AU2018312508A1 - Field emission propulsion system and method for calibrating and operating a field emission propulsion system - Google Patents
Field emission propulsion system and method for calibrating and operating a field emission propulsion system Download PDFInfo
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- 238000000034 method Methods 0.000 title claims description 22
- 238000000605 extraction Methods 0.000 claims description 21
- 238000010884 ion-beam technique Methods 0.000 claims description 21
- 239000000446 fuel Substances 0.000 claims description 18
- 239000013598 vector Substances 0.000 claims description 11
- 239000002828 fuel tank Substances 0.000 claims description 10
- 230000005684 electric field Effects 0.000 claims description 8
- 239000007788 liquid Substances 0.000 claims description 7
- 239000012811 non-conductive material Substances 0.000 claims description 4
- 150000002500 ions Chemical class 0.000 description 97
- 229910001338 liquidmetal Inorganic materials 0.000 description 5
- 238000005259 measurement Methods 0.000 description 5
- 239000011248 coating agent Substances 0.000 description 4
- 238000000576 coating method Methods 0.000 description 4
- 230000008021 deposition Effects 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 230000001419 dependent effect Effects 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 230000007774 longterm Effects 0.000 description 3
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000012530 fluid Substances 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- 229910052702 rhenium Inorganic materials 0.000 description 2
- WUAPFZMCVAUBPE-UHFFFAOYSA-N rhenium atom Chemical compound [Re] WUAPFZMCVAUBPE-UHFFFAOYSA-N 0.000 description 2
- 229910052715 tantalum Inorganic materials 0.000 description 2
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 2
- 229910052719 titanium Inorganic materials 0.000 description 2
- 239000010936 titanium Substances 0.000 description 2
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 2
- 229910052721 tungsten Inorganic materials 0.000 description 2
- 239000010937 tungsten Substances 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- GYHNNYVSQQEPJS-UHFFFAOYSA-N Gallium Chemical compound [Ga] GYHNNYVSQQEPJS-UHFFFAOYSA-N 0.000 description 1
- 229910052797 bismuth Inorganic materials 0.000 description 1
- JCXGWMGPZLAOME-UHFFFAOYSA-N bismuth atom Chemical compound [Bi] JCXGWMGPZLAOME-UHFFFAOYSA-N 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000010292 electrical insulation Methods 0.000 description 1
- 229910052733 gallium Inorganic materials 0.000 description 1
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 239000010931 gold Substances 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 229910052738 indium Inorganic materials 0.000 description 1
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
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- 230000003071 parasitic effect Effects 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 230000011218 segmentation Effects 0.000 description 1
- 125000006850 spacer group Chemical group 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
- F03H—PRODUCING A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
- F03H1/00—Using plasma to produce a reactive propulsive thrust
- F03H1/0037—Electrostatic ion thrusters
- F03H1/005—Electrostatic ion thrusters using field emission, e.g. Field Emission Electric Propulsion [FEEP]
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Physics & Mathematics (AREA)
- Plasma & Fusion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Electron Sources, Ion Sources (AREA)
- Physical Or Chemical Processes And Apparatus (AREA)
- Ignition Installations For Internal Combustion Engines (AREA)
- Selective Calling Equipment (AREA)
- Microwave Tubes (AREA)
Description
Field emission propulsion system and methods for calibrating and operating a field emission propulsion system
Technical field
The present invention relates to field emission propulsions for a spacecraft. Furthermore, the present invention relates to methods for operating a field emission propulsion.
Technical background
A number of different propulsion technologies are known for a spacecraft, such as chemical propulsions, cold gas propulsions, gas ion propulsions, plasma propulsions and the like. These propulsion technologies have the disadvantage that they may not be miniaturized satisfactorily for smaller satellites due to physical or efficiency reasons. However, the increasing use of very small satellites requires the provision of suitable propulsion technologies with high efficiency. In particular, field emission propulsions are especially suitable for use in very small satellites due to their very high specific pulses of several 1,000 s.
