Patent Publication Number: US-7581380-B2

Title: Air-breathing electrostatic ion thruster

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     None. 
     BACKGROUND OF THE INVENTION 
     A. Field of the Invention 
     The field of the present invention relates generally to propulsion systems that utilize charged particles to generate the propulsive forces to propel an object. More particularly, the present invention relates to ion thrusters that are adapted for use in the Earth&#39;s atmosphere. Even more particularly the present invention relates electrically powered, air-breathing ion thrusters capable of operating in low-Earth atmosphere. 
     B. Background 
     Propulsion systems that are capable of propelling a vehicle through the atmosphere that do not require a large quantity of fuel to be carried by the vehicle for its own consumption have long been desired. As is well known, a significant portion of the overall weight of a vehicle that travels through the atmosphere can be the fuel necessary to propel the vehicle. This generally results in a balance being chosen between the weight of non-fuel materials that can be carried by the vehicle or the distance the vehicle can travel, with a greater amount of materials reducing the quantity of fuel available, and therefore the distance the vehicle can travel, and the additional fuel for greater distance limiting the weight of materials that can be carried. To overcome this problem, propulsion systems with greater efficiency have been developed, particularly those that utilize readily available natural resources as the fuel, such as solar powered aircraft that utilize solar cell technology to power the vehicle&#39;s engine. Although other types of fuel systems have been developed or suggested for atmospheric vehicles, including various magnetically or nuclear powered propulsion systems, limitations due to efficiency and safety concerns have generally prevented full acceptance of such systems. 
     Propulsion systems utilizing ion engines for use in high atmosphere and space vehicles, including those which are configured for travel in the atmosphere of other planets, have been developed and somewhat successfully utilized for many years. The typical ion engine propulsion systems requires a propellant such as mercury, xenon, argon or cesium for ionization and operates as a Hall effect thruster. Electrons emitted by a cathode are directed into a discharge chamber where propellant is introduced to collide with the electrons in order to create positively charged ions that are rapidly expelled from the discharge chamber to generate the engine&#39;s thrust. An example of such a system is disclosed in U.S. Pat. No. 4,838,021 to Beattie, which describes an ion thruster having an ionization chamber formed by a cylindrical metallic conductive sidewall that functions as the anode in which propellant gas, such as xenon, is ionized by electrons emitted by a cathode to produce a plasma that expels an ion beam to create thrust. U.S. Pat. No. 3,952,228 to Reader, et al, describes a cylindrical shell which defines a chamber in which an ionizable propellant, such as argon, is introduced. Disposed symmetrically within the shell is a cylindrical anode, which has a cathode centrally positioned therein. An apertured screen and an aligned apertured grid at the open end of the cylinder draw ions along a beam path to create thrust. A major limitation to such propellant systems, as with conventional fuel powered vehicles, is the need to carry sufficient propellant to achieve the desired operation of the vehicle. Longer flight or other engine operation time requires the vehicle to carry larger quantities of propellant, which increases the weight of the vehicle and thrust requirements for the engine, which then requires a larger and generally heavier engine that needs even more propellant to effectively operate. As a result, there has been a need for vehicle propulsion systems utilizing ion powered engines that do not require the use of stored and carried propellant. 
