Patent Application
20170036782
The invention was not made under nor is there any relationship of the invention to the performance of any work under any contract of the National Aeronautics and Space Administration.
Field of Invention
The present invention relates generally to space launch vehicles that use rocket engines to move payloads from the surface of the Earth to a desired orbit or trajectory. The present invention is also useful in the art of suborbital sounding rockets. More specifically, the present invention is a launch apparatus that utilizes a space frame truss structure to transfer propulsive loads to the payload and to simultaneously distribute vibration loads over the truss structure of the space frame of the launch vehicle and to further distribute these vibration loads to the space frame's truss structure's connecting nodes.
Another purpose of the present invention is to provide a space launch apparatus whose load bearing members form a triangular pyramid whose structural geometry distributes force applied to any part of its structure throughout its entire structure and all of its structural members and connecting nodes to allow the apparatus to withstand loads caused by resonance between the vibration spectra produced by operation of its rocket engines and the resonant frequencies of its structure.
The present invention also has the purpose of providing a space launch apparatus that has a plurality of modular space frame truss structures that can be prefabricated, moved to the launch site as a kit of parts and then the majority of the space launch apparatus can be assembled at the launch site from these parts.
Yet a further purpose of the present invention is to provide a launch apparatus whose structural integrity is maintained by a space frame comprised of truss structures whose elements include a plurality of compression and tension members including tension members that are flexible cables, whereby the said space frame is structurally robust, inexpensive to manufacture and easy to construct.
Background
All currently operating space launch apparatuses use rocket motors as reaction engines that create thrust by expelling mass. Chemical rockets create thrust by reacting propellants within a combustion chamber pressure vessel to produce gas at high pressure. This hot gas is accelerated by being compressed and passed through a venturi tube and then expanding through a bell or aerospike nozzle. Space launch apparatuses are usually multistage and have a diameter to height ratio of greater than 1 to 10. These multi-stage apparatuses sometimes fail due to vibration, accelerated loads, and other forces acting on their structure. They are susceptible to failure at the separation planes between stages of vehicle in a multistage vehicle. An example of such a space launch apparatus is the Saturn V rocket built by NASA for the Apollo program. The Saturn V has a diameter to height aspect ratio of approximately 1 to 10. It is the largest rocket ever flown being about 110 m long and about 10 m in diameter. All space launch vehicles share the Saturn V geometric form, i.e. a plurality of relatively skinny tall cylinders stacked on top of each other. A multistage rocket comprised of a plurality of stacked cylinders, must balance all of the rocket stage cylinders on top of each other during its operation. The interface planes between these rocket stages must withstand the loads acting on the structure without structural failure. Detailed and complex coupled loads analysis is required to verify that these interfaces between the rocket stages, and between the rocket stages and the payload are capable of withstanding the launch and separation loads. This analysis is a critical part of launch vehicle flight qualification. For large multistage launch vehicles carrying heavy payloads, these loads must be managed with great precision for the rocket to operate without failure. As such, current launch vehicles are delicate structures with little safety margin for mechanical failure.
In the 1960s and 70s aerospace companies proposed to design and construct much larger launch vehicles. As the inventor cannot at this early stage demonstrate an embodiment of the present invention by building and testing a working model, background information about these earlier vehicles is presented to facilitate an understanding of how to make and use an embodiment of the present invention to those skilled in the art.
Chrysler's single stage earth orbital reusable vehicle (SERV); a NASA 1971 phase A space shuttle study, proposed a rocket that was 96 feet wide and 101 feet tall to carry over 50 tons to low Earth orbit (LEO) using a single reusable rocket stage. SERV proposed to use this aspect ratio of diameter to height because it returned from orbit like a gigantic Apollo capsule. SERV was proposed to be powered by a 32 meganewton aerospike rocket motor. A ground test version of part of this rocket engine was designed, built and ground tested by the Rocketdyne Corporation. The entire SERV was to launch, fly to orbit, release its payload, reenter the atmosphere like an Apollo capsule, and then land vertically using turbojet engines. [Final report of NASA Contract NAS8-26341]
Aeroj et Corporation proposed the Sea Dragon; a 1963 design study for a fully reusable two-stage rocket that would launch 508 metric tons to low earth orbit. This rocket was 150 m long by 23 m in diameter. Aeroj et proposed to build the Sea Dragon in a naval shipyard and then tow the entire launch vehicle out into the ocean where it would be launched from a partially submerged position. Launching from the ocean was considered beneficial because it required fewer and less expensive infrastructure support systems compared to a land launched rocket. The Sea Dragon was proposed to be made mainly of 8 mm steel sheeting. Aeroj et technically validated all aspects of the Sea Dragon proposal, including conducting multiple trial launches of smaller rockets from the ocean. These ocean test launches were not conducted from ships. The rockets were submerged in the ocean and launched from the water. The Sea Dragon was designed by Robert Truax, who also designed the US Navy's Polaris missile to be fired from a submerged nuclear submarine. Aeroj et claimed that a sea launch could reduce the launch site costs by up to 95%. The Sea Dragon vehicle had two stages. The first stage was to be powered by a single 360 meganewton rocket motor burning hydrocarbon, RP-1 as fuel and liquid oxygen as oxidizer at 17 atmospheres pressure. This engine was pressure fed. For comparison, the space shuttle's liquid fueled main engine cluster produces 5.7 meganewtons of thrust. The most powerful liquid fueled engine ever built, the Russian RD-170, produces 7.9 meganewtons of thrust and the solid rocket boosters used by the American space shuttle, which are the largest solid fuel rockets yet built, produce 14 meganewtons of thrust each. [Final Report, NASA contract NAS8-2599 summary]
A space launch apparatus comprising a solid triangular space frame constructed of a plurality of connected truss members that are attached to each other at nodes and are also attached to at least one rocket motor and to at least one payload whereby the force produced by the operation of the rocket motor is transferred to the payload and aerodynamic and vibration loads are distributed through the truss members and their nodes.
An embodiment of the present invention is a space launch apparatus comprising a triangular space frame truss structure for transmitting acceleration loads to a payload while at the same time distributing vibration loads across the truss structure and its intersection nodes. The truss structure of an embodiment of the present invention may have elements in both compression and in tension. In one embodiment of the present invention, the load carrying structure of the apparatus is a triangular space frame comprising a plurality of equilateral triangular truss members structurally and functionally connected to the rocket motors, guidance equipment, stage separation equipment, stage interface structures, payload separation and interface structures and apparatus and aerodynamic fairings by fastening means capable of withstanding the vibration and acceleration loads produced during the operation of the rocket motors. The triangular structure of this embodiment of the present invention comprises truss members braced or cross-braced either in compression or in tension by additional truss members or cables. The truss members and other elements of an embodiment of the present invention may be connected by any means capable of carrying the mechanical loads generated by the invention's operation. These affixing means would include, by means of example only and not by way of limitation, bolting, welding, adhesive attachment, or construction by 3-D printers as a single structure. The apparatus taught by an embodiment of the present invention may use any form of rocket engine; for example multi-propellant liquid rocket engine, solid rocket engine, bell rocket engine, aerospike rocket engines or hybrid rocket engines. The structure of an embodiment of the present invention may be constructed of any material having strength and mechanical characteristics that can withstand its operating loads without failure; for example steel, titanium, composite materials including carbon-carbon composite and carbon nanotube reinforced materials. Throughout this specification, specific examples are given to show different embodiments of the invention. These specific embodiments are illustrative and are not intended to limit the scope of the invention.
The present invention is limited only by the appended claims and their equivalent. The inventor believes that an embodiment of the present invention can be constructed using material that can be worked outside of the aerospace industry; specifically in a commercial or naval shipyard. The space frame structures used by an embodiment of the present invention may be constructed in modular sections in a factory or shipyard and then shipped as a “kit of parts” to the launch site where the launch apparatus may be assembled and integrated together with all of its constituent systems, such as rocket engines, recovery systems, control and guidance apparatus, and any other subsystem required for its operation as a space launch apparatus. The inventor believes that this aspect of an embodiment of the present invention makes it suitable for the construction of extremely large launch vehicle apparatus, which would be very difficult or impossible to build without using the present invention.
An embodiment of the present invention may use liquid fueled multi-propellant rocket engines, solid fuel rocket engines or hybrid rocket engines.
An embodiment of the present invention may be operated from a fixed land launch site or it may be launched while it is partially submerged in a lake or ocean.