For example, document AMR Propulsions Innovations, IFM Nano Thruster, data sheet,
July 26, 2017, http://www.propulsion.at, discloses a field emission propulsion which uses a liquid metal ion source with several liquid metal ion emitters. Since only one common extractor electrode is used for all liquid metal ion emitters, the individual emitters may not be controlled individually.
Also, due to manufacturing tolerances, the individual emitters do not ignite simultaneously and they ignite in an uncontrolled sequence. In addition, each of the liquid metal ion emitters has an individual emission behavior, such that the field arrangement of the liquid metal ion emitters usually produces an unpredictable thrust vector.
In addition, Bock, D., Tajmar, M., Highly Miniaturized FEEP Propulsion System (NanoFEEP) for Attitude and Orbit Control of CubeSats, Proceedings of the 67th International Astronautical
TUD3108WO
Congress (IAC), IAC-16-C4.6.5, September 26 to 30, 2016, Guadalajara, Mexico, have published a field emission propulsion system for a very small satellite.
It is an object of the present invention to provide a field emission propulsion system and a method for its operation that is suitable for use in very small satellites, achieving high efficiency and operating with low losses. In addition, a variable thrust range of several orders of magnitude is to be achieved. It is a further object of the present invention to control the ignition sequence and to compensate for a varying thrust vector or to enable active control of the thrust vector in order to enable controlled operation of the propulsion system.
Summary
These objects are achieved by the method of operating a field emission propulsion system as claimed in claim 1, by a method of calibrating a field emission propulsion system, and a method of operating a field emission propulsion system according to the dependent claims.
Further embodiments are specified in the dependent claims.
According to one embodiment a field emission propulsion system for a spacecraft is provided, comprising:
- a control unit;
- a propulsion assembly having a plurality of field emission propulsion units comprising an ion source having a plurality of ion emitters and extractor electrodes associated with the ion emitters and arranged in a field arrangement;
- a plurality of extractor electrode voltage sources, which are each assigned to the extractor electrodes, in order to control them by the control unit with an individual extractor electrode voltage.
The above field emission propulsion system comprises a field arrangement of several ion emitters, each of which is assigned an extractor electrode. The ion emitter may be assigned a common emitter voltage or a common emitter voltage potential, while the extractor electrodes are electrically isolated from each other and may be controlled by means of extractor electrode
TUD3108WO voltage sources with individually adjustable extractor electrode voltages and with individually adjustable extractor electrode voltage potentials, respectively.
In addition, the control unit may be configured to adjust the field strength of an electric field between the ion emitters and the associated extractor electrode to a specific extractor electrode voltage corresponding to a predetermined level of an ion current. The specific extractor electrode voltage for at least one specific propulsion unit is determined in a calibration method by measuring a current-voltage characteristic of the respective propulsion unit by measuring an emitter current through the ion emitter with the other propulsion units deactivated at the same time at different voltage differences between the extractor electrode and the ion emitters, and by adjusting the extractor electrode voltage or the extractor electrode voltage potential in such a way that an emitter current which corresponds to the predetermined level of the ion current is produced.
The above calibration method therefore provides to control the extractor electrodes of the field emission propulsion units individually with varying voltage differences between the respective extractor electrode and the respective ion emitters and simultaneously measuring a current flow from the emitter voltage source in order to measure a characteristic of the corresponding ion emitter. Thus, a voltage-dependent ion current may be determined for each ion emitter, such that a desired level of the ion current may be specifically set by adjusting the respective extractor electrode voltage or the respective extractor electrode voltage potential, respectively. Thus, ion emitters in a field arrangement may be assigned the same emitter voltage (with the same emitter voltage potential), and the extractor electrodes assigned to the ion emitters may be individually controlled to adjust the ion current of each individual ion emitter. Since the ion emitters are at the same voltage potential, they may be operated with the same emitter voltage source or with a common potential source, thereby reducing losses during high-voltage generation and reducing the installation space and mass of the overall system. Alternatively, the extractor electrode voltage sources for each of the extractor electrodes may be connected to each other and to the ion emitters with their positive potential terminal. The separate control of the extractor electrodes also allows for more precise adjustment of the thrust and direction of thrust of the propulsion assembly.
