WO2018167603A1

WO2018167603A1 - Method of manufacturing composite solid propellant grains

Info

Publication number: WO2018167603A1
Application number: PCT/IB2018/051418
Authority: WO
Inventors: R. Arun CHANDRU; Nikhil BALASUBRAMANIAN; Charlie OOMMEN; B. N. Raghunandan
Original assignee: Indian Institute Of Science
Priority date: 2017-03-15
Filing date: 2018-03-06
Publication date: 2018-09-20

Abstract

A method to manufacture composite solid propellant (CSP) grains for rocket propulsion is disclosed. The method uses additive manufacturing to eliminate problems with existing methods and provides for CSP grains with unlimited possibilities of complex grain geometries, precise and tailored pore densities and composition variations to enable varied thurst-time profiles and burn rates. Propellant slurry is prepared and extruded at room temperature layer by layer using a 3D printer to make 3D model of CSP grain directly from CAD data that is then cured further. Composition of the propellant slurry is elaborated upon as well as different grain geometries and porosities are investigated. Proposed method leads to significant improvement in burn rates and burn rate profiles over usually cast CSP grains and can be readily adapted for remote manufacturing with extremely high repeatability and accuracy. Proposed method can also be used for other energetic materials. A CSP grain using method disclosed is elaborated upon.

Description

METHOD OF MANUFACTURING COMPOSITE SOLID PROPELLANT GRAINS

FIELD OF DISCLOSURE

[0001] The present disclosure relates to solid propellants. In particular, it pertains to solid propellants for rocket propulsion and gas generating systems.

BACKGROUND OF THE DISCLOSURE

[0002] The background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[0003] A rocket is a missile, spacecraft, aircraft or other vehicle that obtains thrust from a rocket engine. Rocket engine exhaust is formed entirely from propellant carried within the rocket before use. Rocket engines work by action and reaction and push rockets forward simply by expelling their exhaust in the opposite direction at high speed, and can therefore work in the vacuum of space.

[0004] An energy source that has proven to be most useful for rocket propulsion is the combustion of chemical propellants. Based on physical state of propellants, chemical propulsion systems can be further classified into solid, liquid and hybrid propellant systems. Solid rocket propellants have the oldest vintage and were used in warfare by Chinese, Mongols, Indians and Persians as early as the 13^th century. They are still extensively used in strategic military vehicles and in launch vehicles for space applications and also find applications in various gas generation systems essential for driving turbine-alternator systems, propelling torpedo units, actuating jet based attitude control systems, thrust vectoring systems, airbag/cushion systems, micro- meteoroid shields, fire suppression systems, pilot ejection systems, deployable mechanisms, harpoons and so on. Solid propellant rockets can remain in storage for long periods, and then reliably launch on short notice.

[0005] Modern solid propellants fall into three general categories, namely, double base propellants where a homogeneous propellant grain usually having nitrocellulose is dissolved in nitroglycerine with some minor percentage of additives; composite propellants that comprise a heterogeneous propellant grain with oxidizer crystals and a powdered fuel, usually aluminum, held together in a matrix of a polymeric binder; and composite modified double base propellants wherein a combination of double base and composite propellant, usually comprised of a crystalline oxidizer and/or powdered solid energetic ingredient are held together in a matrix of nitrocellulose and nitroglycerin.

[0006] Composite solid propellants (CSP) for rockets have high densities, high specific impulses (specific impulse being the change in momentum per unit mass for rocket fuels, higher the specific impulse, the more push a rocket receives for the fuel that rushes out) and a wide range of burning rates. CSPs are essentially heterogeneous mixtures of oxidizer and fuel. Crystalline materials such as KNO₃, NH₄NO₃ and NH₄CIO₄ are used as oxidizers because of high oxygen content in their molecular structures. The oxidizers are embedded in a polymeric matrix and generate high concentrations of gaseous oxidizing materials when thermally decomposed. Hydrocarbon based polymers such as polybutadiene, which also act as the matrix to give mechanical integrity, generate high concentrations of gaseous fuel fragments when thermally decomposed. These gaseous fragments from the oxidizer and fuel components diffuse and mix together above burning surface of propellant to form diffusional flamelets and/or premixed flame. The combustion reaction generates large amount of hot gaseous products that can be ejected out through the nozzle of a rocket engine to generate thrust or to perform some other task.

[0007] Additionally, solid fuel particles such as aluminum and boron are sometimes embedded in the propellant matrix to increase specific impulse and act as propellant opacifier and combustion stabilizer. Various additives such as bonding agents, surfactants, cross- linkers and curing agents are also added in small amounts to tailor the propellant processing considerations, mechanical properties of the composite propellant grain and so on. Burning rate catalysts or modifiers such as Fe₂C>3, copper chromite, CuO, Ti0₂, ferrocene etc. are other crucial ingredients that are incorporated in small amounts to obtain a wide range of burning rates.

[0008] Typical mass proportions in high performance composite solid propellant compositions tend to be 70: 15: 15 : : Ammonium Perchlorate (AP): Hydroxy- Terminated PolyButadiende (HTPB): Aluminum (Al), whereas low smoke compositions generally have mass proportions of roughly 80: 18:2 :: AP:HTPB:A1.

[0009] Regardless of the composition, however, all propellants are processed into a similar basic geometric form, referred to as a propellant grain (interchangeably termed as grain). As a general practice, propellant grains are cylindrical in shape to fit neatly into a rocket motor in order to maximize volumetric efficiency. The grain may consist of a single cylindrical segment, or may contain many segments. A single or multiple central ports that extend the full length of the grain is introduced, in order to increase the propellant surface area initially exposed to combustion.

[00010] Selection of oxidizer, fuel, and other components is mainly dictated by energetics, kinetics, sensitivity and physical properties required of the solid propellant grain and its processing considerations. The composition of composite propellants can also vary significantly depending on the application, intended burning rate characteristics, specific impulse requirement, and constraints such as temperature of exhaust gases and exhaust plume signature.

