support inside the tank. 
     Engine thrust structure may be incorporated into the vehicle tankage either as part of the pressurized membrane of the vessel, or extending through the fluid storage chamber. This assumes that a typical lower vessel head (dome) and polar fitting are not sufficiently strong or stiff to support the engine thrust loads on their own. 
     Inclusion of the thrust structure as part of the pressurized membrane may be accomplished by incorporating a conical, truncated cone, cylindrical, or other appropriate engineered shaped thrust structure shell into the vessel wall. The thrust structure could, in effect, replace a vessel dome, and may extend out from the tank so as to be pressurized internally, or penetrate into the tank volume so as to be loaded in external compression. 
     Referring to FIGS.  1 ( a ) through  1 ( h ), several possible embodiments of the integrated tank and thrust structure are shown, in which the engine thrust structure is part of the pressurized membrane of the vessel. The configurations shown in FIGS.  1 ( c ) through  1 ( h ) have a thrust structure that is at least partially loaded in external compression. Fibers with high compressive strength, such as boron fibers, may be used in the fabrication of externally compressed composite thrust structures. A few options for fluid access are also shown. Access may be achieved through openings in the tank dome, through the thrust structure, or through the outer tank wall. 
     In FIG.  1 ( a ), portion of a vehicle  10  includes a tank  12  with a gas inlet  14  and a fluid outlet  16 , which receive gas and expel propellant, respectively, in the case of a rocket. The lower vessel head  20 , or dome  20 , takes the form of a flared dome  20 , which is conical in shape and extends outward from the fluid outlet  16  to reach the outer wall  22  of the tank  12 . In the following descriptions, “flared” and “conical,” as used with reference to tank domes, are defined with reference to the direction of the thrust load. A dome that begins close to the central axis of the tank, and then spreads out to the outer wall  22  in a forward direction, or along the direction of the thrust load, is “flared.” Similarly, a dome that begins at the outer wall  22 , and then narrows toward the axis of the tank in a forward direction, is “tapered.” 
     The flared dome  20  and the outer wall  22  may be separate pieces assembled before installation in the vehicle  10 , or they may be integrally fabricated. The outer wall  22  is preferably unitary with the main body  24  of the vehicle  10 . An upper vessel head  26 , or rounded dome  26 , extends inward from the outer wall  22  to reach the gas inlet  14 . 
     Engine thrust, represented by arrows  30 , received from an engine located aft of the tank  12 , impinges upon a polar fitting  32  proximate the fluid outlet  16 . The compressive stress induced by the engine thrust  30  travels along a thrust load path  34  through the flared dome  20  to reach the outer wall  22  of the tank  12  and the main body  24  of the vehicle. Consequently, in this embodiment, the flared dome  20  and the outer wall  22  constitute the thrust structure  36  for the vehicle  10 . The thrust structure  36  is thus integrated with the tank. If needed, the flared dome  20  may be thickened or otherwise reinforced to bear the compressive force of the engine thrust  30  along the thrust load path  34 . Generally, the thrust structure includes any structures within the thrust load path  34  between the engine and the main body of the vehicle. Since the tank  12  is generally radially symmetrical about the axis of the vehicle  10 , the thrust load path extends not along a single linear pathway, but around the full circumference of the tank  12 . 
     In FIG.  1 ( b ), the rounded dome  26  of FIG.  1 ( a ) has been replaced by a tapered dome  42 , which is also conical in shape. This embodiment is different in operation from that disclosed previously because the thrust load path  46 , in this case, extends through the tapered dome  42  to reach a polar fitting  44  proximate the gas inlet  14 . The polar fitting  44  will then transfer the thrust to the main body (not shown) of the vehicle  40 . The outer wall  22  may be decoupled from the main body of the vehicle  40 , so as not to bear any of the engine thrust  30 . 
     In FIG.  1 ( c ), the flared dome  20  of FIG.  1 ( a ) has been replaced with a tapered dome  52 , which carries the thrust load path  54  of the vehicle  50 . Since the tapered dome  52  extends into the tank  56 , it bears a tensile load from the engine thrust  30 , which adds to the tensile load caused by the pressure of fluid in the tank  56 . Consequently, the tapered dome  52  may need to be made thicker to bear the externally compressive stresses due to fluid pressure. However, such a configuration may be advantageous in that there is open space for components aft of the tapered dome  52 . 