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Furthermore, a current measuring unit may be provided which is configured to measure an electric current flowing from one of the ion emitters, from several of the ion emitters or from all ion emitters and/or into the extractor electrode.
According to one embodiment, at least one of the extractor electrodes may be formed with two, three, four or more than four electrically isolated extractor electrode segments, which together form a particularly annular shaped extractor electrode, wherein the extractor electrode voltage source is configured to provide the extractor electrode segments with individual segment voltages, such that a predetermined direction of the emitted ion beam is adjusted in operation, and/or wherein separate segment voltage sources are provided for a plurality of the extractor electrode segments to provide the extractor electrode segments with individual segment voltages such that a predetermined direction of the ion beam is adjusted in operation.
Preferably, the extractor electrodes are each composed of several electrically isolated extractor electrode segments, which in turn may be controlled with different segment voltages. The levels of the individual segment voltages are based on an extractor electrode voltage to be applied or an extractor electrode voltage potential to be applied.
In particular, the segment voltages may be adjusted by separate segment voltage sources, by voltage dividers, which generate segment voltages by dividing the extractor electrode voltage assigned to the respective extractor electrode, or by adjustable series resistors of the extractor electrode segments.
This allows for compensation of possible misalignment of a resulting thrust beam during operation due to component tolerances or the like. Due to the possibility of selecting different segment voltages, the requirements on the component tolerances for the propulsion units may be greatly reduced, since alignment errors of the resulting thrust beam or geometrical alignment errors of the ion emitters to the extractor electrodes may be actively compensated.
By repeating the calibration process at regular intervals, undesired changes in the ion emission behavior of the individual ion emitters may be detected and, if necessary, compensated during long-term operation.
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Furthermore, a neutralizer may be provided to supply an electron current of controllable strength.
According to one embodiment, the ion source of the propulsion assembly may comprise a fuel tank for a liquid or liquefiable electrically conductive fuel, wherein the fuel may be ejected for field ionization at the tips of the ion emitters facing the respective extractor electrode.
Preferably, the extractor electrodes are annular shaped with a central opening arranged concentrically with respect to an extension direction of the ion emitters.
According to one embodiment, the extractor electrodes may be supported by an extraction plate and electrically insulated from each other, wherein the extraction plate is made of nonconductive material, preferably.
Furthermore, the extractor electrode voltage sources may each have an adjustable voltage divider to provide an adjustable extractor electrode voltage.
Preferably, one, at least one, several or each of the extractor electrodes comprises, along a full or partial circumference, an electrically conductive first shielding structure projecting in the direction of the ion emitters, and/or one, at least one or each of the extractor electrodes comprises, along a full or partial circumference, an electrically conductive second shielding structure projecting in the direction facing away from the ion emitters.
The above described method is based on a field emission propulsion system with a common emitter electrode and separate extractor electrodes which may be controlled separately with individual extraction potentials.
According to a further aspect, a method for calibrating the above described field emission propulsion system is provided, wherein a field strength of an electric field between the ion emitters and the respective associated extractor electrode may be set for each of the several field emission propulsion units to an extractor electrode voltage corresponding to a predetermined ion current to be adjusted, which results from a current-voltage characteristic of the field emission propulsion units and the predetermined ion current to be adjusted of a respective one of the several propulsion units, comprising the following steps:
TUD3108WO
- for each of the field emission propulsion units, measuring a current-voltage characteristic by measuring an emitter current through the ion emitter of the field emission propulsion unit, with remaining field emission propulsion units simultaneously deactivated or operated with constant current at different extractor electrode voltages;
- setting the extractor electrode voltages for each of the field emission propulsion units depending respectively on the current-voltage characteristic and the predetermined ion current so as to produce an emitter current of the respective field emission propulsion units corresponding to the predetermined ion current to be adjusted.
