Solid rocket motor
The optimized star-shaped propellant grain design in solid rocket motors enhances initial thrust without increasing weight by controlling the burning surface area and internal pressure, ensuring structural integrity.
Patent Information
- Application Number
- JP2024089829
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-06-03
- Publication Date
- 2025-12-15
AI Technical Summary
Conventional solid rocket motors fail to achieve the required initial thrust without increasing the weight by modifying the motor case thickness to accommodate higher internal pressures during combustion.
The design incorporates propellant grains with a star-shaped hollow section comprising central circular spaces and radially protruding rays, where the number and size of these rays are optimized to control the burning surface area and internal pressure, ensuring a large initial thrust without increasing the motor case thickness.
The design achieves a large initial thrust while maintaining the motor case's structural integrity and weight, by optimizing the burning surface area and internal pressure through a specific arrangement of rays in the propellant grains.
Smart Images
Figure 2025182354000001_ABST
Abstract
Description
[Technical Field]
[0001] The present invention relates to a solid rocket motor, and more particularly to a solid rocket motor in which internal combustion propellant grains are loaded inside a motor case. [Background technology]
[0002] A solid rocket motor has a motor case and a nozzle as its main components, and the motor case is filled with propellant grains, which are made by kneading solid fuel and oxidizer together with a binder.
[0003] There are various combustion methods for propellant grains, but the method in which combustion begins on the inner surface (the outer surface of the hollow part) of a propellant grain formed in a hollow cylindrical shape is called the internal combustion method. The hollow part of a propellant grain that uses this method can have a simple circular cross section, but some have a star-shaped cross section. By changing the cross-sectional shape of the hollow part, it is possible to control the change in the burning surface area over time during the combustion process, and therefore the change in the pressure of the combustion gas (and therefore the thrust of the solid rocket motor) over time, and to adapt these to the flight mission of the solid rocket.
[0004] Figure 1 is a schematic diagram of a conventional solid rocket motor loaded with cylindrical propellant grains partially hollowed with a star-shaped cross section. (A) is a schematic cross-sectional view of the motor case loaded with the propellant grains, and (B) is a schematic diagram showing the combustion process of the portion of the propellant grain that has the hollowed portion of the star-shaped cross section (the ignition time of the propellant grain (0 seconds), and after Xi, Xii, Xiii, Xiv, and Xv seconds).
[0005] In Figure 1(A), 1 is a motor case and 2 is a propellant grain. Although not shown, an igniter is attached to the front end (left end in the figure) of the motor case 1, and a nozzle is attached to the rear end (right end in the figure). Also, although not shown, insulation (a liner made of a heat insulating material) is arranged between the motor case 1 and the propellant grain 2.
[0006] The propellant grain 2 is formed in a hollow cylindrical shape, and the cross-sectional shape of the hollow part is circular in the front part 2F and the center part 2M (HC in the figure). F and H.C. M (See HS in the figure), and the rear 2R is star-shaped (See HS in the figure).
[0007] The star-shaped hollow space HS is composed of a central circular space HSc and a space protruding radially outward from the outer periphery of the circular space HSc, i.e., a beam of light HSb. A plurality of beams of light HSb (seven in the illustrated embodiment) are provided at equal intervals in the circumferential direction.
[0008] In the rear part 2R of the propellant grain 2, the curve Cb drawn in the upper half is a curve that connects the points of the outermost diameter part of the beam HSb in the axial direction, and the curve Cc drawn in the upper and lower halves is a curve that connects the points on the outer peripheral surface of the space HSc with a circular cross section in the axial direction.
[0009] When an igniter arranged at the front of the motor case 1 is activated, the propellant grains 2 start burning from their inner surfaces. That is, in the front part 2F and the central part 2M, a hollow part HC with a circular cross section is formed. F and H.C. M At the rear portion 2R, combustion begins on the outer peripheral surface of the circular cross-section space HSc in the star-shaped cross-section hollow portion HS, and the combustion progresses radially outward.
