Propeller adopting electron cyclotron resonance

Abstract

The present invention relates to a satellite thruster (10) employing electron cyclotron resonance and a magnetic nozzle, the satellite thruster (10) extending at least partially along a longitudinal axis (X), the satellite thruster (10) comprising an outer conductor (22) and an ionization chamber (8) extending longitudinally along the axis, the outer conductor delimiting the ionization chamber in the transverse direction, the outer conductor (22) being arranged in the outer conductor (22), and the ionization chamber (8) being arranged in the outer conductor (22). The ionization chamber comprises a circular transverse aperture (24) having a diameter D, characterized in that the satellite thruster (10) further comprises shielding means (6) coaxial to the longitudinal axis (X), the shielding means (6) having a maximum transverse dimension D 'such that the ratio of D' divided by D is between 3 and 15, said shielding means (6) comprising a portion made of a dielectric material (61) and / or a portion made of an electrically conductive material (62).

Description

Technical Field

[0001] The present invention relates to an electron cyclotron resonance thruster. Background Art

[0002] Artificial satellites require thrusters to position and maintain their positions, and to perform trajectory or attitude correction operations. Similarly, space probes for exploring the solar system have thrusters that allow them to position the space probe very precisely around a selected planet, or even to land on an asteroid to collect material samples.

[0003] Generally speaking, the thrust provided by these small thrusters does not exceed a few newtons. Chemical thrusters use liquid propellants such as hydrazine (N2H2) or hydrogen peroxide (oxygenated water). During the decomposition of these propellants, chemical energy is converted into heat, and then the hot gas is converted into thrust during expansion in a suitable nozzle. Materials are ejected at high speed and generate a reaction force called thrust. This thrust is used to change the moment of a spacecraft, probe or satellite, and to affect the trajectory of a spacecraft, probe or satellite. The well-known limitations of these technologies are related to the ejection speed achievable by the gas. In addition, the mass of the propellant may account for a large part of the total mass of the satellite, thus reducing the payload of the satellite, which constitutes a second limitation.

[0004] However, by using ionized gas particles that are accelerated and ejected from the vehicle by means of an electric field and / or a magnetic field, the ejection speed of the propellant gas can be increased by several orders of magnitude. These so-called plasma or plasma thrusters make it possible to perform tasks with greater trajectory correction with an equal amount of material carried, or to perform tasks with equal trajectory correction with less material carried. This can reduce the mass of the satellite, or increase its payload while keeping the mass unchanged.

[0005] As the number of new satellites equipped only with plasma thrusters increases, it is obvious that these thrusters have great application value. However, they also pose many technical challenges.

[0006] For example, the earliest ECR (English abbreviation for "electron cyclotron resonance") type plasma propellant used in spacecraft, that is, the propellant using electron cyclotron resonance, has the disadvantage that it cannot be miniaturized. Its size is determined by the size of its cavity for coupling electromagnetic waves with the plasma, because this coupling is necessary for plasma ignition. Patent FR 1162545B1 proposed a small electron cyclotron resonance thruster, the core of which is capable of igniting plasma in a very small volume through magnetized electron resonance (ECR). This benefits from a special configuration of the ionized gas inlet, magnetic field lines and electromagnetic wave coupling.

[0007] Nevertheless, it is still desirable to improve the performance of such thrusters. In addition, problems related to extending the service life still exist. Problems with component corrosion and wear due to plasma discharge still exist.

[0008] Technical problems

[0009] In view of this situation, the object of the present invention is to provide a novel electron cyclotron resonance thruster that does not have the above-mentioned drawbacks, or reduces some of the above-mentioned drawbacks of the electron cyclotron resonance thruster. Summary of the invention

[0010] The present invention particularly aims to provide a particularly efficient electron cyclotron resonance thruster. Thus, one aspect of the present invention relates to an electron cyclotron resonance thruster that extends at least partially along a longitudinal axis, the electron cyclotron resonance thruster including an outer conductor and an ionization chamber that extend longitudinally along the axis, the outer conductor laterally defining the ionization chamber, the ionization chamber including a circular lateral opening 24 having a diameter D, characterized in that the electron cyclotron resonance thruster further includes a shielding device coaxial with the longitudinal axis, the shielding device having a maximum lateral dimension D' such that the ratio of D' divided by D is between 3 and 15, the shielding device including a portion made of a dielectric material and / or a portion made of a conductive material.

[0011] With the present invention, the performance of the thruster can be significantly improved. Compared with prior art plasma thrusters, the thrust generated by such a thruster can be increased by a factor of 1.3. The overall efficiency of the system (here defined as the ratio of the power contained in the plasma jet to the electrical power supplied to the thruster) is increased by a factor of 1.7 compared with prior art plasma thrusters. When the thruster operates and ejects a plasma including ions and electrons, the coaxial shielding device prevents electrons trapped in the most divergent magnetic field lines from contacting a part of the thruster. Thus, these divergent electrons are not collected by the thruster in the form of a current, but instead accumulate near the shielding device, thereby forming a local negative charge. This allows other divergent electrons to be repelled and thus redirected into the emitted particle beam. Therefore, the plasma flow ejected by the thruster is increased.