[00011] Internal ballistics of solid propellant, particularly rate of gas generation is strongly dependent on burning rate of propellant and burning surface area. At a given set of operating conditions such as pressure and temperature, burning rate of propellant mainly depends on its chemical composition and geometry of its grain including that formed by the port. Solid propellant grains are conventionally manufactured as long cylinders with one or more internal ports that run the length of the grain so as to modulate evolution of burning surface area and rate of gas generation during radial burning process. Geometry of a solid propellant grain governs the burning surface area and its evolution over time as the combustion progresses, and has a profound influence on the shape of thrust-time profile of a rocket. Numerous port geometries of composite propellant grains have been studied and reported in literature, and are used regularly in practical applications to tailor the rate of gas generation and the thrust profile. FIG.1 illustrates some such port geometries and the thrust-time profiles that can be achieved using them.

[00012] Present manufacturing methods, however, do not allow for much variation in CSP grain geometries. Traditionally, composite propellant slurries are cast into cylindrical grains with one or more longitudinal ports within the grains to enable radial burning. A mandrel in a desired shape is placed in a casting mold and subsequently removed from cured propellant mechanically, leaving vacant ports that run along the length of the grain. Geometry of the port dictates evolution of burning surface over time and thus thrust-time profile of rocket motor. Shape of the port is decided by shape of mandrel used, and a complex mandrel is required to achieve a corresponding shape of the port. Various port geometries have been used in the past to achieve intended internal ballistics. As can be appreciated, it is difficult to achieve port geometries in which removal of mandrel post-curing is difficult. For example, it would be difficult to achieve helical or double-helical port geometry. Fully submerged ports or pores are not possible as the removal of mandrel would not be possible. Geometry of ports cannot be easily varied along the length of the grain. Overall, this mandrel-based process of introducing ports in CSP grains using traditional mandrels that are removed after the curing process limits the complexity of port shapes that can be realized and prohibits the introduction of internally closed ports or pores

[00013] Further, removal of mandrel from a cured composite solid propellant grain poses safety concerns due to the large 'breaking' force usually required to remove mandrel from cured propellant grain, and the sensitivity of the solid propellant to associated friction and shocks. Several aspects like surface finish, tolerances, coatings, release agents etc. are to be considered for facile and safe removal of mandrels.

[00014] Another difficulty in manufacture of propellant grains relates to introduction of internal pores in them. Internal pores or slots in propellant grains drastically increase burning rate and rate of gas generation. Porous propellants offer a mechanism to enter the forbidden regime of steady state burning rates that lie between deflagration and detonation speeds of a conventional propellant. This is because of convective heat transfer mechanism from the flame to the 'cold' propellant. Pores with micro- to macro- dimensions have been incorporated in the propellant grain and the subsequent enhancement of burning rate has been studied by several researchers in the past, for example by Jerold W. Emhoff and Lawrence W. Hunter ("Simulating Burning of Randomly Porous Propellant", 45th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit 2 - 5 August).

[00015] However, there are several limitations that prohibit adoption of porous propellants in practical systems. Size and shape of pores cannot be tailored precisely with the present methods, and further they cannot be precisely placed at predetermined locations within the solid propellant grain. The process of introducing porosity in propellant grain is often cumbersome, and involves additional and complex steps in propellant mixing, casting and post-curing. So much so that inspite of their possible advantages, they are deliberately avoided during the conventional propellant processing method, and carefully checked for during the post-curing inspections of propellant grains. Presence of undesired or undetected pores/cracks in the cured propellant grains can lead to explosions in solid rocket motors. Thus, though porous solid propellants offer much higher burning rates than non-poroussolidpropellants, these limitations and unpredictability prohibit their practical adoption.

[00016] Further, present manufacturing methods do not allow for precise compositional variations within a propellant grain. In conventional composite solid propellant grains, the composition is more or less uniform throughout the grain. However, variation of composition within the grain could give rise to thrust profile not possible via conventional propellant grains. For example, there can be a gradual increase in concentration of catalyst along the length of the grain (in case of end burning grains), variation in catalyst concentration radially (in case of radial burning grains), and so on, and could lead to generation of complex thrust profiles in an easy manner.

[00017] 3D printing, also known as additive manufacturing (AM) is a recently developed and evolving field. It refers to processes used to synthesize a three-dimensional object in which successive layers of material are formed under computer control to create an object. Objects can be of almost any shape or geometry and are produced from digital model data 3D model or another electronic data source such as an Additive Manufacturing File (AMF) file. Additive manufacturing significantly relaxes the geometric design constraints imposed by traditional manufacturing technologies. This ability to print complex parts without much regard to geometric complexity opens up new avenues for design flexibility and optimization. Layer by layer manufacturing can be performed by a variety of methods such as fused deposition, direct extrusion, stereo-lithography, selective laser sintering, binder jetting, selective electron beam melting, and so on. The choice of method primarily depends on type of material, resolution, structural integrity, costs etc. Materials ranging from plastics, metals, ceramics to living cells have been used for additive manufacturing.

[00018] Additive manufacturing or 3D printing may be well adapted to removal of above constraints and problems in CSP grain manufacturing. However, there are severe practical difficulties, mainly due to safety aspects of dealing with highly explosive materials. There has been one report ("Additive manufacturing of sugar based solid propellants by Laser Sintering technique") of an attempt to 3D print composite solid rocket propellant grains. However, the approach has not led to any successful 3D printed grains. The approach uses laser based sintering and powder bed methodology to arrive at 3D printed propellant grains. This approach is a wide deviation from conventional propellant processing methods, and involves additional steps and complexities. Use of focused lasers and localized high temperatures are not desirable for propellant processing. The powder bed based method of 3D printing requires raw material to be in powder form, and requires more material than required to make the grain geometry. The propellant composition used to arrive at proof-of-concept in the study is based on sugar and potassium nitrate based composition, and has low specific impulse and utility. The reported 3D printed propellant grains also do not seem to have good mechanical properties.