[0010] In the star-shaped hollow space HS of the rear section 2R, combustion begins on the outer circumferential surface of the beam of light HSb almost simultaneously with the initiation of combustion on the outer circumferential surface of the circular space HSc. As combustion progresses, the outer diameter of the circular space HSc gradually increases, and the diameter of the outermost portion of the beam of light HSb gradually increases (thus, its radial length remains constant), while its circumferential width gradually increases (see Figure 1(B)).
[0011] As the combustion progresses in this way, the total surface area of the outer surface of the hollow part HS of star-shaped cross section (the sum of the surface area of the outer surface of the space HSc of circular cross section and the total surface area of the outer surface of the beam HSb) does not change much until interference between adjacent beams HSb in the circumferential direction begins or the diameter of the outermost part of the beam HSb reaches the outer diameter of the propellant grain 2. F and H.C. M The total surface area of the outer periphery of the shaft gradually increases with the increase in its outer diameter. F and H.C. M The total combustion area, which includes the above, gradually increases, and the internal pressure of the motor case 1 also increases accordingly.
[0012] The change in the internal pressure of the motor case 1 over time during the combustion process described above is shown by the dashed line P CA In this graph, the dashed line P is shown only during the time period from time t1 to time t2 (note: time t=0 is the time when the propellant grains are ignited). CA can be recognized, but the dashed line P CA is the solid line P shown in the same figure. D Note that this is not visible because it coincides with the internal pressure change over time that satisfies the initial thrust requirement, which will be discussed later.
[0013] Furthermore, since the thrust of a solid rocket motor is proportional to the internal pressure of the motor case, the changes in both over time are displayed as essentially the same curve on a graph. Therefore, when explaining the changes in thrust over time below, we will use the graph showing the changes in the internal pressure of the motor case over time (for example, Figure 3(A)).
[0014] The internal pressure of the motor case 1 is indicated by the dashed line P in Figure 3(A). CA As shown in Fig. 1, after the ignition of the propellant grain (time t = 0), the total burning area increases as described above, and at time t m In the maximum value P max At this time t m is the time when the diameter of the outer periphery of the circular cross-section space HSc and the diameter of the outermost part of the light beam HSb both coincide with the inner diameter of the motor case 1 (strictly speaking, the inner diameter of the insulation, which is not shown in FIG. 1(A)), and all the light beams HSb disappear. max However, the propellant grain 2 is designed (specifically, the composition of the propellant, the shape of the hollow portion HS of the star-shaped cross section, etc.) so that the pressure is below the maximum allowable pressure in terms of the structural strength of the motor case 1. Summary of the Invention [Problem to be solved by the invention]
[0015] In a solid rocket flight mission, it is generally required to increase the thrust immediately after ignition of the propellant grains, i.e., the initial thrust.
[0016] The change over time in the internal pressure of the motor case 1 that satisfies the requirement for such initial thrust (hereinafter referred to as the required internal pressure) is shown by the solid line P D The solid line P indicates the change in required internal pressure over time. D is the time period from time t1 to time t2. i In the maximum value P i The temporary rise in pressure corresponding to this peak provides a large initial thrust that meets the requirements.
[0017] On the other hand, the internal pressure of the motor case 1 in a conventional solid rocket motor is shown by the dashed line P CA As shown in the figure, the solid line P D The internal pressure is below the required value indicated by , and does not meet the initial thrust requirement.
[0018] In such a case, one possible measure to satisfy the requirement for initial thrust is to increase the burning rate of the propellant by, for example, changing the composition. The change over time in the internal pressure of the motor case 1 of a solid rocket motor that adopts this measure is shown by the dashed line P CA ' is indicated.
[0019] Dashed line P CA The internal pressure indicated by ' is the solid line P D The internal pressure is equal to or greater than the required internal pressure shown in (2), and the initial thrust requirement is met.