[0012] According to one aspect of the present invention, the portion made of a dielectric material covers the portion made of a conductive material. According to one aspect of the present invention, the portion made of a dielectric material completely covers the portion made of a conductive material. According to one aspect of the present invention, the dielectric material portion completely covers the conductive material portion such that the outer surface of the shielding device is made of a dielectric material.

[0013] According to another aspect of the present invention, the shielding device is attached to the outer conductor. According to another aspect of the present invention, the thruster includes a magnetic field source, and the shielding device is attached to the magnetic field source. According to another aspect of the present invention, the thruster includes a body, and the shielding device is attached to the body. According to another aspect of the present invention, the thruster includes a magnetic field source and a body, and the shielding device is attached between the magnetic field source and the body. According to one aspect of the present invention, the shielding device is fastened by screws made of dielectric material.

[0014] According to one aspect of the present invention, the part made of dielectric material is configured to electrically insulate the part made of conductive material from the outer conductor. According to one aspect of the present invention, the component made of dielectric material is configured to electrically isolate the part made of conductive material from the rest of the thruster. In this variant, the rest of the thruster includes all the thruster elements except the shielding device.

[0015] According to another aspect of the present invention, the thruster further includes a dielectric material element configured to electrically insulate the shielding device from the outer conductor.

[0016] According to a variant, the part made of conductive material covers the part made of dielectric material. According to one aspect of the present invention, the part made of conductive material completely covers the part made of dielectric material. According to one aspect of the present invention, the part made of conductive material completely covers the part made of dielectric material such that the outer surface of the shielding device is made of conductive material.

[0017] According to one aspect of the present invention, the part made of conductive material has a polarization different from the polarization of the outer conductor or other elements of the thruster. According to one aspect of the present invention, the part made of conductive material has a polarization different from the polarization of the outer conductor or other elements of the thruster except the shielding device. According to one aspect of the present invention, the part made of conductive material has a negative polarization with respect to the outer conductor or with respect to other elements of the thruster. According to one aspect of the present invention, the part made of conductive material has a negative polarization with respect to the outer conductor or with respect to other elements of the thruster except the shielding device.

[0018] With the present invention, the performance of the thruster can be significantly improved. Compared with plasma thrusters of the prior art, the thrust generated by such a thruster can be increased by more than 1.3 times. The overall efficiency of the system (here defined as the ratio of the power contained in the plasma jet to the electrical power supplied to the thruster) is increased by more than 1.7 times compared with plasma thrusters of the prior art. When the thruster operates and ejects a plasma including ions and electrons, the negatively polarized coaxial shielding device pushes the electrons trapped in the most divergent magnetic field lines and thus allows these divergent electrons to be redirected into the emitted particle beam. As a result, the plasma flow ejected by the thruster is increased.

[0019] According to another aspect of the present invention, the shielding device is in the form of a concave disc or has a flared shape, such as a hollow frustum or a nozzle, in the center of the shielding device.

[0020] According to one aspect of the present invention, the outer conductor includes an inner wall made of graphite. According to one aspect of the present invention, the outer conductor includes an inner wall in an integral columnar shape, the inner wall being made of graphite. According to one aspect of the present invention, the outer conductor is entirely made of graphite. According to one aspect of the present invention, the outer conductor is made of a conductive material, and the outer conductor includes an inner wall made of graphite. According to one example, the outer conductor includes a graphite deposit on the inner wall of the outer conductor. According to another example, the outer conductor includes a graphite sleeve on its inner wall.

[0021] Under the impact of plasma ions, the degree of corrosion of graphite is less than that of materials in the prior art (such as aluminum). Therefore, the outer conductor has a longer service life. In addition, plasma electrons impinging on the graphite inner wall of the outer conductor are less likely to re-emit electrons through secondary emission, thus maintaining good plasma confinement and ultimately avoiding energy loss of the plasma to the inner wall of the outer conductor. This significantly improves the performance of the thruster. Compared with plasma thrusters of the prior art, the thrust generated by such a thruster is increased by 1.6 times. Compared with plasma thrusters of the prior art, the overall efficiency of the system (here defined as the ratio of the power contained in the plasma jet to the electrical power supplied to the thruster) is increased by 2.5 times.

[0022] According to one aspect of the present invention, the part made of a dielectric material is made of a mixture of glass fiber and epoxy resin. According to one aspect of the present invention, the part made of a dielectric material is made of a mixture of carbon fiber and epoxy resin. This combination makes it possible to obtain a more robust shielding device while making it lighter and thinner.

[0023] According to other exemplary embodiments, the part made of a dielectric material is made of resin, or made of a type of polyimide, or made of a ceramic (such as alumina or boron nitride or ceramics).

[0024] According to one aspect of the invention, the part made of a dielectric material is made of polyetheretherketone (PEEK) or polyetherketoneketone (PEKK).

[0025] According to one aspect of the invention, the part made of a conductive material is, for example, a metal reinforcement.

[0026] According to one aspect of the invention, the part made of a conductive material is made of stainless steel or graphite or aluminum.