All or part of an embodiment of the present invention may be reused; either by recovering the stages or their structural elements, i.e. part or all of the apparatus; or by using the upper stage of the apparatus in orbit as an orbital habitat, orbital storage facility or as a part of an interplanetary spacecraft; it is the intent of the inventor to provide a reusable apparatus for space launch operations, all parts of which remain functional when used multiple times or for multiple purposes.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
Within the space frame triangle defined by an embodiment of the present invention are spherical rocket motors 116, 118 and 120. These rocket motors are closely packed, tangent to one another, and tangent to the interior of triangular space frame 101. Spherical propellant component tanks 122, 124 and 126 are disposed tangent to rocket motors 118, 120 and 116, respectively and are also tangent to the interior truss elements of the space frame 101. The said rocket motors and the said propellant component tanks are shown as spheres. An embodiment of the present invention may use any solid, liquid, or hybrid rocket motor that can be contained in the interior volume of the space frame 101 of the present invention. The spherical tanks shown in
For convenience of illustration, the first stage of the embodiment of the present invention shown in
In
The truss structures of an embodiment of the present invention may be made of steel, aluminum, carbon-carbon composition, titanium, or any combination of materials that are capable of withstanding the acceleration and vibrational loads produced by the combined action of the rocket motors and the structure of an embodiment of the present invention during its operation as a space launch apparatus. It is generally desirable to use the most cost-effective and lowest weight material capable of performing the function of the truss structure. The truss members of the space frame of an embodiment of the present invention may be cylinders, or they may be triangular, square or of other geometry. Triangular truss members and space frames have been shown in this embodiment of the present invention to illustrate the invention and not to limit scope, which should be limited only by the appended claims and their legal equivalents. Likewise, the rocket engines and attachment means between the truss structures and the rocket engines are considered to be within the alternatives that may be selected by a person skilled in the art to make best use of an embodiment of the present invention as an apparatus and a method to accomplish its intended purpose as a space launch apparatus.
In
In
Within payload carrier 302, a payload 307 is affixed to the payload carrier by a holding fixture 309. Insert A of
All of the structural elements of the truss structure of the space frames in accordance with an embodiment may be modular. By that the inventor means that the launch vehicles space frame structure can be shipped to the launch site as individual structural elements and then assembled by connecting the nodes of the truss structures of the space frames and bracing them in tension using tensioning members 313, which may be flexible cables made of braided steel using materials such as carbon-carbon composites. The embodiment of the present invention illustrated in this specification makes extensive use of equilateral triangles as truss structures and space frames because the equilateral triangle is the best geometric form to distribute the forces acting on the apparatus of the present invention; including aerodynamic forces, vibrational forces and rocket acceleration forces across all of the nodes of the truss structure and the space frames of an embodiment of the present invention during launch to low earth orbit. The use of tensioning means between the truss structure elements further increases the strength and distributes the forces acting on the structure of the present invention.
There are many types of rocket motors. Among these types, chemical rocket motors are commonly used in launch vehicles. Chemical rocket motors are reaction engines wherein a chemical reaction liberates energy and generates a hot gas. Examples of chemical rocket propellants are shown in Table 1 below. Different combinations of chemical rocket propellants produce different values of specific impulse and density impulse. These terms are well known to those skilled in the art of chemical rocket engines. A useful summary of information about rocket propulsion may be found in the eighth edition of the survey work “Rocket Propulsion Elements” written by George P Sutton and Oscar Bablarz and published by John Wiley & Sons, Inc. in 2010. Within this reference, table 13-1 “characteristics of some operational solid propellants” should be especially noted and it is incorporated into this specification by reference.
The rocket engine taught by the co-pending patent application comprises a casing which functions as a pressure vessel, plurality of solid phase propulsion components that are nonhomogeneous in their composition layered radially from the center axis of the engine, and a rocket nozzle in fluid communication with the interior of said pressure vessel. This novel rocket motor burns one composition of fuel at the beginning of its separation and another composition of fuel later in its operation. By varying the composition of the fuel layers radially the thrust force and burning time of the engine may be varied during the engine's operation. This is desirable because over 90% of the mass of the engine is its fuel components; which are rapidly consumed during operation. If the thrust level of the engine is not changed during its operation, the acceleration imparted by the engine to the launch vehicle will increase to an unacceptable level. Currently, solid rocket engines are formed with the central burning cavity being a star shape to increase the initial burning surface area of the propellants. As the propellant is burned radially from the center axis of the engine, the surface area available for burning decreases. In the case of the space shuttle solid rocket booster, which is the most powerful solid rocket booster ever built, the propellant has an 11 point star shape preparation in the forward motor segment and a double truncated cone preparation in each of the upper segments and after closure. This configuration provides high thrust of ignition and reduces the thrust by approximately a third by 50 seconds after liftoff to avoid over stressing the vehicle during its flight through the regime of maximum dynamic pressure.
The rocket motor disclosed herein initially burns a first propellant, such as ammonium perchlorate composite propellant (APCP), which is the fuel used by the space shuttle's solid rocket boosters, and which may be suspended in a gel, for the first part of its operation and then transitions to burning a second propellant, for example gelled kerosene with ammonium perchlorate oxidizer suspended and dispersed in the gel, during a second portion of the rocket motor's operation. APCP develops a specific impulse of 242 seconds at sea level or 268 seconds in a vacuum. Its main fuel is aluminum. Aluminum is used because it has a specific energy density of about 31.0 MJ per kilogram, a high-volume metric energy density and thus it is difficult to inadvertently ignite. The rocket motor taught by the co-pending application also can vary the mixture ratio between the fuel components by burning a plurality of propellant compositions that are disposed within the rocket motor pressure vessel so they burn sequentially.
The rocket motor can, by varying the mixture ratio of the fuel components, provide propellant layers that have a deficit of one fuel component; usually, but not necessarily, the oxidizer fuel component. Without sufficient oxidizer to react with all the fuel, the propellant produces less energy. Additional oxidizer to make up the deficit can be directly injected into the engine as in a hybrid rocket motor. The amount of this additional oxidizer can be controlled to vary the rocket motor's operating characteristic, for example the thrust of the rocket motor. The hybrid rocket motor used by Spaceship-1 used one fuel component in a solid phase, butyl rubber within the pressure vessel casing of the engine and introduced the second fuel component, nitrous oxide the oxidizer, as a liquid. Such a hybrid rocket motor can be throttled and even turned off and restarted, but since all of the second fuel component must be injected, it is difficult to scale to large engines. This rocket motor can be operated either as a solid rocket motor or as a hybrid rocket motor. The rocket motor disclosed herein in accordance with an embodiment of the present invention may be operated as a solid rocket motor, i.e. with all of both fuel components for all of the fuel layers within the pressure vessel casing of the motor in the correct chemical ratio to cause complete combustion of the propellant. In an alternate embodiment, the rocket motor disclosed in this patent application may be operated as a hybrid motor with only a portion of one of the fuel components present in the gelled layers. If in this example the deficit fuel component is oxidizer, then that deficit is corrected by adding a fuel component, which may be, but does not have to be, the same fuel component as is present in the casing, into the engine from an external source. For example, the first layer of fuel in the engine burned could be APCP exactly as it is composed for use in the space shuttle solid rocket booster. The second layer could be a gelled hydrocarbon such as mineral oil, gasoline, kerosene or the like gelled with styrene gelling agent. This gel can contain up to 75% weight percent of solids; such as an oxidizer comprising of finely dispersed ammonium perchlorate within the stiff gel. The second injected oxidizer could be concentrated hydrogen peroxide, liquid oxygen, nitrous oxide or liquid fluorine, although liquid fluorine would be technically difficult to handle safely. If the propellant components have the optimal mixture ratio within the rocket motor casing, then only a small amount of additional oxidizer would have to be injected into the operating rocket engine in order to change the mixture ratio, which would change the engine's thrust. If, however, one of the oxidizer components is in stoichiometric deficit in one or more of the propellant layers, a larger amount of external oxidizer could be introduced to both correct the mixture ratio and to control thrust that the engine produces. This type of rocket motor is defined as a “partially hybrid” rocket motor. This manner of “partially hybrid” rocket motor operation is defined, for the purpose of this patent specification, as a “partially hybrid” method of operation. The fuel in this type of rocket motor is non-homogeneous and may also be non-stoichiometric.
The partially hybrid non-homogeneous propellant rocket motor taught herein results in a rocket motor whose thrust can be varied over a very wide range by the selection of fuel components layered within the motor casing and this thrust can further be varied controllably and precisely by controlling the amount of deficit fuel component injected into the engine. If more than one rocket motor is used in a vehicle, then changing the thrust of each engine may be used to control the trajectory of the rocket without moving the rocket motors, other than the movement of the control valve controlling the amount of propellant, for example oxidizer, injected into the engine pressure vessel. This method of control may be used in combination with gimbaling the motors to control their thrust vector and may also be used in combination with a reaction control system comprising a plurality of smaller rocket motors attached to the vehicle structure proximate it vertexes to provide a steering impulse, if such is required by a specific embodiment of the present invention to provide the invention with positive control during its operation.