     For operation in the Earth or other Earth-like atmospheres, there have been developed air-breathing ion engines that utilize ambient atmospheric gas, which is sufficiently ionizable, as the propellant. These engines draw in the atmospheric gas and ionize a portion of it utilizing cathode devices, instead of having to carry ionizable fuel on the vehicle, to achieve the desired thrust from the rapid discharge of charged ions. Some of these ion engines have been patented. For instance, U.S. Pat. No. 6,834,492 to Hruby, et al. describes an air-breathing electrically powered Hall effect thruster having a thruster duct with an inlet, an exit and a discharge zone therebetween, an electrically charged cathode for emitting electrons, an anode in the discharge zone that attracts the electrons and a magnetic circuit that establishes a radial magnetic field in the discharge zone. The magnetic field creates an impedance to the flow of electrons toward the anode to better ionize the atmospheric gas moving through the discharge zone. This enables ionization of the atmospheric gas and creates an axial electric field in the thruster duct for accelerating the ionized air through the exit to create thrust. U.S. Pat. No. 6,145,298 to Burton, Jr. describes an ion engine propulsion system that utilizes a high voltage power source to ionize a portion of high altitude ambient atmospheric gas to create a negative ionic plasma which bombards and accelerates the remaining atmospheric gas in a focused and directed path to an anode receiver to create thrust for propulsion. The cylindrical cathode is tapered, preferably to a fine point, and the anode is substantially ring-shaped or comprised of a plurality of concentric rings of decreasing diameter that are axially aligned with the tapered cathode. The tapered cathode and ring-shaped anode are disposed in a housing that has an inlet for receiving ambient atmospheric gas and an outlet for discharge. A voltage power source having a negative potential is connected to the cathode and a power positive source is connected to the anode. An electromechanical arrangement is provided to adjust the distance between the cathode and anode. 
     Despite the foregoing, there exists a need for an improved air-breathing electrostatic ion thruster for use in low-Earth atmosphere. The preferred ion thruster should utilize ambient atmospheric gases as the propellant so as to eliminate the need for the vehicle to store and carry a sufficient quantity of propellant. The preferred ion thruster should have a housing with an electrically conductive inner surface that defines a ionization chamber in which is disposed an electrically charged inner electrode and which has electrically charged screen electrodes at its inlet and outlet to repel, attract and accelerate ions so as to generate thrust due to the ionization of the atmospheric gas. The preferred ion thruster should be configured to be relatively simple to manufacture and operate and will provide long and reliable operation. 
     SUMMARY OF THE INVENTION 
     The air-breathing electrostatic ion thruster of the present invention discloses an improved electrostatic ion thruster that utilizes ambient atmospheric gas as the propellant, thereby eliminating the need for the vehicle having the ion thruster to store and carry propellant fuel. In the preferred embodiment, the ion thruster of the present invention has a housing formed with an non-conductive outer surface and a conductive inner surface that defines an ionization chamber into which the atmospheric gas is received and ionized by electrons emitted by an inner electrode (i.e., a cathode). In this preferred embodiment, an electrically charged screen electrode at the forward end of the chamber allows the atmospheric gas into the chamber where electrons from the inner electrode collide with the atmosphere gas to provide charged ions that are discharged rearward to create thrust. The preferred electrostatic ion thruster also has a screen electrode and an accelerator electrode at its rearward end to draw the charged ions rearward and accelerate them outward. In a preferred embodiment, one or more magnets act on the electrons to spiral them in a helix shape to increase their interaction with the atmospheric gas and improve the formation of ions. A neutralizing assembly at the rearward end of the housing maintains the ion thruster in a neutral electrical potential. 
     In one general embodiment of the present invention, the air-breathing electrostatic ion thruster comprises a housing having a forward end, a rearward end, an electrically conductive inner surface that defines an ionization chamber and an electrically non-conductive outer surface. The ionization chamber has an inlet at the forward end of the housing to receive ambient atmospheric gas and an outlet at the rearward end of the housing to discharge charged ions so as to create thrust to propel a vehicle utilizing the ion thruster of the present invention. Positioned at the inlet of the chamber is an electrically charged forward screen electrode that has a plurality of forward screen apertures which are configured to allow the atmospheric gas to flow into the ionization chamber. An inner electrode is disposed in the ionization chamber near the inlet and generally rearward of the forward screen electrode. In the preferred embodiment, the inner electrode is a cathode configured to emit electrons to ionize the atmospheric gas in the ionization chamber and generate a plurality of positively charged ions. At or near the outlet of the chamber is positioned an electrically charged rearward screen electrode that has a plurality of rearward screen apertures. Positioned generally rearward of the rearward screen electrode is an electrically charged accelerator electrode of a grid configuration having a plurality of accelerator apertures. The rearward screen apertures are substantially aligned with the accelerator apertures so as to allow the charged ions to pass through the outlet to generate thrust. A source of electrical power, which can be solar cells, a battery or a generator, is electrically connected to the inner surface, the forward screen electrode and the rearward screen electrode so as to provide current of a first polarity, which in the preferred embodiment is positive. The source of electrical power is also electrically connected to the inner electrode and the accelerator electrode to provide a current of a second polarity, which in the preferred embodiment is negative. A controller operatively connects to the source of electrical power to vary the current and/or the polarity supplied by the source of electrical power. The controller includes an microprocessor and is suitable for controlling locally or from a remote location (i.e., a land station). One or more magnets are disposed about the ionization chamber to provide a magnetic field that increases the mixing of the electrons and the atmospheric gas so as to improve ionization in the ionization chamber. A neutralizing mechanism, which can comprise a neutralizer electrode (i.e., in the preferred embodiment it is a cathode), is positioned at or near the outlet to maintain the ion thruster in an electrically neutral condition. 