     In FIG.  1 ( d ), a tapered dome  42  is combined with a tapered dome  62  having a closed polar fitting  64 , which receives engine thrust  30  apart from the fluid outlet  16 , which may be located elsewhere on the tapered dome  62 . The thrust load path  66  then travels through the tapered dome  62 , the outer wall  22 , and the tapered dome  42  to reach a polar fitting  44  similar to that described in connection with FIG.  1 ( b ). 
     In FIG.  1 ( e ), a rounded dome  72  is provided, with an opening through which an interior passageway  74  extends to exit through a flared dome  76 . The interior passageway  74  may convey fluids, control lines, or other equipment to and from the engine (not shown). Furthermore, as embodied in FIG.  1 ( e ), the interior passageway  74  carries the thrust load path  78  to the flared dome  76 , which then conveys the thrust load to the main body  79 . The gas inlet  14  and the fluid outlet  16  are offset to accommodate the interior passageway  74 . 
     In FIG.  1 ( f ), the interior passageway  74  is also included, but the flared dome  76  has been replaced by a tapered dome  82 . The gas inlet has been positioned near the polar fitting  32  on the rounded dome  72 . The thrust load path  84  thus extends through the interior passageway  74  and the tapered dome  82  to reach the main body  86 . 
     In FIG.  1 ( g ), a rounded dome  92  with an opening for the interior passageway  74  is used with the rounded dome  72 . The interior passageway  74  extends from the rounded dome  72 , completely through the rounded dome  92 , to carry the thrust load path  94  to a polar fitting  44 . The polar fitting  44  is then coupled to the main body  96 . 
     In FIG.  1 ( h ), the rounded dome  72  has been replaced by an indented dome  102  with a closed polar fitting  64 . The thrust load path  104  extends through the indented dome  102  to reach the main body  106  of the vehicle  100 . The indented dome  102  may be a useful configuration for interfacing with other interior components aft of the tank  108 . 
     As described above, configurations ( e ), ( f ), and ( g ) have thrust structures that extend through the middle of the tank, creating a second pressure load path from end to end. In order to allow vessel strain due to pressure to occur unimpeded by this type of thrust structure, the two structures may be uncoupled at one end, allowing the two structures to strain at different rates and translate with respect to each other. To prevent leakage between the two structures, a plastic or elastomeric liner may be used to contain the fluid, or an O-ring, lip-type seal, or rod packing may be used between the two translating surfaces. 
     Referring to FIGS.  2 ( a ) through ( c ), an aft portion of a tank with an exemplary liner, O-ring, or other seal is shown, as may be incorporated into FIGS.  1 ( e ),  1 ( f ), or  1 ( g ). More specifically, FIG.  2 ( a ) shows one way in which a plastic or elastomeric liner  112  may be configured in a vehicle  110 . The liner  112  has an annular shape with an integral lined hole  114  extending through its center. This integral lined hole  114  of the liner  112  is supported by the thrust structure  116  (bulkhead or other internal supporting feature  116  ) but is not bonded to the supporting feature  116  near the meeting point  118  of the dome  120  and the supporting feature  116 . This allows the un-bonded liner to compress and stretch as the supporting feature  116  translates in and out of the dome  120 . A compliant pad  122  near the meeting point  118  between the liner  112  and support structure  116  may help distribute local liner strain. 
     FIG.  2 ( b ) shows a similar tank  130  with an O-ring seal  132  instead of a liner with an inner penetration. The O-ring seal  132  may comprise one or more O-rings in sealable engagement with the supporting feature  116  and the dome  120 . As with FIG.  1 ( a ), the supporting feature  116  and the dome  120  are able to slide relative to each other to accommodate different rates of strain. FIG.  2 ( c ) depicts a similar tank  140  with a rod packing type seal  142 . As with FIGS.  2 ( a ) and  2 ( b ), the supporting feature  116  is able to slide in and out of the dome  120 . The rod packing  142  serves essentially the same function as the O-ring seal  132 ; it permits relative translation while maintaining a fluid seal. Any variety of seal types may be used depending on the operating pressures and anticipated relative movement. 