In
In
The rocket motor in
Additionally, each of the layers of propellant of differing compositions contains only a portion of one of the fuel components. The component that is in deficit in the propellant composition may be controllably supplied from an external tank 513 through propellant line 511 and control valve 509. One advantage of this embodiment is that a nonstoichiometric mixture of fuel components is less dangerous to mix and to transport because it does not as easily ignite or explode. A conventional solid rocket engine contains all of the fuel components within its casing pressure vessel. This mixture of all rocket propellant components can be explosive; dangerous to transport; and difficult to safely mix and cast into the rocket motor pressure vessel. A conventional hybrid rocket engine contains all of but one fuel component in the pressure vessel of the rocket motor and introduces the entire second fuel component from an external source. One example is the use of butyl rubber as a cast fuel and nitrous oxide as oxidizer.
In the rocket engine shown in
For the purpose of an embodiment of the present invention the benefit of this type of multi-propellant composition rocket motor is that the gross thrust of the motor's may be controlled by the annular composition of the propellant components in a plurality of layers; and the fine thrust of the rocket motor's may be controlled by modulating the amount of deficit fuel component introduced into the pressure vessel from an external source. The first benefit allows the ascent profile of the space launch apparatus in accordance with an embodiment of the present invention to be controlled so as to control the rate of acceleration of the launch vehicle during each phase of the launch. This allows the launch vehicle to move relatively slowly through the thick lower atmosphere and then to accelerate to orbit after jettisoning its first stage, second stage and payload carrier fairings. The second benefit, i.e. fine thrust control, allows the three engines to slightly vary their thrust to provide steering to the rocket without moving parts or a separate heavy reaction control system. Alternatively, if only a single rocket motor is used by the present invention, a plurality of reaction control system rocket motors 920 located sufficiently proximate to the corners of the geometric structure of the launch vehicle will allow the RCS motors 920 to operate through the lever arm between the reaction control system motor and the center of mass; this will produce torque around the invention's center of mass, and may be used to control the direction of flight of an embodiment. The inventor believes that the fuel components as described above that are inside the pressure vessel of the rocket motor herein disclosed are inherently safer than solid rocket motor fuel taught by the prior art, because the motor disclosed herein has one fuel component in deficit. Thus the rocket motors may safely be filled with fuel at the launch site. By using a hydrocarbon gel, comprising a hydrocarbon such as kerosene and a gelling agent such as a diblock or triblock styrene, either all or a substantial portion of the second fuel component can be contained within the hydrocarbon gel. As was mentioned above, the composition of the fuel components can be varied to change the thrust and burning time of the engine. Since a great many hydrocarbons and other chemical fuels having different chemical and burning characteristics, and are capable of being made into a gel that can contain a portion of the oxidizer for the rocket motor, the inventor believes that the disclosed rocket motor will work synergistically with embodiments of the present invention. A hydrocarbon and oxidizer fueled rocket motor has a higher specific impulse than most conventional solid fuel motors. This is determined by the energy released by the combustion of the specific chemicals used as fuel components. If the fuel component is gelled kerosene and the oxidizer component is hydrogen peroxide, then the specific impulse of the fuel is roughly the same as a liquid kerosene liquid oxygen liquid fueled rocket motor. If the rocket motor fuel is gelled, as is taught by the present disclosure, the mechanical characteristics of the gel, including its stiffness, may be designed to selectively absorb the vibration spectra produced by the rocket motor's operation.
The rocket motor pressure vessels may be made of steel, filament wound carbon-carbon composition or any other material capable of safely withstanding the required pressure loads.
In operation, a control signal is sent from control unit 523 through actuating line 521 to a pyrotechnic igniter, which may be a NASA standard solid rocket igniter, in the igniter/sensor chain 519. At the same time, additional deficit fuel component is injected through valve 509 into the interior space 507 within the pressure vessel 503. The rocket motor ignites in the conventional way and produces high-pressure hot gas that is expelled through a nozzle 515, which is in fluid communication with the interior of the engine space 507. Nozzle 515 is preferably an ablatively cooled carbon fiber composite nozzle constructed so that it erodes as the rocket engine operates.
As rocket motor 501 operates and hot gas exits the rocket nozzle the rocket motor imparts force to the space frame of the present invention. Specific numerical examples equivalent to some historical and proposed conventional launch vehicles will be given below. As the rocket motor 501 burns fuel it consumes successively the various radial layers of differing combination propellant. The burning of the different propellants controls the thrust and burn time profile of the motor to impart a desired impulse to the space launch apparatus taught by the present invention. During the operation of rocket motor 501, the control valve 509 may modulate the amount of the propellant component introduced from tank 513 through line 511 and valve 509 into the central space of the operating rocket motor. Injection of this fuel component will change the mixture ratio of the fuel components which will vary the thrust produced by this rocket motor. The change of thrust in the three motors shown in the embodiment of the present invention in the specification will allow present invention to be steered in any direction. If there is some problem, the supply of fuel component through valve 509 can be stopped and the thrust of the engine will be reduced either to zero or to a low value.
10%
Table 1 is a data table that shows several parameters related to the distribution of mass between the major elements of actual and proposed space launch vehicles and a space launch apparatus constructed according to the teachings of the present disclosure that have similar capabilities to launch payloads into space as the comparable space launch vehicle. Table 1 shows inter alia: the gross lift off weight (GLOW) and the percentage of the GLOW that comprises the structural mass of the vehicle, the fuel mass of the vehicle and the vehicle's payload capacity. Actual values of these parameters are shown for the launch vehicles: the two-stage Ukrainian Zenit and the American Saturn V. Table 1 also shows the calculated and proposed values for the Chrysler SERV, which was a proposed as single stage to orbit vehicle; and the Aeroj et Sea Dragon, which was a proposed as large two-stage launch vehicle. Table 1 also shows these values for comparable space launch apparatuses constructed according to the teachings of present invention which have similar capabilities as the Chrysler SERV and the Aeroj et Sea Dragon. Because the inventor has not yet built and tested the space launch apparatus taught by the present invention, these parametric comparisons between characteristics of operational and proposed launch vehicles are useful to establish the technical credibility of the present invention.
An embodiment of the present invention has more aerodynamic drag during the early phase of the central orbit than the Zenit launch vehicle, the Saturn V launch vehicle, the proposed SERV or the proposed Sea Dragon because it presents a larger surface area to the atmosphere as it accelerates. In the embodiment shown in the specification, the embodiment uses a propellant that is a sequentially burning a combination of APCP, which is the same propellant used by the space shuttle solid rocket booster, and gelled kerosene with a non-stoichiometric inclusion within the gel of ammonium perchlorate oxidizer. Additional oxidizer, which may be liquid oxygen, nitrous oxide, or hydrogen peroxide is introduced into the rocket engine combustion chamber from an external source. The oxidizer examples given are for illustration only and should not be considered limiting to the present invention. The ammonium perchlorate composite propellant has a density of 1.7 to 1.8 metric tons per cubic meter. It produces a specific impulse of 277 seconds at sea level and has a density impulse of 476 kg seconds per liter. The kerosene fuel component has a density of about 0.8 metric tons per cubic meter and the density of the ammonium perchlorate oxidizer that is gelled with this kerosene is 1.95 metric tons meter. The amount of these propellant components can be adjusted so that the total density of the propellant used by an embodiment of the present invention is about 1.5 tons per cubic meter. Trade studies can be done on subscale rocket motors to determine the optimum propellant composition for each embodiment of the present invention. For the purpose of this embodiment, a fuel density average of 1.5 metric tons per cubic meter, a specific impulse of 277 and an average density impulse of 300 is assumed. It should be noted that the ammonium perchlorate composition propellant burned at the beginning of the flight has a high density impulse and produces higher thrust while the kerosene/ammonium perchlorate propellant that is burned toward the end of the flight will have a specific impulse roughly equal to the second stage performance of the Zenit launch vehicle. These assumption as to aerodynamic drag, the propellant used, propellant density and specific impulse will be assumed and applied towards comparing the operational equivalent of a space launch vehicle constructed according to the teachings of the present invention to the Zenit two stage launch vehicle, the Saturn V launch vehicle and the proposed SERV and Sea Dragon launch vehicles.
