Voltage generation device

Abstract

This voltage generation device is provided in a Hall thruster system that generates thrust of a spacecraft. In the voltage generation device, a first end is connected to a first line on an anode electrode side in an anode power source for supplying power between an anode electrode and a cathode electrode that are included in a Hall thruster constituting the Hall thruster system, and a second end for outputting an output voltage corresponding to an input voltage at the first end is connected to a keeper electrode disposed close to a hollow cathode connected to the cathode electrode.

Description

Voltage Generator

[0001] This application claims priority from Japanese Patent Application No. 2024-007466, filed on Jan. 22, 2024, the contents of which are incorporated herein by reference.

[0002] The use of electric propulsion devices, which generate thrust to control the orbit and attitude of spacecraft such as satellites, is expanding, and the market is growing rapidly. Compared to chemical propulsion devices, electric propulsion devices require less propulsion gas on board spacecraft, and therefore are increasingly being adopted not only for deep space exploration satellites and geostationary satellites, but also for constellation satellites operating in low orbit. In recent years, the use of electric propulsion systems, particularly those using Hall thrusters, has been rapidly increasing. This is due to the advantage that Hall thruster systems generate high thrust per unit of power.

[0003] A Hall thruster generates thrust by ionizing a specific gas, such as xenon, to generate plasma, accelerating ions extracted from the plasma, and then ejecting the ions into space. In a Hall thruster system, a power processing unit (PPU) supplies power to the Hall thruster to generate a discharge, which then extracts ions from the plasma generated by the discharge. The power processing unit includes a power controller and multiple power sources, such as an anode power supply, a keeper power supply, a heater power supply, and a coil power supply. The power processing unit accounts for a large proportion of the weight and cost of a Hall thruster system. Therefore, reducing the cost and size of the power processing unit is crucial for achieving a Hall thruster system.

[0004] In response to this, various technologies have been proposed for miniaturizing and reducing the cost of power processing units. One such proposal is to miniaturize the anode power supply, which accounts for a large portion of the power supplied to the Hall thruster among the multiple power sources constituting the power processing unit. Examples of miniaturizing the anode power supply include a resonant converter (see, for example, Patent Document 1) and a filter included in the anode power supply that reduces the size by varying the output voltage of the anode power supply at a high frequency to suppress the discharge instability specific to Hall thrusters (see, for example, Patent Document 2). Another proposal is to eliminate the heater power supply for the hollow cathode of the Hall thruster among the multiple power sources constituting the power processing unit, and instead apply a high-voltage pulse generated by a keeper power supply to initiate discharge in the hollow cathode (see, for example, Patent Document 3). In this conventional technology, the electron-emitting material is not heated by a heater power supply, but rather electrons are powerfully drawn out from the hollow cathode by a high voltage pulse generated by a keeper power supply, generating a discharge and plasma between the hollow cathode and the keeper electrode.

[0005] US Patent No. 6,169,668 Specification Japanese Patent Application Laid-Open No. 2014-005762 Japanese Patent Application Laid-Open No. 2022-530748

[0006] However, in conventional technologies that reduce the size and cost of the power processing unit by miniaturizing the anode power supply, the anode power supply, which is a power source essential for accelerating and ejecting gas in a Hall thruster, is miniaturized, which may result in other issues for ensuring the performance of the Hall thruster system, such as the need to increase the power density of the anode power supply. On the other hand, in conventional technologies that reduce the size and cost of the power processing unit by eliminating the heater power supply, other issues for ensuring the continued operation of the Hall thruster system may arise, such as the need to prevent material wear on the keeper electrode (or the end of the hollow cathode facing the keeper electrode) due to arcing of the high-voltage pulse generated by the keeper power supply and the need to prevent deterioration of insulation between the electrodes due to material wear. For this reason, in conventional technologies, it may be difficult to reduce the size and cost of the power processing unit when considering the mission of the spacecraft.

[0007] The present invention has been made based on the above-mentioned problem recognition, and aims to provide a voltage generating device that can realize miniaturization of a power processing unit that supplies power to a Hall thruster.

[0008] In order to achieve the above object, one aspect of the present invention provides a voltage generator that is provided in a Hall thruster system that generates thrust for a spacecraft, the voltage generator having a first end connected to a first line on the anode electrode side of an anode power supply that supplies power between an anode electrode and a cathode electrode of a Hall thruster that constitutes the Hall thruster system, and a second end that outputs an output voltage according to an input voltage to the first end, connected to a keeper electrode that is arranged close to a hollow cathode that is connected to the cathode electrode.

[0009] According to one aspect of the present invention, it is possible to provide a voltage generating device that can realize miniaturization of a power processing unit that supplies power to a Hall thruster.

[0010] Fig. 1 is a diagram showing an example of the configuration of a Hall thruster system including a power processing unit having a voltage generator according to an embodiment; Fig. 2 is a diagram showing an example of the operation of a Hall thruster system using a voltage generator according to an embodiment; Fig. 3 is a diagram showing an example of another configuration of a voltage generator according to an embodiment; Fig. 4 is a diagram showing an example of yet another configuration of a voltage generator according to an embodiment; Fig. 5 is a diagram showing an example of the configuration of an anode power supply used by a voltage generator according to an embodiment, and an example of connection of the voltage generator.

[0011] Embodiments of a voltage generator of the present invention will now be described with reference to the drawings. When this application is translated from Japanese to English, the singular forms "a," "an," and "the," as used throughout this disclosure, may be deemed to include plural references unless the context clearly indicates otherwise. The voltage generator of the present invention is applied to a Hall thruster system including a Hall thruster. A Hall thruster is an electric propulsion device that generates thrust to control the trajectory and attitude of a spacecraft as it moves through space by ionizing a specific gas (propulsion gas) such as xenon, accelerating the ions extracted from the resulting plasma, and then ejecting the ions into space. The propulsion gas may be, for example, krypton, argon, nitrogen, oxygen, vaporized iodine, water, or other gases.

