Assembly and method for attaching a pressure vessel to another object

Abstract: An attachment assembly (2) for connecting a pressure vessel to another object, but preferably for connecting rocket motors to one another, including several successive layers, which are arranged in the following order: first, a reinforcement section (41) on an outer casing (9) of a first pressure vessel; second, a layer of resilient shear ply material (37) adhered to the outermost surface of the reinforcement section; third, a saddle (3) positioned over the shear ply; fourth, an overwrap (7) which secures the saddle to the shear ply; fifth, a plurality of lugs (4,8) which are secured to the saddle; sixth, a connecting means attached to one of the lugs; seventh, a strut wherein a first end thereof is attached to at least one of the lugs; and, eighth, a attachment means for connecting a second end of the strut with a second pressure vessel. The method includes constructing the reinforcement section; adhering the shear ply to the reinforcement section; positioning the saddle over the shear ply and attaching lugs to the saddle; applying an overwrap over the saddle; attaching a connecting means to one of the lugs; connecting a strut to both the connecting means as well as to the second pressure vessel.

Description: The present invention pertains to the field of fasteners, and is especially applicable to fastening a pressure vessel to another object, especially another pressure vessel. The invention particularly pertains to means for fastening two rocket motors or engines to one another, for example a booster rocket motor to a main rocket motor. Multi-engine rocket-powered aircraft are well known. More than one rocket engine in a single aircraft (or spacecraft) can be utilized to extend the range, speed or payload of the craft. The addition of separate rockets can also be used to produce added directional control or special maneuverability, spin, etc., to the craft. Most commonly, one or more booster rocket engines are employed along side a main rocket engine, in order to increase the thrust. U.S. Patent 3,070,329 (HASBROUCK) relates to directional control for rockets. HASBROUCK utilizes a plurality of independent movable steering rockets which are fastened along side the main rocket engine, and which exert a steering thrust at an acute angle to the line of thrust of the main propulsive nozzle. The steering rockets are affixed to the main rocket with gimbal joints, as well as a supporting ring which is lugged. Two struts, comprising ball and socket joints on the respective ends thereof, are affixed to the steering rocket and the main rocket. The purpose of the steering rockets is to provide a means for steering the main rocket in the desired direction, and this is why the gimbal joint is utilized in fastening the steering rocket to the main rocket. U.S. Patent 3,532,304 (PYPTIUK) relates to rocket powered space vehicles in which four rocket motors are equally spaced around the roll axis of the vehicle, universally mounted on a common frame. Each motor is separately mounted to a tubular thrust ring by means of a coupling. The coupling may be a ball and socket joint, and the coupling permits the motor to pivot relative to the thrust ring. The arms which connect the rocket nozzles to the non-pivoting portion of the machine may also be fitted with ball and socket joints. U.S. Patent 4,892,435, U.S. Patent 4,904,109, and U.S. Patent 4,909,659, all in the name of Robert ANDERSON, relate to interlocking structural members employing transverse locking wedges or locking means. ANDERSON fastens composite materials together that comprise polymers having reinforcing fibers therein. All three of these patents are particularly directed at aircraft wing skins which are attached to a support substructure by means of a fastenerless joint. Fastenerless joints are utilized to avoid the problem of leaks which are common when rivets are used to attach the aircraft wing skin to the supporting substructure. Fastenerless joints also avoid passing rivets through various plies of the laminated structure which can cause rupture of the wing skin. ANDERSON's fastenerless joint comprises a wedge which interlocks a wing skin structure to a support substructure. The wing skin laminate has hollowed projections for receiving mating recesses in the composite wing substructure. The wedge is forced into the hollow projections after the projections are interdigitated with the mating recesses in the composite wing substructure. The wedges are transversely positioned across the mating recesses, and extend therefrom axially, so that they serve to lock the wing skin structure to the supporting substructure. It is important to utilize lightweight, but structurally strong components in building rocket engines, in order to improve the thrust-to-weight ratio, and thereby increase the payload capacity, range or speed of travel of the rocket. To this end, composite materials (i.e., fiber reinforced resins) have been developed and utilized extensively throughout the aeronautical industry. Even the outer casing (i.e. housing or "skin") of the body of a craft can be made from such fiber reinforced composite materials. Some composite materials have a strength to weight ratio significantly higher than the metals traditionally used in the manufacture of aircraft body panels. Since it remains important to keep the craft as light as possible, such elements as the outer casing of a rocket engine are manufactured to as thin a gauge as possible, while simultaneously maintaining an adequate margin against structural failure due to the various forces to which the casing will be subjected. The outer casings of solid propellant rockets are typically manufactured thin enough so that the internal pressure produced by the operation of the engine causes the circumference of the casing to increase in size by about 1 percent. Such an increase can create tremendous shear forces at fixed points on the casing, for example, if the casing is fastened to another rocket engine with a rigid connection at a fixed location. Large shear forces either risk structural failure or require greater weight in order to achieve a level of structural strength to carry the force. Such shear forces can be especially troublesome if the casing is made of a fiber-reinforced polymeric resin, since the fibers are generally laid down in layers having a directional orientation and hence are much stronger in some directions