JP5303368B2 - Solid rocket motor propellant molding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a molding method for a solid rocket motor propellent capable of increasing a filling rate and eliminating or minimizing a relief boot. <P>SOLUTION: A thermoplastic propellent 3 softened in slurry is extruded from a casting tube 2 while a motor case 1 is rotated about the axis (a) thereof, and the casting tube 2 is relatively moved with respect to the motor case 1 to form annular thermoplastic propellent layers stepwise in the radial direction inside the motor case 1. In the formation of each stage, a next thermoplastic propellent is formed inside a solidified thermoplastic propellent layer. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a method for forming a solid rocket motor propellant.

  The solid rocket motor uses a solid propellant as a thrust source, and is configured to generate thrust by discharging high-temperature and high-pressure gas generated by the combustion reaction. Conventionally, as a method of forming an internal combustion type solid propellant having an inner hole (hollow part), there is a “straight type” in which the propellant is directly cast into a motor case.

  Conventionally, when a solid propellant is molded by a straight type, as shown in FIG. 1, a core 21 having a blade portion or the like corresponding to the shape of an inner hole to be formed is set in a motor case 20. The slurry-like thermosetting propellant 22 is supplied into the motor case 20 from a hopper 24 disposed above the motor case 20, and the propellant 22 is poured into the space formed by the motor case 20 and the core 21. Then, the temperature was returned to room temperature, and the core was pulled out from the cured propellant 22 to form a solid rocket motor propellant.

  In the solid rocket motor shown in FIG. 1, relief boots 23 are provided at both ends of the motor case 20 to be bonded to the peripheral portions of both ends of the propellant 22. The relief boot 23 moves together with the heat-shrinkable propellant 22 when the thermosetting propellant 22 is returned to room temperature, so as to relieve thermal stress caused by the heat shrinkage.

  In addition, as a prior art document regarding the molding method of a solid rocket motor propellant, there exist the following patent documents 1 and 2, for example.

Japanese Patent No. 2880932 Japanese Patent No. 3138987

  In the conventional solid rocket motor propellant molding method described above, heat shrinkage occurs in the process of returning the solid propellant to room temperature. In this heat shrinkage, a force that pulls the inner portion by the outer portion of the propellant acts, and therefore stress and strain are generated on the surface of the inner hole of the solid propellant and the end portion of the solid propellant. When such stress / strain exceeds the strength range of the solid propellant, a crack occurs on the surface of the inner hole of the solid propellant. In a solid propellant, the higher the propellant filling rate, the greater the thermal strain on the inner hole surface, so that cracks are more likely to occur, and cracks are more likely to occur in the inner hole shape where stress concentration tends to occur. For this reason, there is a problem that it is difficult to mold a solid propellant having an inner hole shape with a high propellant filling rate and a large stress concentration. In addition, there is a problem that the propellant filling rate is limited by the amount of relief boots.

  The present invention has been made in view of the above problems, and it is an object of the present invention to provide a method for molding a solid rocket motor propellant that can increase the filling rate and can eliminate or minimize the relief boot. To do.

  In order to solve the above-described problem, the solid rocket motor propellant molding method of the present invention casts a thermoplastic propellant that has been softened into a slurry while rotating the motor case around the case axis. Extruded from the tube, the casting tube was moved relative to the motor case, and a layer of an annular thermoplastic propellant was formed radially in steps inside the motor case, and solidified in the formation of each step A next stage thermoplastic propellant is formed inside the thermoplastic propellant layer.

  According to the present invention described above, the thermal stress / strain generated in the inner hole can be greatly reduced by casting the propellant in a plurality of stages. This is because, by dividing the propellant casting into multiple stages, the inner hole strain becomes the same as when the solid propellant filling rate is lowered or the solid propellant is molded in a small motor case. It is. Therefore, according to this invention, the filling rate of a propellant can be raised. Further, since the distortion is greatly reduced, the relief boot can be unnecessary or minimized.

  Further, in the above solid rocket motor propellant molding method, after the thermoplastic propellant cast into the motor case divided into a plurality of stages is solidified, the thermoplastic propellant has a melting point higher than that of the thermoplastic propellant. The core heated to the temperature is pressed into a predetermined inner hole shape.