As shown in Table 1 the two stage Ukrainian Zenit launch vehicle has a total mass at launch of 448.8 metric tons. It will carry 13.5 metric tons to 200 km low Earth orbit at 51.6° inclination if it is launched from Baikonur cosmodrome in Kazakhstan. At liftoff, the Zenit launch vehicle has a mass distribution of 78% for the first stage, 18.1% for the second stage and 3% for the payload. The structure of the launch vehicle apparatus, including both first and the second stage, is 8% of the total mass and the propellant in the first and second stages is 88.4% of the total mass. The propellants are liquid oxygen and kerosene at a mixture ratio of 2.29 oxidizer to fuel, which produces a specific impulse of 309 seconds at sea level and a density impulse of 294 kg seconds per liter at sea level. These physical characteristics of the Zenit launch vehicle and its propellant defined the operational characteristics of the Zenit launch vehicle during its ascent from the ground to lower Earth orbit.
In order to provide a conservative comparison between the Zenit two-stage launch vehicle and the equivalent embodiment of the present invention, the propellant mass of the first and second stage engines of this embodiment of the present invention has been assumed to use approximately twice the propellant mass of the two-stage Zenit in order to compensate for the greater aerodynamic drag of the present invention. It will be necessary to run a launch trajectory analysis study to specifically define the optimal fuel load for an embodiment.
At the conservative assumed propellant mass for the comparative equivalent embodiment of the present invention to the Zenit an embodiment of the present invention will have a GLOW of 848.4 metric ton and a total propellant weight of 750 metric tons for both stages. The propellant mass for the first stage of an embodiment of the present invention at the conservative assumption will be 600 metric tons. Where an embodiment of the present invention uses the spherical rocket motor described in
The Table 1 also shows mass distribution values for the Saturn five launch vehicle, the proposed Chrysler SERV single stage launch vehicle and the proposed Sea Dragon two-stage launch vehicle; together with mass distribution values for embodiments of the present invention that are operationally similar to these launch vehicles.
The American Saturn V launch vehicle uses its first two stages to put a 120 ton third stage into low earth orbit. It has a gross liftoff weight of between 2800 to 3000 metric tons and its first stage engines produce 3469.7 ton-of-force; which is 34.6 meganewtons of thrust. Thus the engines produce a thrust at takeoff that is 124% of the Saturn V's mass weight.
A two-stage launch vehicle apparatus constructed according to the teachings of the present disclosure that is operationally equivalent to the Saturn V launch vehicle will have the characteristics listed in Table 1 (Column 7). The assumptions relating to type of propellant, density and specific impulse are applied towards the comparative equivalent embodiment of the present invention. In order to provide a conservative comparison between the Saturn V launch vehicle and the equivalent embodiment of the present invention, the propellant mass of the first and second stage engines of this embodiment of the present invention has been assumed to use approximately twice the propellant mass of the Saturn V launch vehicle in order to compensate for the greater aerodynamic drag of the present invention.
At the conservative assumed propellant mass for the comparative equivalent embodiment of the present invention to the Saturn V an embodiment will have a GLOW of 5359 metric tons and a total fuel weight of 5000 metric tons for both stages. The propellant mass for the first stage of an embodiment of the present invention at the conservative assumption will be 4200 metric tons. Where an embodiment of the present invention uses the spherical rocket motor described in
The Chrysler SERV example in Table 1 has a lower payload as a percentage of its launch vehicle mass because it is a single stage to orbit launch vehicle and thus does not gain the benefit of dropping off the mass of the first stage as it flies to orbit. Its gross mass at lift off is 2040.8 metric tons and its payload is 52.8 metric tons. The vehicle has a diameter of 18.3 meters and its height is 20.3 meters and its single aero spike engine produces 31.9 meganewtons of thrust. Extensive launch trajectory analyses and aerodynamic studies were done by Aeroj et Corporation on the SERV launch vehicle. Despite the fact that its aspect ratio produces higher aerodynamic drag than any conventional launch vehicle, Aeroj et certified that it can fly to orbit as stated in their proposal to NASA. The SERV, as proposed to NASA, used liquid oxygen and liquid hydrogen as propellants, which produces a specific impulse at sea level of 367 seconds and have a density impulse that is very low at 124 kg seconds per liter at sea level. An embodiment of the present invention has a similar aspect ratio to the SERV but uses a propellant mix that has a lower specific impulse. An embodiment of the present invention also drops off its first stage on the way to orbit in order to improve its payload fraction. The purpose of discussing the SERV is to show that a space launch apparatus having the aspect ratio of an embodiment of the present invention is technically credible, despite its higher aerodynamic drag.
The SERV is a single stage launch vehicle, in comparing a launch vehicle constructed according to an embodiment of the present invention with similar capabilities as the SERV and comparable to the SERV, the total propellant mass weight of the SERV was applied equally to the 4 spherical rocket motors that will be used in the present invention. The SERV holds a total propellant weight of 1761.3 metric tons at take off. The two-stage launch vehicle apparatus constructed according to the teachings of the present disclosure which applies the assumptions with regard to propellant, specific impulse and propellant density stated earlier that is comparable to the SERV launch vehicle will have the characteristics listed in Table 1 (Column 10). In order to provide a conservative comparison between the SERV launch vehicle and the equivalent embodiment of the present invention, the total propellant mass of this embodiment of the present invention has been assumed to use approximately twice the total propellant mass of the SERV launch vehicle in order to compensate for the greater aerodynamic drag. It will be necessary to run a launch trajectory analysis study to specifically define the optimal fuel load for the present invention.
At the conservative assumed propellant mass for the comparative equivalent embodiment of the present invention to the SERV, an embodiment of the present invention will have a GLOW of 4079 metric tons and a total fuel weight of 3520 metric tons for both stages. The propellant mass for the first stage of an embodiment of the present invention at the conservative assumption will be 2640 metric tons. Where an embodiment of the present invention uses the spherical rocket motors described in
The Aeroj et Sea Dragon example in Table 1 has a pay load of 508.5 tons which is approximately 4 times the pay load of the Saturn V. The Sea Dragon was proposed to be launched from the sea and had a Gross loft off weight of 18130 metric ton and was proposed to be 150 meters height with a diameter of 23 meters. The first stage had a single pressure fed, thrust chamber of 36 million kgf thrust, burning LOX/Kerosene. The purpose of discussing the Sea Dragon is to show how an embodiment of the present invention would be adopted to a higher payload.
The two-stage launch vehicle apparatus constructed according to the teachings of the present disclosure that applied the assumptions in Table 1 and which is operationally equivalent to the Aeroj et Sea Dragon launch vehicle will have the characteristics listed in Table 1 (Column 13). The assumptions relating to type of propellant, density and specific impulse are applied towards the comparative equivalent embodiment of the present invention. In order to provide a conservative comparison between the Sea Dragon launch vehicle and the equivalent embodiment of the present invention, an embodiment of the present invention is assumed to use approximately twice the propellant mass of the Sea Dragon launch vehicle in order to compensate for the greater aerodynamic drag. It will be necessary to run a launch trajectory analysis study to specifically define the optimal fuel load for embodiments of the present invention.
At the conservative assumed propellant mass for the comparative equivalent embodiment of the present invention to the Saturn V the embodiment will have a gross lift off weight of 36136 metric tons and a total fuel weight of 31500 metric tons for both stages. The propellant mass for the first stage of an embodiment of the present invention at the conservative assumption will be 22800 metric tons. Where an embodiment of the present invention uses the spherical rocket motor described in
Table 2 is a data base of the specific impulse of the first stage at sea level and the first stage thrust of the Zenit two stage rocket, the Saturn V and the proposed Chrysler SERVE single stage launch vehicle and the proposed Sea Dragon launch vehicle and the comparative launch vehicle constructed according to the teachings of the present disclosure. Table 2 also shows the specific impulse of the fuel used in each of the launch vehicles that have been launched and proposed.
Table 2 is a data table listing the specific impulse of the first stage at sea level and the first stage thrust of the Zenit two stage rocket, the Saturn V and the proposed Chrysler SERVE single stage launch vehicle and the proposed Sea Dragon launch vehicle and the comparative launch vehicle constructed according to the teachings of the present disclosure. Table 2 also shows the specific impulse of the fuel used in each of the launch vehicles that have been launched and proposed.
At takeoff, the Zenit two-stage launch vehicle has a gross lift off weight of 444.8 metric tons and a first stage thrust of 769.8 metric tons of force. This is 7.55 Meganewtons. Thus the takeoff thrust is 173% of the takeoff mass. The equivalent embodiment of the present invention has a total propellant weight of 750 metric tons. Given the assumption stated above, in order to produce a takeoff thrust of 173% of the takeoff mass of this embodiment of the present invention, the first stage engines must produce 1467.7 metric tons of force; which is 14.4 Meganewtons. Since the fuel load of a comparable embodiment is about twice the fuel load of the Zenit, it is reasonable it that would require about twice the thrust at takeoff to achieve the same performance. It should be noted that the American space shuttle solid rocket booster produces 14 Meganewtons of thrust and has been operated hundreds of times successfully. Having twice as much fuel in the rocket motors will allow them to burn longer and provide more total impulse. The space shuttle solid rocket booster separates from the space shuttle at an altitude of 45 km. They are then recovered for reuse. The first stage components of embodiments of the present invention can also be recovered for reuse, as will be described below.