[0012] A spacecraft employing a Hall thruster system may be an artificial satellite that moves along a predetermined orbit above the surface of the Earth or another celestial body or object, or it may be an observation satellite that travels to observe other celestial bodies or objects (and may return to Earth). Other celestial bodies include planets other than Earth, such as Mars and Venus, moons such as the Moon and Titan, and asteroids such as Itokawa and Ryugu. Other objects include rocks.

[0013] [Configuration of Hall Thruster System] FIG. 1 is a diagram illustrating an example of the configuration of a Hall thruster system including a power processing unit with a voltage generator according to an embodiment. The Hall thruster system 1 includes, for example, a Hall thruster 10 and a power processing unit (PPU) 20. FIG. 1A illustrates an example of the Hall thruster 10 as viewed from the side where ions extracted from plasma are ejected into space. FIG. 1B illustrates an example of a cross-sectional view of the Hall thruster 10 shown in FIG. 1A along the line A-A', and an example of the connection between the Hall thruster 10 and the power processing unit 20. FIG. 1C illustrates an example of the configuration of the Hall thruster system 1 by enlarging the area B of the Hall thruster 10 shown in FIGS. 1A and 1B.

[0014] First, the structure of the Hall thruster 10 will be described using FIGS. 1A and 1B. The Hall thruster 10 has a hollow cathode 15 disposed in the center of a cylindrical housing. From the center toward the periphery, an internal electromagnet 14a, a channel 11, and an external electromagnet 14b are arranged in a ring shape in this order. In the following description, when there is no need to distinguish between the internal electromagnet 14a and the external electromagnet 14b, they will simply be referred to as the "electromagnet 14." In the Hall thruster 10, the channel 11 is formed as a groove that runs along the electromagnet 14, and the groove is surrounded by a wall 13 made of, for example, ceramic. An anode 12 is disposed at the bottom of the groove that forms the channel 11.

[0015] Next, a more detailed configuration of the Hall thruster 10 and the power processing unit 20, and the connection between the Hall thruster 10 and the power processing unit 20 will be described using FIG. 1C. As described above, the Hall thruster 10 includes, for example, a channel unit 11, an anode 12, a wall unit 13, an electromagnet 14, and a hollow cathode unit 15. The hollow cathode unit 15 includes, for example, a hollow cathode body 15a, a keeper electrode body 15b, a heater 15c, and a gas supply pipe 15d. The power processing unit 20 includes, for example, an anode power supply 30, an igniter unit 40, a heater power supply 50, a coil power supply 60, and a power control unit 100. The power processing unit 20 is configured such that the keeper power supply included in the power processing unit in a conventional Hall thruster system is eliminated (deleted) and instead includes an igniter unit 40.

[0016] The anode power supply 30, heater power supply 50, and coil power supply 60 are each a DC power supply that supplies the necessary power to the corresponding components of the Hall thruster 10. More specifically, the anode power supply 30 is a switching power supply that supplies, for example, power with a maximum voltage of 300 V and a current of 3 A or power with a maximum voltage of 300 V and a current of 20 A to the anode 12 in accordance with control from the power control unit 100. When the anode power supply 30 supplies power with a maximum voltage of 300 V and a current of 3 A to the anode 12, a 1 kW-class Hall thruster 10 is configured. When the anode power supply 30 supplies power with a maximum voltage of 300 V and a current of 20 A to the anode 12, a 6 kW-class Hall thruster 10 is configured. The power supplied by the anode power supply 30 is not limited to a maximum voltage of 300 V. The anode power supply 30 may supply power with a maximum voltage value of, for example, 150 V or 1000 V depending on the performance of the Hall thruster 10 .

[0017] The heater power supply 50 is a DC power supply that supplies, for example, power with a voltage of 100 V and a current of 1 A, power with a voltage of 10 V and a current of 10 A, or power with a voltage of 20 V and a current of 5 A to the heater 15 c in response to control from the power control unit 100. While FIG. 1C illustrates a configuration in which the negative electrode of the heater power supply 50 is connected to the negative electrode of the anode power supply 30 (connected to the cathode electrode Ec connected to the hollow cathode main body 15 a), the negative electrode of the heater power supply 50 may be connected to, for example, a dedicated electrode provided in the Hall thruster 10. The heater power supply 50 may be omitted, for example, when a high-voltage pulse is applied to the keeper electrode main body 15 b by an igniter unit 40 (described later).

[0018] The coil power supply 60 is a DC power supply that supplies, for example, power with a voltage value of 100 [V] and a current value of 1 [A], power with a voltage value of 10 [V] and a current value of 10 [A], or power with a voltage value of 20 [V] and a current value of 5 [A] to the electromagnets 14, i.e., the internal electromagnet 14a and the external electromagnet 14b, respectively, in accordance with control from the power control unit 100.

[0019] The heater power supply 50 and the coil power supply 60 may be DC power supplies with a fixed voltage value or a fixed current value, whose power output is turned on and off in accordance with control from the power control unit 100. The heater power supply 50 and the coil power supply 60 may be switching power supplies whose supplied voltage value or current value is controlled in accordance with control from the power control unit 100.

[0020] The igniter unit 40 is a component that applies voltage to the keeper electrode body 15b in place of a keeper power supply included in a conventional power processing unit. Thus, like a conventional keeper power supply, the igniter unit 40 functions as a power supply circuit that performs voltage application and current supply operations. The voltage application operation is an operation of outputting (applying) a high voltage, for example, a no-load voltage value of 100 to 300 V, to generate a discharge between the hollow cathode body 15a and the keeper electrode body 15b. The current supply operation is an operation of flowing a current, for example, a few amperes to several amperes, to maintain the discharge state between the hollow cathode body 15a and the keeper electrode body 15b after the voltage application operation generates a discharge between the hollow cathode body 15a and the keeper electrode body 15b, at least until a discharge occurs between the anode 12 and the hollow cathode body 15a and the extraction of ionized ions from the plasma begins. The igniter unit 40 generates a voltage to be applied to the keeper electrode main body 15b based on the voltage applied to the anode 12 by the anode power supply 30. The igniter unit 40 has a first end a connected to the positive-side line La of the anode power supply 30 and a second end b connected to the keeper electrode main body 15b (more specifically, a keeper electrode Ek disposed in the Hall thruster 10 and connected to the keeper electrode main body 15b). The igniter unit 40 generates an output voltage having a magnitude (voltage value) corresponding to the input voltage to the first end a, i.e., the voltage value applied from the positive side by the anode power supply 30, and outputs the output voltage from the second end b. Conventional keeper power supplies have been switching power supplies configured by combining a large number of semiconductor components and passive elements (coil elements, resistor elements, capacitor elements) to convert (boost) the voltage of a system power supply in a spacecraft to perform voltage application and current supply operations. In contrast, the igniter section 40 is composed only of passive elements such as resistor elements and capacitor elements.