     In operation, the source of electrical power supplies electrical current having a first polarity to the inner surface, forward screen electrode and rearward screen electrode and supplies electrical current having a second polarity to the accelerator electrode and inner electrode. In the preferred embodiment, the first polarity is positive and the second polarity is negative, with the inner electrode being a cathode. The ambient atmospheric gas enters the ionization chamber through the forward screen electrode at the inlet to mix with the electrons emitted by the cathode to generate positively charged ions (in the preferred embodiment). Because the polarity of forward screen electrode is also positive, the forward screen electrode repels the positively charged ions away from the inlet in a generally rearward direction. The positively charged screen electrodes and inner surface will attract the electrons from the cathode to facilitate mixture thereof with the atmospheric gas to generate the positive ions. The negatively charged accelerator electrode attracts the positively charged ions and accelerates them through the chamber outlet at the rearward end of the housing to provide accelerated ions for generating thrust. 
     Accordingly, the primary objective of the present invention is to provide an air-breathing electrostatic ion thruster that provides the advantages discussed above and overcomes the disadvantages and limitations associated with presently available ion thrusters. 
     It is also an important object of the present invention to provide an air-breathing electrostatic ion thruster that utilizes ambient atmospheric gases as the propellant to eliminate the need to store and carry propellant in a vehicle powered by the present ion thruster. 
     It is also an important object of the present invention to provide an air-breathing electrostatic ion thruster that operates efficiently and effectively in the low-Earth atmosphere for extended periods of time. 
     It is also an important object of the present invention to provide an air-breathing electrostatic ion thruster that utilizes a screen electrode at the forward end of an ionization chamber, defined by an electrically conductive inner surface, that allows atmospheric gas into the chamber where electrons emitted by a cathode disposed in the chamber ionizes the atmospheric gas and a screen electrode and a spaced apart but aperture aligned accelerator electrode at the rearward end of the chamber draws and accelerates the ions out the rear of the thruster to create thrust. 
     It is also an important object of the present invention to provide an air-breathing electrostatic ion thruster that utilizes one or more magnetic assemblies to cause the electrons within the chamber to spiral in a manner so as to improve the interaction with the atmospheric gas and increase the formation of ions. 
     It is also an important object of the present invention to provide an air-breathing electrostatic ion thruster that is relatively simple to manufacture and operate and which preferably does not require moving parts so as to improve the usefulness and reliability thereof. 
     The above and other objectives of the present invention will be explained in greater detail by reference to the attached figures and the description of the preferred embodiment which follows. As set forth herein, the present invention resides in the novel features of form, construction, mode of operation and combination of processes presently described and understood by the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings which illustrate the preferred embodiments and the best modes presently contemplated for carrying out the present invention: 
         FIG. 1  is cross-sectional side view of an air-breathing electrostatic ion thruster configured according to a preferred embodiment of the present invention showing atmospheric gas being drawn into the ionization chamber and accelerated ions being discharged therefrom to create thrust; and 
         FIG. 2  is a schematic view of the electrical circuit for an air-breathing electrostatic ion thruster configured according to a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the figures where like elements have been given like numerical designations to facilitate the reader&#39;s understanding of the present invention, the preferred embodiments of the present invention are set forth below. As will be readily understood by those skilled in the art, the enclosed figures and drawings are merely illustrative of a preferred embodiment and represents one of several different ways of configuring the present invention. Although specific components, materials, configurations and uses are illustrated, a number of variations to the components and to the configuration of those components described herein and in the accompanying figures can be made without changing the scope and function of the invention set forth herein. For instance, although the figures and description provided herein are directed to a generally cylindrical housing having certain materials and arrangement of components, those skilled in the art will readily understand that this is merely for purposes of simplifying the present disclosure and that the present invention is not so limited. 