[00019] There are few reports of 3D printed or additively manufactured fuel grains for hybrid rocket motors (Jerome K. (Jerry) Fuller, Daniel A. Ehrlich, Paul C. Lu, Ryan P. Jansen and Justin D. Hoffman, "Advantages of Rapid Prototyping for Hybrid Rocket Motor Fuel Grain Fabrication", 47th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit, 31 July - 03 August 2011, San Diego, California). 3D printed fuel grains are also been explored for ramjet applications. Helical ports introduced within the fuel grains could enhance the regression rate by several times magnitude. However, these reports only describe fuel grains and not composite propellant grains. Fuel grains for hybrid rocket motors are much easier to manufacture via 3D printing due to the less severe safety issues, and the general thermoplastic nature of fuel polymers used. However, CSPs are a combination of fuel and oxidizer, do not allow severe manufacturing techniques involving high temperature, and involve thermosetting polymers.

[00020] In another prior art, (Additive manufacturing using pressurized slurry feed WO 2016064489 Al), solid energetics are 3D printed. However, their composition contains thermoplastic polymers like polyvinyl chloride and nitrocellulose. The slurry composition is subjected to heating at temperatures that is equal to or above the cure temperature of the slurry. This method cannot be translated or adopted for CSP grains.

[00021] Hence, there is a need in the art for a method to manufacture CSP grains that eliminates above elaborated difficulties, and that deviates minimally by the present manufacturing method of CSP grains.

[00022] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply. [00023] In some embodiments, the numbers expressing quantities or dimensions of items, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term "about." Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[00024] As used in the description herein and throughout the claims that follow, the meaning of "a," "an," and "the" includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of "in" includes "in" and "on" unless the context clearly dictates otherwise.

[00025] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. "such as") provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.

[00026] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.

OBJECTS OF THE INVENTION

[00027] It is an object of the present disclosure to provide a method for composite solid propellant (CSP) grain manufacturing that offers unparalleled design and manufacturing flexibility without constraints of tooling.

[00028] It is another object of the present disclosure to provide a method for CSP grain manufacturing that avoids mandrels, thereby eliminating their various disadvantages.

[00029] It is yet another object of the present disclosure to provide a method for CSP grain manufacturing using which grains with complex geometries can be manufactured, thereby providing intricate thrust control.

[00030] It is an object of the present disclosure to provide a method for CSP grain manufacturing that allows for manufacturing of CSP grains with precise and tailored pore densities that can lead to very significant increase in burn rate compared to non-porous conventional grains.

[00031] It is another object of the present disclosure to provide a method for CSP grain manufacturing that allows for incorporation of pores and ports in grainswith unprecedented ease, directly from CAD data.

[00032] It is an object of the present disclosure to provide a method for CSP grain manufacturing that enables composition variations in the same grain with its consequent advantages such as providing different ballistic modifiers to enable ballistic dampers or providing different propellant compositions in thesame grain.

[00033] It is another object of the present disclosure to provide a method for CSP grain manufacturing that can be successfully extended to other energetic materials.

[00034] It is yet another object of the present disclosure to provide a method for CSP grain manufacturing that can facilitate remote manufacturing of energetic material grains, thereby aiding the industry. SUMMARY OF THE INVENTION

[00035] The present disclosure mainly relates to propellants for rocket propulsion systems. In particular, the present disclosure relates to a novel method of composite solid propellant (CSP) grains manufacturing.

[00036] In an aspect, the proposed invention discloses a method of CSP grain manufacturing using additive manufacturing /3D printing, wherein Computer Aided Design (CAD) data can be coupled with a mechanical extruder to build a variety of CSP grain geometries at room temperature. The method can maintain grain's shape fidelity during and after the printing process. Details of the custom 3D printer assembled for printing propellant grains, optimization of the propellant 'ink' and the printing process are elaborated herein.

[00037] In another aspect, method disclosed enables complex composite solid propellant grain port geometries to be directly manufactured from digital data in an easy and reproducible manner and without of mandrels or other such tooling. Further, internal pores with pre-defined porosity can be introduced in propellant grains, leading to a significant increase in observed burning rates. Such 3D printed composite solid rocket propellant grains with customizable internal port geometries and controllable porosity can enable super burning rates and mission specific thrust profiles, and can redefine the scope and versatility of conventional composite solid propellants. Further, the methodology can be extended to other composite energetic materials such as gun propellants, thermites, pyrotechnics and explosives.

[00038] In yet another aspect, the manufactured composite solid propellant grain can include any or a combination of ports, pores, slots, other complex shapes and compositional variations, and can be repeatedly manufacturable with a high degree of accuracy.

[00039] In another aspect, during 3D printing of composite propellants, the shape fidelity has to be maintained post printing and pre curing. This tends to limit the size of un-cured propellant grains that can be printed. However, it is not necessary that the grains have to be unsupported. Support structures can be integrated with the CSP grains being printed so that the size of the printed grain can be made larger without slumping of model. These supporting structures can be sacrificial, temporary or permanent, Also, CSP grains can be 3D printed directly inside the rocket motor casing using extrusion based 3D printing method being elaborated herein.

[00040] In an aspect, proposed invention discloses a method for manufacturing composite solid propellant (CSP) grain using a 3D printer, said method including the steps of: preparing a propellant slurry having a major portion of an oxidizer and a minor portion of a fuel cum binder; loading the propellant slurry in an extrusion mechanism that is operatively coupled with the 3D printer; extruding, through nozzle of the extrusion mechanism , the propellant slurry layer-by- layer to make a 3D model of desired geometry of the CSP grain; and curing the 3D model.

[00041] In another aspect, any or both steps of preparing and extruding can be carried out at room temperature.

[00042] In yet another aspect, the oxidizer can be any of Ammonium Perchlorate (AP), Ammonium Nitrate (AN) and Potassium Nitrate.