[0021] The igniter unit 40 is an example of a "voltage generator." The line La is an example of a "first line."

[0022] The power control unit 100 controls the power (applied voltage and current) supplied from each of the anode power supply 30, heater power supply 50, and coil power supply 60 included in the power processing unit 20 to the corresponding components of the Hall thruster 10. For example, the power control unit 100 controls the time it takes for the voltage applied from the anode power supply 30 to change from 0 V to 300 V, i.e., the voltage rise time, to be a predetermined time. For example, the power control unit 100 controls the voltage applied from the heater power supply 50 to the heater 15 c and the voltage applied from the coil power supply 60 to the coil that constitutes the electromagnet 14 to be switched between on (e.g., a state where the voltage is 100 V) and off (e.g., a state where the voltage is 0 V).

[0023] The hollow cathode body 15a ionizes the propellant gas supplied into the channel portion 11 to extract ions, thereby supplying electrons for initiating operation of the Hall thruster 10, and also serves as an electron source for emitting electrons for maintaining plasma and electrically neutralizing accelerated ions during operation of the Hall thruster 10. The same propellant gas as that supplied to the anode 12 is supplied to the hollow cathode body 15a through a gas supply pipe 15d. The hollow cathode body 15a ionizes the propellant gas supplied through the gas supply pipe 15d and emits the generated electrons toward the channel portion 11. The negative side of an anode power supply 30 is connected to a cathode electrode Ec connected to the hollow cathode body 15a. 1B and 1C show an example in which the cathode electrode Ec is disposed on the side of the housing of the Hall thruster 10 opposite the side where ions extracted from the plasma are ejected into space. However, the hollow cathode body 15a itself (which may be part of the gas supply pipe 15d) may serve as the cathode electrode Ec. A keeper electrode body 15b is disposed adjacent to the tip of the hollow cathode body 15a. However, the hollow cathode body 15a and the keeper electrode body 15b are insulated from each other. Furthermore, the outer periphery of the hollow cathode body 15a is covered with a heater 15c. The heater electrode Eh connected to the heater 15c is connected to the positive side of a heater power supply 50. In other words, the heater power supply 50 is connected between the heater 15c (heater electrode Eh) and the hollow cathode body 15a (cathode electrode Ec). The heater 15c generates heat in response to power supplied from the heater power supply 50, thereby heating components called an emitter and electron-emitting material (not shown) provided in the hollow cathode body 15a, thereby causing more electrons to be emitted from the hollow cathode body 15a. The keeper electrode body 15b is supplied with power generated by an igniter unit 40 connected to the keeper electrode Ek. When a high voltage is applied to the keeper electrode body 15b by the power supplied from the igniter unit 40, a discharge occurs between the hollow cathode body 15a and the keeper electrode body 15b, and this discharge ionizes the propellant gas supplied into the hollow cathode body 15a from the gas supply pipe 15d, generating plasma.Electrons drawn from the plasma by the potential gradient between the hollow cathode body 15a and the keeper electrode body 15b are emitted toward the channel portion 11. In the following description, the discharge between the hollow cathode body 15a and the keeper electrode body 15b is also referred to as "keeper ignition," and the plasma generated by this discharge (keeper ignition) is also referred to as "cathode plasma."

[0024] The anode 12 is a positive electrode that ionizes the propellant gas supplied into the channel portion 11 through the gas supply pipe 12a to extract ions. The supply of the propellant gas into the channel portion 11 through the gas supply pipe 12a and the amount of the propellant gas supplied are controlled, for example, by controlling the opening and closing of a valve disposed in the gas supply pipe 12a. A valve power supply (not shown) may be provided in the power processing unit 20. In this case, the power control unit 100 may control the opening and closing of the valve disposed in the gas supply pipe 12a by controlling the voltage and current supplied to the valve from the valve power supply (not shown). The positive side of an anode power supply 30 is connected to the anode electrode Ea of the anode 12. That is, the anode power supply 30 is connected between the anode 12 (anode electrode Ea) and the hollow cathode body 15a (cathode electrode Ec). In (b) and (c) of FIG. 1, an example is shown in which the anode electrode Ea is disposed at the end of the housing of the Hall thruster 10, similar to the cathode electrode Ec, but the anode 12 itself may serve as the anode electrode Ea.