At takeoff, the Saturn V launch vehicle has a gross lift off weight of 2900 metric tons and a first stage thrust of 3469.07 metric tons of force. This is 34.6 Meganewtons. Thus the takeoff thrust of the Saturn V is 124% of the takeoff mass. The equivalent embodiment of the present invention has a total propellant weight of 5000 metric tons and gross lift off weight of 5359 metric tons. Given the same assumption as stated above, in order to produce a takeoff, thrust of 124% of the takeoff mass of this embodiment of the present invention, the first stage engines must produce 6645 metric tons of force; which is 65.1 Meganewtons.
The proposed Chrysler SERV launch vehicle estimated a gross lift off weight of 2040.8 metric tons and a first stage thrust of 3261.1 metric tons of force at takeoff. This is 31.9 Meganewtons. Thus the takeoff thrust is 160% of the takeoff mass. The equivalent embodiment of the present invention has a total propellant weight of 2640 metric tons and gross lift off weight of 4079 metric tons. Given the assumption stated above, in order to produce a takeoff thrust of 160% of the takeoff mass of this embodiment of the present invention, the first stage engines must produce 6526 metric tons of force; which is 64 Meganewtons.
At takeoff, the proposed Sea Dragon launch vehicle was projected to have a gross lift off weight of 18130 metric tons and a first stage thrust of 36709 metric tons of force. This is 360 Meganewtons. Thus the takeoff thrust is 202% of the takeoff mass. The equivalent embodiment of the present invention has a total propellant weight of 31655 metric tons and gross lift off weight of 36136 metric tons. Given the assumption stated above, in order to produce a takeoff thrust of 202% of the takeoff mass of this embodiment of the present invention, the first stage engines must produce 73356 metric tons of force; which is 730 Meganewtons.
In
As shown in
At this point, shown as 719 on the cyclogram shown in
As shown in the cyclogram depicted in
Step four shows a plurality of shroud lines 710 connected to the first stage 100 and also connected to a hypersonic deceleration tether means 712. This hypersonic deceleration tether means is the subject of the inventor's co-pending patent application [U.S. application Ser. No. 14/025,822]. The hypersonic aerodynamic drag produced by this tether could reduce the thermal load on the reentering first stage by approximately a factor of 10. Details of this apparatus may be found in the co-pending application, which is incorporated by reference. This hypersonic aerodynamic decelerate or tether allows some measure of steering by varying the length of the shroud lines and thus changing the angle of attack of the reentering first stage. The mechanism required to provide the thermal protective blanket around the reentering first stage and to provide the hypersonic aerodynamic decelerator tether should not weigh more than a few metric tons and is considered a parasitic weight on the first stage. Detailed aerodynamic reentry analysis will have to be performed on this apparatus to optimize its design and operation.
Alternatively, if the tether and parachutes produce sufficient aerodynamic deceleration of the intact first to allow the first stage to be landed intact without incurring significant damage, it would be practical to land the entire stage, rather than separating the first stage components and having them land separately. If the first stage 100 decelerates sufficiently this entire first stage 100 could land in the ocean without structural damage to it.
Reuse is an important aspect of certain embodiments of the present invention. The first stage of an embodiment of the present invention is recovered for reuse by landing it back on the Earth's surface, as will be described below. The second stage of certain embodiments of the present invention is recovered in orbit so its component parts, i.e. pressure vessels, linear beams, electronics and the like, can be used as habitation modules and structural components to build space stations and deep space vehicles and habits. The entire second stage of certain embodiments can be reused instead of being discarded as space debris. An embodiment of the present invention that connects the major second stage components together by bolting them together rather than welding can be taken apart in space and used like an “erector set” to construct many useful things for space exploration and settlement. For example, the fuel tanks could be used as a propellant depot if they had sufficient insulation and a cryostat to prevent boil off of cryogenic fuel components. Or the rocket motor pressure vessels could be used as habitat modules, as was done with Skylab. This could require fitting the pressure vessels with windows and ports that would be sealed during the motor operation by covers. These “after the rocket has flown” uses of the components of embodiments of the present invention are within the scope of the invention. The geometric form of embodiments of the present invention allows the use of large pressure vessels that can be adapted to be components of a space station or deep space vehicle, a space fueling station or the like. Certain embodiments of the present invention can thus be entirely reusable even though the second stage does not return to the Earth's surface.
The inventor has not yet been able to conduct wind tunnel or flight tests of embodiments of the invention. In the absence of these experimental results, in order to give information about the performance of embodiments of the present invention, an ascent trajectory analysis was performed on an embodiments of the present invention at several scales. An embodiment of the present invention is called the “Bulldog” launch vehicle for the purpose of this ascent analysis. The Bulldog is a multi-stage, pyramid-shaped launch vehicle that is rocket powered by proprietary rocket systems. This analysis provides initial trajectory results for three different scaled versions of this vehicle.
Ascent flight performance of the Bulldog launch vehicle was evaluated using the 3D version of POST (Program to Optimize Simulated Trajectories) [See further: Capabilities and Applications of the Program to Optmize Simulated Trajectories (POST). Brauer, G. L., Cornick, D. E., and Stevenson, R. NASA CR-2770, February 1977. http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770012832.pdf and Program to Optimize Simulated Trajectories (POST II). Volume II, Utilization Manual. Powell, R. W., et al. NASA Langley Research Center; Brauer, G. L., et al. Lockheed Martin Corporation, May 2000.]
POST has been an industry-standard modeling program that provides for trajectory simulation optimization subject to assumptions and constraints imposed by the user. POST was set up for Bulldog to maximize the remaining mass at orbit injection. Initial input consisted of overall masses and propulsion characteristics of the two stages of the launch vehicle, basic geometry, ascent aerodynamics, launch site locations and injected orbit parameters.
Three scaled Bulldog vehicles (1, 2, 3) were sized to match the payload capabilities of land-launched Zenit, Saturn V, and conceptual Sea Dragon launch vehicles (i.e. reference vehicles). Initial usable propellant, burnout, and gross masses for the Bulldog were provided to the author and used in initial POST runs. It was determined revisions in vehicle scales were needed to get payload matches between the Bulldog vehicles and the above mentioned reference vehicles. At this point in the design process for Bulldog, detailed mass statements are not yet available. Thus, a simplified methodology using propellant mass fraction, or pmf, was used for mass estimation where, in this definition,
pmf=usable propellant mass/(usable propellant mass+burnout mass)
Usable propellant mass is that propellant mass actually used during ascent. Burnout mass is the dry mass of the stage plus any fluids, residual and reserve propellants.
Propellant mass fractions typically vary with the overall propellant load. As total propellant loads increase, pmf increases and produces increased payload fraction. Without specific, detailed mass statements for Bulldog, an alternative approach is to examine prior actual or conceptual vehicles whose pmf are known. Koelle [Handbook of Cost Engineering for Space Transportation Systems with TRANSCOST 7.0. Koelle, D. E. TCS-TransCostSystems. TCS-TR-168(2000), November 2000] presents a chart of such information for a family of reusable ballistic launch vehicles of which Bulldog could be considered a member. A pmf vs. total propellant load chart was defined from Koelle's information and is presented in
Given a particular payload mass, the vehicle under study was scaled up or down from initial supplied vehicles until POST determined the total propellant load that provided the correct final orbital mass (payload plus burnout second stage). The pmf was reset using
The author was provided with general propulsion characteristics for the stages of the Bulldog launch vehicle. The first stage motors have gelled propellants that will switch composition during ascent and the second stage also has gelled propellants. The assumed vacuum specific impulses of the motors are:
Thrust requirements were determined as follows. From the author's experience, the sea level thrust at liftoff that maximizes payload is set at 1.3 times the vehicle liftoff mass (or T/W). This can be varied, but too low a number increases gravity losses whereas too high a number increases drag losses. The final payload mass is relatively insensitive to a range from 1.2 to 1.4.
POST requires general propulsion characteristics of engine vacuum thrust, vacuum specific impulse and nozzle exit area. A factor of 1.0897 was used to multiply first stage sea level thrust to determine vacuum thrust. This was based on the RD-171 engine, but is fairly typical for many rocket engines. The engine flow rates are determined from:
Flow rate=Thrust vacuum/Specific impulse vacuum
The exit area is determined from:
Exit area (sq m)=[Thrust vacuum (mt)−Thrust sea level (mt)]/22780
The first stage burns propellants at high thrust and lower specific impulse. It was assumed that the switch over to mode 2 (lower thrust, higher specific impulse) occurs at 70 seconds after liftoff—past the point of maximum dynamic pressure. In future studies, this time can be varied to determine impacts on maximum dynamic pressure and payload. The vacuum thrust mode 2 was assumed to be 75% of the thrust in mode 1.