[0027] According to one aspect of the invention, the part made of a dielectric material is a film made of an insulating material. For example, the part made of a dielectric material is a polyimide film of the type.

[0028] According to one aspect of the invention, the part made of a dielectric material is a polymer-based coating layer, for example a coating layer based on polydimethylsiloxane (PDMS).

[0029] According to one aspect of the invention, the part made of a dielectric material has a thickness of from 200 nanometers to 1 millimeter. According to one aspect of the invention, the part made of a dielectric material has a thickness greater than 1 micrometer.

[0030] According to one aspect of the invention, the part made of a conductive material has a thickness of from 200 nanometers to 1 millimeter. According to one aspect of the invention, the part made of a conductive material has a thickness greater than 1 micrometer.

[0031] A thickness greater than one micrometer allows the shielding device to have better durability and withstand the erosion associated with the space environment.

[0032] According to one aspect of the invention, the part made of a dielectric material includes a resin reinforcement and a polyimide film of the type.

[0033] According to one aspect of the invention, the part made of a conductive material is joined to the part made of a dielectric material.

[0034] According to one aspect of the invention, the part made of a dielectric material is joined to the part made of a conductive material.

[0035] According to one variant, the outer conductor includes: an inner wall and an outer wall separated by a transverse thickness portion; and a homogenization chamber hollowed out into the transverse thickness portion of the wall, the chamber extending longitudinally over a part of the outer conductor and having an overall hollow columnar shape. The homogenization chamber allows gas to be uniformly injected along the perimeter of the ionization chamber. The homogenization chamber allows propellant gas to be injected in a controlled manner.

[0036] According to another aspect of the present invention, the thruster includes means for injecting gas, and the means includes:

[0037] - at least one injection channel that radially penetrates the outer wall of the outer conductor and leads to a homogenization chamber,

[0038] - a homogenization chamber,

[0039] - a connection means configured such that the homogenization chamber leads to an ionization chamber.

[0040] According to one aspect of the present invention, the connection means includes a transverse circular part that partially closes the longitudinal end of the homogenization chamber, and the transverse circular part includes at least three radial grooves that connect the homogenization chamber to the ionization chamber; alternatively, the connection means includes a hole that radially penetrates the inner wall of the outer conductor and leads into the homogenization chamber.

[0041] According to a variant, the thruster further includes a so-called "inner conductor" having a solid columnar geometry, and the inner conductor extends along the longitudinal axis in the ionization chamber. According to one aspect of the present invention, the outer surface of the inner conductor is made of graphite.

[0042] According to one aspect of the present invention, the inner conductor is entirely made of graphite. According to another aspect of the present invention, the inner conductor is made of a conductive material and includes a graphite outer coating. According to another aspect of the present invention, the inner conductor is made of a conductive material and includes a graphite sleeve on its outer surface. According to another aspect of the present invention, the inner conductor is made of a conductive material and includes graphite deposits on its outer surface. Under the impact of plasma ions, the corrosion degree of graphite is lower than that of prior art materials (such as aluminum). Graphite can extend the service life of the thruster.

[0043] The present invention also relates to a method of using a thruster according to the present invention, and the method includes:

[0044] - an electrical connection between a part made of a conductive material and the negative pole of an electrical supply device,

[0045] - an electrical connection between the outer conductor or other components in the thruster except the shielding device and the positive pole of the power supply device,

[0046] - putting the power supply device and the thruster into operation.

[0047] The present invention also relates to a device that includes an electrical supply device and a thruster according to the present invention.

[0048] The present invention also relates to a device that includes:

[0049] - An electron cyclotron resonance thruster, which at least partially extends along a longitudinal axis. The electron cyclotron resonance thruster includes an outer conductor and an ionization chamber. The outer conductor and the ionization chamber extend longitudinally along the axis. The outer conductor laterally defines the ionization chamber. The ionization chamber includes a circular lateral opening having a diameter D. It is characterized in that the electron cyclotron resonance thruster further includes a shielding device coaxial with the longitudinal axis. The shielding device has a maximum lateral dimension D', such that the ratio of D' to D is between 3 and 15. The shielding device includes a part made of a dielectric material and a part made of a conductive material. The part made of the dielectric material is configured to electrically isolate the part made of the conductive material from the rest of the thruster.

[0050] - An electrical supply device, which includes a negative electrode electrically connected to the part made of the conductive material and a positive electrode electrically connected to the outer conductor.

[0051] According to one aspect of the present invention, the device includes a thruster, which includes a magnetic field source and a body. The positive electrode of the electrical supply device is electrically connected to the magnetic field source or the body.

[0052] According to one aspect of the present invention, the device includes a thruster, which includes an inner conductor. The positive electrode of the electrical supply device is electrically connected to the inner conductor.

[0053] Such a device enables a potential difference to be applied to the part made of the conductive material and a part made of the conductive material having a negative polarity with respect to the outer conductor, the inner conductor, the magnetic field source, or the thruster body to be obtained. When the device operates and ejects a plasma including ions and electrons, the negatively polarized coaxial shielding device will push the electrons trapped in the most divergent magnetic field lines and thus allow these divergent electrons to be redirected into the beam of the emitted particles. Therefore, the plasma flow ejected by the thruster is enhanced.

