Electric power supply system for a hall effect electric thruster

Abstract

An electric power supply system for a Hall effect electric thruster. The Hall effect electric thruster includes an anode, a cathode, a heater for the cathode and an igniter. The electric power supply system includes a first power supply source to power the anode, a second power supply source to power the heater and a power supply unit to electrically supply the igniter. The power supply unit includes a third power supply source and a passive electric circuit. The third power supply source powers the passive electric circuit and is configured to generate a voltage in the form of at least one pulse.

Claims

1. An electric power supply system of a Hall-effect electric thruster, the Hall-effect electric thruster comprising an anode, a cathode, a heater for the cathode, and an igniter, the electric power supply system comprising: a first power supply source, a second power supply source and an entirely passive electrical circuit, wherein the anode is electrically connected to a first terminal of the first power supply source, wherein the entirely passive electrical circuit is electrically connected between the first terminal and a second terminal of the first power supply source, wherein the entirely passive electrical circuit provides an igniter voltage to the igniter less than a first power supply source voltage between the first terminal and the second terminal, wherein the igniter voltage is provided in the form of at least one pulse, wherein the igniter voltage generates a discharge current between the igniter and the cathode, and wherein the heater is electrically connected to the second power supply source.

2. The electric power supply system as claimed in claim 1, wherein the entirely passive electrical circuit is configured to generate the igniter voltage as a series of successive pulses.

3. The electric power supply system as claimed in claim 1, wherein the entirely passive electrical circuit comprises a capacitor.

Description

DESCRIPTION OF THE FIGURES

(1) The invention will be better understood after reading the following description, given as a non-limiting example, and made by referring to the figures below which represent:

(2) FIG. 1, already described, is an electric power supply system of a Hall-effect electric thruster according to the prior art,

(3) FIG. 2 is an example of electric power supply system of a Hall-effect electric thruster according to the invention,

(4) FIG. 3a is a curve graph illustrating a voltage signal at the terminals of the capacitor,

(5) FIG. 3b is a curve graph illustrating the emission of electrons by the cathode and the discharge current, and

(6) FIG. 4 is a variant of the electric power supply system of a Hall-effect electric thruster according to the invention.

(7) In these figures, identical references from one figure to another denote the same or analogous elements. For reasons of clarity, the elements shown are not to scale, unless stated otherwise.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

(8) This invention relates to an electric power supply system 1 of a Hall-effect electric thruster 1.

(9) A Hall-effect thruster usually comprises, on the one hand, a discharge channel to which an anode 50 is connected and, on the other hand, a cathode assembly situated near the outlet of the discharge channel. The cathode assembly comprises a cathode 51 and a heater 53 situated close to the cathode 51 and meant to heat said cathode to allow it to emit electrons. A magnetic circuit surrounds the discharge channel and creates a radial magnetic field within the discharge channel. A propellant gas, e.g. xenon, is injected at the rear of the discharge channel and in the cathode. The propellant gas is ionised in the discharge channel by collision with the electrons emitted by cathode 51. The ionisation of the propellant gas generates plasma. The ions produced are accelerated and ejected at very high speed (15 to 25 km/s) by an axial electric field created between the anode and the cathode, so as to generate the thrust effect. The electric field is generated by the combination of the magnetic field and a difference in electrostatic potential between the anode and the cathode.

(10) FIG. 4 represents an electric power supply system 1 of the Hall-effect electric thruster, according to an embodiment of the invention.

(11) The electric power supply system 1 includes a first power supply source 10 for electrically powering anode 50. Said first power supply source is for example a, preferably direct, high-voltage source. It provides a maximum voltage V.sub.anode.

(12) The electric power supply system 1 comprises a second power supply source 11 meant to electrically power the heater 53 to heat the cathode 51 and enable it to emit electrons. The second power supply source 11 is preferentially a current source.

(13) The electric power supply source 1 has a power supply unit 13 to electrically power an igniter 52. Said power supply unit comprises an electric power supply source known as the third power supply source 70, and a passive electrical circuit 131. The third power supply source 70 is for example a, preferably direct, high-voltage source.