than others. The layers having fibers oriented in the weakest direction with respect to the shear are subject to an increased risk of failure, which could cause a failure throughout the entire thickness of the casing. The present invention relates to an attachment assembly for fastening a pressure vessel to another object. In general, the attachment assembly comprises: A. a pressure vessel wall reinforcement section adapted to be mounted on an outer casing of the pressure vessel; B. a layer of shear ply positioned over the reinforcement section; C. a saddle positioned over the shear ply, wherein the saddle has at least two lugs thereon; D. an overwrap positioned over at least a portion of the saddle; and E. a connecting means for connecting a first end of a strut to at least one of the lugs. The pressure vessel wall reinforcement section comprises a plurality of layers of fiber embedded in a resin. The layers of fiber are positioned across one another, preferably at an angle of from about 0 degrees to about 90 degrees. The shear ply is constructed from a resilient material, wherein an adhesive adheres the shear ply over an outermost fiber-reinforced resin layer of the reinforcement section. The shear ply is resilient enough to prevent damage to the casing of the first pressure vessel during a period of use of the pressure vessel. The saddle has at least two lugs thereon, wherein the lugs are attached to the saddle with a means for attachment thereof. The overwrap secures the saddle against the shear ply. A second end of the strut is adapted to be connected to the other object with an attachment means therefor. Preferably the pressure vessel is a first pressure vessel (most preferably a solid propellant booster rocket engine), and preferably the "other object" is a second pressure vessel (most preferably a liquid propellant main rocket engine). Furthermore, the present invention relates to a method of attaching a pressure vessel to another object. The method comprises the steps of: A. constructing a pressure vessel wall reinforcement section on an outer casing of the pressure vessel; B. adhering a layer of a shear ply over an outermost layer of the reinforcement section; C. positioning a saddle over the shear ply; D. attaching at least two lugs onto the saddle; E. applying an overwrap over at least a portion of the saddle so that the saddle is secured against the shear ply; F. attaching a connecting means to at least one of the lugs; G. connecting a first end of a strut to the connecting means; and H. connecting a second end of the strut to the other object. The wall reinforcement section comprises a plurality of layers of fiber embedded in a resin. The layers of fiber comprise fibers which are oriented parallel to one another, in which entire layers of fiber are positioned across one another, and/or the fibers within a given layer are positioned across one another, i.e. not parallel to one another. The shear ply is constructed from a resilient material, wherein an adhesive adheres the shear ply to the outermost layer of the reinforcement section. The shear ply is resilient enough to prevent damage to the casing of the pressure vessel during a period of use of the pressure vessel. The assembly and process of the present invention allow for the use of a relatively lightweight pressure chamber outer casing which has an assembly thereon for attaching the pressure chamber to another object. The assembly is constructed in such a manner that even if the outer casing is made in such a manner that a 1 percent increase (or greater) in circumference is produced upon pressurization of the chamber, there is no substantial risk of producing shear forces which will rupture the casing. Rather, the attachment assembly is constructed to avoid the production of shear forces which have a substantial risk of producing structural failure of the casing during operation of the pressure chamber. The attachment assembly is also constructed to enable the casing to be relatively lightweight, in comparison with the weight required to ensure no substantial chance of structural failure, if a conventional attachment assembly (i.e. a bolt, etc.) is utilized. The present invention permits the use of a lightweight outer casing in a pressure vessel having an assembly thereon for attachment of the pressure vessel to another object. It also permits the use of a lightweight outer casing for a pressure vessel, where the casing is substantially free of risk of structural failure while having an assembly thereon for attachment of the pressure vessel to another object. The present invention also provides an attachment assembly which can be attached to a rocket housing at any desired axial attachment point, especially a point which corresponds to an internal region which is pressurized during operation of the rocket motor. An attachment assembly is provided that can attach to the outside of a pressure vessel and permits movement of the relative positions of the pressure vessel with respect to the other object. The attachment assembly is secure in holding the pressure vessel, but also permits the pressure vessel to be detachably engaged with the other object. The attachment assembly is easy to assemble and is also light in weight. The attachment assembly is used for attaching at least two rocket engines to one another and is flexible enough to accommodate the expansion and contraction which accompany the normal use of the rocket engines, while substantially avoiding the production of an amount of shear which poses a substantial risk of structural failure to the casing of either rocket engine. This attachment assembly comprises a saddle which extends only partially around the casing. The saddle rests upon a flexible, resilient member, so that destructive shear forces are avoided. Figure 1 illustrates a longitudinal side view of a rocket (1) having a portion of attachment assembly (2) thereon. The rocket has an outer casing (9) thereon. Attachment assembly (2) comprises a wall reinforcement section (41), a saddle (3), a center lug (4), an overwrap (7), and a side lug (8). Figure 2 illustrates an enlarged longitudinal sideview of attachment assembly (2) of Figure 1 with enlarged views of saddle (3), center lug (4), T-element (5), ball element (6), overwrap (7), side lug (8), and outer casing (9). Figure 3 illustrates a cross-sectional view of a portion of the rocket taken through line 3-3 of Figure 2, with additional elements shown that are not