  In this way, when the core heated to a temperature equal to or higher than the melting point of the thermoplastic propellant is pushed into the solidified propellant, the propellant melts and softens, so an inner hole having a shape corresponding to the shape of the core is formed. Is done. Therefore, an inner hole having a desired shape can be formed.

  Further, in the above-described solid rocket motor propellant molding method, the motor case includes a parallel portion having an inner diameter constant in the axial direction, and one end portion and the other end portion whose inner diameter decreases from both ends of the parallel portion. When casting a thermoplastic propellant at one end or the other end, the casting tube is moved relative to the motor case in the direction from the parallel portion toward the one end or the other end. , Stacking thermoplastic propellant.

  Thus, by stacking the thermoplastic propellant while moving the casting tube relative to the motor case in the direction from the parallel part toward the front end part or the rear end part, the front end part or the rear end part of the motor case is stacked. The propellant can be cast in layers.

  In the solid rocket motor propellant molding method, the casting tube is configured such that the angle of the outlet is adjustable, and the angle of the outlet is adjusted according to the position where the thermoplastic propellant is poured.

  By allowing the angle of the outlet portion of the casting tube to be adjusted in this way, the shape of the propellant on the front end side or the rear end side is narrow, or the opening of the motor case into which the casting tube is inserted is small. Even in this case, the propellant can be filled by adjusting the angle of the outlet portion according to the filling position.

  Further, in the above-described solid rocket motor propellant molding method, the casting tube is configured such that an extension tube can be attached to the tip, and the length is adjusted according to the position where the thermoplastic propellant is poured.

  By making the extension tube connectable to the outlet portion of the casting tube in this way, the shape of the propellant on the front end side or the rear end side is narrow, or the opening of the motor case for inserting the casting tube is small. Even in this case, the propellant can be filled by connecting the extension pipe to the outlet portion and adjusting the length according to the filling position.

  Further, in the above-described method for forming a solid rocket motor propellant, when forming the second and subsequent thermoplastic propellants, the surface layer portion of the solidified thermoplastic propellant is locally heated and melted by a heating means. Then, the slurry-like thermoplastic propellant is deposited on the melted portion.

  Since the surface layer portion of the propellant once solidified in this manner is locally melted and the slurry-like propellant is deposited on the melted portion, the bonding force between the layers can be increased.

  Further, in the above-described solid rocket motor propellant molding method, the slurry-like thermoplastic propellant extruded from the casting tube is cooled and solidified by the cooling means.

  As described above, the propellant pushed out from the casting tube is forcibly cooled and quickly solidified, so that the propellant does not flow down even if the rotation speed of the motor case is increased. Therefore, the processing speed can be increased by increasing the rotation speed of the motor case.

  Further, in the above-described method for forming a solid rocket motor propellant, in the formation of the thermoplastic propellant in the second and subsequent stages, the thermoplastic propellant formed in a part or each stage of the thermoplastic propellant formed in the previous stage is used. The propellant has a different fuel speed.

  When casting is performed by such a method, since the propellant filled in the motor case has different fuel speeds in the radial direction, it is possible to manufacture solid rocket motors having different thrusts on the way.

  According to the solid rocket motor propellant molding method of the present invention, the filling rate can be increased and the relief boot can be made unnecessary or minimized.

It is a figure explaining the shaping | molding method of the conventional solid rocket motor propellant. It is a 1st figure explaining 1st Embodiment of the shaping | molding method of the solid rocket motor propellant which concerns on this invention. It is a 2nd figure explaining 1st Embodiment of the shaping | molding method of the solid rocket motor propellant which concerns on this invention. It is a 3rd figure explaining 1st Embodiment of the shaping | molding method of the solid rocket motor propellant which concerns on this invention. It is a figure explaining the effect of the molding method of the solid rocket motor propellant concerning the present invention. It is a figure explaining the modification of 1st Embodiment of the shaping | molding method of the solid rocket motor propellant which concerns on this invention. It is a figure explaining 2nd Embodiment of the shaping | molding method of the solid rocket motor propellant which concerns on this invention. It is a figure which shows the other modification of the shaping | molding method of the solid rocket motor propellant which concerns on this invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the common part in each figure, and the overlapping description is abbreviate | omitted.