(14) The passive electrical circuit 131 includes a first resistance R.sub.a, connected directly to the third power supply source 70, assembled in series with a diode D and capacitor C. A second resistance R.sub.b is assembled between, on the one hand, the diode D and the capacitor C and, on the other hand, the igniter 52. The capacitor C is connected, at its other terminal, to the cathode reference point CRP.

(15) The electric power supply system 1 can include a fourth power supply source to electrically power the magnetic circuit. The magnetic circuit and the fourth power supply source are not depicted in FIG. 4.

(16) In a preferred embodiment, and as illustrated in FIG. 2, for limiting the number of power supply sources, the first power supply source 10 and the third power supply source 70 are one and the same power supply source. Such an embodiment is preferred when, according to the type of electric thruster that is selected, the working voltage of the electric thruster is approximately equal to the voltage required to switch on said electric thruster. The passive electrical circuit 131 includes a first resistance R.sub.a, connected directly, or through a switch, to the first power supply source 10 assembled in series with a diode D and a capacitor C. A second resistance R.sub.b is assembled between, on the one hand, diode D and capacitor C and, on the other hand, the igniter 52. The capacitor C is connected, at its other terminal, to the cathode reference point CRP.

(17) The passive electrical circuit 131 is powered by the first power supply source 10, or the third power supply source as per the selected configuration of FIG. 2 or 4, and is configured to generate voltage in the form of at least one pulse as output.

(18) The charging and the discharging of the capacitor C respectively form the ascending and descending edges of a pulse.

(19) The functioning of such a circuit is presently explained in connection with the curve graphs depicted in FIGS. 3a and 3b, to allow for the start-up of the Hall-effect electric thruster.

(20) FIG. 3a illustrates the changes in the voltage signal V.sub.c at the terminals of the capacitor C over time.

(21) FIG. 3b illustrates the changes in the emission of electrons by the cathode (solid line) and the discharge current (broken line) over time.

(22) A first stage consists of the heating phase of the cathode 51.

(23) During this heating phase, the cathode 51 is heated up to a predetermined temperature. The cathode 51 is heated by means of the heater 53 that is powered by the second power supply source 11.

(24) The cathode 51 is heated until it reaches a temperature corresponding to the minimum temperature which enables cathode 51 to emit the volume of electrons required to establish a discharge current in the discharge channel which is adequate to ionise the atoms of the propellant gas in said discharge channel.

(25) In an example of implementation, when the material of the cathode is lanthanum hexaboride (LaB6), the temperature is about 1,600 C.

(26) In a second phase, a direct voltage is applied between the anode 50 and the cathode 51, through the first power supply source 10.

(27) In the configuration where the first power supply source 10 is common between the anode 50 and the igniter 52, a voltage in the form of at least one pulse is applied between the igniter 52 and the cathode 51, through the first power supply source and the passive electrical circuit.

(28) In the configuration where the first and the third power supply sources are separate, a voltage in the form of at least one at least one pulse is applied between the igniter 52 and the cathode 51, through the third power supply source and the passive electrical circuit.

(29) This second phase is preferentially to be executed simultaneously with the first phase, but can be executed following the same without modifying the result of said phases.

(30) At the same time as this second phase, a voltage is applied to the terminals of the magnetic circuit and a propellant gas is injected through the anode.

(31) Once the capacitor C is powered by the first power supply source 10 or the third power supply source 70 according to the configuration of FIG. 2 or 4 used, said capacitor C is charged with a time constant R.sub.aC until a voltage is established at its terminals which is close to the voltage V.sub.anode of the anode. A steady electrical state is established until the cathode 51 attains an adequate level of electron emission.

(32) At this point in time, a first discharge current appears between the igniter and the cathode, discharging the capacitor C.

(33) As in the prior art, a discharge current appears when the voltage at the terminals of the igniter 52 is near the voltage at the terminals of the anode 50. In the invention, the presence of the capacitor C creates a delay in the generation of voltage at the terminals of igniter 52. This delay depends on the time constant of the circuit and thereby on the choice of the first resistance R.sub.a and the capacitor C.