included in Figure 2. The relative arrangement is shown of center lug (4), T-element (5), ball element (6), two side lugs (8), outer casing (9), a portion of a strut member (10), two thrusters (11) and annular clamp element (12). Thrusters (11) apply pressure between the main rocket (not shown) and side lugs (8) to keep the booster rocket in a fixed position with respect to the main rocket. The thrusters are chained to saddle (3) in order to adequately secure the thrusters so that they do not move in an uncontrolled manner upon detachment of the booster which could damage the main rocket or the housing of the booster rocket. Although not shown in Figure 3, the other end (13) of each of the thrusters (11) is placed into contact (i.e., either directly or indirectly) with the outer casing of the main rocket engine (not shown). Figure 4 illustrates a top view of a portion of the rocket having thereon a portion of attachment assembly (2) illustrated in Figure 1. Saddle (3) provides a surface upon which are mounted center lug (4) and two side lugs (8). T-element (5) is shown atop center lug (4), and ball element (6) is positioned over T-element (5). Overwrap (7) is positioned over both a portion of saddle (3) as well as a portion of center lug (4). Figure 5, which is an end view of the rocket, illustrates an enlarged view of a portion of the attachment assembly illustrated in Figure 1. Figure 5 illustrates a side view of saddle (3) having a center lug (4) and two side lugs (8) thereon. Saddle (3) and the lugs are shown unitary therewith, without illustrating any other elements of the attachment assembly. Figure 6 illustrates an enlarged view of center lug (4) and the attachment of strut member (10) thereto. T-element (5) is slidably engaged within a slot in center lug (4). A ball-and-socket joint is formed by ball element (6) in combination with a socket. The socket is formed from at least two elements: a concave surface (15) within the end of strut (10), and a ring element (14) having an inner concave surface (16) which mates with the curvature of ball element (6). Ring element (14) is forced against ball element (6) through the tightening of an annular clamp element (12) having a groove (19) with beveled sides into which are positioned a mating surface (17) on ring element (14) as well as a mating surface (18) on a flared end (40) of strut member (10). Annular clamp element (12) is preferably present in the form of a ring which is closed by a bolt (not shown) which threadably engages a nut affixed to the ring, so that the clamp is drawn towards a closed position, so that the clamp is tightened against and over both ring member (14) and flared end (40) of strut member (10). A set screw (20) is threadedly engaged into a hole (21) in the ball element, in order to lock the threads on the T-element (5) into mating threads within the ball element (6). Figure 6 also illustrates the various layers of material which are present on outer casing (9) of the pressure vessel. Positioned immediately over outer casing (9) of the pressure vessel is a set of fiber-reinforced resin layers (41). Positioned over the layers of fiber-reinforced resin (41) is a layer of shear ply (29), which is constructed from a resilient material, such as rubber. Positioned immediately over the layer of shear ply (29) is saddle (3). A supplemental (i.e. optional, but preferred) layer of shear ply (37) is positioned immediately over saddle (3). Finally, overwrap (7), which is a composite comprising multiple layers of fiber embedded in resin (see Figure 13), is positioned over the supplemental layer of shear ply (37). Figure 7 illustrates an enlarged view of a side lug (8) having a thruster (11) connected thereto. A tang pin (22) is hingedly attached to two clevis posts (23) via a retaining pin (24) which passes through both of the clevis posts (23) as well as through tang pin (22). The arrangement of the tang pin, the clevis posts, and the retaining pin is commonly referred to as a tang and clevis joint. Tang pin (22) is secured (preferably welded) to an anchor plate (35). To the anchor plate (35) is secured (again, preferably welded) a retaining shaft (36) which is adjustably mounted within a passageway through side lug (8). Preferably retaining shaft (36) is threadedly engaged with the threaded passageway through side lug (8). However, it is most preferred that the retaining shaft has a rotatable housing thereover (not illustrated), wherein the housing is smooth on its interior surface and threaded on its exterior. The smooth interior of the housing has an elevated section therein which is permanently keyed into an annular groove in retaining shaft (36). Since the exterior of the housing is threadedly engaged with the threaded interior surface of side lug (8), this arrangement allows for a high degree of adjustment of the position of the thruster with respect to side lug (8). Thruster (11) applies pressure to side lug (8) by applying pressure through the following series of parts: (11)-(23)-(24)-(22)-(35)-(36)-(8). As in Figure 6, Figure 7 also illustrates the various layers positioned over outer casing (9) of the pressure vessel, such as fiber-reinforced resin layer (41), shear ply (29), and saddle (3). For purposes of clarity, upper layer of shear ply (37) and overwrap (7) are not illustrated in Figure 7. Figure 8 illustrates an end view of a preferred embodiment of connecting member (5), this preferred embodiment herein termed a "T-element". T-element (5) represents a cross-sectional shape having a "head" (34) which mates with the slot in the center lug (4) illustrated in Figure 5. Figure 9 illustrates a side view of this same T-element upon a 90° rotation of the T-element of Figure 8 along the axis of the threaded portion thereof. This view illustrates the side surface of the T-element which contacts the slot surfaces of center lug (4). Figure 10 illustrates a top view of the T-element threadedly engaged into ball element (6). This view clearly illustrates the difference between the side views of Figures 8 and 9 due to the head (34) of the T-element having a length substantially greater than its width. Figure 11 illustrates ball element (6) which has threaded internal surface (26) which threadedly engages threaded sections (25) of T-element (5). Threaded passageway (21) is preferably provided within ball element (6) in order that set screw (20) may be threadedly engaged therein, for locking threads (26) of ball element (6) to threads (25) of