FIG. 2 is a diagram for explaining a first embodiment of a solid rocket motor propellant molding method according to the present invention.
In the solid rocket motor propellant molding method of the present invention, while the motor case 1 is rotated about the case axis a, the thermoplastic propellant 3 that has been softened and turned into a slurry is extruded from the casting tube 2. The casting tube 2 is moved relative to the motor case 1, and an annular thermoplastic propellant layer is formed stepwise in the radial direction inside the motor case 1. In the formation of each stage, the next stage thermoplastic propellant is formed inside the solidified thermoplastic propellant layer. This will be specifically described below.

  In FIG. 2, the motor case 1 is rotated around the axis a by a rotary drive device (not shown) with the axis a oriented in the horizontal direction. The motor case 1 includes a parallel portion 1a having an inner diameter constant in the axial direction, and one end 1b and the other end 1c whose inner diameter decreases from both ends of the parallel portion 1a. Both the one end 1b and the other end 1c of the illustrated motor case 1 have openings.

The casting tube 2 is configured so that the slurry-like thermoplastic propellant 3 flows inside and the slurry-like thermoplastic propellant 3 is pushed out from the outlet portion 2b provided at the tip.
The casting tube 2 is inserted into the motor case 1 through the opening of the one end 1b or the other end 1c of the motor case 1, and in the illustrated example, the casting tube 2 is inserted into the motor case through the one end 1b of the motor case 1. 1 is inserted.

  The casting tube 2 is configured to move in the axial direction of the motor case 1 by a driving device (not shown). Thereby, the casting tube 2 and the motor case 1 are relatively movable in the axial direction. Instead of the configuration of FIG. 2, the casting case 2 and the motor case 1 may be relatively moved in the axial direction by moving the motor case 1 in the axial direction.

  In the present embodiment, the casting tube 2 includes an introduction tube 2a, an outlet portion 2b, and a flexible joint 2c. The exit part 2b is connected by the flexible joint 2c so that angle adjustment is possible.

  In the conventional method for forming a propellant, a thermosetting propellant was used. However, in the present invention, it is solid at a use temperature near normal temperature (for example, 20 ° C.), but it is high (for example, 50 to 60 ° C. or higher). Use a thermoplastic propellant that melts when heated. From the viewpoint of manufacturability and safety of the solid rocket motor, the melting point of the thermoplastic propellant used in the present invention is preferably 100 ° C. or less.

Such thermoplastic propellants include, for example, those composed of a binder containing a thermoplastic material, ammonium perchlorate and aluminum. The composition ratio in this case may be, for example, a binder of 16 to 20% by weight, ammonium perchlorate of 66 to 80%, and aluminum of 0 to 18%.
The binder is made of, for example, butadiene elastomer, liquid butadiene, a plasticizer, and a fluidizing agent. In this case, the composition ratio in the binder may be, for example, 20 to 30 wt% butadiene elastomer, 0 to 20 wt% liquid butadiene, 50 to 75 wt% plasticizer, and 5 wt% fluidizing agent.
The thermoplastic propellant that can be used in the present invention is not limited to the above-described composition, and may be other thermoplastic propellants having appropriate flammability and mechanical properties as a propellant. .

In order to form a propellant by the method of the present invention, the procedure is as follows.
As shown in FIG. 2A, the motor case 1 is rotated about the axis a. The thermoplastic propellant is heated and softened to form a slurry, and the slurry-like thermoplastic propellant 3 is moved from the casting tube 2 with the outlet 2b facing downward toward the inner surface of the rotating motor case 1. Push down. At the same time, when the casting tube 2 is moved in the axial direction, the thermoplastic propellant adheres spirally to the inner surface of the motor case 1, and an annular thermoplastic propellant layer is formed. Here, the symbol “4A” in FIG. 2 indicates the first-stage thermoplastic propellant.

  The rotational speed of the motor case 1 and the extrusion amount of the thermoplastic propellant from the casting tube 2 are such that the thermoplastic propellant extruded from the casting tube 2 moves as the motor case 1 rotates and the motor case 1 Even when it comes to a position where there is no support from below, it is preferable to set so that the time for the thermoplastic propellant to solidify is secured to such an extent that it does not flow down due to its own weight.