[0025] The electromagnet 14 has an anode 12 disposed therein and generates a magnetic field in an area surrounded by the wall portion 13. The electromagnet 14 has a configuration in which a coil is wound around a core material made of a magnetic material. The positive side of a coil power supply 60 is connected to a coil positive electrode Em+ connected to the positive terminal of the coil. The negative side of the coil power supply 60 is connected to a coil negative electrode Em- connected to the negative terminal of the coil. The electromagnet 14 generates a magnetic field in the channel portion 11 in response to the power supplied to the coil by the coil power supply 60. Although detailed connections between the coil power supply 60 and the coils are omitted in FIG. 1, power from the coil power supply 60 is supplied to both the coil of the internal electromagnet 14a and the coil of the external electromagnet 14b. For example, power from the coil power supply 60 is supplied to each of the coils of the internal electromagnet 14a and the external electromagnet 14b via a path that runs from the positive side of the coil power supply 60 through the coil positive electrode Em+, the positive terminal of the coil of the external electromagnet 14b, the negative terminal of the coil of the external electromagnet 14b, the positive terminal of the coil of the internal electromagnet 14a, the negative terminal of the coil of the internal electromagnet 14a, and the coil negative electrode Em-, and returns to the negative side of the coil power supply 60. The coil positive electrode Em+ and the coil negative electrode Em- are not limited to being configured to correspond to the coil of the internal electromagnet 14a and the coil of the external electromagnet 14b, respectively. For example, the electromagnet 14 may be configured to include a coil positive electrode Em+ and a coil negative electrode Em- corresponding to the coil of the internal electromagnet 14a, and a coil positive electrode Em+ and a coil negative electrode Em- corresponding to the coil of the external electromagnet 14b. In other words, the coil of the internal electromagnet 14a and the coil of the external electromagnet 14b may each be provided with a separate coil positive electrode Em+ and a separate coil negative electrode Em-. Furthermore, the configuration for supplying power to each of the coils of the internal electromagnet 14a and the external electromagnet 14b is not limited to the coil power supply 60. For example, the power processing unit 20 may not be provided with a coil power supply 60 (and therefore may not be provided with a coil positive electrode Em+ and a coil negative electrode Em-). In this case, for example, the coil of the internal electromagnet 14a and the coil of the external electromagnet 14b may each be connected between the hollow cathode body 15a and the cathode electrode Ec.More specifically, the hollow cathode body 15a may be connected to the cathode electrode Ec via the positive terminal of the coil of the external electromagnet 14b, the negative terminal of the coil of the external electromagnet 14b, the positive terminal of the coil of the internal electromagnet 14a, and the negative terminal of the coil of the internal electromagnet 14a, thereby supplying power to each of the coils of the internal electromagnet 14a and the external electromagnet 14b. In this case, the electromagnet 14 generates a magnetic field in the channel portion 11 according to the power supplied to the coil by passing a current through the coil that flows when the hollow cathode body 15a extracts ions from the plasma in the channel portion 11.

[0026] In the Hall thruster 10, the anode 12 and hollow cathode body 15a are insulated from each other. In the Hall thruster 10, a magnetic field is generated in the channel portion 11 by the electromagnet 14, and a high voltage is applied to the anode 12 by power supplied from the anode power supply 30. These operations are performed in this order, in reverse order, or simultaneously. When electrons are extracted from the propulsion gas ionized by the cathode plasma in the hollow cathode body 15a and released toward the channel portion 11, a discharge occurs between the anode 12 and the hollow cathode body 15a. This discharge ionizes the propulsion gas supplied from the gas supply pipe 12a into the channel portion 11, generating plasma. In the Hall thruster 10, the potential gradient within the generated plasma accelerates and extracts ions from the plasma, and the ions are ejected from the channel portion 11 into space. In the following description, the discharge between the anode 12 and the hollow cathode body 15a is also referred to as "anode ignition," and the plasma in the channel portion 11 generated by this discharge (anode ignition) is also referred to as "anode plasma."

[0027] [Operation of the Hall Thruster System] Next, the operation of the Hall thruster system 1 will be described. FIG. 2 is a diagram showing an example of the operation of the Hall thruster system 1 using the voltage generator (igniter unit 40) according to the embodiment. FIG. 2 schematically shows components related to the extraction of ions to be ejected into space by the Hall thruster 10 and their operation. More specifically, FIG. 2 shows the anode electrode Ea, cathode electrode Ec, and keeper electrode Ek of the Hall thruster 10, which are related to the extraction of ions from the anode plasma, as well as the anode power supply 30 and igniter unit 40 connected to these electrodes. FIG. 2 also shows an example of the configuration of the igniter unit 40, which is configured by a resistor element Rig and a capacitor element Cig. More specifically, FIG. 2 shows an igniter unit 40 configured such that one end of the resistor element Rig serves as a first end a and is connected to the line La, the other end of the resistor element Rig and one end of the capacitor element Cig are connected in series, and the other end of the capacitor element Cig serves as a second end b and is connected to the keeper electrode Ek.

[0028] While FIG. 2 shows an example in which the igniter unit 40 is configured with one resistor element Rig and one capacitor element Cig, the number of resistor elements Rig and capacitor elements Cig included in the igniter unit 40 is not limited to one. That is, the resistor element Rig may be configured with multiple resistor elements connected in series and parallel. Furthermore, the capacitor element Cig may be configured with multiple capacitor elements connected in series and parallel. For example, when a large current is expected to flow through the igniter unit 40, the resistor element Rig may be configured with two resistor elements connected in parallel. For example, when the capacitance of the capacitor element Cig included in the igniter unit 40 is increased to prevent deterioration of frequency characteristics, a configuration in which multiple small-capacity capacitor elements are connected in parallel may be used.

[0029] In the following description of the operation of the Hall thruster system 1, for ease of explanation, it is assumed that power related to the extraction of ions from plasma is supplied to the corresponding components under control of the power control unit 100. More specifically, it is assumed that power for controlling a valve to an open state is supplied from a valve power supply (not shown) to a valve disposed in the gas supply pipe 12a to supply at least a propulsion gas to the anode 12. In addition, power may be supplied from a heater power supply 50 to a heater 15c to heat an emitter or electron-emitting material (not shown), and power may be supplied from a coil power supply 60 to a coil constituting the electromagnet 14 to generate a magnetic field within the channel unit 11.

[0030] 2 shows the impedance component Zk of the space between the keeper electrode Ek and the cathode electrode Ec, and the impedance component Za of the space between the anode electrode Ea and the cathode electrode Ec. In FIG. 2, the impedance component Zk and the impedance component Za are each represented by a resistance symbol, but each of the impedance components Zk and Za includes not only a resistance component but also an inductance component and a capacitance component. When the voltage applied to the corresponding electrode is low (when keeper ignition or anode ignition is not occurring), each of the impedance components Zk and Za has a high resistance value, for example, of several MΩ or more, and functions as an insulating resistor with an infinite resistance value, preventing current from flowing between the electrodes. On the other hand, when the voltage applied to the corresponding electrode increases and keeper ignition or anode ignition occurs, the impedance component Zk and impedance component Za each have a low resistance value of, for example, several kΩ (sometimes several tens to several hundred Ω) due to the newly generated (emerging) conductive plasma caused by this discharge, and a current begins to flow between the electrodes via the impedance component Zk or impedance component Za.