     An air-breathing electrostatic ion thruster that is manufactured out of the components and configured pursuant to a preferred embodiment of the present invention is shown generally as  10  in the figures. Ion thruster  10  generally comprises a housing  12  having a first or forward end  14 , a second or rearward end  16 , an electrically conductive inner surface  18  and an electrically non-conductive outer surface  20 , as shown in  FIG. 1 . In a preferred embodiment, housing  12  will be made out of a generally lightweight material that has its interior coated with a conductive material to form inner surface  18  and its exterior coated with a non-conductive/insulating material to form outer surface  20 . In an alternative embodiment, both inner  18  and outer  20  surfaces are formed from separate cylindrically shaped shells that are joined in abutting relation, with the inner shell, defining inner surface  18 , disposed symmetrically within the outer shell, defining outer surface  20 , to substantially provide an integral housing  12  having an inner conductive layer and an outer non-conductive layer. Preferably, inner surface  18  will be formed from a metallic material that is known to be highly conductive, such as brass, aluminum, magnesium, copper or like materials. Conversely, outer surface  20  should be formed from an electrically non-conductive, insulating material such as plastic or nylon, with materials such as Delrin, a trademark of DuPont, or the like being preferred due to its resistance to high voltage and high temperature breakdown. Inner surface  18  defines an ionization chamber  22  having an inlet  24  at the forward end  14  of housing  12  and an outlet  26  at the rearward end  16 . As explained in more detail below, ambient atmospheric gas  28  is received through inlet  24  and is ionized in ionization chamber  22 , with inner surface  18  functioning as an anode (a cylindrical anode in  FIG. 1 ), to discharge accelerated ions  30  through outlet  26  at the rearward end  16  of housing  12  so as to create thrust to propel a vehicle (not shown) utilizing ion thruster  10  of the present invention. 
     Positioned inside inlet  24 , generally at or near forward end  14  of housing  12  and attached thereto, is forward screen electrode  32 . In one embodiment, forward screen electrode  32  has a plurality of spaced apart electrically conductive metallic wires or members  34  that define a plurality of forward screen apertures  36  of sufficient size to easily permit atmosphere gas  28  to pass therethrough into ionization chamber  22 . Alternatively, forward screen electrode  32  can be other screen or screen-like devices, such as a plate having the plurality of forward screen apertures  36 . As explained below, however, the wires or other electrically conductive members  34  forming forward screen electrode  32  must have sufficient surface area to apply an electrical charge thereto. As will be clearly understood by those skilled in the art, a variety of different configurations are possible for forward screen electrode  32 , including a typical screen configuration having square, rectangular, circular or oval apertures  36  or formed from metallic or other electrically conductive wires or members  34  that are joined together in a manner that provides sufficient gaps for apertures  36  (i.e., slits or slots similar to blinds, etc.). Positioned inside outlet  26  generally at or near rearward end  16  of housing  12 , and attached thereto, is rearward screen electrode  38  having rearward screen apertures  40  and accelerator electrode (or grid)  42  having accelerator apertures  44 . As shown in  FIG. 1 , accelerator electrode  42  is positioned rearward of and in spaced apart relation to, although generally close to, rearward screen electrode  38  in a manner such that the rearward screen apertures  40  are aligned with accelerator apertures  44 . As with forward screen electrode  32 , the apertures  40  and  44  of both rearward screen electrode  38  and accelerator electrode  42  can be defined by a plurality of metallic wire or other electrically conductive members, shown as  46  and  48 , that provide sufficient surface area to apply an electrical charge thereto (alternatively it can be other screen or screen-like devices, such as a plate having the plurality of rearward screen apertures  40 ). The apertures  40  and  44  of rearward screen electrode  38  and accelerator electrode  42 , respectively, should be sufficiently sized and configured to permit the flow of charged, accelerated ions  30  to generally pass therethrough. The function of forward screen electrode  32 , rearward screen electrode  38  and accelerator electrode  42  in ion thruster  10  of the present invention is explained below. 