T-element (5). Region (38) between horizontal lines (39) across ball member (6) is "flat", i.e. no spherical curvature is present here. The flat is present in order to ensure a clean detachment of strut (10) from ball element (6). Detachment of strut (10) from ball element (6) is carried out by using an "exploding bolt" (not illustrated) for closing the annular clamp (12, as illustrated in Figure 6) around both flared ends (40) of strut (10) and ring member (14). Upon exploding the bolt, the ring formed by annular clamp (12) opens, and ball member (6) is permitted thereafter to separate from strut (10), thereby allowing, for example, a booster rocket to which the attachment assembly is attached, to separate from the central rocket engine (not shown). Figure 12 illustrates a cross-sectional view of the ball element illustrated in Figure 11, taken through line 12-12 thereof. Figure 13 illustrates an exploded diagrammatic cross-sectional view of a pressure vessel wall reinforcement section to be utilized in the attachment assembly of the present invention. A plurality of parallel layers (27) of fiber are shown positioned directly over outer casing (9). Each of the layers (27) designated "O" extend into the plane of the figure, i.e., around the circumference of outer casing (9) of the rocket, in a direction generally perpendicular to the axis of the rocket. Each of the layers (27) designated "X" are actually two discrete fibrous layers, each of which is generally oriented 45° to the circumferential fibers. These two discrete, angled fiber layers are oriented approximately 90° with respect to one another, i.e. the helical path of each of these fiber layers extend in opposite directions. Each of the fiber layers is completely embedded in a resin (28), which is illustrated as a transparent material located between each of fiber layers (27), as well as over and under the fiber layers. The combination of fiber layers (27) and resin (28) together comprise reinforcement section (41), as indicated in Figure 13. Above uppermost layer (27) of fiber is a layer of resin (28), over which is positioned a layer of shear ply (29). Immediately over layer of shear ply (29) is positioned saddle (3). The layer of shear ply (29) extends slightly beyond the saddle, both in length and width. No lugs are illustrated in Figure 13. A split supplemental shear ply (37) is positioned over saddle (3), each portion of supple-mental shear ply (37) being positioned over a portion of the width of saddle (3), along the edge thereof. Supplemental shear ply (37), together with overwrap (7), serves to provide added cushion and containment of saddle (3). Over supplemental shear ply layer (37) are positioned a plurality of layers of fibers (32) which are embedded in, and serve to reinforce, a resin (31, illustrated as transparent). Together these layers of fiber and resin represent overwrap (7). The fibers present in overwrap (7) are all oriented around the circumference of the rocket's outer casing (9), i.e. in a direction generally perpendicular to the axis of the rocket. Unlike wall reinforcement section (27), the axes of fibers (33) in overwrap (7) are all positioned in substantially parallel alignment with one another. The attachment assembly is utilized for the purpose of attaching a pressure vessel to virtually any other object. The other object could be another rocket engine, an aircraft fuselage, or even a stationary object. However, the preferred pressure vessel is a booster rocket motor, and the preferred "other object" is a main rocket motor. Preferably, the booster rocket motor is a solid propellant motor, and preferably the main rocket engine is a liquid propellant rocket motor. Although the attachment assembly may be used to permanently affix the pressure vessel to the object, the attachment assembly is preferably used in conjunction with a means for detachment, in order to produce a releasable attachment of the pressure vessel to the other object. The wall of the pressure vessel (i.e. the outer casing, 9) is preferably as described above, i.e. the casing preferably expands slightly upon pressurization of the vessel. In general, the wall of the pressure vessel can be constructed of any material capable of withstanding the forces to which the wall is subjected during use. Preferred materials for construction of the wall are steel, aluminum, titanium, and fiber-reinforced resin. The attachment assembly of the present invention is useful for rocket engines having outer casings comprising composites such as fiber reinforced resins as well as rocket casings comprising metals such as steel, aluminum, etc. If the wall of the pressure vessel is constructed to minimize weight, as is desired in the design of rocket motors, it becomes necessary to reinforce the wall at the section thereof at which an attachment assembly is attached thereto. Reinforcement is necessary here because the wall would otherwise be subject to a substantial risk of structural failure due to shear produced between the expanded wall and a rigid strap attached to the wall. In general, any means for reinforcing a section of the pressure vessel wall may be used. The means is located on the outer casing of the pressure vessel. The wall reinforcement section (41) on the outer casing of the pressure vessel can be located anywhere over the outer casing. That is, the wall reinforcement section (41) may be positioned on top of the outer casing, and bonded to the outermost surface of the casing, as is shown in Figures 1-4, 6, 7, and 13. The wall reinforcement section (41) reinforces that portion of the wall at which the attachment assembly is affixed, so that the remaining portion of the casing may be constructed of an overall lighter design, i.e. of lesser wall thickness. The wall reinforcement section (41) comprises a plurality of layers of fiber (27) embedded in a resin (28). In general, resin (28) may be any resin which is compatible with the fiber and which can withstand the conditions of use while simultaneously reinforcing the wall section. Preferably, resin (28) is at least one member selected from the group consisting of an epoxy resin and a phenolic resin. Most preferably the resin is an epoxy resin. In general, the resin (28) is present in the reinforcement section in an amount which, when mixed with the reinforcing fibers, produces a wall reinforcement section (41), a section of the wall of the pressure vessel wherein there is reinforcement to a desired