[0054] According to one aspect of the present invention, the device further includes a measurement unit and a processing electronic circuit. The measurement unit and the processing electronic circuit are configured to control the potential difference applied between the part made of the conductive material and the outer conductor, or between the part made of the conductive material and the magnetic field source, or between the part made of the conductive material and the body, or between the part made of the conductive material and the inner conductor.

[0055] According to the present invention, the outer conductor, the inner conductor, the magnetic field source, or the body is referred to as a reference.

[0056] The present invention also relates to a method for controlling the potential difference applied between the part made of the conductive material and the reference by means of the device according to the present invention. The method includes:

[0057] - Measuring the potential difference between a part made of a conductive material and a reference, which is called the effective potential difference; when the power supply device 9 does not apply a potential difference, this potential difference is called the floating potential;

[0058] When the power supply device applies a potential difference, it is called the potential difference,

[0059] - Calculating the difference between the effective potential difference and a predetermined set value,

[0060] - If the difference exceeds a predetermined threshold, then apply a potential difference equal to the set value to the part made of the conductive material through the power supply device, and then the method returns to the first step; if the measured result of the difference does not exceed the predetermined threshold, the method directly returns to the first step.

[0061] According to one aspect of the present invention, the absolute value of the set value is between 10 volts and 1 kilovolt, preferably, the absolute value of the set value is between 100 volts and 500 volts. Description of the Drawings

[0062] Other features and advantages of the present invention will also become apparent from the following description, which is purely illustrative and not restrictive and should be read in conjunction with the accompanying drawings, in which:

[0063] Figure 1 shows in part and schematically a longitudinal cross-sectional view of a thruster according to the present invention;

[0064] Figure 2a , Figure 2b , Figure 2c and Figure 2d show in part and schematically longitudinal cross-sectional views of an open coaxial conductor of a thruster according to the present invention;

[0065] Figure 3a and Figure 3b show in part and schematically longitudinal cross-sectional views of the outer conductor and the inner conductor of a thruster according to the present invention;

[0066] Figure 4a and Figure 4b show in part and schematically a longitudinal cross-sectional view of a thruster according to the present invention;

[0067] Figure 5 shows in part and schematically a longitudinal cross-sectional view of a thruster according to the present invention;

[0068] Figure 6 shows in part and schematically a longitudinal cross-sectional view of a thruster according to the present invention;

[0069] Figure 7 ​​​​​​​Partially and schematically shows a longitudinal cross-sectional view of a thruster according to the present invention;

[0070] Figure 8a and Figure 8b Partially and schematically shows a longitudinal cross-sectional view of an open coaxial conductor and an open coaxial shielding device of a thruster according to the present invention;

[0071] Figure 9 Shows a schematic diagram of a device according to the present invention. Detailed Description

[0072] For clarity, the dimensions of the elements shown in these figures do not correspond to the actual dimensions, nor do they represent the scale of the actual dimensions. In addition, some of these elements are shown only symbolically, and the same reference numerals shown in different figures represent the same elements or have the same functions.

[0073] Figure 1 has partially and schematically shown an electron cyclotron resonance thruster according to the present invention. The thruster 10 extends at least partially along the longitudinal axis X, and the thruster 10 includes: an open coaxial conductor 2, an ionization chamber 8, a gas injection device 3, a microwave power injection device 4, a magnetic field source 1, and a coaxial shielding device 6.

[0074] Briefly review the principle of an electron cyclotron resonance satellite thruster. The device 3 for injecting gas can introduce gas into the ionization chamber 8, and the gas is ionized in the ionization chamber 8 due to the action of microwaves. The microwaves provide the electric power required for ionizing the gas. The microwaves are generated, transmitted, and deposited by the microwave power injection device 4. The signal frequency of the deposited electric power is between 600 MHz and 50 GHz. The electric power is transmitted to the propellant gas according to the coaxial geometry described below, or by means of a waveguide. The magnetic field source 1 can apply a magnetic field to the plasma and thus to the electrons in the plasma. The electrons in the plasma perform a cyclotron motion in a plane perpendicular to the magnetic field (i.e., the quasi-transverse plane). The frequency of this cyclotron motion is determined by the value of the magnetic field. The value of the magnetic field and the microwave signal frequency are selected such that the cyclotron frequency of the electrons is equal to the frequency of the microwave signal. In this way, the electric power provided by the microwave signal will be effectively deposited in the electron population of the plasma through the resonance phenomenon. The alternating electric field of the microwave signal will cause the electrons to accelerate during their cyclotron motion and increase their kinetic energy in the plane perpendicular to the magnetic field (quasi-transverse). In this way, the plasma can maintain excellent energy efficiency. The generated electrons are then ejected at high speed under the action of the magnetic force and thermal expansion. The ejection of the electrons will generate an electric field, which accelerates the ions in the plasma. These ions are ejected at high speed, thereby generating thrust.