POST will determine the end of first stage burn when the propellant consumed equals the usable propellant load. Two seconds after all usable propellants are consumed, the two stages are separated. Six seconds after that, the second stage engine 217 ignites. A typical thrust level at staging is the thrust (mt) which is equal to the staging mass (mt) although lower thrust can be used. Future POST simulations would examine the impact of varying initial second-stage thrust on payload capability.
POST requires a couple of input values for geometry—the reference area for aerodynamics calculations and a reference length. The reference area is based on the SERV launch vehicle that uses a circular planform area for aerodynamics coefficients. Since Bulldog has a triangular planform area, it was decided to approximate an equivalent circular reference area using the length of the triangular side as a diameter.
SERV ascent aerodynamics were used to estimate ascent aerodynamics. The vehicle follows a near-zero lift trajectory. Drag is calculated using the drag coefficient vs. Mach number for the Chrysler SERV (
1. Mach number: 0.0, 0.5, 1.0, 1.5, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0. 8.0 and 25.0
Bulldog 3: 2316.4 sq m
For Zenit equivalent Bulldog 1.
Baikinor: Latitude: 45.9 deg North
KSC: Latitude: 28.5 deg North
KSC: Latitude: 28.5 deg North
For Zenit equivalent Bulldog 1.
Altitude: 200 km (108 nmi) circular
Inclination: 51.4 deg
For Saturn V equivalent Bulldog 2
Altitude: 200 km (108 nmi) circular
Inclination: 28.5 deg
For Sea Dragon equivalent Bulldog 3
Altitude: 185 km (100×300 nmi) then burn to 300 nmi circular
Inclination: 28.5 deg
1. 1976 U.S. Standard Atmosphere and no winds
2. Second-stage payload fairings jettisoned at 295 sec (as for Zenit). In future POST simulations the fairings will be jettisoned when the free-molecular heating rate (FMHR) has decreased to a value of 0.1 BTU/ft2-sec.
3. Maximum g forces: Bulldog 1: 4.06 (Zenit limit) Bulldog 2 & 3: 4.00
Only Bulldog 2 reaches the g limit briefly during first stage burn. However, all vehicles reach the g limit during second-stage burn. This can be constrained by continuously reducing thrust from the second stage engine 217, or by doing a single step-down to lower thrust during the burn. This has implications in the propellant design for Bulldog. Future simulations will also look at reducing the staging thrust/weight to lower values to reduce or eliminate reaching the g limit. This has implications for reduced payload.
Geometry and mass statements for the three Bulldog vehicles are given in
Bulldog 1 is in nearly a vertical climb during the first ˜70 seconds after liftoff (varying from 90 deg to 80 deg climb angle). Thereafter, the vehicle starts to arc over in the trajectory during Mode 2 first-stage burn as it exits the densest part of the atmosphere.
It is clear during the initial Mode 1 first-stage burn that drag is taking a toll on this vehicle as the vehicle is holding a near-constant acceleration of 1.5. Acceleration drops to ˜1.0 at the switchover to Mode 2, but then does rapidly build as the vehicle drag decreases and the vehicle is able to arc over towards horizontal flight. The switchover to the second-stage thrust is evident by the initial lower acceleration, but eventually it does reach the 4.0 g limit as the vehicle achieves horizontal flight where gravity losses are non-existent.
For Bulldog 2 the flight-path angle reduces more quickly than for Bulldog 1. Also, in
The acceleration history for Bulldog 2 is a little different since it briefly reaches a 4.0 g limit during Mode 2 first stage burn whereas Bulldog 1 did not. This is in line with the somewhat lower impacts of drag for the larger vehicle.
For Bulldog 3, the vehicle begins a tilt towards horizontal flight earlier than for the other Bulldog vehicles thus showing the decreasing role of drag in the overall optimization of maximum injection mass. This vehicle is different than Bulldog 1 and 2 in that the orbital injection is to an elliptical orbit 100×300 nmi (injection point 185 km) to simulate the Sea Dragon mission.
The acceleration level during first stage burn falls well short of 4 g's. One reason is that this vehicle has the highest percentage of second-stage propellant. Thus, the first stage burns out at the earliest time of the three vehicles (see Table II). On the other hand the second stage burns for the longest time of the three vehicles in part because of the higher mass of propellant available, but also due to the higher injection velocity required to reach the 100×300 nmi orbit. In addition, there is another burn of the second stage required to circularize the orbit at 300 nmi−the apogee of the 100×300 nmi orbit. This vehicle has the highest maximum dynamic pressure (637 psf). But the drag/thrust percentage is the lowest of the three vehicles (24 & vs. 33% and 45% for Bulldog 2 and Bulldog 1 respectively).
Trajectory conclusions from this POST ascent analysis of an embodiments of the present invention:
An initial set of trajectory simulations has been obtained for three scaled Bulldog vehicles. Each represents a usable trajectory based on the input parameters and constraints. The analysis, however, has pointed out some follow-on work that can improve these initial results.
First, the propellant splits between the first and second stage as shown at the bottom of Table 1 should be made consistent with scaling.
Second, there is an optimization to be performed to examine whether a lower second-stage initial thrust (assumed to be T/W=1.0) will impact injected mass much and may allow a reduction or elimination of reaching a 4.0 g limit. This has an impact on the design of the specific solid and gelled propellants used in embodiments of the present inventions pseudo-hybrid nonstoichiometric rocket motors.
For the same basic mass properties and propulsion as ISAS/JAXA, Bulldog's ascent drag has a significant impact on its use as a single-stage sounding rocket in terms of altitude achieved and microgravity times. However, as is shown in the table in
The scalability of embodiments of the present invention from a small sounding rocket to an ultra-heavy orbital launch vehicle is a significant advantage of embodiments of the present invention. This scaling occurs because as the vehicle gets larger more the vehicle is fuel and less of it is structure. That is the payload mass fraction benefits as the size the vehicle gets larger because the fraction of the vehicle that comprises fuel becomes larger faster than the growth in mass of the vehicle's structure. For an embodiment the structural mass of the vehicle gross is a function that is the square of the vehicle's linear size, while the mass of the fuel increases as a function of the cube of the vehicle's linear size (linear size being the size of one edge of the triangular structure.)
It is not practical to build and test embodiments of present invention prior to filing this patent application, so the inventor includes a launch vehicle feasibility analysis to assist those having ordinary skill in the art to make and use the invention. Two embodiments are presented below. The first is an embodiment of the present invention that is equivalent in performance to the Ukrainian/Russian “Zenit” launch vehicle, which was considered as part of the POST analysis above. This first embodiment is called “Bulldog” for ease of identification. This is a large commercial launch vehicle suitable for providing launch services for LEO cargo and GTO communications satellites. The second embodiment of the present invention is a smaller launch vehicle capable of providing launch services to LEO for a one metric ton payload. This second embodiment of the invention is called “Bulldog Puppy” for the remainder of this specification for ease of identification. Both the Bulldog and Bulldog Puppy are shown using conventional liquid rocket motors for their main propulsion. The requirements of these motors are developed as part of the analysis. Any rocket motors meeting the disclosed requirements may be used. For the Bulldog, the motor may be a bespoke designed plurality of Russian RD-171 liquid rocket motors. The Bulldog Puppy is designed to use an off the shelf Russian RD-120 liquid rocket motor, which has been operated successfully for many years commercially. Because a Bulldog embodiment might not use the novel pseudo hybrid rocket motor disclosed in this application, and because this rocket motor is not yet developed and proven; a Bulldog embodiment can rely on the conventional gimbal system 930 to steer the RD-171 to provide active first stage guidance control. Because a Bulldog Puppy embodiment uses only one main rocket motor, it will use a plurality of RCS rocket motors 920 near the apexes of the embodiment's pyramidal structure to provide active trajectory control.
Two different sized embodiments are called herein the Bull Dog and the Bull Dog Puppy. An important design driver is the quantity of fuel needed to provide a specified payload capacity to LEO. Specified payload capacity is differentiates Bull Dog and Bull Dog Puppy embodiments. Fuel quantity can be estimated by comparison to comparable launch vehicles and by a high-level analysis of the propulsion system. This analysis also gives an estimated size of the engine nozzles which is necessary since the second (upper) stage engines 217 must fit within the vehicle. For a Bull Dog Puppy embodiment this analysis was expanded to include requirements for the attitude control system. Next, an embodiment's primary structure can be modeled. The primary structure 101, 201 comprises components which form an embodiment's pyramid shape. Finally, an embodiment's engine support structure can be modeled. The engine support structure is the most complex part of a vehicle in accordance with an embodiment since it connects the engines 116, 118, 120 to the primary structure 101, 201 and transfers very large loads between the two. The size of major components can be determined by the Finite Element Method (FEM) of analysis. Sizing of components consumes the largest amount of time in such analysis. An embodiment's structure 101, 201 is deemed feasible if the structure can be made lighter than the specified target weight while showing with FEM that all analyzed major components are strong enough to carry the load exerted on them.