degree. Preferably, the resin is present in the reinforcement section in an amount of from about 27 to about 47 weight percent, based on the combined weight of fiber layers (27) and the weight of resin (28). Most preferably, the resin is present in the reinforcement section in an amount of about 37 weight percent. In general, the reinforcing fiber present in the wall reinforcement section may be any fiber compatible with the resin that can withstand the conditions of use while simultaneously producing a reinforced wall section. Preferably, the fiber is at least one member selected from the group consisting of a graphite fiber, fiberglass fiber, and aramid fiber. Most preferably, the fiber is a graphite fiber. In general, the reinforcing fiber is arranged as a plurality of layers, wherein each layer is a set of parallel yarns or fibers. The layers of fibers are illustrated in Figure 13. Although any number of fiber layers effective to produce an adequate degree of reinforcement may be utilized, preferably from about 8 layers of fiber to about 20 layers of fiber are present in the reinforcement section. Although the fibers may, in general, be present in any form which results in adequate reinforcement, the fibers are preferably present as 11 layers. In general, the fiber is present in the reinforcement section in an amount which, when combined with the resin, produces a wall reinforcement section. Preferably, the fiber is present in the reinforcement section in an amount of from about 53 weight percent to about 73 weight percent, based on the combined weight of the fiber layers (27) and the weight of the reinforcing resin (28). Most preferably, the fiber is present in the reinforcement section in an amount of about 63 weight percent. In the wall reinforcement section (41), a plurality of resin impregnated fiber layers are placed in a stacked relationship. However, the layers of fiber are positioned whereby the fibers cross one another. Preferably, the adjacent layers of fiber designated with an "X" in Figure 13 cross one another at an angle of about 90 degrees, with each layer being angled at about 45 degrees with respect to the axis of the rocket. Preferably, the fibers in the layer designated with an "O" in Figure 13 cross the fibers in the "X" fiber layers at an angle of about 45 degrees, since the fibers in the "O" layers cross the axis of the rocket at an angle of about 90 degrees. Preferably, every third layer of fiber has the same direction of fiber orientation. Preferably the reinforcement section (41) is positioned around the entire circumference of the pressure vessel. By extending the reinforcement section (41) around the entire circumference of the pressure vessel, a higher degree of reinforcement may be produced. A layer of shear ply (29) is positioned over the reinforcement section and serves as a means for absorbing shear forces produced by the expansion of the outer casing or the pressure vessel during its use. The shear ply (29) is constructed from a resilient material. In general, the material should be resilient enough to prevent damage to the outer casing of the pressure vessel during its use. Preferably, the resilient material is at least one member selected from the group consisting of a styrene-butadiene rubber (i.e. SBR), an acrylonitrile-butadiene rubber (i.e. NBR), an ethylene-propylene-diene rubber (i.e. EPDM). Most preferably, the resilient material is a styrene-butadiene rubber. In general, the shear ply (29) should have a thickness which, when combined with the degree of resilience of the shear ply, prevents damage to the outer casing due to expansion of the pressure vessel during a period of use thereof. Preferably, the thickness of the shear ply (29) is from about 0,508 mm (0.02 inch) to about 3,048 mm (0.12 inch). Most preferably, the thickness of the shear ply is about 2,032 mm (0.08 inch). Although the length and width of the shear ply can be any length and width which adequately reduces the shear forces produced by the expansion of the outer casing against the saddle, the shear ply preferably has a length and width at least as large as the saddle which is positioned over the shear ply. An adhesive adheres the shear ply over an outermost fiber-reinforced resin layer of the reinforcement section. Although in general any adhesive capable adhering to both the uppermost layer of the reinforcement section as well as the lowermost layer of the reinforcement section is satisfactory so long as it is also capable of withstanding the forces, temperatures, and pressures, during use of the pressure vessel, preferably the adhesive is at least one member selected from the group consisting of an epoxy adhesive and a phenolic adhesive. Most preferably, the adhesive is an epoxy adhesive. A saddle is positioned over the shear ply. The saddle has at least two lugs thereon, wherein the lugs are attached to the saddle with a means for attachment thereof. The saddle is merely one example of the means for providing at least two points of attachment to the pressure vessel, wherein the means for providing at least two points of attachment to the pressure vessel is positioned over the means for reinforcing the pressure vessel wall. Preferably, the saddle has a center lug and a plurality of side lugs thereon. Preferably, the saddle extends only partially around the circumference of the pressure vessel. The saddle preferably extends only partially around the circumference of the pressure vessel in order to reduce the weight of the assembly, as well as the efficient use of materials of construction. The saddle is preferably a rigid, inflexible member which, if extended around the entire circumference of the pressure vessel, would tend to increase the risk of damage to the pressure vessel upon expansion of the pressure vessel during use. Preferably, the saddle has a length which extends only part way around the circumference of the outer casing of the rocket, i.e. from about 45 degrees to about 225 degrees. Most preferably, the saddle extends about 100 degrees around the circumference of the rocket's outer casing. In general, the thickness of the saddle may be any thickness suited to the conditions of use of the pressure vessel and the saddle. Preferably, the saddle has a thickness of from about 1,27 mm (0.05 inch) to about 12,7 mm (0.5 inch). Most preferably, the saddle has a thickness of about 7,62 mm (0.3 inch). In general, the saddle may be constructed from any material suited to the conditions of use