[00043] In an aspect, the fuel cum binder can be any of Hydroxy-Terminated PolyButadiende (HTPB), carboxy terminated polybutadiene (CTPB), Polybutadiene acrylonitrile (PBAN) and Glycidylazide polymer (GAP).

[00044] In another aspect, the propellant slurry can include a curing agent that is ranging from 2-10% of the binder.

[00045] In yet another aspect, the curing agent can be isophorone di-isocyanate (IPDI).

[00046] In an aspect, the propellant slurry can include a plasticizer that is ranging from 2- 10% of the binder.

[00047] In another aspect, the plasticizer can be dioctyladipate (DOA).

[00048] In yet another aspect, the propellant slurry can include a catalyst ranging from

0.1-5% of the oxidizer.

[00049] In an aspect, the catalyst can be any of Fe₂0₃, CuO, copper chromite or ferrocene.

[00050] In an aspect, proposed invention discloses a composite solid propellant (CSP) grain manufactured through a 3D printer using a propellant slurry having a major portion of an oxidizer and a minor portion of a fuel cum binder, wherein the propellant slurry can be loaded in an extruder that is operatively coupled with the 3D printer, and can be extruded through nozzle of the extruder to make a 3D model of desired geometry of the CSP grain.

[00051] In another aspect, the oxidizer of the grain can be Ammonium Perchlorate (AP).

[00052] In yet another aspect, the fuel cum binder of the grain can be Hydroxy- Terminated PolyButadiende (HTPB). [00053] Various objects, features, aspects and advantages of the present disclosure will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like features.

BRIEF DESCRIPTION OF DRAWINGS

[00054] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure. The diagrams are for illustration only, which thus is not a limitation of the present disclosure, and wherein:

[00055] FIG. 1 illustrates various existing port cross-section geometries of different propellant grains and their corresponding thrust-time profiles.

[00056] FIG. 2A illustrates a simple schematic of an extrusion-based 3D printer used in an exemplary embodiment of the present disclosure, while FIG. 2B illustrates extrusion mechanism used in the printer.

[00057] FIG. 3 illustrates propellant slurry composition in accordance with an exemplary embodiment of the present disclosure.

[00058] FIG. 4 illustrates an additively manufactured composite solid propellant grain in accordance with an exemplary embodiment of the present disclosure.

[00059] FIG. 5 illustrates comparison of mechanical properties between a conventionally cast propellant grain and corresponding 3D printed propellant grain in accordance with an exemplary embodiment of the present disclosure.

[00060] FIG. 6 illustrates additive manufacturing of a cylindrical CSP grain with pores in accordance with an exemplary embodiment of the present disclosure.

[00061] FIG.7 illustrates a CSP grain with ports made using additive manufacturing method elaborated herein in accordance with an exemplary embodiment of the present disclosure.

[00062] FIG.8 illustrates a CSP grain with complex ports and pores made using additive manufacturing method elaborated herein in accordance with an exemplary embodiment of the present disclosure. [00063] FIG.9 illustrates numerous port cross-section geometries of different composite solid propellant grains possible using additive manufacturing method elaborated herein in accordance with an exemplary embodiment of the present disclosure. 'A' figures are CAD models, and 'B' figures are the actual 3D printed grains.

[00064] FIG. 10 illustrates additively manufactured composite solid propellant strands with grid like porous structure and with varying porosity (0% to 80% v/v) in accordance with an exemplary embodiment of the present disclosure.

[00065] FIG. 11 illustrates in a tabular form burn rate of 3D propellant grains with different porosities and at different pressures while FIG.12 puts same results in a graphical form in accordance with an exemplary embodiment of the present disclosure.

[00066] FIG. 13 illustrates burning rate profile achieved from grains with varying porosity along grain length manufactured using additive manufacturing method elaborated herein, in accordance with an exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

[00067] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.

[00068] If the specification states a component or feature "may", "can", "could", or "might" be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.

[00069] As used in the description herein and throughout the claims that follow, the meaning of "a," "an," and "the" includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of "in" includes "in" and "on" unless the context clearly dictates otherwise.

[00070] Exemplary embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. These exemplary embodiments are provided only for illustrative purposes and so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those of ordinary skill in the art. The invention disclosed may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Various modifications will be readily apparent to persons skilled in the art. The general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. Moreover, all statements herein reciting embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure). Also, the terminology and phraseology used is for the purpose of describing exemplary embodiments and should not be considered limiting. Thus, the present invention is to be accorded the widest scope encompassing numerous alternatives, modifications and equivalents consistent with the principles and features disclosed. For purpose of clarity, details relating to technical material that is known in the technical fields related to the invention have not been described in detail so as not to unnecessarily obscure the present invention.

[00071] Thus, for example, it will be appreciated by those of ordinary skill in the art that the diagrams, schematics, illustrations, and the like represent conceptual views or processes illustrating systems and methods embodying this invention. The functions of the various elements shown in the figures may be provided through the use of dedicated hardware as well as hardware capable of executing associated software. Their function may be carried out through the operation of program logic, through dedicated logic, through the interaction of program control and dedicated logic, or even manually, the particular technique being selectable by the entity implementing this invention. Those of ordinary skill in the art further understand that the exemplary hardware, software, processes, methods, and/or operating systems described herein are for illustrative purposes and, thus, are not intended to be limited to any particular named element.

[00072] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.

[00073] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., "such as") provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.

[00074] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.

[00075] The present disclosure mainly relates to propellants for rocket propulsion systems. In particular, the present disclosure relates to a novel method of composite solid propellant (CSP) grains manufacturing.

[00076] In an aspect, the proposed invention discloses a method of CSP grain manufacturing using additive manufacturing /3D printing, wherein Computer Aided Design (CAD) data can be coupled with a mechanical extruder to build a variety of CSP grain geometries at room temperature. The method can maintain grain's shape fidelity during and after the printing process. Details of the custom 3D printer assembled for printing propellant grains, optimization of the propellant 'ink' and the printing process are elaborated herein.