[0031] When ions extracted from the plasma are ejected from the Hall thruster 10 into space, the power control unit 100 controls the anode power supply 30 to output a high voltage (300 V in this example) and apply it to the anode 12. At this time, the power control unit 100 controls the voltage output from the anode power supply 30 so that the voltage value rises from 0 V to 300 V over a rise time of, for example, several tens of microseconds. As a result, the voltage output from the anode power supply 30 is applied to the anode electrode Ea (i.e., the anode 12). FIG. 2A shows a state in which the anode voltage Va from the anode power supply 30 is applied to the anode electrode Ea under control of the power control unit 100.

[0032] A voltage corresponding to the increase in the anode voltage Va is applied to the keeper electrode Ek (i.e., the keeper electrode main body 15b) via the igniter unit 40. More specifically, when the anode voltage Va is applied to the anode electrode Ea, the capacitor element Cig provided in the igniter unit 40 is charged by the anode voltage Va, and a voltage corresponding to the difference between the anode voltage Va and the voltage of the capacitor element Cig is applied to the keeper electrode Ek. FIG. 2A shows a state in which the keeper voltage Vk from the igniter unit 40 is applied to the keeper electrode Ek. In the Hall thruster 10 at this stage (a state in which keeper ignition has not occurred), a current corresponding to the impedance component Zk and the keeper voltage Vk flows between the keeper electrode Ek and the cathode electrode Ec, but the impedance component Zk is extremely large, so the current value is small. For reference, (a) of Figure 2 shows a state in which a predetermined keeper current Ik corresponding to the keeper voltage Vk applied from the igniter unit 40 flows through the keeper electrode Ek, the impedance component Zk of the space between the keeper electrode main body 15b and the hollow cathode main body 15a, and the cathode electrode Ec.

[0033] Here, the keeper voltage Vk rises to the same voltage value as the anode voltage Va in a predetermined rise time determined by the anode voltage Va, which rises in response to control by the power control unit 100, the resistance value of the resistor element Rig, and the capacitance value of the capacitor element Cig. For example, if the anode voltage Va and the resistor element Rig have the same voltage value and resistance value, the larger the capacitance value of the capacitor element Cig, the longer it takes to charge (i.e., the slower the rate at which the voltage of the capacitor element Cig rises), but the keeper voltage Vk, which is the difference between the anode voltage Va and the voltage of the capacitor element Cig, becomes higher. The keeper voltage Vk is a voltage that causes a discharge (keeper ignition) between the hollow cathode body 15a and the keeper electrode body 15b, generating cathode plasma and drawing electrons from it to emit them toward the channel portion 11. Therefore, when focusing on keeper ignition, it is considered better to increase the capacitance value of the capacitor element Cig and increase the voltage value of the keeper voltage Vk. However, a large capacitance value of the capacitor element Cig means that the volume of the capacitor element Cig, which is a high-voltage capacitor element, becomes large and the weight also becomes heavy. For this reason, it is considered preferable to use a capacitor element Cig with as small a capacitance value as possible within the range that can ignite the propulsion gas in the igniter unit 40 mounted on the spacecraft, in order to ensure the performance of igniting the propulsion gas while making the igniter unit 40 smaller, reducing costs, and further reducing the weight of the spacecraft.

[0034] Subsequently, when the voltage value of the keeper voltage Vk reaches a predetermined voltage value that causes a discharge between the hollow cathode body 15a and the keeper electrode body 15b, keeper ignition occurs between the hollow cathode body 15a and the keeper electrode body 15b, generating plasma (cathode plasma). The potential gradient in the region where this cathode plasma is generated draws electrons from the propellant gas. At this time, because an anode voltage Va (=300 V) is applied to the anode 12, electrons drawn from the propellant gas ionized by the cathode plasma move toward the anode 12, i.e., are emitted toward the channel portion 11. Figure 2(b) shows the state in which electrons drawn by the generated cathode plasma are being emitted toward the channel portion 11.

[0035] At this time, the energy required to generate the cathode plasma is supplied by the capacitor element Cig. After the cathode plasma is generated, the keeper voltage Vk becomes a voltage value corresponding to the potential of the cathode plasma at the keeper electrode Ek, and the capacitor element Cig is charged to a voltage value that is the difference between the anode voltage Va and the keeper voltage Vk (anode voltage Va - keeper voltage Vk).

[0036] When keeper ignition occurs between the hollow cathode body 15a and the keeper electrode body 15b, a large current (inrush current) flows instantaneously through the capacitor element Cig. The resistor element Rig reduces this instantaneous inrush current flowing through the capacitor element Cig. Therefore, in order to reduce the inrush current flowing through the capacitor element Cig, it is considered better to increase the resistance value of the resistor element Rig to further suppress the peak of the inrush current. However, a high resistance value of the resistor element Rig increases the heat generation (heat generation during steady-state operation) of the resistor element Rig, which is a high-voltage resistance element. For this reason, in the igniter unit 40 mounted on a spacecraft, it is considered preferable to employ a resistor element Rig with a resistance value that can suppress the peak of the inrush current to a level that prevents the capacitor element Cig from being destroyed by the inrush current flowing therethrough, in order to reduce the size and cost of the igniter unit 40 and further reduce the weight of the spacecraft.

[0037] Thereafter, in the Hall thruster 10, electrons emitted from the hollow cathode 15 toward the channel 11 (electrons moving toward the anode 12) cause a discharge (anode ignition) between the anode 12 and the hollow cathode body 15a, generating plasma (anode plasma). Figure 2C shows a state in which anode plasma is generated between the anode 12 and the hollow cathode body 15a, and an anode current Ia corresponding to the anode voltage Va flows through the anode electrode Ea, the impedance component Za of the space between the anode 12 and the hollow cathode body 15a, and the cathode electrode Ec. As a result, in the Hall thruster 10, ions of the propulsion gas drawn out by the potential gradient inside the anode plasma are accelerated and ejected from the channel 11 into space. In other words, the Hall thruster system 1 begins to operate to provide thrust to the spacecraft.