[0020] However, the dashed line P CA The internal pressure indicated by ' increases at time t m The maximum value P is reached at the time when all the rays HSb disappear (as mentioned above). max ' is the maximum value P mentioned above. max (This is also shown in the graph of Figure 3(B)), and therefore exceeds the maximum allowable pressure in terms of the structural strength of the motor case 1. Therefore, in order to ensure the structural soundness of the motor case 1, modifications such as increasing the plate thickness of the motor case 1 would be necessary, but this would increase the weight of the solid rocket motor, which is not desirable.
[0021] The present invention has been made in consideration of the above problems, and aims to provide a solid rocket motor that can obtain a large initial thrust without increasing the weight that would accompany an increase in the thickness of the motor case. [Means for solving the problem]
[0022] In order to solve the above problems, a solid rocket motor of a first aspect of the present invention comprises a motor case loaded with propellant grains, the propellant grains being formed in a hollow cylindrical shape, a portion of which has a star-shaped hollow section, the star-shaped hollow section consisting of a central circular space and rays of light that protrude radially outward from the outer periphery of the circular space, the rays of light being composed of a plurality of first rays of the same size arranged at equal intervals in the circumferential direction, and a plurality of second rays of the same size arranged midway between two of the first rays of the same size that are adjacent in the circumferential direction, and the area of the outer surface of each of the second rays of the same size is smaller than the area of the outer surface of each of the first rays of the same size.
[0023] In the solid rocket motor of the second aspect of the present invention, the number of the first beams is a prime number, and the number of the second beams is also the prime number.
[0024] In the solid rocket motor of the third aspect of the present invention, the number of the first beams is a natural number having a divisor, and the number of the second beams is a divisor of the natural number other than 1.
[0025] In the solid rocket motor of the fourth aspect of the present invention, the sum of the areas of the outer surfaces of the plurality of second rays is determined so that the pressure inside the motor case corresponds to the initial thrust to be generated by the solid rocket motor.
[0026] In the solid rocket motor of the fifth aspect of the present invention, when the number of the first rays and the number of the second rays are the same, the area of the outer surface of each of the second rays is 1 / 10 to 1 / 30 of the area of the outer surface of each of the first rays. [Effects of the Invention]
[0027] According to the present invention, in a solid rocket motor, the excellent effect of being able to obtain a large initial thrust can be obtained without incurring an increase in weight due to an increase in the plate thickness of the motor case. [Brief explanation of the drawings]
[0028] [Figure 1] These are schematic diagrams of a conventional solid rocket motor loaded with cylindrical propellant grains having a hollow portion with a star-shaped cross section. (A) is a schematic cross-sectional view of the motor case loaded with the propellant grains, and (B) is a schematic diagram showing the combustion process of the portion of the propellant grain that has a hollow portion with a star-shaped cross section (from the ignition time of the propellant grain (0 seconds) to Xv seconds later). [Figure 2] 1A and 1B are schematic explanatory diagrams of a solid rocket motor according to an embodiment of the present invention, in which cylindrical propellant grains having a hollow portion with a star-shaped cross section are loaded. FIG. 1A is a schematic cross-sectional view of a motor case in which the propellant grains are loaded, and FIG. 1B is a schematic explanatory diagram showing the combustion process of the portion of the propellant grain having a hollow portion with a star-shaped cross section (from the ignition time of the propellant grain (0 seconds) to Xv seconds later). [Figure 3] FIG. 1 is a schematic diagram illustrating the combustion process of a portion of a propellant grain having a hollow portion in a star-shaped cross section, showing the change in the internal pressure of the motor case over time. DETAILED DESCRIPTION OF THE INVENTION
[0029] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0030] FIG. 2 is a schematic diagram of a solid rocket motor according to an embodiment of the present invention, in which cylindrical propellant grains having a hollow portion with a star-shaped cross section are loaded. (A) is a schematic cross-sectional view of the motor case in which the propellant grains are loaded, and (B) is a schematic diagram showing the combustion process of the portion of the propellant grain having the hollow portion with a star-shaped cross section (the ignition time of the propellant grain (0 seconds), and after Xi seconds, Xii seconds, Xiii seconds, Xiv seconds, and Xv seconds).