of the pressure vessel. Preferably, the saddle is constructed from at least one composition selected from the group consisting of steel, aluminum, titanium, and a fiber-reinforced, cured polymeric resin. Most preferably, the saddle is steel. Preferably, the saddle, the center lug, and the two side lugs are all made of the same composition, wherein the composition is at least one member selected from the group consisting of steel, aluminum, titanium, and a fiber-reinforced, cured polymeric resin. Most preferably, the steel saddle has a steel center lug and two steel side lugs welded thereto, whereby the saddle, the center lug, and the side lugs are one unitary device. Optionally, the attachment assembly of the present invention may further comprise a supplemental layer of shear ply (37) to accommodate differential expansion between the saddle and the overwraps. This supplemental layer of shear ply is positioned on top of the saddle, i.e. between the saddle and the overwrap. This supplemental layer of shear ply is also made from a resilient material, preferably the same resilient material from which the shear ply layer below (i.e. shear ply layer 29, as shown in Figures 6, 7, and 13) is constructed. In general, supplemental layer of shear ply (37) has a thickness effective to retain the saddle on the case if the saddle-to-casing bond fails. Preferably, supplemental layer of shear ply (37) has a thickness of from about 1,524 (0.06) to 3,048 mm (0.12 inch), most preferably a thickness of about 2,032 mm (0.08 inch). Preferably, the supplemental layer of shear ply is present in two portions, each portion being located along and over each long side of the saddle (3), as is illustrated in Figure 13, described above. The supplemental layer of shear ply (37) is held in the attachment assembly by overwrap (7) which forces the supplemental layer of shear ply (37) against saddle (3). The attachment assembly of the present invention further comprises an overwrap (7). The overwrap is positioned over at least a portion of saddle (3), wherein the overwrap secures the saddle against shear ply (29). The overwrap functions as a means for securing in place the means for providing at least two points of attachment to the pressure vessel. In general, overwrap (7) may comprise any means for securing saddle (3) against shear ply (29). Preferably, overwrap (7) comprises a resin (31) having a plurality of layers of fiber (32) embedded therein. This arrangement is illustrated in Figure 13. In general, the overwrap may comprise any number of layers of fiber which ensure that the overwrap adequately secures saddle (3) to shear ply (37) positioned below saddle (3). Preferably, the overwrap comprises from 5 to 15 layers of fiber (32) embedded in the resin (31). Most preferably, the overwrap comprises 7 layers of fiber embedded in the resin. In general, the organic resin can be any resin which satisfactorily serves to secure the saddle to the shear ply below the saddle. Preferably, the organic resin is at least one member selected from the group consisting of an epoxy resin and a phenolic resin. In general, the resin can be present in the overwrap in any amount effective to perform the purposes of the overwrap. Preferably, the resin is present in the overwrap in an amount of from about 25 weight percent to about 33 weight percent, based on the weight of the overwrap. Most preferably, the resin is present in the overwrap in an amount of about 29 weight percent, based on the weight of the overwrap. In general, the fiber in the overwrap can be any fiber which satisfactorily serves to secure the saddle to the shear ply below the saddle. Preferably, the fiber is at least one member selected from the group consisting of a fiberglass fiber, graphite fiber, and aramid fiber. Most preferably the fiber is a fiberglass fiber. In general, the fiber can be present in the overwrap in any amount effective to perform the purposes of the overwrap. Preferably, the fiber is present in the overwrap in an amount of from about 61 weight percent to about 81 weight percent, based on the weight of the overwrap. Most preferably, the fiber is present in the overwrap in an amount of about 71 weight percent, based on the weight of the overwrap. Preferably the fiber present in the overwrap is a continuous filament fiber, as opposed to a staple fiber. Preferably, the overwrap is positioned around the entire circumference of the pressure vessel, as opposed to around only a portion of the circumference of the pressure vessel. By extending around the entire circumference of the pressure vessel, the overwrap is a continuous band having greater strength because the multiple layers of fiber and resin serve to reinforce one another more, and are further supported by the various layers underneath. The attachment assembly of the present invention further comprises a connecting means for connecting a first end of a strut to at least one of the lugs affixed to the saddle (i.e. to at least one of the attachment points). A second end of the strut is connected to the other object (e.g. a main rocket engine) with an attachment means. Although the connecting means may be made from any material suited to connecting the strut to the lug, preferably the connecting means is made from a material selected from the group consisting of steel, aluminum, titanium, and a fiber reinforced polymeric material. Most preferably, the connecting means is made from steel. The connecting means has a means for engaging the lug as well as a means for attachment to the strut. The connecting means preferably comprises the T-element, the ball element, the ring element, the annular clamp element, and the flared end on the strut. See Figures 2, 3, 4, 6, and 8-12. T-element (5) slidably engages a slot in center lug (4). The T-element also threadedly engages ball element (6) having threads therein. As is evident from Figures 2, 3, and 6, the connecting means serves as a pivotable joint. Although the attachment assembly of the present invention comprises a plurality of lugs affixed to the saddle, preferably only one lug is attached to a strut member which attaches the pressure vessel to the other object. Preferably, the lug which is attached to the strut member is the center lug, i.e. a lug around which an even number of other lugs are preferably symmetrically arranged. Preferably the remaining lugs (i.e. side lugs (8)) are attached to "thrust devices" (11). As used herein, the phrase "thrust device" is used