[0075] ​​​As for the rest, the front part of the thruster is defined as the longitudinal end of the thruster through which the propellant gas escapes. Thus, in the Figure 1 embodiment, the coaxial shielding device is positioned at the front part of the thruster. Similarly, the rear part of the thruster is defined as the opposite longitudinal end. Thus, the microwave power generator 41 is located at the rear part of the thruster.

[0076] The thruster includes an open coaxial conductor 2 which includes an outer conductor 22 and an inner conductor 21. The outer conductor 22 has an integral hollow columnar shape and is coaxial with the longitudinal axis X, and the outer conductor 22 extends longitudinally along this axis. The inner conductor 21 has a solid columnar geometry and extends longitudinally along the axis X and is located within the outer conductor 22. The thruster includes a transverse plate 23 called the rear plate which has an integral disc shape. The back plate 23 contacts the longitudinal rear end of the outer conductor 22.

[0077] The ionization chamber 8 is formed by the volume located between the outer conductor 22, the inner conductor 21 and the rear plate 23. In other words, the ionization chamber is laterally defined by the outer conductor 22, and the ionization chamber is axially defined by the rear plate 23 at the rear longitudinal end of the ionization chamber. The ionization chamber includes a lateral opening 24 at the front longitudinal end of the ionization chamber. This lateral opening 24 allows the propellant gas to escape. The lateral opening 24 is circular and has a diameter D.

[0078] The outer conductor 22 includes an inner wall 221. As shown in Figure 1 and Figure 2a , the inner wall has a columnar geometry. Alternatively, as shown in Figure 2b , the inner wall 221 has a frustum cone geometry. Alternatively, and as shown in Figure 2c , the inner wall 221 includes: a first part 2211 located at the rear of the ionization chamber 8 and having a columnar geometry, and a second part 2212 having a frustum cone geometry, the second part being positioned to align with the first part, and the rotational axes of the first part and the second part coinciding with the longitudinal axis X. In the previously described embodiments, the outer conductor is machined from a single piece of material. In the Figure 2d shown embodiment, the outer conductor is made of two separate parts. The outer conductor includes a second frustum cone geometry part 225 which is attached to a first part 224 having an integral columnar geometry, and the second frustum cone geometry part 225 extends longitudinally beyond the longitudinal free end 213 of the inner conductor 21. Alternatively, the inner wall geometry is defined by any rotational surface. The outer conductor can radially accommodate the propellant gas to force it to be ejected axially through the opening 24.

[0079] The outer conductor 22 is made of a conductive material. More specifically, according to the present invention, the outer conductor is entirely made of graphite. Alternatively, the outer conductor is made of a conductive material and includes a graphite deposit on its inner wall 221. The graphite deposition is carried out using PVD technology (i.e., the abbreviation for "Physical Vapor Deposition"). For example, the graphite deposition is performed by plasma spraying or magnetron sputtering of a graphite target. A graphite layer with a thickness of 10 microns can be obtained by this technique, which significantly improves the performance of the thruster. Alternatively, a graphite sleeve is inserted into the outer conductor made of a conductive material.

[0080] The inner conductor 21 has a solid columnar geometry and extends longitudinally along the axis X. The inner conductor includes an outer surface made of graphite. For example, as Figure 3a shown, the inner conductor 21 is entirely made of graphite. Alternatively, the inner conductor is made of a conductive material that includes a graphite outer coating. For example, the conductive material is coated with a graphite deposit, such as by magnetron sputtering or plasma sputtering of a graphite target. A graphite layer with a thickness of 10 microns can be obtained by this technique, which significantly improves the performance of the thruster. In another example and as Figure 3b shown, the inner conductor includes a first part 211 made of a conductive material and a second part 212 made of graphite. The first part 211 includes a first solid column and extends along the longitudinal axis X. The first part 211 extends axially out of a columnar head, and the diameter of the columnar head is larger than the diameter of the first column. The second part 212 includes a sleeve complementary to the first part, such that the combination of the first part and the second part forms a solid column extending along the X axis in the ionization chamber. In this example, the columnar head is covered with a graphite deposit, which is not shown in Figure 3b .

[0081] The outer conductor 22 and the inner conductor 21 form an open coaxial conductor 2, which allows microwaves to be deposited in the ionization chamber. The microwaves are generated and provided by a microwave power generating device 4 described later.

[0082] The outer conductor 22 includes an outer wall 222, and the outer wall 222 is separated from the inner wall 221 by a transverse thickness portion 223. The outer conductor includes a homogenization chamber 32 hollowed out into the transverse thickness portion 223. The homogenization chamber 32 extends longitudinally on a part of the outer conductor 22. The homogenization chamber has an overall hollow columnar shape.

[0083] The gas injection device 3 includes:

[0084] - at least one injection channel 31, which radially penetrates the outer wall 222 of the outer conductor and partially penetrates the transverse thickness portion 223 and leads into the homogenization chamber 32,

[0085] - the homogenization chamber 32,

[0086] - A connection device configured to connect the homogenization chamber to the ionization chamber.