[0031] The solid rocket motor of the embodiment of the present invention shown in FIG. 2 differs from the conventional solid rocket motor shown in FIG. 1 only in the shape of the star-shaped cross-section hollow portion HS of the rear portion 2R of the propellant grain 2, and only this point will be described in detail below.
[0032] As shown in Figure 2(A), the star-shaped hollow section HS in the solid rocket motor of the embodiment of the present invention is composed of a central circular space HSc and spaces protruding radially outward from the outer periphery of the circular space HSc, i.e., rays HSb. The rays HSb are composed of multiple first rays HSb1 and multiple second rays HSb2 that are smaller than the first rays HSb1, and both are arranged at equal intervals in the circumferential direction. Note that each of the first rays HSb1 and each of the second rays HSb2 are formed to be the same size.
[0033] In the rear portion 2R of the propellant grain 2 in FIG. 2(A), the curve Cb1 drawn in the upper half is a curve connecting points on the outermost diameter portion of the first ray HSb1 in the axial direction, the curve Cb2 drawn in the lower half is a curve connecting points on the outermost diameter portion of the second ray HSb2 in the axial direction, and the curve Cc drawn in the upper and lower halves is a curve connecting points on the outer peripheral surface of the space HSc with a circular cross section in the axial direction.
[0034] In the illustrated embodiment, the light beams HSb are made up of seven first light beams HSb1 and seven second light beams HSb2 that are arranged midway between two adjacent first light beams HSb1 in the circumferential direction.
[0035] However, the numbers of the first beams of light HSb1 and the second beams of light HSb2 are not limited to those described above. When the number of first beams of light HSb1 is a prime number Np (e.g., 11, 13, etc.) as in the above-described embodiment, the number of second beams of light HSb2 is also Np. On the other hand, when the number of first beams of light HSb1 is a natural number Nc (e.g., 9, etc.) having a divisor, the number of second beams of light HSb2 may be Nc or a divisor of Nc other than 1 (e.g., 3 or 9 when Nc=9). However, even when the number of second beams of light HSb2 is a divisor of Nc other than 1, the second beams of light HSb2 are arranged at equal intervals in the circumferential direction and midway between two first beams of light HSb1 adjacent in the circumferential direction, as described above.
[0036] When an igniter disposed at the front of the motor case 1 is activated, the propellant grains 2 begin to burn from their inner surfaces.
[0037] In the star-shaped hollow space HS of the rear section 2R, combustion begins on the outer circumferential surfaces of the first and second beams HSb1 and HSb2 slightly after combustion begins on the outer circumferential surface of the circular space HSc. As combustion progresses, the outer diameter of the circular space HSc gradually increases, and the radial lengths of the first and second beams HSb1 and HSb2 gradually decrease. As a result, the second beam HSb2 disappears Xv seconds after the ignition of the propellant grains (see Figure 2(B)).
[0038] As the combustion progresses in this manner, the total surface area of the outer surface of the star-shaped cross-section hollow portion HS (the sum of the surface area of the outer surface of the circular cross-section space HSc and the total surface area of the outer surface of the light beam HSb (first light beam HSb1 and second light beam HSb2)), i.e., the total combustion area, gradually increases, and the internal pressure of the motor case 1 also increases accordingly.
[0039] The change in the internal pressure of the motor case 1 over time during the combustion process described above is shown by the solid line P IV Shown in.
[0040] The internal pressure of the motor case 1 in the solid rocket motor according to the embodiment of the present invention is shown by the solid line P IV As shown in Fig. 1, after the ignition of the propellant grain (time t = 0), the total burning area increases as described above, and at time t i At the maximum value P i After reaching t, it drops temporarily until time t2, then rises again, and reaches time t m In the maximum value P max reaches.
[0041] Here, time t2 corresponds to the time when the second beam HSb2 disappears in the combustion process shown in FIG. 2(B) (in the example shown in the figure, t=Xv seconds). In the solid rocket motor according to the embodiment of the present invention, since the second beam HSb2 is provided in addition to the first beam HSb1, in the time period until the second beam HSb2 disappears, if the second beam HSb2 is not provided (dotted line P in FIG. 3(A) CA ) the internal pressure of the motor case 1 becomes higher (corresponding to the peak in the time period from time t1 to time t2), and as a result, a large initial thrust that meets the requirements can be obtained.