According to a further aspect, a method of operating the above described field emission propulsion system is provided, wherein a field strength of an electric field between the ion emitters and the respective associated extractor electrode is adjustable for each of the plurality of field emission propulsion units to an extractor electrode voltage corresponding to a predetermined ion current to be adjusted resulting from a current-voltage characteristic and the predetermined ion current to be adjusted of a respective one of the plurality of field emission propulsion units, wherein a predetermined thrust vector of the field emission propulsion system is set by controlling each of the field emission propulsion units with an individual extractor electrode voltage such that the predetermined thrust vector results as the sum of the ion currents from the field emission propulsion units.
Brief description of the drawings
The following drawings provide a more detailed explanation of the various embodiments, wherein:
Figure 1 illustrates a schematic representation of a field emission propulsion system comprising several propulsion units;
Figure 2 illustrates a cross-sectional representation of propulsion units arranged side by side;
Figure 3 illustrates a detailed cross-sectional representation of a propulsion unit;
TUD3108WO illustrates a possible arrangement of the propulsion units of the propulsion system of Figure 1;
Figure 4
Figure 5
Figure 6 is a flow chart illustrating a method for calibrating the propulsion units;
is an exemplary current-voltage characteristic of a propulsion unit; and
Figures 7a to 7c illustrate different perspective views of modifications of an extractor electrode segmentation.
Description of embodiments
Figure 1 schematically illustrates the structure of a field emission propulsion system 1 comprising a propulsion assembly 2, a neutralizer 3, and a control unit 4. Figure 2 illustrates a detailed view of a section of the propulsion assembly 2.
As shown in more detail in the cross-sectional view of Figure 2, propulsion assembly 2 comprises a heater unit 21 for an ion source 22, which comprises a fuel tank 221 with fuel 223 and an ion emitter 222 electrically and fluidly connected to it. The heating unit 21 serves to put the fuel in the fuel tank 221 into a liquid state and to keep it liquid. The heating unit 21 is supplied with power by means of a heating controller 41 as part of the control unit 4 and may be temperature controlled by this.
The fuel tank 221 is made of an electrically conductive material such as tantalum, rhenium, tungsten, graphite or titanium. As shown in the more detailed cross-sectional view of propulsion units 23 in Figures 2 and 3, ion emitters 222 are configured with a tip, in particular needleshaped, conical or pyramidal in shape, and comprise a device or configuration to pump liquid electrically conductive fuel 223 from fuel tank 221 for field ionization from ion emitter 222. In particular, a fluid line 224 running inside to the tip may be provided, which discharges the liquid electrically conductive fuel from the fuel tank 221 for field ionization from the ion emitter 222, e.g supplied by the capillary effect. Alternatively, the ion emitters 222 may also be porous with a plurality of lines, wherein the fuel 223 may be supplied to the tip of the ion emitter 222 due to the
TUD3108WO open porosity. Ion emitters 222 may be formed of tantalum, tungsten, rhenium, titanium or other refractory i.e. high-melting metals.
The fuel is passed through the fluid lines 224 of the ion emitters 222 by means of a capillary effect. An electrically conductive liquid or a low-melting metal, such as gallium, indium, bismuth, lead, gold or similar, may be considered as the material for the fuel.
Above the tip of each of the ion emitters 222 there is a respective extractor electrode 24 having a central opening 241 substantially coaxial with the tip of the ion emitter 222. Extractor electrodes 24 are preferably supported by an extraction plate 25, and are electrically isolated from each other, e.g. by an extraction plate 25 formed of non-conductive material.
The fuel tank 221 is electrically connected to the ion emitters 222 and receives a high voltage potential from an emitter voltage supply source 42. The emitter voltage supply source 42 may be adjustable and sets the emitter voltage or the emitter voltage potential to a fixed value.