[0087] The connection device includes, for example, a transverse circular portion 331 that presses against the rear plate 23. The transverse circular portion 331 partially encloses the longitudinal rear end of the homogenization chamber 32. The transverse circular portion 331 includes at least three radial grooves for connecting the homogenization chamber 32 to the ionization chamber 2. Alternatively, holes that radially penetrate the inner wall 221 of the outer conductor and lead to the homogenization chamber may also be provided. In this second embodiment, the rear end of the homogenization chamber is directly closed by the rear plate 23 or by the transverse circular portion 331, and in this example, the transverse circular portion 331 does not contain grooves.

[0088] The propellant gas is injected into the homogenization chamber via at least one injection channel 31. Then, the gas propagates longitudinally and transversely in the homogenization chamber 32 and then enters the ionization chamber via the radial grooves of the transverse circular portion 331. The ionization chamber enables the gas to be injected into the ionization chamber in a controlled manner.

[0089] The rear plate 23 includes a dielectric material that enables it to withstand high thermal loads while being relatively transparent to microwaves. For example, the rear plate is made of ceramic or quartz. The rear plate allows the propellant gas to diffuse to the opening 23 of the thruster. It also receives most of the heat flux from the plasma. The thruster includes a body 5 integrated with the rear plate 23.

[0090] The body 5 of the thruster is made of a conductive material. The body 5 ensures the mechanical fastening of the various elements of the thruster. It also enables an electrical connection to be established between the microwave power injection device 4 and the open coaxial conductor 2.

[0091] The microwave power injection device 4 includes a microwave power generator 41 and a transmission coaxial conductor 42. In an alternative not described herein, the device for injecting microwave power includes a waveguide 42.

[0092] The microwave power generator 41 generates the microwaves required for the operation of the thruster. The microwave power generator 41 generates a signal with a frequency of 2.45 GHz (gigahertz) from several tens of W (watts) to several kW (kilowatts). This signal is generated by a DC voltage of several tens of V (volts) and using microwave oscillation techniques. This signal is amplified by a solid-state amplifier or a field-effect amplifier (traveling-wave tube, klystron).

[0093] The transmission coaxial conductor 42 transmits the microwave signal from the generator 41 to the open coaxial conductor 2. The transmission coaxial conductor 42 has an impedance of 50 ohms. The transmission coaxial conductor 42 includes an inner conductor 421 and an outer conductor 422 that are concentric with each other. The inner conductor 421 and the outer conductor 422 are separated from each other by a concentric insulating layer 423, which is made of, for example, polytetrafluoroethylene (PTFE) or boron nitride (BN).

[0094] The magnetic field source 1 includes a coil 12 or a set of coils powered by an electric current. Alternatively, the magnetic field source includes a permanent magnet or a set of permanent magnets. For a microwave signal with a frequency of 2.45 GHz, the magnetic field strength is adjusted to 875 gauss so that the electron cyclotron resonance region is located at the first two centimeters downstream of the rear plate 23. The magnetic field is stronger inside the source 1 but rapidly weakens at a distance from the thruster outlet, thus forming a longitudinal magnetic field gradient. In addition, the magnetic field diverges locally at the outlet of the ionization chamber, thus forming a magnetic nozzle that helps accelerate the plasma ions.

[0095] The thruster 10 according to the present invention includes a coaxial shielding device 6. As Figure 1 shown, the coaxial shielding device 6 extends transversely to the axis X. The coaxial shielding device 6 is directly fastened to the longitudinal front end of the outer conductor 22 by means of three screws 63. Alternatively, the coaxial shielding device 6 is fastened at another axial position on the outer conductor 22. For example, the coaxial shielding device 6 is advantageously fastened to the outer conductor 22 at the shoulder 226 of the outer conductor 22, as shown by Figure 4b . Alternatively and as shown by Figure 7 , the coaxial shielding device 6 is fixed between the body 5 and the magnetic field source 1. In this exemplary embodiment, the shielding device is fixed by three screws 63 that pass through the shielding device and hold the magnetic field source 1 as a whole to the body of the thruster 5. Alternatively and as shown by Figure 4a , the coaxial shielding device 6 is fixed to the magnetic field source 1. In this exemplary embodiment, the shielding device is fastened to the cover 13 by means of screws 63. In another example not shown, the shielding device is between two covers 13 and 14 that hold the coil 12, and the covers 13, 14 and the shielding device 6 are screwed together in the longitudinal direction.

[0096] The coaxial shielding device 6 has a concave disc shape in the middle to keep the opening 24 of the ionization chamber unobstructed, thus allowing the propellant gas to be ejected. Alternatively, and as shown by Figure 5 , the coaxial shielding device has a hollow frustum shape in the middle.

[0097] The coaxial shielding device 6 has a maximum lateral dimension D'. In the Figure 1 exemplary embodiment, this maximum lateral dimension is the diameter D'. In the Figure 5In the exemplary embodiment in [], the maximum lateral dimension D' is the dimension obtained by projecting the shielding device in the lateral direction. The maximum lateral dimension D' is selected such that the ratio of D' / D is between 3 and 15. In Figure 1 In the exemplary embodiment in [], the ratio of D' / D is 9. The drawings do not quantitatively depict this ratio. These are only schematic diagrams and no dimensions or dimension ratios can be extracted from them.