[0042] Furthermore, after time t2, the internal pressure of the motor case 1 rises again, but m The maximum value P reached at max is kept below the maximum allowable pressure in terms of the structural strength of the motor case 1. Therefore, the structural integrity of the motor case 1 is guaranteed. In other words, the plate thickness of the motor case 1 can be kept the same as that of conventional solid rocket motors.
[0043] As described above, in the solid rocket motor according to the embodiment of the present invention, the hollow portion HS of the star-shaped cross section of the propellant grain 2 is composed of a plurality of first rays HSb1 and a plurality of second rays HSb2 that are smaller than the first rays HSb1. Therefore, compared to a case where the second rays HSb2 are not provided, the total burning area in the time period from the ignition of the propellant grain to the disappearance of the second rays HSb2 is larger, thereby obtaining a larger initial thrust, while also avoiding an increase in the maximum internal pressure of the motor case 1 that occurs during the combustion process. Therefore, the initial thrust required for the flight mission of the solid rocket can be obtained without incurring an increase in weight due to an increase in the plate thickness of the motor case 1 to accommodate the increase in internal pressure.
[0044] The shape and dimensions of the second beam HSb2 can be set appropriately so as to obtain the initial thrust required for the solid rocket flight mission.
[0045] For example, the size of the second light beam HSb2 can be 1 / 10 to 1 / 30, for example 1 / 20, of the size of the first light beam HSb1. Here, the sizes of the first light beam HSb1 and the second light beam HSb2 refer to the area of the outer circumferential surface of each light beam (one beam).
[0046] In simple terms, when the area of the hatched region between the curve Cb1 and the curve Cc in the upper half of the rear part 2R of the propellant grain 2 in FIG. 2(A) is Sb1 (corresponding to the size of the first ray HSb1), and the area of the hatched region between the curve Cb2 and the curve Cc in the lower half is Sb2 (corresponding to the size of the second ray HSb2), if the number of the first ray HSb1 and the number of the second ray HSb2 are the same, Sb1:Sb2 = 1 / 10 to 1 / 30 (e.g., 1 / 20) It can be said that: [Explanation of symbols]
[0047] 1 Motor case 2 propellant grains HS Star-shaped cross-section hollow section HSc Central circular space HSb rays of light HSb1 1st beam HSb2 2nd beam
Claims
1. A solid rocket motor in which propellant grains are loaded inside a motor case, The propellant grain is formed in a hollow cylindrical shape, and a part of the grain has a hollow portion with a star-shaped cross section, The hollow portion of the star-shaped cross section is composed of a central circular cross section space and a light beam which is a space protruding radially outward from the outer periphery of the circular cross section space, the beams of light are composed of a plurality of first beams of light of the same size arranged at equal intervals in the circumferential direction, and a plurality of second beams of light of the same size arranged midway between two of the first beams of light that are adjacent to each other in the circumferential direction, A solid rocket motor, characterized in that the area of the outer circumferential surface of each of the second beams is smaller than the area of the outer circumferential surface of each of the first beams.
2. 2. The solid rocket motor according to claim 1, wherein the number of the first beams is a prime number, and the number of the second beams is also the prime number.
3. 2. The solid rocket motor according to claim 1, wherein the number of the first beams is a natural number having a divisor, and the number of the second beams is a divisor of the natural number other than 1.
4. The sum of the areas of the outer peripheral surfaces of the plurality of second beams is determined so that the pressure inside the motor case corresponds to the initial thrust to be generated by the solid rocket motor. A solid rocket motor according to any one of claims 1 to 3.
5. 5. The solid rocket motor according to claim 4, wherein when the number of the first rays and the number of the second rays are the same, the area of the outer circumferential surface of each of the second rays is 1 / 10 to 1 / 30 of the area of the outer circumferential surface of each of the first rays.