     Disposed inside ionization chamber  22 , preferably near forward screen electrode  32  at inlet  24 , is inner electrode  50 . As shown in the preferred embodiment of  FIG. 1 , inner electrode  50  is generally positioned at or near the center of ionization chamber  22  and held in place by insulating struts  52 , which preferably connect to inner surface  18  or housing  12 . Alternatively, struts  52  can connect to forward screen electrode  38  or rearward screen electrode  38 . Various different configurations for inner electrode  50  can be utilized with ion thruster  10  of the present invention. In the preferred embodiment of  FIG. 1 , inner electrode  50  comprises a support tube  54  connected to struts  52  with a plurality of conductive electrode emitters  56  extending rearward therefrom. In the preferred embodiment, inner electrode  50  is a cathode configured to emit electrons into ionization chamber  22  to ionize the atmospheric gas  28  entering through inlet  24 . As explained in more detail below, once the atmospheric gas  28  is ionized it will be drawn toward rearward and accelerated by accelerator screen  42  to displace accelerated ions  30  rearward of ionization chamber  22  to create thrust so as to propel a vehicle utilizing ion thruster  10  of the present invention. 
     As shown in the schematic of  FIG. 2  for the electrical circuit for ion thruster  10  of the present invention, a source of electrical power  58  supplies current to the conductive inner shell (anode)  18 , inner electrode  50  and the various electrodes  32 ,  38  and  42  utilized for ion thruster  10 , as well as other components described below. In a preferred embodiment, the source of electrical power  58  is a solar cell array connected to a battery or fuel cell. Alternatively, various other sources of electrical power  58 , such as a small generator or the like, which is suitable for the vehicle utilized with ion thruster  10  may be provided as the source of electrical power  58 . Preferably, a controller  60  is utilized with ion thruster  10  of the present invention to control the voltages supplied to the various components and the polarity thereof. In a preferred configuration, controller  60  controls the source of electrical power  58  to deliver a first polarity  62 , which is positive, to inner surface  18 , forward screen electrode  32  and rearward screen electrode  38  and deliver a second polarity  64 , which is negative, to accelerator electrode  42  and inner electrode (cathode)  50 , as shown in  FIG. 2 . Alternatively, the polarity supplied by the source of electrical power  58  can be switched so as to be reversed. As well known to those skilled in the art, the electronic signals from controller  60  are preferably controlled by a microprocessor that initiates and regulates the amount of thrust generated by ion thruster  10 . As also well known, the controller  60  can be positioned on ion thruster  10 , in the vehicle using ion thruster  10  or at a ground station or other remote station. Depending on the desired effects, the various voltages and/or the polarity thereof can be controlled by controller  60  to create the optimal thrust based on the circumstances. In an alternative configuration, ion thruster  10  comprises a plurality of separate sources of electrical power  58  and/or a plurality of separate controllers  60  that individually, but in cooperative fashion, operate the components of ion thruster  10 . 