  As shown in FIG. 2A, when a thermoplastic propellant is cast on the other end 1c, the thermoplastic propellant is moved while moving the casting tube 2 in the direction from the parallel portion 1a toward the other end 1c. Stack medicines. By carrying out like this, a thermoplastic resin can be reliably cast inside the other end part 1c in which an internal diameter reduces as it goes to the opening part side from the parallel part 1a.

  When the first stage of the thermoplastic propellant is cast into the other end 1c, the casting tube 2 is moved in the axial direction as shown in FIG. The thermoplastic propellant 3 is pushed downward toward the inner surface of the rotating motor case 1, and the first stage thermoplastic propellant is cast into the parallel portion 1a.

  When the first stage of the thermoplastic propellant is cast into the parallel part 1a, as shown in FIG. 2 (C), while moving the casting tube 2 in the direction from the parallel part 1a toward the one end 1b, Stack thermoplastic propellants. By carrying out like this, a thermoplastic resin can be reliably cast inside the one end part 1b in which an internal diameter reduces as it goes to the opening part side from the parallel part 1a side.

  After casting the first-stage thermoplastic propellant 4A, the temperature of the propellant cast in the motor case 1 is once lowered to near room temperature and solidified. Thereafter, as shown in FIG. 3, the second-stage thermoplastic propellant 4B is cast in the same manner as the first-stage casting. In the casting of the second-stage thermoplastic propellant 4B, when the slurry-like propellant 3 touches the solidified first-stage propellant 4A, the first-stage propellant 4A is heated by the slurry-like propellant 3. Then, only the touched part melts locally, and then the first stage and the second stage solidify, so that both are joined.

  Thereafter, in the same manner, the casting of the thermoplastic propellant is repeated step by step until a predetermined filling rate is reached. When the motor case 1 is large and the propellant at the other end 1c that has been cast first returns to room temperature and solidifies when the casting into the one end 1b is completed, no cooling time is provided. In the next stage, casting may be performed.

As shown in FIG. 3, the angle of the outlet 2b may be adjusted according to the filling position. In this way, when the shape of the propellant at one end 1b or the other end 1c is narrow and the outlet 2b of the casting tube 2 needs to be positioned in a narrow place, the outlet 2b of the casting tube 2 By making the angle of the shallower, it becomes possible to cast the propellant into that part.
Moreover, when the opening part of the motor case 1 for inserting the casting pipe 2 is small and the vertical movement range of the casting pipe 2 is limited, each of the parallel part 1a, the one end part 1b, and the other end part 1c. By changing the angle of the outlet 2b of the casting tube 2 according to the position, the propellant can be cast at each position.

  When the thermoplastic propellant is cast at a predetermined filling rate and the thermoplastic propellant 4 is solidified, the motor case 1 is held in an upright posture as shown in FIG. The core 6 heated to a temperature equal to or higher than the melting point of the medicine 4 is pushed in to form a predetermined inner hole shape. The core 6 has, for example, a cross shape or a star shape in cross section.

  In the configuration example of FIG. 4, the core 6 is formed of a metal (aluminum alloy or the like) having good thermal conductivity, and a flow path 6 a for flowing a heating fluid 7 is formed inside the core 6. As the heating fluid 7, for example, hot water heated to a temperature higher than the melting point of the thermoplastic propellant (for example, 70 ° C. to 100 ° C.) can be used. As a configuration for heating the core 6, a configuration in which a heating element that generates heat due to electric resistance or other physical phenomenon may be incorporated in the core 6.

  FIG. 5A is a sectional view of a motor having an outer diameter of about 1 m having a round hole inner hole with a propellant filling rate of 95%. FIG. 5B shows the relationship (calculated value) between the number of casting steps and the inner hole strain when the propellant having the shape as shown in FIG. 5A is cast into the motor case 1. In FIG. 5 (B), when the number of casting steps is 1 as in the conventional casting method, the inner hole strain is about 9.0%, but the casting is divided into a plurality of steps as in the present invention. When implemented, the inner hole strain is greatly reduced. For example, the inner hole strains when the number of casting steps is 2 and 3 are about 3.0% and 1.8%, respectively.