     Transitioning the thrust load path directly through the fluid storage area may be accomplished by incorporating a conical, truncated cone, or cylindrical thrust structure into the tank&#39;s interior where both sides of the structure are exposed to fluid pressure. The purpose of this thrust structure would be to transfer engine thrust loads from the engine to the outer surface of the tank or the opposite dome. Internal thrust structure may also be used to transfer loads from the engine or outer surface of the tank to a payload attachment/interface at or beyond the forward dome. This thrust structure may also double in function as a separating membrane or bulkhead between two propellant fluids. This would further reduce the part count by consolidating two or more tanks into one tank with multiple internal chambers. 
     Referring to FIGS.  3 ( a ) through  3 ( d ), a few tank configurations showing the use of an internal thrust structure are illustrated. More specifically, FIG.  3 ( a ) shows a vehicle  150  with a tank  152  with a polar fitting  32  receiving engine thrust force  30 . As with FIG.  1 ( g ), a rounded dome  72  is provided, with an opening for an interior passageway  74 . The tubular polar fitting  32  flares into an internal thrust structure  154  and carries the thrust load path  156  into the outer wall  22 . Vents  158  are provided in the flared support  154  to allow passage of a single fluid on both sides of the flared support  154 . 
     In FIG.  3 ( b ), a tapered support  162  has been added, so that the thrust load path  164  extends through the flared support  154 , the outer wall  22 , and then the tapered support  162 . As with the configurations of FIGS.  1 ( e ),  1 ( f ), and  1 ( g ), a polar fitting  44  has been provided to further transmit the thrust load path  164  to the main body (not shown) of the vehicle  160 . As with FIG.  3 ( a ), vents  166  have been provided in the flared support  154 , and also in the tapered support  162 , to permit fluid communication across the flared support  154  and the tapered support  162 . 
     In FIG.  3 ( c ), a tank/structure  170  is configured to contain two different fluids separated by an internal thrust structure. In this embodiment, a first tank  172  and a second tank  174  are provided. The first tank has a rounded dome  176  situated within the polar fitting  34 , an interior wall  178 , and a rounded dome  180  situated within the forward polar fitting  44 . The gas inlet  14  is located on the rounded dome  180 , and the fluid outlet  16  is on the rounded dome  176 . The second tank  174  is annular in shape and is disposed around the first tank  172 . From the interior wall  178 , rounded annular caps  182 ,  184  extend outward to reach the outer wall  22 . The second tank  174  is equipped with its own gas inlet  186  and gas outlet  188 . The thrust load path  189  extends straight through the interior wall  178  to reach the polar fitting  44 . Because the first and second tanks  172  and  174  are entirely sealed from each other, they may contain two separate fluids. 
     In FIG.  3 ( d ), an alternative embodiment of a vehicle  190  is shown, incorporating a dual-tank design. A first tank  192  is conical in shape, and a second tank  194  is roughly annular, with a conical interior accommodating the first tank  192 . The fluid outlet  16  of the first tank  192 , which may act as the polar fitting  32 , leads directly to a flared support  196 , which broadens to reach the polar fitting  44 , within which the rounded dome  180 , with the gas inlet  14 , is disposed. A rounded annular dome  198  is provided with a gas inlet  186  and a fluid outlet  188 , and extends outward to the outer wall  22 . As with FIG.  3 ( c ), a rounded annular dome  184  connects the outer wall  22  to the first tank  192  and the polar fitting  44 . The thrust path  199  goes through the polar fitting  32 , through the flared support  196 , and through the polar fitting  44  to reach the main body (not shown) of the vehicle  190  or a payload attachment fitting. 
     In order to allow vessel strain due to pressure to occur unimpeded by the thrust structure, the two structures may be uncoupled at one end of a given thrust structure, allowing the two structures to strain at different rates and translate with respect to each other. In order to prevent leakage between the two structures, a plastic or elastomeric liner may be used to contain the fluid, or an O-ring, lip-type, rod packing type, or other seal may be used between the two translating surfaces as shown in FIGS.  2 ( a ) through  2 ( c ). 
     Vehicle length, volume, weight, and part count may also be reduced by incorporating all or part of the vehicle&#39;s engine into the tankage as part of the pressurized membrane. The engine&#39;s injector head may become, or be attached directly to, a tank polar fitting and minimize required plumbing. Thrust vectoring for this configuration may be accomplished through the use of an articulating nozzle (rubber/shim joint) similar to those used on many solid rocket motors. 