An important driver for an embodiment's size is the required quantity of fuel and oxidizer. An estimate for the amount of fuel and oxidizer can be based on comparison to the Zenit-2 and a high-level analysis of the engines. This analysis was performed in detail for a Bull Dog embodiment. Sizing for a Bull Dog Puppy embodiment can be achieved by assuming the same vehicle mass fraction breakdown but for a smaller payload.
A Bull Dog embodiment can use a proprietary fuel-oxidizer combination of RP-1 and Ammonium Perchlorate. The reaction is assumed to be
32NH4ClO4+7C2H2→100H2O+16Cl2+14CO2+32NH3 (1)
In reality the reaction would contain free ions and diatomic gases due to the high temperature; however, here the goal is only to obtain an estimate of the molar weight of the products flowing through the engine nozzle. The estimated molar weight is
The flow through the nozzle is analyzed under several assumptions. Most notably, no energy is lost to the wall of the nozzle and the nozzle perfectly expands the exhaust to match the ambient air pressure at sea-level. The expression for the thrust from an ideal nozzle is derived from Newton's Second law as
F={dot over (m)}vE (3)
where F is the thrust produced, {dot over (m)} is the mass flow rate through the nozzle, and vE is the velocity of the gases exiting the nozzle. The expression for the exit velocity is
where R=R′/M and where R′ is the universal gas constant 8.314 [kg·m2·s−2·K−1·mol−1], k assumed to be 1.3 is the ratio of specific heats of the gas, and p0 is the combustion chamber pressure of the engine. Assuming a constant mass flow rate for the engine and a burn time of t, the quantity of fuel is
For an embodiment's specified thrust of 4.8MN and burn time of 180 s, the result is shown in
To refine an estimate of an embodiment's required thrust, the Zenit-2 vehicle is considered for comparison with a Bulldog embodiment. The Zenit-2 by mass is 3% payload (13,500 kg), 88.4% fuel-oxidizer (397800 kg), and 8.6% structure (38,700 kg). If the weight of the structure is doubled and the fuel to payload and structure ratio is kept the same, the new vehicle breakdown is 2% payload (13,500 kg), 86.6% fuel-oxidizer (589,841 kg), and 11.4% structure (77,400 kg).
The Zenit-2 has four nozzles each with a dedicated 81,112 kg of fuel-oxidizer. Considering the new mass breakdown, a Bulldog embodiment has three nozzles each with 141,758 kg of fuel-oxidizer.
The Zenit-2 has a total first-stage thrust of 8.18 MN and gross liftoff weight (GLOW) of 450,000 kg. This gives a take-off acceleration of 18.2 m/s. The total first-stage of thrust for a Bull Dog embodiment to achieve this acceleration must be 12.4 MN. Each engine must produce 4.12 MN and have about 142,000 kg of fuel-oxidizer.
To get the previously presented engine analysis to match the Zenit-2 mass breakdown using the Zenit-2 thrust quantity, the thrust must be reduced by 70%. This accounts for the change in atmospheric pressure during the flight and throttling performed during the max-Q flight regime. Using this same scaling factor, the thermodynamic analysis predicts slightly more necessary fuel than the mass breakdown method. It is estimated that each engine requires 175,000 kg of fuel-oxidizer. Increasing the burn time from 150 s (as is the case for the Zenit-2) to 180 s to account for the Bulldog embodiment's different flight path, the fuel-oxidizer mass per engine is 220,000 kg as shown in Table 2.
The final mass breakdown and thrust figures used in the structural analyses are shown in Table 3.
For this Bulldog embodiment, the number of moles of reactant in the combustion equation is computed by
Where mTotal is the total mass of fuel & oxidizer, MAC is the molar mass of Ammonium Perchlorate, and MRP-1 is the molar mass of RP-1. The total number of moles of Ammonium Perchlorate and RP-1 is thUS 1,718,323 and 375,883. Using the molar mass of each, the mass of each is 201,877 kg and 18,123 kg respectively. The densities of RP-1 and Ammonium Perchlorate are 900 kg·m−3 and 1950 kg·m−3 respectively. The volumes are 104 m3 and 20 m3.
Because of the overall similarity between the considered Bulldog and Bulldog Puppy embodiments, the mass breakdown for a Puppy embodiment is assumed to have similar mass and thrust fractions to a Bulldog embodiment.
The size of an embodiment's engine nozzles 515 should be estimated so their weight can be included in the vehicle's mass and to ensure adequate room within the vehicle for the second stage engine 217. The size of the nozzle can be estimated based on the same thermodynamic analysis used to estimate the fuel-oxidizer mass. Manipulation of the common rocket parameter c-star gives an expression for the area of the throat of the nozzle
The temperature at the exit can be computed using the isentropic relationship
The Mach number at the exit is
Finally, the exit area is
An embodiment's calculated throat area and nozzle exit area is about 0.5 m2 and 2.5 m2 respectively.
A Bulldog Puppy embodiment's analysis was expanded to include an estimate of the thrust required for Vernier thrusters 920 in the bottom three vertices and the top apex to provide attitude control during ascent. Because the Bulldog concept has a mass distribution which places the center-of-mass near the bottom of the vehicle, gimballing the main engine would likely not provide an adequate moment to control the vehicle during ascent. To assess this claim, a comparison is made with another launch vehicle: the Atlas V. The Atlas can gimbal its main engines up to 8 degrees, is 58 meters tall, weighs 334,500 kg at liftoff, and has 3827 kN of thrust. At the extent of the gimbal range, the moment exerted about the center of mass is thus
Approximating the rocket as a homogenous mass, the moment of inertia about the center of gravity (CG) is
This suggests that a full-range gimbal maneuver can pitch the fully loaded rocket at an angular acceleration of
It is assumed that the Bulldog Puppy embodiment's attitude control system must be able to generate a moment about the CG which corresponds to this angular acceleration to maintain controllable flight. The Puppy embodiment presented here has a moment of inertia about the CG of 320,000 kg×m2. This marks an advantage to the Bulldog embodiment; most of the mass is close to the CG so the moment of inertia is less. To achieve 8.5 deg/s2 the attitude control system must produce a torque equal to 48,000N×m. If Vernier thrusters 920 are placed vertically at the three bottom vertices and horizontally at the apex, they are about 4 meters from the CG of the vehicle. Their thrust must be throttleable up to about 6,000N. This requirement could possibly be reduced if the main engine can also gimbal.
The addition of the RCS thruster loads to the structure does not cause any significant changes to the stress results presented previously. Other than a simple bracket to hold the RCS thruster, the stress levels due to the primary propulsion system dwarf any additional loads generated by the RCS.
Structural components are generally assumed to be “Plain Carbon Steel” as SolidWorks defines it. This material has essentially averaged properties of most common steel alloys. The engine components are assumed to be AISI 347 Stainless Steel. The pertinent material properties of these materials are listed in TABLE 5. It should be appreciated that embodiments can comprise additional materials.
Most connections in the embodiments are designed using I-beams or box beams with end flanges. An example is shown in
Due to the complexity of Bulldog embodiments' structure, structural design comprises iterative steps. No hand-calculation analysis could give results of any meaning, so the Finite Element Method (FEM) is the primary tool. In an example structural design of an embodiment, to start, the primary structure of the vehicle is drawn and a guess is taken as to how to attach engines to the primary structure 101, 201. This guess is primarily formulated taking into account the feasibility of construction. Once the preliminary model is completed, the FEM analysis is performed and all structural failure conditions are addressed. After changing the structure, another FEM analysis is performed. These steps are repeated until all components in the vehicle are not at risk of failure. The primary changes involve resizing the thickness of beams, adding/removing braces, or completely changing load paths by adding and removing components.
The Finite Element Method (FEM) is the primary structural analysis method used to assess the feasibility of the example Bulldog embodiment. The FEM model consists of the geometry of all structural components, the external loads, and fixtures. There are several types of FEM models; a static model is assessed here. In a static model the structure is loaded and its steady-state stress is computed. No vibration or fatigue is considered. Because of the propulsion system and aerodynamic loading, a dynamic model which includes vibration should be performed after feasibility is determined since dynamic loading can reveal problems unknown to the static model. A dynamic model, however, takes much more time to build, compute, and interpret results.