[00077] In another aspect, method disclosed enables complex composite solid propellant grain port geometries to be directly manufactured from digital data in an easy and reproducible manner and without of mandrels or other such tooling. Further, internal pores with pre-defined porosity can be introduced in propellant grains, leading to a significant increase in observed burning rates. Such 3D printed composite solid rocket propellant grains with customizable internal port geometries and controllable porosity can enable super burning rates and mission specific thrust profiles, and can redefine the scope and versatility of conventional composite solid propellants. Further, the methodology can be extended to other composite energetic materials such as gun propellants, thermites, pyrotechnics and explosives. [00078] In yet another aspect, the manufactured composite solid propellant grain can include any or a combination of ports, pores, slots, other complex shapes and compositional variations, and can be repeatedly manufacturable with a high degree of accuracy.

[00079] In another aspect, during 3D printing of composite propellants, the shape fidelity has to be maintained post printing and pre curing. This tends to limit the size of un-cured propellant grains that can be printed. However, it is not necessary that the grains have to be unsupported. Support structures can be integrated with the CSP grains being printed so that the size of the printed grain can be made larger without slumping of model. These supporting structures can be sacrificial, temporary or permanent, Also, CSP grains can be 3D printed directly inside the rocket motor casing using extrusion based 3D printing method being elaborated herein.

[00080] In an aspect, proposed invention discloses a method for manufacturing composite solid propellant (CSP) grain using a 3D printer, said method including the steps of: preparing a propellant slurry having a major portion of an oxidizer and a minor portion of a fuel cum binder; loading the propellant slurry in an extrusion mechanism that is operatively coupled with the 3D printer; extruding, through nozzle of the extrusion mechanism , the propellant slurry layer-by- layer to make a 3D model of desired geometry of the CSP grain; and curing the 3D model.

[00081] In another aspect, any or both steps of preparing and extruding can be carried out at room temperature.

[00082] In yet another aspect, the oxidizer can be any of Ammonium Perchlorate (AP), Ammonium Nitrate (AN) and Potassium Nitrate.

[00083] In an aspect, the fuel cum binder can be any of Hydroxy-Terminated PolyButadiende (HTPB), carboxy terminated polybutadiene (CTPB), Polybutadiene acrylonitrile (PBAN) and Glycidylazide polymer (GAP).

[00084] In another aspect, the propellant slurry can include a curing agent that is ranging from 2-10% of the binder.

[00085] In yet another aspect, the curing agent can be isophorone di-isocyanate (IPDI).

[00086] In an aspect, the propellant slurry can include a plasticizer that is ranging from 2- 10% of the binder.

[00087] In another aspect, the plasticizer can be dioctyladipate (DOA).

[00088] In yet another aspect, the propellant slurry can include a catalyst ranging from

0.1-5% of the oxidizer. [00089] In an aspect, the catalyst can be any of Fe₂03, CuO, copper chromite or ferrocene.

[00090] In an aspect, proposed invention discloses a composite solid propellant (CSP) grain manufactured through a 3D printer using a propellant slurry having a major portion of an oxidizer and a minor portion of a fuel cum binder, wherein the propellant slurry can be loaded in an extruder that is operatively coupled with the 3D printer, and can be extruded through nozzle of the extruder to make a 3D model of desired geometry of the CSP grain.

[00091] In another aspect, the oxidizer of the grain can be Ammonium Perchl orate (AP).

[00092] In yet another aspect, the fuel cum binder of the grain can be Hydroxy- Terminated PolyButadiende (HTPB).

[00093] Various objects, features, aspects and advantages of the present disclosure will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like features.

[00094] As elaborated above, additive manufacturing is a group of technologies that use computers to make 3 -dimensional shapes. This technology transforms 2-dimensional layers of raw material into a three dimensional finished product that is capable of structural nuances and complexity that might otherwise be impossible with traditional production techniques.

[00095] In an aspect, proposed method employs this layer by layer building process performed by simple extrusion to manufacture intricate grain designs with complex port geometries, without any additional machining or tooling steps and directly from CAD data.

[00096] In exemplary embodiments elaborated herein, several grains of oxidizer Ammonium Perchlorate (AP) -fuel cum binder Hydroxyl Terminated Polybutadiene (HTPB) composite solid propellant (CSP) with varying degrees of porosity and complex port structures can be printed, and a thorough ballistic analysis with strand burner and model rocket thruster can be performed for the printed propellant grains. High regression rates can be observed in case of highly porous CSP grain.

[00097] In an exemplary aspect, complete flexibility can be achieved in fabrication of solid propellant grains incorporating ports, pores, slots and other complex shapes with high degree of accuracy and repeatability. A high degree of control of propellant fabrication can be based on thrust profile where a single propellant grain can be fabricated with varying structural intricacy to create complex thrust profiles. In another aspect, high regression rates can be achieved in AP-HTPB CSP (Ammonium Perchlorate - Hydroxyl Terminated Polybutadiene (HTPB) composite solid propellant) formulation of the grains printed.

[00098] FIG. 1 (prior art) illustrates various port cross-section geometries of different propellant grains and their corresponding thrust-time profiles. As illustrated in various representations, only simple port geometries are possible using present techniques of using a mandrel to form the ports since shape of the port is decided by the shape of mandrel used, and complex mandrels cannot be used due to inherent problem of taking them out once the propeller slurry has been cured. Hence only limited thrust profiles, as illustrated, are presently achievable.

[00099] FIG. 2A illustrates a simple schematic of an extrusion- based 3D printer used in an exemplary embodiment of the present disclosure, while FIG. 2B illustrates extrusion mechanism used in the printer. In an aspect, proposed method can use extrusion based 3D printing technique to additively manufacture (interchangeably termed as print) composite propellant grains. Propellant slurry (made as elaborated further) can be extruded through nozzle 252 of syringe pump extruder 202 and deposited layer by layer in appropriate patterns to build 3D model 206.