According to the method of the present invention described above, the thermal stress / strain generated in the inner hole can be greatly reduced by casting the propellant in a plurality of stages. This is because, by dividing the propellant casting into multiple stages, the inner hole strain becomes the same as when the solid propellant filling rate is lowered or the solid propellant is molded in a small motor case. It is.
Therefore, according to this invention, the filling rate of a propellant can be raised. Further, since the distortion is greatly reduced, the relief boot can be unnecessary or minimized.

  Further, by allowing the angle of the outlet 2b of the casting tube 2 to be adjusted, the motor case 1 in which the shape of the propellant at the one end 1b or the other end 1c is narrow or the casting tube 2 is inserted. Even in the case where the opening portion is small, the propellant can be filled by adjusting the angle of the outlet portion 2b according to the filling position.

  Further, by pushing the core 6 heated to a temperature equal to or higher than the melting point of the thermoplastic propellant into the solidified thermoplastic propellant 4, an inner hole having a shape corresponding to the shape of the core 6 is formed. Inner holes can be formed.

  In the above-described embodiment, the configuration in which the angle of the outlet portion 2b of the casting tube 2 is changeable is shown as a configuration that is connected by the flexible joint 2c. However, as shown in FIG. You may employ | adopt the structure which connects the extension pipe | tube 5 to the front-end | tip. Thus, by making the extension pipe 5 connectable to the tip of the casting pipe 2, the shape of the propellant at one end 1b or the other end 1c is narrow, or the motor case 1 into which the casting pipe 2 is inserted. Even if the opening portion of this is small, the propellant can be filled by connecting the extension tube 5 and adjusting the length according to the filling position. A plurality of types of lengths of the extension pipe 5 may be prepared.

  FIG. 7 is a diagram for explaining a second embodiment of the method for molding a solid rocket motor propellant according to the present invention. FIG. 7 is a cross-sectional view of the motor case 1, the propellants 4A and 4B, the casting tube 2 and the like in a plane perpendicular to the axis of the motor case 1, and the motor case 1 rotates clockwise in this figure. A state in which the second stage thermoplastic propellant 4B is being cast is shown.

  While rotating the motor case 1 around the case axis, the thermoplastic propellant 3 that has been softened and turned into a slurry is pushed out of the casting tube 2, and the casting tube 2 is moved relative to the motor case 1. An annular thermoplastic propellant layer is formed stepwise in the radial direction inside the motor case 1, and the next stage thermoplastic propellant is placed inside the solidified thermoplastic propellant layer in each step formation. The point which forms a medicine is the same as a 1st embodiment.

  In the second embodiment, when forming the second and subsequent layers of the thermoplastic propellant, the surface layer portion of the solidified thermoplastic propellant is locally heated and melted by the heating means 9, and the melted portion The slurry-like thermoplastic propellant 3 is deposited on the surface.

  In the configuration example of FIG. 7, the heating means 9 is a heating tube 9 </ b> A configured to flow hot water heated to a temperature higher than the melting point of the thermoplastic propellant (for example, 70 ° C. to 100 ° C.). The heating tube 9A is in contact with the solidified thermoplastic propellant at the tip, so that the slurry-like thermoplastic propellant 3 coming out of the casting tube 2 overlaps the thermoplastic propellant melted by the heat. It is provided at a position adjacent to the mold tube 2.

Thus, since the surface layer part of the propellant once solidified is locally melted and the slurry-like thermoplastic propellant 3 is deposited and adhered to the melted part, the bonding force between the layers can be increased.
The heating means 9 may use a heating element instead of the heating tube 9A described above.

  Moreover, in 2nd Embodiment, as shown in FIG. 7, the slurry-like thermoplastic propellant 3 extruded from the casting pipe | tube 2 is cooled and solidified by the cooling means 11. As shown in FIG. In FIG. 7, the cooling means 11 is a cooling pipe 11 </ b> A configured to flow water at a temperature suitable for solidifying the thermoplastic propellant (for example, around 20 ° C.). The cooling pipe 11A is provided at a position adjacent to the casting pipe 2 so as to cool the slurry-like thermoplastic propellant 3 coming out of the casting pipe 2 by contacting the slurry-like thermoplastic propellant at the tip. It has been.

  Thus, the slurry-like thermoplastic propellant 3 pushed out from the casting tube 2 is forcibly cooled and quickly solidified, so that the propellant does not flow down even if the rotation speed of the motor case 1 is increased. Therefore, the processing speed can be increased by increasing the rotation speed of the motor case 1.