[0038] Here, in the Hall thruster 10, the keeper voltage Vk oscillates but is fixed at a constant voltage value during the operation of ejecting ions from the channel portion 11. Therefore, in the igniter portion 40, the capacitor element Cig continues to be charged with a voltage equal to the difference between the anode voltage Va and the keeper voltage Vk (anode voltage Va - keeper voltage Vk). In other words, in the Hall thruster system 1, while the Hall thruster 10 continues to operate in a steady state to provide thrust to the spacecraft, some AC component of the keeper current Ik continues to flow, but this does not result in a significant loss, and thrust can continue to be provided to the spacecraft. In other words, the Hall thruster system 1 can continue to operate in a steady state with almost no power loss or heat generation.

[0039] [Modification of Igniter Unit Configuration (Part 1)] Fig. 2 shows an example in which the igniter unit 40 is configured with a resistor element Rig and a capacitor element Cig. However, the configuration of the igniter unit 40 is not limited to the configuration shown in Fig. 2. Fig. 3 is a diagram showing another example of the configuration of the voltage generator (igniter unit 40) according to the embodiment. Fig. 3 shows two other examples of the configuration of the igniter unit 40.

[0040] FIG. 3A shows an example of an igniter unit 40 (hereinafter referred to as "igniter unit 40a") configured with a capacitor element Cig. That is, FIG. 3A shows an igniter unit 40a configured in such a manner that the resistor element Rig is omitted from the igniter unit 40 shown in FIG. 2. In the igniter unit 40a, one end of the capacitor element Cig serves as a first end a and is connected to the line La, and the other end of the capacitor element Cig serves as a second end b and is connected to the keeper electrode Ek. In the igniter unit 40a, as in the example shown in FIG. 2A, a keeper voltage Vk corresponding to an increase in the anode voltage Va is applied to the keeper electrode Ek. In the igniter unit 40a, as in the example shown in FIG. 2A, a state in which the keeper voltage Vk from the igniter unit 40a is applied to the keeper electrode Ek is shown. Even in the configuration shown in Figure 3(a), in the Hall thruster 10 at this stage (when keeper ignition has not occurred), a current flows according to the impedance component Zk between the keeper electrode Ek and the cathode electrode Ec and the keeper voltage Vk, but the impedance component Zk is extremely large, so the current value is small. As with the example shown in Figure 2(a), Figure 3(a) also shows, for reference, a state in which a predetermined keeper current Ik according to the keeper voltage Vk applied from the igniter unit 40a flows through the keeper electrode Ek, the impedance component Zk of the space between the keeper electrode main body 15b and the hollow cathode main body 15a, and the cathode electrode Ec. As described above, the resistor element Rig reduces the inrush current that instantaneously flows through the capacitor element Cig when keeper ignition occurs between the hollow cathode main body 15a and the keeper electrode main body 15b. Therefore, if the inrush current that instantaneously flows through the capacitor element Cig when keeper ignition occurs is within an allowable range, or if the inrush power can be suppressed (reduced) by the resistance component of the capacitor element Cig, the resistance element Rig can be omitted from the igniter unit 40, and the igniter unit 40a can be configured to include only the capacitor element Cig. In this case, the igniter unit 40 can be further reduced in size and cost, and the spacecraft can be further lightened in weight.

[0041] FIG. 3B shows an example of an igniter unit 40 (hereinafter referred to as "igniter unit 40b") configured with a resistive element Rig. That is, FIG. 3B shows an igniter unit 40b configured in such a manner that the capacitor element Cig is omitted from the igniter unit 40 shown in FIG. 2. In the igniter unit 40b, one end of the resistive element Rig serves as a first end a connected to the line La, and the other end of the resistive element Rig serves as a second end b connected to the keeper electrode Ek. In the igniter unit 40b, as in the example shown in FIG. 2A, a keeper voltage Vk corresponding to an increase in the anode voltage Va is applied to the keeper electrode Ek. In FIG. 3B, as in the example shown in FIG. 2A, a state in which the keeper voltage Vk from the igniter unit 40b is applied to the keeper electrode Ek is shown. Even in the configuration shown in Figure 3(b), in the Hall thruster 10 at this stage (when keeper ignition has not occurred), a current flows according to the impedance component Zk between the keeper electrode Ek and the cathode electrode Ec and the keeper voltage Vk, but the impedance component Zk is extremely large, so the current value is small. As with the example shown in Figure 2(a), Figure 3(b) also shows, for reference, a state in which a predetermined keeper current Ik according to the keeper voltage Vk applied from the igniter unit 40b flows through the keeper electrode Ek, the impedance component Zk of the space between the keeper electrode main body 15b and the hollow cathode main body 15a, and the cathode electrode Ec. As described above, the capacitor element Cig continues to be charged with the voltage equal to the difference between the anode voltage Va and the keeper voltage Vk (anode voltage Va - keeper voltage Vk), so that a small AC component of the keeper current Ik flows, but this does not result in a significant loss. In other words, the capacitor element Cig, in combination with the resistor element Rig, suppresses the DC component of the keeper current Ik that flows while the Hall thruster 10 continues to operate steadily. Therefore, if it is acceptable for a small DC component of the keeper current Ik to flow while the Hall thruster 10 continues to operate steadily and for this small DC component to cause a somewhat large loss, the igniter unit 40 can be configured with only the resistor element Rig, omitting the capacitor element Cig.In this case, the igniter section 40b can further reduce the size and cost of the igniter section 40, thereby making the spacecraft even lighter.

[0042] The igniter unit 40a and the igniter unit 40 are also examples of the "voltage generator."

[0043] [Modification of the Igniter Unit Configuration (Part 2)] Fig. 2 shows an example in which the igniter unit 40 is connected (placed) between the anode electrode Ea and the keeper electrode Ek of the Hall thruster 10. However, the connection between the igniter unit 40 and the Hall thruster 10 is not limited to the connection shown in Fig. 2. Fig. 4 is a diagram showing another example of the configuration of the voltage generator (igniter unit 40) according to the embodiment.