with respect to a device which stabilizes the position of the pressure vessel with respect to the other object. For example, if there is one central lug (attached to a strut) flanked by two side lugs each of which is attached to a thrust device (11), as is most preferred, the pressure vessel is held to the other object by three contact points. That is, the thrust devices stabilize the position of the pressure vessel by maintaining a three-point contact with the other object. In addition to acting as stabilizers, thrust devices (11) also serve to absorb shock and vibration. Furthermore, the attachment means for connecting the second end of the strut to the second pressure vessel may comprise a concave depression in the second pressure vessel and an associated convex strut end. The fixed attachment at the center lug holds the rocket in place and a compressive load in each thruster holds the thruster in place and keeps the booster (i.e. the first pressure vessel) from moving side-to-side, stabilizing the booster rocket. In the method of the present invention, in which the pressure vessel is attached to another object, the first step of the method is to construct the pressure vessel wall reinforcement section (41) on an outer casing (9) of the pressure vessel. Wall reinforcement section (41) comprises a plurality of layers of fiber embedded in a resin, wherein the layers of fiber are positioned across one another. The wall reinforcement section is constructed by applying each layer to the case in order of inside to outside. The angled (i.e. the fiber layers oriented ±45° to the axis of the casing are preferably hand laid up, and the fiber layers oriented 90° to the axis of the casing are preferably filaments which are wound thereon via machine). Once the reinforcement section is formed, the next step in the process is that of adhering the layer of a shear ply to the outermost layer of the reinforcement section. The shear ply is adhered to the outermost layer of the reinforcement section by bonding the shear ply to the outermost reinforcement layer with structural epoxy adhesive. Once shear ply layer (29) is adhered to the outermost layer of reinforcement section (41), saddle (3) is positioned over shear ply (29). Preferably, at least two lugs are securely attached to the saddle before the saddle is positioned over the shear ply. After the lugged saddle is positioned, overwrap (7) is applied over at least a portion of saddle (3), so that saddle (3) is secured against shear ply (29). The overwrap is applied by filament winding process, preferably via machine. After the overwrap is applied, the connecting means is installed on at least one of the lugs. Preferably, the lug is slotted and a head portion of a T-element is designed to precisely engage the slot. A ring member (14) is placed over the upwardly positioned threads of T-element (5), following which ball element (6) is threadedly engaged with T-element (5), and preferably locked thereto by the tightening of setscrew (20) located within ball member (6). The flared end (40) of strut (10) is then positioned against ring member (14), following which an annular clamp (12) is positioned around both ring member (14) and flared end (40) of strut (10), after which the clamp is tightened so that ring member (14) is drawn tight against flared end (40) of strut (10). In the practice of the process of the present invention, the second end of the strut is connected to the other object (i.e. the second pressure vessel), following which the first end of the strut is connected to the connecting means positioned on the first pressure vessel.

Claims: An attachment assembly (2) for fastening a pressure vessel to another object, the attachment assembly (2) comprising: A. a pressure vessel wall reinforcement section (41) adapted to be mounted on an outer casing of the pressure vessel, wherein the wall reinforcement section (41) comprises a plurality of layers (27) of fiber embedded in a resin, wherein the layers (27) of fiber are positioned across one another; B. a layer of shear ply (29) positioned over the reinforcement section (41), wherein the shear ply (29) is constructed from a resilient material, wherein an adhesive adheres the shear ply (29) over an outermost fiber-reinforced resin layer of the reinforcement section (41), wherein the shear ply (29) is resilient enough to prevent damage to the casing (9) of the pressure vessel during a period of use of the pressure vessel; C. a saddle (3) positioned over the shear ply (29), wherein the saddle (3) has at least two lugs (8) thereon, wherein the lugs (8) are attached to the saddle (3) with a means for attachment thereof; D. an overwrap (7) positioned over at least a portion of the saddle (3), wherein the overwrap (7) secures the saddle (3) against the shear ply (29); and E. a connecting means (5, 6, 12, 14) connecting a first end of a strut (10) to at least one of the lugs (4, 8), wherein a second end of the strut (10) is adapted to be connected to the other object with an attachment means therefor. An attachment assembly (2) as described in claim 1, wherein the resin (28) present in the reinforcement section (41) comprises at least one member selected from the group consisting of an epoxy resin, and a phenolic resin, wherein the fiber present in the reinforcement section (41) comprises at least one member selected from the group consisting of a graphite fiber, a fiberglass fiber, and an aramid fiber, wherein the resin is present in the reinforcement section (41) in an amount of from about 27 to 47 weight percent, based on the weight of the reinforcement section (41), and wherein the fiber is present in the reinforcement section (41) in an amount of from about 53 to 73 weight percent, based on the weight of the reinforcement section (41). An attachment assembly (2) as described in claim 1, wherein from about 8 to 20 layers (27) of fiber are present in the reinforcement section (41), wherein the layers (27) of fiber are positioned across one another at an angle of from about 45 to 90 degrees, and wherein the reinforcement section (41) was positioned around a circumference of the pressure vessel. An attachment assembly (2) as described in claim 1, wherein the shear ply (29) comprises at least one composition selected from the group consisting of a styrene-butadiene rubber, an acrylonitrile-butadiene rubber, and an ethylene-propylene-diene rubber, and wherein the shear ply (29) has a thickness of from about 0,508 mm (0.02 