Extractor electrodes 24 are each individually connected to a controllable extractor electrode voltage source 43, which is part of control unit 4. The extractor electrode voltage sources 43 are individually adjustable in order to set an individual extractor electrode voltage and thus an individual electric field strength between the ion emitter 222 and the extractor electrode 24 for each of the propulsion units 23. As an alternative to separate extractor electrode voltage sources 43 for each of the extractor electrodes 24, a common extractor electrode voltage source 43 may be provided, wherein the different voltages for the extractor electrodes 24 may be set by means of correspondingly assigned voltage dividers. Other options for setting individual extractor electrode voltages for the extractor electrodes 24 are also conceivable.
The control unit 4 is especially configured to individually control the extractor electrode voltage or the extractor electrode potential of the extractor electrodes 24, such that the timings of ignition and the levels of ion emission may be controlled from the individual correspondingly assigned ion emitters 222. Thus, individual ion emitters 222 may be switched on or off and different emission currents may be controlled for each of the ion emitters 222. The potential difference between the emitter voltage potential and the extraction voltage potential is usually several +1000 volts.
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Since due to the emitter ion current from positively charged fuel ions, which current is emitted from the propulsion units 23 during operation, the propulsion system 1 is charged negatively, an electron current is usually generated and emitted by means of the neutralizer 3. Neutralizer 3 may, for example, be configured as a field emission electron source or thermal electron source in a manner known per se. For this reason, the control unit 4 comprises a neutralizer control unit 45 which may control and supply power to the neutralizer 3 in a manner known per se, e.g. to keep the charge of the entire propulsion system 1 as neutral as possible.
Figure 4 illustrates an arrangement of extractor electrodes 24 in a plan view. The extractor electrodes 24, for example, are arranged around and concentric to the ion emitter 222. In the center of the extractor electrodes 24 there are substantially round openings 241 which are arranged concentrically to the ion emitters 222 in order to emit the ion beam from the ion emitter 222. The arrangement of the extractor electrodes 24 may be provided as a field arrangement, wherein the extractor electrodes 24 are arranged in rows and are offset from each other to achieve the highest possible arrangement density.
The extractor electrodes 24 are connected to each other on the extraction plate 25, which retains the extractor electrodes 24 in position. The extraction plate 25 may be formed of electrically non-conductive material, or the extractor electrodes 24 may be mounted isolated on the extraction plate 25. One, at least one or each of the extractor electrodes 24 comprises an electrically conductive first shielding structure 242 projecting circumferentially in the direction of the ion emitter 222, which prevents, by the principle of shading, the continuous coating of one side of the extraction plate 25, which side is facing the ion emitters, with accumulating fuel material. This prevents the formation of an electrically conductive path between the individual extractor electrodes 24, and between the electrodes and the fuel tank 221 during operation, which would result in an electrical short circuit.
Alternatively or additionally, one, at least one, several or each of the extractor electrodes 24 may comprise an electrically conductive second shielding structure 245 projecting circumferentially in the direction of the ion beam to be emitted, which prevents, by the principle of shading, the continuous deposition of one side of the extraction plate 25, which side is facing away from the ion emitters 222, with accumulating fuel material. The second shielding structure 245 may be formed torus-like. This prevents the formation of an electrically conductive path between the
TUD3108WO individual extractor electrodes 24, and between the electrodes and the fuel tank 221 during operation, which would result in an electrical short circuit.
Furthermore, the extraction plate 25 may comprise, between the extractor electrodes 24, structures and/or recessed structures which are labyrinth-like or meander-like, i.e. projecting orthogonally to the surface direction of the extraction plate 25, which structures extend along the surface direction of the extraction plate 25, and thereby preventing, by the principle of shading, a continuous conductive coating during long-term operation by deposition of the fuel material. For example, a support between heating unit 21 and extraction plate 25 may have a corresponding labyrinth-like or meander-like form or steps which also prevent continuous coating by shading.