[0044] The igniter unit 41 shown in FIG. 4A is configured by adding a protection circuit 70 to the igniter unit 40 shown in FIG. 2 . The protection circuit 70 is a snubber circuit, a circuit that absorbs a surge current (injected current) that flows transiently when keeper ignition occurs. The igniter unit 41 includes the igniter unit 40 and the protection circuit 70 connected in series. More specifically, the igniter unit 41 has a first end a of the igniter unit 40 connected to a line La on the positive side of the anode power supply 30 and a second end b of the igniter unit 40 connected to the keeper electrode Ek. The igniter unit 41 also has a first end c of the protection circuit 70 connected to a line connecting the second end b of the igniter unit 40 to the keeper electrode Ek, and a second end d of the protection circuit 70 connected to the cathode electrode Ec. As a result, in the igniter section 41, the protection circuit 70 absorbs the input current that transiently flows between the keeper electrode Ek and the cathode electrode Ec when keeper ignition occurs, thereby protecting the hollow cathode section 15.

[0045] The protection circuit 70 has a configuration in which a resistor Rs and a capacitor Cs are connected in series, as shown in FIG. 4B . More specifically, the protection circuit 70 has one end of the resistor Rs as a first end c connected to the igniter unit 40 and the keeper electrode Ek, the other end of the resistor Rs and one end of the capacitor Cs connected in series, and the other end of the capacitor Cs as a second end d connected to the cathode electrode Ec. The configuration of the protection circuit 70 is not limited to the configuration shown in FIG. 4B . The protection circuit 70 may have a Zener diode instead of the resistor Rs and the capacitor Cs, or may have a Zener diode in addition to the resistor Rs and the capacitor Cs.

[0046] The igniter unit 41 is also an example of a "voltage generator."

[0047] [Modifications of Igniter Unit Connection] In the above-described embodiment and modification, the configuration of the anode power supply 30 was not described in detail. Therefore, FIG. 2 illustrates a case in which the first end a of the igniter unit 40 is connected to the line La on the positive side of the anode power supply 30. However, depending on the configuration of the anode power supply 30, the first end a of the igniter unit 40 (which may be igniter unit 40a or igniter unit 40b) may be connected to a line different from the line La of the anode power supply 30. An example of this case is described below. FIG. 5 illustrates the configuration of the anode power supply 30 used in the voltage generator (igniter unit 40) according to the embodiment, and an example of the connection of the voltage generator (igniter unit 40). FIG. 5 illustrates two example configurations of the anode power supply 30 having a maximum voltage value of 300 V.

[0048] FIG. 5A shows an example in which an anode power supply 30 (hereinafter referred to as the “anode power supply 30a”) is configured by connecting three DC / DC converters 31 (DC / DC converters 31A to 31C) in series. Each of the DC / DC converters 31A, 31B, and 31C is, for example, a DC / DC converter that converts (boosts) the voltage of a system power supply in a spacecraft and outputs the converted voltage. The system power supply is, for example, a storage battery that stores power generated by a solar panel (photovoltaic power generation device) provided on the spacecraft. In the example shown in FIG. 5A, each DC / DC converter 31 outputs a voltage of 100 V. When the first end a of the igniter unit 40 is connected to the positive electrode of the DC / DC converter 31A that constitutes the anode power supply 30a, the operation of the Hall thruster system 1 is similar to that of the Hall thruster system 1 shown in FIG. 2. In contrast, the igniter unit 40 shown in Fig. 5A has a first end a connected to a line Laa that connects the positive side of the DC / DC converter 31B and the negative side of the DC / DC converter 31A, and a second end b connected to the keeper electrode Ek. In this case, the igniter unit 40 generates an output voltage having a magnitude (voltage value) corresponding to the input voltage to the first end a, i.e., the voltage value (voltage value = 200 V) output from the positive side of the DC / DC converter 31A, and outputs the output voltage from the second end b. As a result, in the example shown in Fig. 5A, the voltage of the capacitor element Cig included in the igniter unit 40 can be lowered below the voltage of the capacitor element Cig included in the igniter unit 40 shown in Fig. 2 (here, the voltage value = 300 V is set to 200 V). This allows the igniter unit 40 to perform the same operation as the igniter unit 40 shown in Fig. 2. Therefore, in the igniter unit 40 shown in Fig. 5(a), a capacitor element Cig with a low withstand voltage can be employed while still ensuring the performance of igniting the propulsion gas, which broadens the options for the capacitor element Cig to be included compared to the igniter unit 40 shown in Fig. 2, potentially enabling further miniaturization and weight reduction of the igniter unit 40. Furthermore, if the igniter unit 40 can be made smaller, the weight of the spacecraft can be further reduced.

[0049] FIG. 5B shows an example of an anode power supply 30 (hereinafter referred to as the "anode power supply 30b") configured by connecting three batteries 32 (batteries 32A to 32C) in series. Each of the batteries 32A, 32B, and 32C is, for example, a storage battery that stores voltage charged by the system power supply of the spacecraft. In the example shown in FIG. 5B, each battery 32 also outputs a voltage value of 100 V. When the first end a of the igniter unit 40 is connected to the positive electrode of the battery 32A that constitutes the anode power supply 30b, the operation of the Hall thruster system 1 is similar to that of the Hall thruster system 1 shown in FIG. 2. In contrast, the igniter unit 40 shown in FIG. 5B has a first end a connected to a line Lab that connects the positive electrode of the battery 32B and the negative electrode of the battery 32A, and a second end b connected to a keeper electrode Ek. In this case, igniter unit 40 also generates an output voltage having a magnitude (voltage value) corresponding to the input voltage at first terminal a, i.e., the voltage value (voltage value = 200 V) of the voltage output from the positive electrode side of battery 32A, and outputs the output voltage from second terminal b. As a result, in the example shown in Fig. 5(b), as in the example shown in Fig. 5(a), the voltage of capacitor element Cig included in igniter unit 40 can be lowered below the voltage of capacitor element Cig included in igniter unit 40 shown in Fig. 2 (again, the voltage value = 300 V is set to 200 V). Therefore, in the igniter unit 40 shown in Fig. 5(b), like the igniter unit 40 shown in Fig. 5(a), a capacitor element Cig with a low withstand voltage can be employed while still ensuring the performance of igniting the propulsion gas, which broadens the options for the capacitor element Cig to be included compared to the igniter unit 40 shown in Fig. 2, potentially enabling further miniaturization and weight reduction of the igniter unit 40. Furthermore, if the igniter unit 40 can be made smaller, the weight of the spacecraft can be further reduced.