     Incorporating the engine&#39;s chamber and nozzle into the tankage may be especially beneficial for upper stages and spacecraft that may use large engine nozzles, but requires that the engine be fixed (non-vectorable) with respect to the tank. Thrust vectoring for this type of configuration may be accomplished by controlled fuel injection into areas of the nozzle, by vanes or paddles redirecting the exhaust, by a separate reaction control system, or by articulating the tank in which the engine is installed or other area of the vehicle. 
     Referring to FIG. 4, a portion of a vehicle  200  incorporating an integrated tank  202  and engine  204  is shown. The engine  204  extends up into the tank  202  and one or both of the tank polar openings  206 ,  208  are sealed around the engine&#39;s exterior surface, while leaving the nozzle  210  exposed. A transition tube  212  may be used to allow access to the engine injector head  214 . 
     In this configuration, the structure of the engine  204  must be capable of supporting the compressive loads of the pressurized fluid of the vessel  202 . Fibers with a high compressive strength, such as boron, may be used in the fabrication of the nozzle  210  and its associated chamber  216 . Syntactic foam or a ceramic-based material may be used on or in the nozzle  210  and chamber  216  to improve the compressive strength and stability of the engine&#39;s structure and insulate the stored fluid and surrounding structure from engine combustion heat. The use of an ablative chamber  216  or nozzle  210  may reduce or eliminate the need for insulation. 
     In order to allow vessel strain due to pressure to occur unimpeded by the engine assembly, the two structures may be uncoupled at one end, allowing the two structures to strain at different rates and translate with respect to each other. To prevent leakage between the two structures, a plastic or elastomeric liner maybe used to contain the fluid, or an O-ring, lip-type, rod packing type, or other seal may be used between the two translating surfaces as shown in FIGS.  2 ( a ) through  2 ( c ). 
     Referring to FIG. 5, an alternative embodiment of the invention is shown, in which a vehicle  220  has a tank  222  integrated with an inverted or aerospike-type engine  224 . The nozzle  226  is then configured around one end of the tank  222  with an annular chamber  228 . In this configuration, the structure of the engine  224  should be capable of containing or assisting in the containment of the pressurized fluid of the tank  222 . 
     If desired, tank-integrated thrust structure may be used in conjunction with the integrated engine to convey engine thrust and vehicle loads to the appropriate structure. With more complete engine integration, the tank dome into which a conventional engine would be inserted would have a relatively large polar opening and shorter, straighter, length of dome remaining. This dome may be adequately strong and stiff to transfer engine thrust to the cylindrical portion of the tank without any additional thrust structure. 
     Referring to FIGS.  6 ( a ) through  6 ( e ), several possible embodiments of an integrated tank, engine, and thrust structure are depicted. In the vehicle  230  shown in FIG.  6 ( a ), the engine  204  is of a conventional type, as depicted in FIG. 4. A flared dome  232  supports the engine  204  within the tank  234 , and also serves to transmit thrust to the outer wall  22  of the tank and into the main body  236  of the vehicle  230 . The thrust load path  238  depicts the transmission of engine thrust force from the engine  204  to the main body  236 . Consequently, the flared dome  232  and the outer wall  22  constitute the thrust structure of this embodiment. A rounded dome  239  is also provided on the forward side of the tank  234 , encircling the transition tube  212 . A gas inlet  14  and a fluid outlet  16  are provided in the rounded dome  239 . 
     In FIG.  6 ( b ), a vehicle  240  has been provided with a broader transition tube  242  to convey thrust from the engine  204 . The flared dome of FIG.  6 ( a ) has been replaced by a rounded dome  244 , and the rounded dome  239  of FIG.  6 ( a ) has been replaced by a rounded dome  246  with a larger opening to accommodate the enlarged transition tube  242 . The thrust load path  248  travels simply along the transition tube  242  and will intersect with the main body (not shown) of the vehicle  240 . 
     In the vehicle  250  of FIG.  6 ( c ), the rounded dome  244  has been replaced by a rounded dome  252  with a fluid outlet  16  near the engine  204 . A truncated transition tube  254  carries thrust loading from the engine  204  to a flared dome  256 , which conveys the thrust to the main body  258  of the vehicle  250 . Consequently, the thrust load path  259  extends through the transition tube  254  and the flared dome  256 . A gas inlet  14  may be located on the outer wall  22 . 