[000100] In an aspect, extrusion mechanism can be that of a syringe pump extruder 202 where propellant slurry can be loaded onto a plastic syringe 204, and then extruded through nozzle 252 of syringe pump extruder 202 in a controllable manner using a stepper motor and a lead screw assembly.

[000101] In an exemplary embodiment, nozzle 252 can have a micropipette tip of internal diameter 0.5 mm so as to achieve printing resolution of similar scale. Extruder 202 can be mounted vertically on an x-y traverse (with tip pointing downwards). The x-y traverse can be made using stepper motors, belts and timing pulleys, and can have a positioning resolution of 0.05 mm, for instance.

[000102] In another exemplary embodiment, propellant slurry can be extruded and deposited on a glass platform 208 that can be positioned on z-axis and can be controlled by a dual stepper motor and a trapezoidal lead screw mechanism to have a resolution of 0.01 mm, for instance. Nozzle 252 can extrude the propellant slurry and appropriate cross-section pattern of same for each particular layer (as per code provided to the printer). Next, glass platform 208 can be lowered by one layer height using the dual stepper motor and trapezoidal lead screw mechanism, and the process can be repeated until 3D model of propellant grain (illustrated as 206in FIG.2A) is completed. One such layer can be shown as 254 (FIG. 2B).

[000103] In yet another exemplary embodiment, printer 200 can include one or more steppermotors(say 5) that can be controlled using an open source Arduino AT mega2560 microcontroller board, RAMPS 1.4 (Reprap Arduino Mega Pololu Shield) and appropriate firmware, and can be interfaced to a desktop computer via USB. Power supply can be provided to the printer 200 via a switched mode power supply (SMPS).

[000104] FIG. 3 illustrates propellant slurry composition in accordance with an exemplary embodiment of the present disclosure. In an exemplary implementation, composition of the propellant slurry (interchangeably termed as 'ink') extruded from nozzle 252 can include Ammonium Perchlorate (AP) as oxidizer, Ferric Oxide(Fe₂0₃) as catalyst, Hydroxyl Terminated Polybutadiene (HTPB) as fuel cum binder, dioctyladipate (DOA) as plasticizer, and isophorone di-isocyanate (IPDI) as curing agent. In an exemplary embodiment, Ammonium Perchlorate (AP, oxidiser) can be 78% w/w, HTPB (fuel cum binder) can be 18% w/w, IPDI (curing agent ) can be 2-10 % of the binder , DOA (plasticizer) can be 2-10% of the binder, Catalyst (Fe₂0₃ or CuO) can be 0.1-5 % of AP and Aluminum or Boron can be 0-25 % w/w. In yet another exemplary implementation, W/w ratios of Fe₂0₃: AP can be 1 :99, and DOA:IPDI:HTPB can be 10: 10:80. W/w ratio of [Fe₂0₃+AP]: [DOA+IPDI+HTPB] can be 76:24. It should be clearly understood that these are only exemplary values, and any other suitable combination of the oxidizer, catalyst, fuel/binder, plasticizer, and curing agent can be implementation to achieve intended impact, and all such ratios, ranges are well within the scope of the present disclosure. For instance, ratio of oxidizer to fuel cum binder can be 60-90:40-10. Similarly, percentage of curing agent and plasticizer in the binder can be ranging from 2% to 15% of the binder. In an aspect, although the propellant ink with this ratio of oxidizer: fuel is fuel-rich, it can be adopted so as to make the propellant slurry flow smoothly through nozzle 252 (which is of 0.5 mm diameter (or say between 0.2 to 20 mm, for instance) and hold its shape after deposition via extrusion. Lower weight % of fuel cum binder can be difficult to extrude through nozzle 252 while a higher weight % of fuel cum binder can result in slumping of 3D model as each successive layer is deposited.

[000105] In an exemplary implementation, AP of less than 125 microns can be sieved and then mixed with 2% w/w Fe₂0₃ catalyst in a V-blender to get a uniform mixture. Appropriate amounts of HTPB, DOA and IPDI can then be added to this mixture, and mixed in a planetary gear based wet mixer. This mixed slurry can be degassed in a vacuum dessicator for about 30 minutes, and then used as propellant slurry. The propellant slurry can then be loaded to syringe 204 fitted with nozzle 252 and extruded to form a 3D model as illustrated in FIG.2A and FIG. 2B.The whole operation of propellant slurry processing and printing may be performed within few hours after adding IPDI.

[000106] In another exemplary implementation, 3D models of propellant grains to be additively manufactured can be designed in AutoCAD and exported as .STL files. A slicing software (such as CURA) can be used to slice the 3D model into layers appropriately, and export the. STL files as machine- readable G-code files. The G-code files can then be exported to suitable software (such as PrinterFace) that can interface with the Arduino motherboard of the 3D printer. The G-code files can include information of tool path and places where material (propellant slurry) has to be extruded and deposited. In an aspect, parameters used in generating the G-code may be dependent on printer specifications and ink (propellant slurry in this case) properties, and can be optimized over time. In an exemplary embodiment, layer height of 0.5 mm and printing speed of20 mm/sec can be used, for instance.

[000107] In an aspect, after printing, additively manufactured composite solid propellant grains can be cured conventionally in a hot-air Oven. In an exemplary embodiment, such curing can be done at 65 Degrees Centigrade for 7 days, for instance. It is to be appreciated that these are only exemplary values, and any other suitable value that enables aspects of the present disclosure is completely within the scope of the present disclosure.

[000108] FIG. 4 illustrates an additively manufactured composite solid propellant grain, in accordance with an exemplary embodiment of the present disclosure. As illustrated, propellant grain 400 with diameter 25 mm, height 42 mm, layer height as 0.5 mm can be manufactured, using nozzle 252 with inner diameter as 0.5 mm. FIGs. 4(a) and 4(b) show side view and top view of CAD design respectively, while FIGs. 4(c) and 4(d) show corresponding photographs of the actual printed propellant grain. Dimensional difference between CAD design and printed model was found to be within 5%. In an aspect, grain can be of red color due to 1% w/w Fe₂03.