In addition, an electrically conductive cover plate 27 may optionally be mounted parallel to the extraction plate 25 on the side of the extraction plate 25 facing away from the ion emitters. In particular, the cover plate 27 comprises circular openings 271 which are located above the extractor electrodes 24 in the direction in which the ion emitters 222 and the extractor electrodes 25 are arranged and which, in particular, have the same or larger dimensions (e.g. radii) than the extractor electrodes 25 in the surface direction of the extraction plate 25. The cover plate 27 may be electrically isolated from the extractor electrodes 24. The electrical insulation between the cover plate 27 and the extractor electrodes 24 may be ensured by means of an electrically insulating spacer 28, which comprises labyrinth-like or meander-shaped structures, in order to protect the insulation as well in long-term operation against a continuous conductive coating by deposition of fuel. The provision of a cover plate 27 is advantageous, since it is possible to prevent particles in the environment from reaching the ion emitters 222 by applying a voltage potential. In addition, deposition of sputter particles or reflected fuel on the upper side of the extraction plate 25 may be prevented during prolonged operation.
During operation in space, the cover plate 27 may prevent the impact of a local surrounding plasma on the propulsion units 23. This prevents the attraction of e.g. free / thermal electrons from the surrounding plasma to the ion emitters 222, which electrons could damage the ion emitters. In addition, the voltage potential of the cover plate 27 prevents false measurement of emitter current by such a secondary electron current.
The control unit 4 also comprises a current measuring unit 44 to measure a current flowing to the extractor electrode voltage sources or from the neutralizer 3.
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For operation of the propulsion system 1, it is desirable to set equal or defined thrust vectors of the ion beam from ion emitters 222. Due to component and assembly tolerances, different thrust vectors occur when the same extractor electrode voltages are applied.
Therefore, a method is provided to control the strength of the ion beam in a defined way. This is performed by the defined individual adjustment of the field strength of the electric field between the ion emitters 222 and the respectively assigned extractor electrode 24 by varying the extractor electrode voltage or the extractor electrode voltage potential or the voltage difference between the extractor electrodes 24 and the associated ion emitters 222. To set the extractor electrode voltage, a method is provided as shown in the flow diagram of Figure 5.
In step S1, one of the propulsion units 23 is selected. In step S2, a current-voltage characteristic graph is measured for the selected propulsion unit 23. The current-voltage characteristic represents a characteristic of a current flow across a voltage difference between the extractor electrode voltage potential and the emitter voltage potential of the respective propulsion unit 23, which occurs at a field strength in the respective propulsion unit 23 set by the extractor electrode voltage. The measurement is performed with the other propulsion units 23 deactivated or operating at constant (known) current (i.e. activated) and by means of the current measuring unit 44, which in this case measures the level of the ion current of all activated propulsion units 23. The ion current level is measured by measuring the electric current flowing from the emitter voltage supply source 42 or the electric current flowing into the ion source. The ion current of the propulsion unit 23 to be measured corresponds substantially to the measured electric current flowing into the ion source minus the known ion currents of the other propulsion units 23 (i.e. with the other propulsion units 23 activated). In other words, if the remaining propulsion units 23 are operated with a known current, the ion current of the respective propulsion unit 23 may be determined by subtracting the currents of the remaining propulsion units 23 from the detected current. If only the propulsion unit 23 to be measured is active for each measurement, the measured electric current corresponds to the ion current at the applied field strength or at the applied voltage difference between the emitter voltage potential and the extractor electrode voltage potential. Thus, a current-voltage characteristic may be determined for each of the propulsion units 23. Figure 6 illustrates an example of such a current-voltage characteristic graph.
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Step S3 checks whether all propulsion units 23 have been measured. If this is the case (alternative: Yes), the method continues with step S4, otherwise the system returns to step S1 and measures a next propulsion unit 23 that has not yet been measured. In this way, a currentvoltage characteristic is recorded for each of the propulsion units 23.
In step S4, the extractor electrode voltages are controlled to set a field strength corresponding to a desired ion current strength for each of the propulsion units 23.