     In operation, the source of electrical power  58  (as controlled by controller  60 ) supplies electrical current having a first polarity  62  to inner shell  18 , forward screen electrode  32  and rearward screen electrode  38  and supply electrical current having a second polarity  64  to accelerator electrode  42  and inner electrode  50 . Ambient atmospheric gas  28  enters ionization chamber  22  through forward screen electrode  32  at inlet  24  to mix with the electrons emitted by the cathode (inner electrode  50 ) at electrode emitters  56  to generate positively charged ions (in the preferred embodiment with first polarity  62  being positive and second polarity  64  being negative), shown as  66  in  FIG. 1 . Because the polarity of forward screen electrode  32  is also positive, the forward screen electrode  32  will repel the positively charged ions  66  away from inlet  24  in a generally rearward direction. The positively charged rearward screen electrode  38  and inner surface  18  (having first polarity  62 ) will attract the electrons from inner electrode/cathode  50  to facilitate mixture thereof with the atmospheric gas  28  to generate positive ions  66 . The negatively charged (second polarity  64 ) accelerator electrode  42  will attract the positively charged ions  66  and accelerate them through the outlet  26  at the rearward end  16  of housing  12  to provide accelerated ions  30  for thrust. The positively charged (first polarity  62 ) conductive inner surface  18  will maintain the positively charged ions  66  moving rearward in ionization chamber  22 . With the preferred solar cell array and battery/fuel cell arrangement for the source of electrical power  58 , ion thruster  10  will be able to operate for an extended period of time without additional input of energy. 
     In the preferred embodiment of ion thruster  10  of the present invention, one or more magnets or series of magnets  68  are positioned outside housing  12 , as shown in  FIG. 1 , or inside ionization chamber  22  to surround portions of the ionization chamber  22 . As known to those skilled in the art, magnets  68  can be permanent or electromagnetic, with the latter being preferred, and magnets  68  can be positioned inside chamber  22 . If electromagnetic magnets  68  are utilized, they can be electrically connected to the source of electrical power  58  and the amount of current supplied thereto can be regulated by controller  60 . The magnetic field produced by magnets  68  will cause the electrons to spiral in a helix shape to obtain improved interaction (i.e., collision) between the electrons and the atmospheric gas  28  to facilitate more efficient and effective formation of the positive ions  66  necessary to provide thrust for ion thruster  10 . In addition, the axial magnetic field within ionization chamber  22  created by magnets  68  will tend to restrain the path of the electrons emitted by cathode  50  to inhibit them from being drawn directly to inner surface  18  (the anode), thereby preventing excessive loss of electrons that are needed to form positively charged ions  66  from atmospheric gas  28 . 
     Also in the preferred embodiment, shown in  FIG. 1 , ion thruster  10  includes a neutralizing mechanism or means  70  near the rearward end  16  of housing  12  (near outlet  26 ) to interact with the accelerated ions  30  exiting ionization chamber  22  at outlet  26  so as to place the ion thruster  10  in an electrically neutral condition. In the preferred polarity arrangement, with first polarity  62  being positive and second polarity  64  being negative, neutralizing mechanism  70  comprises a negatively charged neutralizer electrode  72  that emits electrons to compensate for the flow of positively charged accelerated ions  30 . As shown on  FIG. 2 , in the preferred embodiment the neutralizer electrodes  72  are electrically connected to the source of electrical power  58  and, also preferably, controlled or regulated by controller  60 . 
     The preferred embodiment of ion thruster  10  of the present invention will incorporate an ozone reduction mechanism (not shown) at or near the rearward end  16  of housing  12  to interact with the discharge gas produced by the ion thruster  10  so as to reduce or even eliminate the ozone that is a by-product of the ionization process. Various other variations are also possible for ion thruster  10 . For instance, the size and configuration of housing  12  and the ionization chamber  22  can be varied, as well as the operating voltages, polarity, positioning and size/shape of the electrodes, size and shape of the inlet and/or outlet (i.e., so as to compress the atmospheric air  28  or otherwise tuned for aerodynamic purposes) and the materials used for the various components of ion thruster  10  so as to obtain the most efficient amount of thrust generation for the desired purposes of the vehicle. In addition, the size, placement (including whether inside or outside ionization chamber  22 ), type (i.e., permanent or electromagnetic magnets), shape and magnetic strength of magnets  68  can be varied. 
     While there are shown and described herein a specific form of the invention, it will be readily apparent to those skilled in the art that the invention is not so limited, but is susceptible to various modifications and rearrangements in design and materials without departing from the spirit and scope of the invention. In particular, it should be noted that the present invention is subject to modification with regard to any dimensional relationships set forth herein and modifications in assembly, materials, size, shape, and use. For instance, there are numerous components described herein that can be replaced with equivalent functioning components to accomplish the objectives of the present invention.