     An alternatively embodied vehicle  260  is shown in FIG.  6 ( d ). A rounded dome  244  is provided, as shown in FIG.  6 ( b ). A transition tube  262  extends from the engine  204  to a tapered dome  264 , in which a gas inlet  14  and a fluid outlet  16  are provided. The tapered dome  264  conveys thrust to the main body  268 , such that the thrust load path  269  travels along the transition tube  262  and through the tapered dome  264  to reach the main body  268 . 
     In FIG.  6 ( e ), yet another configuration is shown in a vehicle  270 . A flared dome  232  and a transition tube  212  are provided, as in FIG.  6 ( a ). However, a tapered dome  272  transmits the thrust load back inward to reach the main body (not shown) somewhere forward of the tank  274 . The thrust load path  279  thus travels through the flared dome  232 , the outer wall  22 , and the tapered dome  272 . A gas inlet  14  and a fluid outlet  16  are provided in the tapered dome  272 . 
     Referring to FIGS.  7 ( a ) through  7 ( c ), internal thrust structure may also be integrated into the tankage along with the engine. More specifically, in FIG.  7 ( a ), a vehicle  300  similar to that of FIG.  3 ( a ) is shown, with the addition of an engine  204  integrated with the tank  302 . A flared internal support  304  is provided to convey a thrust load from the engine  204 . A transition tube  212  extends through the rounded dome  239  at the forward end of the tank  302 . The thrust load path  308  extends from the engine  204 , through the flared support  304 , to the outer wall  22 , and to the main body  309 . As with the configurations of FIGS.  3 ( a ) and  3 ( b ), vents (not shown) may be provided to permit fluid communication across the flared support  304 . 
     In FIG.  7 ( b ), the engine  204  is enlarged with respect to the vehicle  310 . Accordingly, a smaller rounded dome  312  is provided to connect the engine  204  to the outer wall  22 , and a shortened transition tube  316  is used to supply necessary fluids or control for the engine  204 . The rounded dome  314  is also smaller, and may have a gas inlet  14  and a fluid outlet  16 . A tapered support  317  extends from the engine  204  to the outer wall  22 , so that the thrust load path  318  travels through the tapered support  317  and the outer wall  22  to reach the main body  319  of the vehicle  310 . As with the configurations of FIGS.  3 ( a ) and  3 ( b ), vents (not shown) may be provided to permit fluid communication across the flared support  304 . 
     In FIG.  7 ( c ), a vehicle  320  having a configuration similar to that shown in FIG.  3 ( c ) is shown, with an integrated engine  204 . An interior wall  322  extends from the engine  204  to reach a rounded dome  324  with a gas inlet  14  and a fluid outlet  16 . The rounded dome  324  also has an opening through which the transition tube  212  travels. A rounded annular dome  326  extends outward from the interior wall  322  to reach the outer wall  22 , and a similar rounded annular dome  328  reconnects the outer wall  22  with the interior wall  322 . Thus, a first tank  330  and a second tank  332  are formed. A gas inlet  186  and a fluid outlet  188  in the second tank  332  provide for separate ingress and egress so that two separate fluids may be maintained. The thrust load path  339  travels through the interior wall  322  to reach the main body (not shown) of the vehicle  320 . 
     It is conceived that the novel bulkhead structures of the present invention are not limited to use for propulsion vehicles. More particularly, hydraulic accumulators, rail car air brake reservoirs, water softeners, and other devices in which it is desirable to store two separate fluids may benefit from the novel integrated tankage and bulkhead designs of the present invention. 
     One or all of these components of the invention may be made of metal by weld fabrication, machining, spinning, hydroforming, casting, forging, plating or metal deposition, or any combination of the above. The preferred materials, however, are composites, utilizing carbon, aramid, boron, glass, silica, ceramic, or other reinforcing fibers in an organic matrix. Metal fittings, liners, bulkheads, and mechanical fasteners along with plastic or elastomeric liners, bladders, or coatings may be utilized in a predominantly composite structural assembly. The preferred method of manufacture of the basic structure is by filament winding, fiber placement, or hand-lay-up, or any combination of the above. 
     The present invention may be embodied in other specific forms without departing from its structures, methods, or other essential characteristics as broadly described herein and claimed hereinafter. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.