Further with reference to Figure 4 and in conjunction with the different views of Figures 7a to 7c, the extractor electrodes 24 may be segmented, with extractor electrode segments 243 being electrically isolated from each other e.g. by spacing, and forming the circular extractor electrode 24 in the assembled state. It is possible to arrange the extractor electrode segments 243 according to the embodiments of Figures 7a to 7c, wherein the extractor electrodes 24 are segmented into four identical extractor electrode segments 243 (see Figure 7a), into two identical extractor electrode segments 243 (see Figure 7b) and into three extractor electrode segments 243 (see Figure 7c). By varying the segment voltages at the individual extractor electrode segments 243 of an extractor electrode 24, an asymmetry of the ion beam emitted by the ion emitter 222, i.e. an inclination of the path of the ion beam with respect to the alignment between the ion emitter 222 and the extractor electrode 24, may be compensated. Such an asymmetry results from component tolerances and manufacturing tolerances of the propulsion units 23.
If the extractor electrodes are segmented, the above described calibration method may first be performed by applying the extractor electrode voltages required for the measurement to each of the extractor electrode segments.
An asymmetry may be determined, for example, during the calibration method or in a separate procedure. For this purpose, each of the extractor electrode segments 243 may be provided with a separate current measurement facility. While each of the propulsion units 23 is measured one after the other to determine the current-voltage characteristic such that an ion beam is formed, a parasitic current is measured through each of the extractor electrode segments 243 at one or more specific extractor electrode voltages. For example, the extractor electrode segment 243 through which the highest current flow is measured corresponds to the extractor electrode segment 243 which deflects the ion beam most strongly in its direction and which is, accordingly,
TUD3108WO arranged closest to the ion beam. The individual segment voltages may now be controlled based on the desired extractor electrode voltage (or the desired field strength).
By varying a segment voltage applied to part of the individual 243 extractor electrode segments of the propulsion unit 23, the direction of the ion beam may be varied as well, in addition to applying the extractor electrode voltage to the other 243 extractor electrode segments. For example, by iterative control of the segment voltages at the part of the extractor electrode segments 243, the direction of the ion beam may be adjusted to a desired direction, in particular the direction parallel to the arrangement direction between the ion emitter 222 and the extractor electrode 24. By iteratively controlling a part of the segment voltages based on the previously determined and set extractor electrode voltage, both the strength of the ion beam may be precisely controlled and the component and manufacturing tolerances of the propulsion unit 23 may be compensated.
Alternatively, all segment voltages may be varied by the extractor electrode voltage to be adjusted such that the mean value of the individual segment voltages corresponds approximately to the extractor electrode voltage.
For example, the control of the individual segment voltages or the direction of the ion beam may be performed using voltage dividers in particular, wherein the respective segment voltage is generated from the extractor electrode voltage. Thus, segment voltages may be generated by voltage dividers, also by adjustable voltage dividers, by the extractor electrode voltage source. A separate control with individual voltage sources for each extractor electrode segment is also possible.
If, for example, in the embodiment of Figure 7a, a high current flow, compared to the currents in the other extractor electrode segments 243 through one of the extractor electrode segments 243a, is measured, the corresponding segment voltage from the extractor electrode voltage may be reduced by setting an adjustable electrical series resistor or by setting an adjustable voltage divider in order to achieve a higher attraction of the fuel ions of the ion beam through the other extractor electrode segments 243. As a result, the ion beam is deflected away from the respective extractor electrode segment 243a, as it is attracted more by the other extractor electrode segments 243. By suitably calibrating the variable series resistors assigned to the extractor electrode segments 243 or the voltage dividers assigned to the extractor electrode
TUD3108WO segments 243, the propulsion unit 23 may be calibrated accordingly. In this way, component tolerances of the extractor electrode 24 and alignment errors may be compensated, and the precision in the production and assembly of the extractor electrode segments 243 and the ion emitter 222 may be reduced.