[000109] FIG. 5 illustrates comparison of mechanical properties between a conventionally cast propellant grain and corresponding 3D printed propellant grain in accordance with an exemplary embodiment of the present disclosure. In an exemplary embodiment, mechanical properties of additively manufactured composite propellant grains were evaluated and compared with that of traditionally casted propellant grains. 50 mm*40 mm* 10 mm propellant slabs were manufactured by both 3D printing and traditional vacuum casting, with the same composition, and cured thermally under same conditions. Dog-bone shaped specimens of appropriate dimensions were cut from these propellant slabs using a surgical blade and used for testing and their mechanical properties were compared.

[000110] Mechanical analyses were performed using a METRAVIB DMA+150 instrument. Similar elongation and tensile strength were observed between a conventionally cast CSP grain and a 3D printed CSP grain, as illustrated in FIG. 5.

[000111] FIG. 6 illustrates additive manufacturing of a cylindrical CSP grain with pores, in accordance with an exemplary embodiment of the present disclosure. FIG. 6a illustrates a close- up view of propellant slurry being extruded from a nozzle, FIG. 6b illustrates a close-up view of a composite propellant grain being built with 30% v/v porosity, and FIG. 6c illustrates close-up view of a sample grid structure.

[000112] FIG.7 illustrates a CSP grain with ports made using additive manufacturing method elaborated herein, in accordance with an exemplary embodiment of the present disclosure.

[000113] In an exemplary embodiment, an additively manufactured CSP grain with diameter 25mm, height 25 mm, layer height as0.5mm and using nozzle inner diameter as 0.85mm can be made. FIGs.7(a), 7(b) and 7(c) show side view, top view and perspective view of the CAD design respectively for such a propellant grain, while FIGs. 7(d), 7(e) and 7(f)show corresponding photographs of the actual printed propellant grain. Propellant slurry can be a non- catalyzed composition with no red Fe₂0₃ added. In an exemplary embodiment, for manufacturing a propellant grain with above dimensions using additive manufacturing method elaborated herein, dimensional difference between CAD design and printed model was found to be within 5%.

[000114] FIG.8 illustrates a CSP grain with complex ports and pores made using additive manufacturing method elaborated herein in accordance with an exemplary embodiment of the present disclosure. In an exemplary embodiment, a composite solid propellant grain with rectangular port geometry (45° twist along grain axis) and internal grid-like pore structure (30% v/v pore density) can be made using the additive manufacturing method elaborated herein. FIG. 8(a) shows top view, FIG. 8(b) perspective view, and FIG. 8(c) split-view of propellant grain manufactured.

[000115] FIG.9 illustrates numerous port cross-section geometries of different composite solid propellant grains possible using the additive manufacturing method elaborated herein, in accordance with an exemplary embodiment of the present disclosure.

[000116] As elaborated, method disclosed does not use a mandrel, and hence avoids all limitations associated with it. As can be appreciated, using the proposed technique, limitless port cross-section geometries are possible, a few of which are illustrated in FIG. 9, wherein FIG. 9a shows CAD designs of port cross-section geometries, and FIG. 9b shows corresponding 3D printed CSP grains.

[000117] FIG. 10 illustrates burning rate of additively manufactured composite solid propellant strands with grid like porous structure, and with varying porosity (0% to 80% v/v), in accordance with an exemplary embodiment of the present disclosure.

[000118] In an exemplary implementation, CSP grains with varying pore densities (0% to 60% v/v) can be additively manufactured as cuboidal slabs (50 mm* 40 mm* 10 mm). Pore densities can be varied sometimes within the slabs also. After thermal curing, the slabs can be cut into strands of40 mm length, 8-10 mm thickness and varying pore density as shown in FIG. 10 (strand with 60% v/v porosity is not shown). Side burning in these strands can be inhibited by covering the sides with a flexible film of paraffin (Parafilm) and coating with uncured HTPB. Usage of Parafilm prevents liquid uncured HTPB from permeating into the porous grains. The strands can be placed vertically and ignited using a heated nichrome wire system. Propagation of flame front can be monitored using a high-speed camera (for example Model: Photron Fastcam SA4) operating at 1000 frames per second with 1024 x 1024 pixel resolution. The propellant strands can be burnt in a strand burner with multiple iterations at isobaric conditions. Data acquisition from Pressure sensors and Fuse timing devices can be recorded as a measure of burn rate. Copper fuse can be administered over a fixed distance on the strand and breakage of said fuse can provide instantaneous time. Difference in time between the two fuse wire breakages can thus provide the burn rate. Similarly, time taken for maximum pressure rise can be recorded from pressure sensors and time difference can give the burn rate. Multiple samples with same pore density and distribution can be burnt to ensure reproducibility of data. [000119] It can be seen that burning rate increases significantly with porosity. An Atmospheric Burn Rate of 3.4 mm/second was determined at 0% v/v porosity while it increased to 219.6 mm/second at 80% v/v porosity.

[000120] FIG. 11 illustrates in a tabular form burn rate of a cast grain and 3D propellant grains at different pressures and different porosities, while FIG.12 puts same results in a graphical form in accordance with an exemplary embodiment of the present disclosure.

[000121] As can be seen at 1102, in a cast grain no porosity, can be introduced and therefore only a single burn rate is possible at a pressure. For example, as shown at 1104, a burn rate of 3.2 mm/second was achieved in a cast grain at 1 atmosphere pressure.

[000122] However, in 3D printed grains of the present invention, significant increases in burn rate are observed as porosity is increased. With an actual porosity of only about 0.1 % v/v, a burn rate of 3.4 mm/sec is observed, as shown at 1106 and the burn rate increases to 219.6 mm/sec with an actual porosity of 77.7 % v/v (as shown at 1108), pressure remaining same as 1 atmosphere.