[0098] According to Figure 1 In the exemplary embodiment in [], the coaxial shielding device 6 is made entirely of a dielectric material, here the coaxial shielding device 6 is entirely made of a mixture of fiberglass and epoxy resin. Alternatively, the shielding device is made of type polyimide or made of a ceramic such as alumina or boron nitride. Alternatively, as shown in Figure 8a In [], the shielding device includes a portion 62 of conductive material, and the conductive material 62 is covered by a dielectric material 61. The portion made of the conductive material 62 is, for example, a metal reinforcement, and the resin 61 is cast on the portion made of the conductive material 62. Alternatively, a film 61 made of an insulating material is attached to a metal frame or structure 62. The film 61 is made of, for example, type polyimide. The screw 63 can be made of a dielectric material, such as polyetheretherketone (PEEK) or polyetherketoneketone (PEKK).

[0099] Alternatively, and as shown in Figure 6 In [] and Figure 8b In [], the shielding device includes a portion 61 made of a dielectric material and a portion 62 made of a conductive material. The portion 61 made of the dielectric material is configured to electrically isolate the portion 62 made of the conductive material from other elements of the thruster. The portion 61 made of the dielectric material is, for example, in the form of an annular member, and the portion 62 made of the conductive material is mounted and fixed on the annular member. Alternatively, and according to Figure 6In the embodiment shown in [], the part made of dielectric material has a conical geometry and is a frustum of a cone, and the part made of dielectric material is attached in a manner aligned with the outer conductor 22. The rotational axes of the part 61 made of dielectric material and the outer conductor 22 coincide with the longitudinal axis X. The part made of dielectric material extends longitudinally beyond the longitudinal free end of the inner conductor 21. The part 62 made of conductive material is attached to the part 61 made of dielectric material. The part 62 made of conductive material is made of, for example, stainless steel, graphite or aluminum. Screws made of dielectric material can be used to attach the shielding device 6 to the outer conductor 22 or any other element of the thruster 10. For example, if the fastening screw penetrates the part 62 made of conductive material and the part 61 made of dielectric material and is fixed to the outer conductor 22, screws made of polyetheretherketone (PEEK) or polyetherketoneketone (PEKK) are used. The part 62 made of conductive material is electrically connected to the negative pole of the power supply device 9, and the positive pole of the supply device is connected to the outer conductor 22. After the power is turned on, the part made of conductive material is negatively polarized. The reference is grounded, and this ground is common with respect to the outer conductor 22, the magnetic field source 1 and the thruster body 5, and the outer conductor 22, the magnetic field source 1 and the thruster body 5 are electrically connected to each other. Alternatively, any element of the thruster (such as the inner conductor 21) can be used as the reference.

[0100] In the Figure 8b embodiment shown, the part 62 made of conductive material covers the part 61 made of dielectric material. The part 61 made of dielectric material is, for example, a reinforcement, and the reinforcement includes an outer layer made of conductive material, and this outer layer constitutes the part made of conductive material. This cladding is obtained, for example, by depositing a conductive material according to PVD technology. The part 62 made of conductive material can also be joined to the part 61 made of dielectric material. For these exemplary embodiments, the electrostatic potential of the part made of conductive material can be uncontrolled and remain floating, or fixed according to the same characteristics described in the previous paragraph with reference to Figure 6 .

[0101] The present invention also relates to a device 113, which device 113 includes a power supply device 9 (as Figure 6 shown) and a thruster 10 according to the present invention.

[0102] The device 113 can include more elements, as Figure 9 shown. Thus, the device 113 includes:

[0103] - An electron cyclotron resonance thruster 10, which at least partially extends along a longitudinal axis. The electron cyclotron resonance thruster 10 includes an outer conductor 22 and an ionization chamber 8. The outer conductor 22 and the ionization chamber 8 extend longitudinally along this axis. The outer conductor 22 laterally defines the ionization chamber 8. The ionization chamber includes a circular lateral opening 24 with a diameter D. It is characterized in that the electron cyclotron resonance thruster 10 further includes a coaxial shielding device along the longitudinal axis X

[0104] 6. The coaxial shielding device 6 has a maximum lateral dimension D', such that the ratio of D' to D is between

[0105] 3 and 15. The shielding device 6 includes a part made of a dielectric material 61 and a part made of a conductive material 62. The part made of the dielectric material 61 is configured to electrically isolate the part made of the conductive material 62 from the rest of the thruster

[0106] - An electrical supply device 9, which includes a negative electrode electrically connected to the conductive material part 62 and a positive electrode electrically connected to the outer conductor 22

[0107] Alternatively, the device 113 includes a thruster, which includes a magnetic field source 1 and a body 5. The positive electrode of the electrical supply device 9 is electrically connected to the magnetic field source 1 or the body 5

[0108] Alternatively, the device 113 includes a thruster 10, which includes an inner conductor 21. The positive electrode of the electrical supply device 9 is electrically connected to the inner conductor 21