inch) to about 3,048 mm (0.12 inch). An attachment assembly (2) as described in claim 1, wherein the saddle (3) has a center lug (4) and a plurality of side lugs (8) thereon, and wherein the saddle (3), the lugs (4, 8), and the connecting members (5, 6, 12, 14) comprise at least one member selected from the group consisting of steel, aluminum, titanium, and a fiber reinforced cured resin, wherein the saddle (3) passes around only a portion of a circumference of the pressure vessel and wherein the saddle (3) has a thickness of from about 1,27 mm (0.05 inch) to about 12,7 mm (0.5 inch). An attachment assembly (2) as described in claim 1, wherein the assembly further comprises a supplemental layer of a shear ply (37), wherein the supplemental layer of shear ply (37) is positioned between the saddle (3) and the overwrap (7), and wherein the supplemental layer of shear ply (37) comprises a resilient material. An attachment assembly (2) as described in claim 1, wherein the overwrap (7) comprises a resin (31) having a fiber (32) embedded therein, wherein the resin (31) comprises at least one member selected from the group consisting of an epoxy and a phenolic, wherein the fiber (32) comprises at least one member selected from the group consisting of fiberglass, graphite and aramid, and wherein the overwrap (7) passes around a circumference of the pressure vessel. An attachment assembly (2) as described in claim 7, wherein the overwrap (7) comprises from 5 to 15 layers of fiber (32) embedded in the resin (31). An attachment assembly (2) as described in claim 5, wherein the connecting members (5, 6, 12, 14) serve as a pivotable joint. An attachment assembly (2) as in claim 9, wherein the pivotable joint comprises a ball and socket joint; wherein the saddle (3), the lugs (4, 8), and the connecting members (5, 6, 12, 14) comprise steel; and wherein a welded joint joins the lugs (4, 8) to the saddle (3). An attachment assembly (2) as in claim 9, wherein the two side lugs (8) are adapted to be connected to devices (11) for holding the pressure vessel in a desired position with respect to the other object. An attachment assembly (2) as in claim 1, wherein the reinforcement section (41) comprises an epoxy resin in an amount of about 37 weight percent, based on the weight of the reinforcement section (41), and wherein the reinforcement section (41) comprises a graphite fiber in an amount of about 63 weight percent, based on the weight of the reinforcement section (41), and wherein about 11 layers (27) of fiber are present in the reinforcement section (41), and wherein the reinforcement section (41) is adapted to be positioned around a circumference of the pressure vessel; and wherein the shear ply (29) comprises styrene-butadiene rubber and has a thickness of about 2,032 mm (0.08 inch); and wherein the saddle (3) comprises steel having a thickness of about 7,62 mm (0.3 inch), and wherein the saddle (3) is adapted to extend around only a portion of the circumference of the pressure vessel, and wherein the saddle (3) has a steel center lug (4) and two steel side lugs (8) unitary therewith; and wherein the attachment assembly (2) further comprises a supplemental layer of shear ply (37) positioned over the saddle (3), wherein the supplemental layer of shear ply (37) comprises styrene-butadiene rubber having a thickness of about 2,032 mm (0.08 inch); and wherein the overwrap (7) comprises an epoxy resin which is present in an amount of about 29 weight percent, based on the weight of the overwrap (7), and wherein the overwrap (7) comprises a fiberglass fiber present in an amount of about 71 weight percent, based on the weight of the overwrap (7), and wherein about 7 layers of fiber (32) are present in the overwrap (7), and wherein the overwrap (7) is adapted to be positioned around the circumference of the pressure vessel; and wherein the connecting means (5, 6, 12, 14) comprises a pivotable ball and socket joint which comprises a steel T-element (5), a steel ball element (6), a ring member (14), a flared strut end (40), and an annular clamp (12) having an exploding bolt thereon; and wherein the two side lugs (8) are adapted to be connected to devices (11) for holding the pressure vessel in a desired position. An arrangement comprising a pressure vessel and another object, wherein said pressure vessel is fastened to said object by the attachment assembly (2) according to one of the preceding claims. An arrangement as described in claim 13, wherein the pressure vessel comprises a first pressure vessel and the other object comprises a second pressure vessel. An arrangement as described in claim 14, wherein the first pressure vessel comprises a first rocket motor (1) comprising a solid propellant and the second pressure vessel comprises a second rocket motor comprising a liquid propellant. An arrangement as described in claim 14, wherein the second pressure vessel comprises a metallic shell and an attachment lug wherein said attachment lug comprises a lug having a concave portion thereon. Method of attaching a pressure vessel to another object comprising the steps of: A. Constructing a pressure vessel wall reinforcement section (41) on an outer casing (9) of the pressure vessel, wherein the wall reinforcement section (41) comprises a plurality of layers (27) of fiber embedded in a resin, wherein the layers (27) of fiber are positioned across one another; B. adhering a layer of shear ply (29) over an outermost layer of the reinforcement section (41), wherein the adhesive adheres the shear ply (29) over the outermost fiber-reinforced resin layer of the reinforcement section (41), wherein the shear ply (29) is resilient enough to prevent damage to the casing (9) of the pressure vessel during a period of use of the pressure vessel; C. positioning a saddle (3) over the shear ply (29); D. attaching at least two lugs (4, 8) onto the saddle (3); E. applying an overwrap (7) over at least a portion of the saddle (3) so that the saddle (3) is secured against the shear ply (29); F. attaching a connecting means (5, 6, 12, 14) to at least one of the lugs (4, 8); G. connecting a first end of a strut (10) to the connecting means (5, 6, 12, 14); and H. connecting a second end of the strut (10) to the other object.

Inventors: RATZ OTTO GREGORY, RYNDERS RICHARD EUGENE, RATZ, OTTO GREGORY, RYNDERS, RICHARD EUGENE
Applicants: HERCULES INC, HERCULES INCORPORATED
Application year: 1993
Main classification: B64G1
IPC codes: B64G1, B65D88, F42B15