[0050] As described above, the igniter unit 40 can be connected in accordance with the configuration of the anode power supply 30 and the power (voltage value) supplied to the keeper electrode Ek (i.e., the keeper electrode body 15b). While FIG. 5 illustrates a case in which the anode power supply 30 is configured with three DC / DC converters 31 or three batteries 32, a case in which the anode power supply 30 is configured with four or more DC / DC converters 31 or four or more batteries 32 can also be considered similar to the above-described example. The configuration and operation in this case need only be equivalent to the configuration and operation shown in FIG. 5 . Therefore, detailed description of the configuration and operation of the Hall thruster system 1 in a configuration in which the anode power supply 30 includes a different number of DC / DC converters 31 or batteries 32 will be omitted.

[0051] The DC / DC converter 31 and the battery 32 are examples of a "power supply module." The DC / DC converter 31A and the battery 32A are examples of a "first power supply module," and the DC / DC converter 31B and the battery 32B are examples of a "second power supply module." The lines Laa and Lab are examples of "lines connecting the first power supply module and the second power supply module in series," and are also examples of "first lines."

[0052] As described above, the Hall thruster system 1 including the power processing unit 20 to which the igniter unit 40 of the embodiment is applied does not have (deletes) the keeper power supply that is included in the power processing unit of a conventional Hall thruster system, and instead includes an igniter unit 40 that is configured with only one or both of the passive elements, i.e., the resistor element Rig and the capacitor element Cig. Similarly to the conventional keeper power supply, the igniter unit 40 of the embodiment also causes keeper ignition between the hollow cathode body 15 a and the keeper electrode body 15 b, and cathode plasma generated by keeper ignition releases electrons extracted from the propulsion gas supplied from the gas supply pipe 15 d into the hollow cathode body 15 a toward the channel unit 11. As a result, in the Hall thruster system 1 including the power processing unit 20 to which the igniter unit 40 of the embodiment is applied, anode ignition occurs between the anode 12 and the hollow cathode body 15a, and the anode ignition generates anode plasma that ionizes the propulsion gas, drawing out ions that are accelerated by the electric field inside the anode plasma and ejected from the channel unit 11 into space, just like in conventional Hall thruster systems. As a result, the Hall thruster system 1 including the power processing unit 20 to which the igniter unit 40 of the embodiment is applied can also provide thrust to a spacecraft, just like conventional Hall thruster systems. Moreover, because the igniter unit 40 of the embodiment is composed only of passive elements, it can be made smaller and less expensive than conventional keeper power supplies, and it can achieve weight reduction in a spacecraft equipped with the Hall thruster system 1 including the power processing unit 20 to which the igniter unit 40 of the embodiment is applied.

[0053] In the above-described embodiment, the igniter unit 40 is provided in the power processing unit 20. However, the igniter unit 40 is not limited to being provided in the power processing unit 20. For example, the igniter unit 40 may be provided in the Hall thruster 10. In this case, the configuration and operation of the Hall thruster system 1, i.e., the igniter unit 40, the power processing unit 20, and the Hall thruster 10, may be equivalent to the configuration and operation of the Hall thruster system 1 including the power processing unit 20 to which the igniter unit 40 of the above-described embodiment is applied. Therefore, detailed description of the configuration and operation of the Hall thruster system 1 in which the igniter unit 40 is provided in the Hall thruster 10 will be omitted.

[0054] The above describes the form for carrying out the present invention using an embodiment, but the present invention is not limited to such an embodiment, and various modifications and substitutions can be made within the scope that does not deviate from the gist of the present invention.

[0055] DESCRIPTION OF SYMBOLS 1...Hall thruster system 10...Hall thruster 11...Channel portion 12...Anode 12a...Gas supply pipe 13...Wall portion 14...Electromagnet 14a...Inner electromagnet 14b...Outer electromagnet 15...Hollow cathode portion 15a...Hollow cathode body 15b...Keeper electrode body 15c...Heater 15d...Gas supply pipe 20...Power processing unit (PPU) 30, 30a, 30b...Anode power supply 31, 31A, 31B, 31C...DC / DC converter 32, 32A, 32B, 32C...Battery 40, 40a, 40b, 41...Igniter portion 50...Heater power supply 60...Coil power supply 70...Protection circuit 100...Power control unit Ea...Anode electrode Ec...Cathode electrode Ek...Keeper electrode Eh...Heater electrode Em+...Positive electrode of coil Em-...Negative electrode of coil Rig...Resistance element Rs...Resistance element Cig...Capacitor element Cs...Capacitor element

Claims

1. A voltage generating device provided in a Hall thruster system for generating the thrust of a space machine, wherein a first end is connected to a first line on the anode electrode side in an anode power supply that supplies power between an anode electrode and a cathode electrode of a Hall thruster constituting the Hall thruster system, and a second end that outputs an output voltage corresponding to the input voltage of the first end is connected to a keeper electrode disposed close to a hollow cathode connected to the cathode electrode. Voltage generating device.

2. The voltage generating device according to claim 1, wherein the first line is a line connecting the anode power supply and the anode electrode.

3. The voltage generating device according to claim 1, wherein the anode power supply has a plurality of power modules connected in series, and the first end is connected to a line connecting any first power module and a second power module in series.

4. The voltage generating device according to claim 3, wherein the power module is a DC / DC converter.

5. The voltage generating device according to claim 3, wherein the power module is a battery.

6. A resistor element and a capacitor element, wherein one end of the resistor element is connected to the first end, the other end of the resistor element and one end of the capacitor element are connected in series, and the other end of the capacitor element is connected to the second end. The voltage generating device according to any one of claims 1 to 5.

7. A capacitor element, wherein one end of the capacitor element is connected to the first end, and the other end of the capacitor element is connected to the second end. The voltage generating device according to any one of claims 1 to 5.

8. A resistor element, wherein one end of the resistor element is connected to the first end, and the other end of the resistor element is connected to the second end. The voltage generating device according to any one of claims 1 to 5.

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