The primary result from the FEM analysis is the von Mises stress in the structural components. The von Mises stress is essentially an average of the compression, tension, and/or shearing of the material is all directions. The stress value is represented using the color scale in
The external load applied to the structure in this model is not a force; it is an acceleration. A 2G acceleration is imposed on the structure such that the mass of all structure, fuel, and payload is considered. The fixture—the source of a reaction force to the external load—is a fixed geometry condition on the engine mounts. The fixed geometry condition mathematically restricts translation of the engine mounts which creates a reaction force which opposes the load created by the vehicle's acceleration.
The “primary” structure 101, 201 of a Bulldog embodiment is the pyramid shape which holds the skin of the vehicle as shown in
The engine support structure as shown in
An embodiment is shown in
To make the model feasible to compute on a PC, the thin metal comprising the fuel tanks and combustion chamber need not be included in the main FEM model. Rather, the points where tanks attach to the structure can be assigned a theoretical mass load. This essentially means that the fuel tanks can be analyzed independently from the structure. This simplification does not significantly affect the analysis when assessing feasibility is the goal. A more complex model can be performed during design—after the feasibility question is answered—prior to construction of a Bulldog embodiment.
The fixtures, loads, and final structural design is shown in
FEM analysis result is shown in
Although this design is not optimized, the analysis result is sufficient to deem the structural concept feasible.
Bulldog Puppy embodiments can have much simpler structures than the Bulldog embodiments because Bulldog Puppy embodiments can comprise a single liquid fuel engine. Therefore, the structure can be analyzed in terms of the load path. The idea behind the load path is to follow loads within the structure from where an external force is exerted (the engine thrust) to where that load is resolved (mass of the fuel). This terminology was not used in the Bulldog analysis because the load path was not as linear, i.e. the load path has many branches.
A Bulldog Puppy embodiment's first stage thrust load path is shown in
The load path for the Bulldog Puppy embodiment is substantially longer and more complex than that of a typical rocket. A typical rocket allows for each stage to for the most part carry its own loads internally, i.e. the first stage structure does not rely on components in the second stage. The Bulldog Puppy embodiment shown in
For a method of designing an embodiment, structural analysis is performed using finite element modeling of the structure. This analysis method constrains part of the structure as fixed from any translation or rotation. A load is then applied elsewhere on the structure. The internal stress and displacement of all components connecting the load to the constraint is then computed. In the analysis presented here, the location where the engine is attached is constrained. The loading is applied in the form of a “body force.” The body force represents the 2G acceleration of the vehicle where all components with mass exert a force on the components to which they are attached. The structural components thus have a load applied by their own mass. The fuel and payload are modeled as external loads.
All components in the model are sized to provide at least a 1.2 factor of safety. The region with the most difficult analysis and complex loading is in the second stage. The region where the vertical members carrying the lifting load from the first stage 100 to the outer diagonal skin incurs some large bending and deflections. This is caused by the vertical compression load having the transition to a diagonal tension load. The vertical members in the results below can be seen to have the lowest factor of safety in the structure. Special attention should be pain to this region during the manufacturing design.
The result of the FEM analyses reveals that for a Bulldog embodiment with comparable performance to the Zenit-2 the Bulldog concept is feasible. A scaled down Bulldog Puppy embodiment is also feasible to deliver 1000 kG to LEO. No obvious advantages of the Bulldog concept were realized through the structural analysis, as the Bulldog is nearly twice as heavy as the Zenit-2 even without the addition of avionics, fuel pumps, etc. It is possible that an embodiment can achieve cost savings in materials and assembly.
Several challenges were encountered during a Bulldog embodiment's design and analysis. The biggest challenges particular to the large Bulldog embodiment lay in the design of the structural components which connect the engines to the vehicle. There are three necessary load paths starting at the engines.
The biggest change to the design—as presented in the patent application—includes separating the oxidizer and fuel into separate cylindrical tanks. This change placed the Ammonium Perchlorate oxidizer in liquid form in multiple tanks, and the RP-1 fuel in gelled form in the combustion chamber. Not using the large spherical tanks was necessary to allow vertical structural members to attach the three main engines to the second stage. The spherical tanks were also deemed not feasible if they were to function as high pressure combustion chambers. Due to the size of the spherical combustion chambers and the high pressure, the thickness of the wall of the combustion chambers would make them too heavy for flight.
In addition to the load paths pertaining to the engines' thrust loads, an embodiment's skin 901 is problematic. In a traditional rocket, the majority of the skin has minimal aerodynamic loading because the skin and airflow are parallel. Only the nose cone sees substantial loading. In Bulldog embodiments all of the skin 901 sees substantial aerodynamic pressure. The problem is exacerbated by the vehicle having flat skin 901. The flat skin 901 very easily collapses into the vehicle and requires substantial stiffening. It is suspected that the skin 901 will also show problems in a vibration analysis because of the large flat surfaces. A traditional rocket has all curved surfaces which naturally support themselves. A traditional rocket also benefits from the skin being part of a pressure vessel which assists in preventing buckling of the skin under compressive loading. While an embodiment's skin 901 is problematic, it is structurally necessary. Because many of an embodiment's structural members are horizontal and very long, skin 901 is needed to prevent these members from sagging. An embodiment's skin 901 is the most effective way to carry the rather large and distributed load associated with beams sagging. Without the skin 901 several structural members are vulnerable to buckling which would require a specialized structural analysis technique to analyze and mitigate.
Bulldog embodiment design methods can comprise iterative steps of modeling additional structures that affect mass properties and conducting dynamic analysis of the resulting model. Based on dynamic analysis, Bulldog embodiments can comprise additional structure to mitigate large amplitude, low frequency oscillations which could excite vibration modes in an embodiment's long beams. A Bulldog embodiment's additional structure will be based on more complete analysis that includes smaller components such as fuel lines, actuators, etc. that impact the mass properties of the vehicle. A Bulldog embodiment can comprise additional structure to support the skin 901 that is planar on the three sides of the vehicle to mitigate oscillations.
Bulldog embodiment design methods can comprise manufacturability assessment steps. Iterative steps can comprise a production engineer modifying Bulldog embodiment designs to account for manufacturing methods of the components, modifications to components to reduce cost, and modifications to components to aide in ease of assembly.
Bulldog embodiment design methods can comprise design modification related to the attitude control system. Design steps comprise reconfiguring the vehicle to move its center of mass or aerodynamic center. A design method comprises iterative steps of modifying structural design and modifying the attitude control system. A typical aerospace vehicle has a center of mass ahead of its aerodynamic center, and the center of mass is typically far away from the engines to allow for a sufficiently long moment-arm between the engines and the center of mass. This long moment arm allows for small engine gimbal movements to provide adequate torque on the structure to control its orientation. By contrast, certain Bulldog embodiments have the center of mass about ⅙ of the height of the vehicle from the bottom. To compensate, the certain Bulldog embodiments can be made taller and thinner. Bulldog embodiments can further comprise control fins. For reference, the center of mass location throughout flight is shown in
Based on certain Bulldog embodiments' center of mass and aerodynamic center, embodiments can comprise an active attitude control system. Certain Bulldog embodiments use the throttle of three off-center-axis engines to control the attitude of the Bulldog embodiments. This is not a known in the art. Bulldog embodiments can comprise attitude elements with fast response and precise throttle. Certain Bulldog embodiments can have the center of mass further forward in the vehicle, and comprise a gimbal style control on the main engines. Bulldog puppy embodiments can comprise Vernier engines 920 to control attitude. The engines control the vehicle's attitude by varying thrust or pulsing rather than gimbaling the engines. Alternatively, the Vernier engines 920 can be turned on at launch to provide additional thrust and throttled or pulsed off to control the trajectory of the Bulldog Puppy. These rocket engines will only have to fire for under 10 minutes, so this should not present a practical problem.
Although specific embodiments of the present invention have been described in this written description and the accompanying drawings, these embodiments are illustrative of the invention for the purpose of allowing those skilled in the art to make and use the invention. Those skilled in the art will be able to use the invention in many other embodiments without departing from the teachings of the present disclosure. Thus these embodiments illustrated should not limit the scope of the invention, which is limited only by the appended claims and their equivalents.
This application claims benefit of 61/906,086 filed on Nov. 19, 2013 and claims benefit of 62/041,050 filed on Aug. 23, 2014 and is a continuation in part of Ser. No. 14/547,543 filed on Nov. 19, 2014.
| Number | Date | Country | |
|---|---|---|---|
| 62041050 | Aug 2014 | US | |
| 61906086 | Nov 2013 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14547543 | Nov 2014 | US |
| Child | 15269944 | US |