[0109] The device 113 further includes a measurement unit 111 and a processing electronic circuit 112. Both the measurement unit 111 and the processing electronic circuit 112 are configured to control the potential difference applied between the conductive material part 62 and the outer conductor 22, or between the conductive material part 62 and the magnetic field source 1, or between the conductive material part 62 and the body 5, or between the conductive material part 62 and the inner conductor 21

[0110] The outer conductor 22 or the inner conductor 21 or the magnetic field source 1 or the body 5 is called a reference

[0111] The present invention also relates to a method for controlling the potential difference applied between a part 62 made of a conductive material and a reference by means of the device 113 according to the present invention. The method includes

[0112] - Measuring the potential difference Vmes between the conductive material part 62 and the reference, which is called the effective potential difference Veff; when the electrical supply device 9 does not apply a potential difference, this potential difference is called the floating potential Vflott; when the electrical supply device applies a potential difference, this potential difference is called Vappl

[0113] - Calculate the difference ε between the effective potential difference Veff and a predetermined set value Vcons.

[0114] - If the difference ε exceeds a predetermined threshold, apply a potential difference Vappl equal to the set value Vcons to the part 62 made of a conductive material through the electrical supply device 9, and then the method returns to the first step; if the measured difference ε does not exceed the predetermined threshold, the method directly returns to the first step.

[0115] The absolute value of the set value Vcons is between 10 volts and 1 kilovolt, and preferably, the absolute value of the set value Vcons is between 100 volts and 500 volts.

Claims

1. A satellite thruster (10), the satellite thruster (10) employing electron cyclotron resonance and a magnetic nozzle, the satellite thruster (10) extending at least partially along a longitudinal axis (X), the satellite thruster (10) comprising an outer conductor (22) and an ionization chamber (8), the outer conductor and the ionization chamber extending longitudinally along the axis, the outer conductor defining the ionization chamber laterally, the ionization chamber including a circular transverse opening (24) having a diameter D, characterized in that, The satellite thruster (10) further comprises a shielding device (6) coaxial with the longitudinal axis (X), the shielding device (6) having a maximum transverse dimension D' such that the ratio of D' to D is between 3 and 15, the shielding device (6) comprising a portion (61) made of a dielectric material and a portion (62) made of a conductive material, the portion made of a dielectric material covering the portion made of a conductive material, or the shielding device being entirely made of a dielectric material.

2. The thruster (10) according to claim 1, characterized in that, The portion (61) made of a dielectric material completely covers the portion (62) made of a conductive material such that the outer surface of the shielding device (6) is made of a dielectric material.

3. The thruster according to any one of the preceding claims, characterized in that, The shielding device (6) is attached to the outer conductor (22).

4. The thruster according to any one of claims 1 or 2, characterized in that The thruster comprises a magnetic field source (1) and a body (5), and the shielding device (6) is attached to the magnetic field source (1), or attached to the body (5), or attached between the magnetic field source (1) and the body (5).

5. The thruster according to any one of the preceding claims, characterized in that, The part (61) made of a dielectric material or the shielding device (6) is made of a mixture of glass fiber and epoxy resin, or a mixture of carbon fiber and epoxy resin, or resin, or a polyimide of the type, or made of ceramic.

6. The thruster according to any one of the preceding claims, characterized in that, The shielding device (6) includes a resin reinforcing member and type polyimide film.

7. The thruster according to any one of claims 1 to 5, characterized in that, The portion made of a conductive material is a metal reinforcement.

8. The thruster according to any one of the preceding claims, characterized in that The shielding device (6) comprises a disk-shaped shape that is recessed in the center of the shielding device or comprises a horn shape, such as a truncated hollow cone or a nozzle.

9. The thruster according to any one of the preceding claims, characterized in that, The outer conductor (22) comprises an inner wall (221) made of graphite.

10. The thruster according to the previous claim, characterized in that, The outer conductor (22) comprises an inner wall (221) and an outer wall (222) separated by a transverse thickness portion (223), and the outer conductor (22) comprises a homogenization chamber (32) hollowed out into the transverse thickness portion (223), the homogenization chamber longitudinally extending on a portion of the outer conductor and having an overall hollow columnar shape.

11. The thruster according to the preceding claim, characterized in that, The thruster comprises means (3) for injecting gas, the means comprising: - at least one injection channel (31) that radially penetrates the outer wall (222) of the outer conductor and partially penetrates the transverse thickness portion (223) of the outer conductor and opens into the homogenization chamber (32), - the homogenization chamber (32), - a communication means configured such that the homogenization chamber (32) opens into the ionization chamber (8).

12. The thruster according to the previous claim, characterized in that, The communication means comprises a transverse circular portion (331) that partially closes the longitudinal end of the homogenization chamber, the transverse circular portion comprising at least three radial grooves that communicate the homogenization chamber with the ionization chamber; alternatively, the communication means comprises a hole that radially penetrates the inner wall (221) of the outer conductor and opens into the homogenization chamber.

13. The thruster according to any one of the preceding claims, characterized in that, The thruster further comprises a so-called inner conductor (21) having a solid columnar geometry that extends along the longitudinal axis (X) in the ionization chamber, the inner conductor comprising an outer graphite surface.

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