[000123] FIG. 13 illustrates burning rate profile achieved from grains with varying porosity along grain length manufactured using the additive manufacturing method elaborated herein, in accordance with an exemplary embodiment of the present disclosure. As already elaborated, using additive manufacturing elaborated herein, porosity of a grain can be minutely controlled at any point of the grain. Such variation can affect the burn rate across the length of the grain strand. FIG. 13(a) illustrates such a strand at (i), wherein half of the strand has a porosity of 50 % v/v with other half having a porosity of 20 % v/v. Likewise, FIG. 13(a) illustrates another such a strand at (ii), wherein the strand is in three equal parts having porosity of 30% v/v, 60%v/v and 10% v/v respectively. The strands can be burnt from top to bottom, and their normalized length can be used in plot as illustrated at FIG. 13(b) that shows graphically burn rate profile of the strands across their lengths, wherein that of strand at (i) is illustrated at 1302 and that of strand at (ii) is illustrated at 1304. As can be seen, variation in porosity leads to different burn rates along the length of the strands.

[000124] In this fashion, as elaborated above, proposed method enables manufacturing of a CSP grain wherein by virtue of tremendous variations possible in grain geometries internal ballistics of a rocket can be tuned to desired parameters. [000125] While the method disclosed above has been elaborated using an example of composite solid propellants for rockets, it can readily be appreciated that it can be employed for other solid propellants and energetic materials such as gun propellants, thermites, pyrotechnics and explosives.

[000126] As used herein, and unless the context dictates otherwise, the term "coupled to" is intended to include both direct coupling (in which two elements that are coupled to each other or in contact each other) and indirect coupling (in which at least one additional element is located between the two elements). Therefore, the terms "coupled to" and "coupled with" are used synonymously. Within the context of this document terms "coupled to" and "coupled with" are also used euphemistically to mean "communicatively coupled with" over a network, where two or more devices are able to exchange data with each other over the network, possibly via one or more intermediary device.

[000127] Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms "comprises" and "comprising" should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refers to at least one of something selected from the group consisting of A, B, C ... .and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.

[000128] While some embodiments of the present disclosure have been illustrated and described, those are completely exemplary in nature. The disclosure is not limited to the embodiments as elaborated herein only and it would be apparent to those skilled in the art that numerous modifications besides those already described are possible without departing from the inventive concepts herein. All such modifications, changes, variations, substitutions, and equivalents are completely within the scope of the present disclosure. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims.

ADVANTAGES OF THE INVENTION

[000129] The present disclosure provides for a method for composite solid propellant (CSP) grain manufacturing that offers unparalleled design and manufacturing flexibility without the constraints of tooling, wherein the grain geometry is mainly limited by designer's imagination.

[000130] The present disclosure provides for a method for CSP grain manufacturing that avoids mandrels thereby eliminating its various disadvantages.

[000131] The present disclosure provides for a method for CSP grain manufacturing using which grains with complex geometries can be manufactured, thereby providing intricate thrust control.

[000132] The present disclosure provides for a method for CSP grain manufacturing that allows for manufacturing of CSP grains with precise and tailored pore densities that can lead to very significant increase in burn rate compared to non-porous conventional grains.

[000133] The present disclosure provides for a method for CSP grain manufacturing that allows for incorporation of pores and ports in grains with unprecedented ease, directly from CAD data.

[000134] The present disclosure provides for method for CSP grain manufacturing that enables composition variations in the same grain with its consequent advantages such as providing different ballistic modifiers to enable ballistic dampers or providing different propellant compositions in the same grain.

[000135] The present disclosure provides for a method for CSP grain manufacturing that can be successfully extended to other energetic materials.

[000136] The present disclosure provides for a method for CSP grain manufacturing that can facilitate remote manufacturing of energetic material grains, thereby aiding the industry.

Claims

We Claim:

1. A method for manufacturing composite solid propellant (CSP) grain using a 3D printer, said method comprising the steps of:

preparing a propellant slurry having a major portion of an oxidizer and a minor portion of a fuel cum binder;

loading the propellant slurry in an extrusion mechanism that is operatively coupled with the 3D printer;

extruding, through nozzle of the extrusion mechanism , the propellant slurry layer-by-layer to make a 3D model of desired geometry of the CSP grain; and

curing the 3D model.

2. The method of claim 1, wherein any or both steps of preparing and extruding are carried out at room temperature.

3. The method of claim 1, wherein the oxidizer is any of Ammonium Per chlorate (AP), Ammonium Nitrate (AN) and Potassium Nitrate.

4. The method of claim 1 , wherein the fuel cum binder is any of Hydroxy-Terminated PolyButadiende (HTPB), carboxy terminated polybutadiene (CTPB), Polybutadiene acrylonitrile (PBAN) and Glycidylazide polymer (GAP).

5. The method of claim 1, wherein the propellant slurry comprises a curing agent that is ranging from 2-10% of the binder.

6. The method of claim 5, wherein the curing agent is isophorone di-isocyanate (IPDI).

7. The method of claim 1, wherein the propellant slurry comprises a plasticizer that is ranging from 2-10% of the binder.

8. The method of claim 7, wherein the plasticizer is dioctyladipate (DOA).

9. The method of claim 1, wherein the propellant slurry comprises a catalyst ranging from 0.1-5% of the oxidizer.

10. The method of claim 9, wherein the catalyst is any of Fe₂03, CuO, copper chromite or ferrocene.

11. A composite solid propellant (CSP) grain manufactured through a 3D printer using a propellant slurry having a major portion of an oxidizer and a minor portion of a fuel cum binder, wherein the propellant slurry is loaded in anextruder that is operatively coupled with the 3D printer, and is extruded through nozzle of the extruder to make a 3D model of desired geometry of the CSP grain.

12. The grain of claim 11, wherein oxidizer is Ammonium Perchl orate (AP).

13. The grain of claim 11, wherein the fuel cum binder is Hydroxy-Terminated PolyButadiende (HTPB).