(34) Thereafter, a series of pulses is generated. Each pulse begins with a partial charge of the capacitor C, followed by a discharge of the same each time a discharge current appears between the igniter 52 and the cathode 51. The peak of each pulse is therefore significantly lower than the voltage V.sub.anode, due to the premature discharging of the capacitor C.

(35) The pulses, i.e., the charging/discharging of the capacitor, continue in succession until a discharge current I.sub.d appears between the anode 50 and the cathode 51. At this moment, plasma is established in anode 50, allowing for the Hall-effect electric thruster to be switched on.

(36) The establishment of plasma in anode 50 may occur during any discharging of the capacitor, even during the first discharge.

(37) In a preferred mode of implementation, to improve the reliability of the powering on of anode 50, it is preferred that the voltage at the terminals of the capacitor C, at the end of its charging, is sufficiently high so that the discharge energy of said capacitor is large enough and suitable to create a discharge current I.sub.d between the anode 50 and the cathode 51.

(38) In an example of implementation, to accumulate more energy at the level of the capacitor C, the second power supply source 11 is discontinued so as to switch off the heating of cathode 51.

(39) The stopping of the heating of cathode 51 leads to gradually reducing the emission of electrons by cathode 51 and consequently reducing the probability of a discharge current appearing between the igniter and the cathode at low voltage. Thus, the maximum amplitude of the pulses increases with the decrease in the emission of electrons by cathode 51. These maximum amplitude values increase until the energy released during the discharging of the capacitor is adequate to trigger a discharge current I.sub.d between the anode 50 and the cathode 51 which generates plasma at the level of the anode, allowing for the Hall-effect electric thruster to be switched on.

(40) When there is plasma in the Hall-effect electric thruster, at the level of the anode and the cathode, the electric conductivity between the igniter and the cathode is very high. Resistance R.sub.a then allows limiting the current circulating from the first power supply source 10 or the third power supply source 70, according to the configuration of the FIG. 2 or 4 that is used, to the igniter 52. The capacitor C keeps a low voltage at these terminals, draining a weak current across the resistance R.sub.b, with a negligible effect on the efficiency of the Hall-effect electric thruster. A device to cut off power supply to igniter 52 is therefore unnecessary as the effect on the engine efficiency is also negligible.

(41) The diode D serves as additional protection to the anode and to the first electrical supply source in case of overvoltage at the level of the capacitor in relation to the anode.

(42) The unit of the third or the first power supply source, according to the selected configuration, and the passive electrical circuit described hereinabove favourably replaces the ignition module and the support module which are part of the equipment of the Hall-effect electric thrusters in the present state of the art.

(43) The dimensioning of the passive components R.sub.a R.sub.b and C is done by standard methods known to persons skilled in the art for astrionics, depending mainly on the characteristics of the Hall-effect electric thruster, especially the technology of the cathode emitter, its thermionic and thermal behaviour and characteristics of the powering of the anode such as the maximum permissible current. This also determines the maximum amplitudes of the pulses and the residual current in continuous operation after the Hall-effect electric thruster is switched on.

(44) In an example of embodiment, let R.sub.a>>R.sub.b be chosen.

(45) R.sub.a should preferably be sufficiently large to protect the first power supply source 10, or the third power supply source 70 according to the configuration of FIG. 2 or 4 that is selected, against a sudden surge in current to a very high level in the phase before the Hall-effect electric thruster is switched on and to have a weak residual current, at the terminals of the capacitor, after the Hall-effect electric thruster is switched on.

(46) R.sub.b is preferably relatively low to enable a rapid discharging of the capacitor C during the switching on phase, before the Hall-effect electric thruster is switched on, which allows the transfer of more energy during this phase.

(47) In the specific case of an SPT100 Hall-effect electric thruster, conclusive tests were carried out with the following values: R.sub.a=200 kilo-ohm; R.sub.b=100 Ohm; C=1 F.

(48) After a heating phase of the cathode for around 160 s, voltage was applied to the anode (300 V). Simultaneously, the heating of the cathode was switched off. The first discharging between the cathode and the igniter was initiated after one second. The discharging at the level of the anode was initiated 15 seconds later, following the emission of pulses of increasing magnitude between the igniter and the cathode.