In addition, in 2nd Embodiment, you may comprise so that the angle of the exit part or the front-end | tip of the casting pipe | tube 2 can be changed with a flexible joint or an extension pipe similarly to 1st Embodiment. Further, in the heating pipe 9A and the cooling pipe 11A, the angle and length of the tip may be adjusted by a flexible joint or an extension pipe depending on the filling position.
Other steps of the method of the second embodiment are the same as those of the first embodiment.

Further, as a modification of the first and second embodiments described above, in the formation of the thermoplastic propellant in the second and subsequent stages, the thermoplastic propellant in some or each stage is formed in the previous stage. The composition may be different from that of the thermoplastic propellant.
For example, if a thermoplastic propellant having a different fuel speed is cast at each stage, the propellant filled in the motor case 1 has a different fuel speed in the radial direction. Different solid rocket motors can be manufactured.
Moreover, it is also possible to improve the secrecy at the time of launch by setting the latter propellant composition to a composition with less smoke like aluminum. That is, the propellant having a low smoke composition may be burned at the time of launch to increase the secrecy of the launch point, and after launch, the propellant having a high smoke composition may be used to fly away.

  Although the embodiments and examples of the present invention have been described above, the embodiments of the present invention disclosed above are merely examples, and the scope of the present invention is the embodiments of these inventions. It is not limited to. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

DESCRIPTION OF SYMBOLS 1 Motor case 2 Casting pipe 2a Introducing pipe 2b Outlet part 2c Flexible joint 3 Slurry thermoplastic propellant 4 Solid propellant 4A First stage thermoplastic propellant 4B Second stage thermoplastic propellant 5 Extension pipe 6 Child 6a Flow path 7 Heating fluid 9 Heating means 9A Heating pipe 11 Cooling means 11A Cooling pipe

Claims (8)

While rotating the motor case around the case axis, the thermoplastic propellant that has been softened and turned into a slurry is pushed out of the casting tube, and the casting tube is moved relative to the motor case. On the inside, a layer of annular thermoplastic propellant is formed stepwise in the radial direction,
A method for forming a solid rocket motor propellant, characterized in that in the formation of each stage, the next stage thermoplastic propellant is formed inside the solidified thermoplastic propellant layer.   After the thermoplastic propellant cast into the motor case divided into a plurality of stages is solidified, a core heated to a temperature equal to or higher than the melting point of the thermoplastic propellant is pushed into the thermoplastic propellant to obtain a predetermined inner diameter. The method for forming a solid rocket motor propellant according to claim 1, wherein the hole shape is formed. The motor case includes a parallel portion having an inner diameter constant in the axial direction, and one end portion and the other end portion whose inner diameter decreases from both ends of the parallel portion,
When casting a thermoplastic propellant at one end or the other end, the thermoplastic propellant is moved relative to the motor case in a direction from the parallel portion toward the one end or the other end. The method for forming a solid rocket motor propellant according to claim 1 or 2, wherein the two are stacked.   4. The method for molding a solid rocket motor propellant according to claim 3, wherein the casting tube is configured such that an outlet portion thereof is adjustable in angle, and an angle of the outlet portion is adjusted in accordance with a position where the thermoplastic propellant is poured.   4. The method for molding a solid rocket motor propellant according to claim 3, wherein the casting pipe is configured such that an extension pipe can be attached to a tip, and the length is adjusted according to a position where the thermoplastic propellant is poured.   When forming the second and subsequent thermoplastic propellants, the surface layer of the solidified thermoplastic propellant is locally heated and melted by a heating means, and a slurry-like thermoplastic propellant is added to the melted portion. The method for forming a solid rocket motor propellant according to any one of claims 1 to 5, wherein the solid rocket motor propellant is attached in a stacked manner.   The method for molding a solid rocket motor propellant according to any one of claims 1 to 6, wherein the slurry-like thermoplastic propellant extruded from the casting tube is cooled and solidified by the cooling means. In the formation of the thermoplastic propellant in the second and subsequent stages, the thermoplastic propellant in some or each stage has a composition different from that of the thermoplastic propellant formed in the preceding stage. A method for forming a solid rocket motor propellant according to any one of claims 1 to 7.

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