The above described field emission propulsion system may be operated by separately controlling the propulsion units 23. The ion currents of the individual propulsion units 23 are determined according to a thrust vector control by specifying a thrust vector. The individual ion currents are each controlled by specifying a corresponding extractor electrode voltage resulting from the current/voltage characteristic, such that in addition to a total thrust strength resulting from the sum of the ion beams, a predetermined moment is also applied to the field emission propulsion system, which results from the arrangement of the individual propulsion units and the respective thrust strengths resulting from the respective ion beams.
Claims (13)
- Claims1. Field emission propulsion system (1) for a spacecraft, comprising:- a control unit (4);- a propulsion assembly (2) having a plurality of field emission propulsion units (23) comprising an ion source having a plurality of ion emitters (222) and extractor electrodes (24) associated with the ion emitters (222) and arranged in a field arrangement;- a plurality of extractor electrode voltage sources (43), which are each assigned to the extractor electrodes (24), in order to control them by the control unit (4) with an individual extractor electrode voltage.
- 2. Field emission propulsion system (1) according to claim 1, having a current measuring unit (44) which is configured to measure an electric current flowing from the ion emitters (222) and/or into the extractor electrodes (24).
- 3. Field emission propulsion system (1) according to one of the preceding claims, wherein the control unit (4) is configured to control a field strength of an electric field between the ion emitters (222) and the respective associated extractor electrode (24) to a determined extractor electrode voltage corresponding to a predetermined level of an ion current, wherein the determined extractor electrode voltage is determined for a determined field emission propulsion unit (23), by measuring a current-voltage characteristic of the respective field emission propulsion unit (23) by measuring an emitter current through the ion emitter (222), with other field emission propulsion units (23) simultaneously being deactivated or operated at constant current at different voltages, and wherein the extractor electrode voltage is set in such a way that an emitter current of the particular field emission propulsion unit (23) sets itself to correspond to the predetermined level of the ion current.
- 4. Field emission propulsion system (1) according to one of the preceding claims, wherein at least one of the extractor electrodes (24) is formed with two, three, four or more than four extractor electrode segments (243) electrically insulated from each other, which together form a particularly annular shaped extractor electrode (24), wherein the extractor electrode voltage source (43) is formed in order to provide the extractorTUD3108WO electrode segments (243) with individual segment voltages such that, in use, a predetermined direction of the ion beam is controlled, and/or wherein separate segment voltage sources are provided for a plurality of the extractor electrode segments (243) in order to provide the extractor electrode segments (243) with individual segment voltages such that, in use, a predetermined direction of the ion beam is adjusted.
- 5. Field emission propulsion system (1) according to claim 4, wherein an adjustable series resistor or an adjustable voltage divider is assigned to each part of the extractor electrode segments (243) or to each of the extractor electrode segments (243) in order to generate the individual segment voltages from the extractor electrode voltage assigned to the respective extractor electrode (24) or another predetermined voltage.
- 6. Field emission propulsion system (1) according to one of the preceding claims, wherein a neutralizer (3) is provided to output an electron current of controllable magnitude.
- 7. Field emission propulsion system (1) according to one of the preceding claims, wherein the propulsion assembly (2) comprises an ion source having a fuel tank (221) for a liquid or liquefiable electrically conductive fuel (223), wherein the fuel (223) can be ejected for field ionization at the tip of the ion emitter (222) facing the respective extractor electrode (24).
- 8. Field emission propulsion system (1) according to one of the preceding claims, wherein the extractor electrodes (24) are in particular of annular shape with a central opening which are arranged concentrically to an extension direction of the ion emitters (222).
- 9. Field emission propulsion system (1) according to one of the preceding claims, wherein the extractor electrodes (24) are supported by an extraction plate (25) and are electrically insulated from one another, wherein the extraction plate (25) is formed in particular from non-conductive material.
- 10. Field emission propulsion system (1) according to one of the preceding claims, wherein the extractor electrode voltage sources (43) each comprise an adjustable voltage divider to provide an adjustable extractor electrode voltage.TUD3108WO
- 11. Field emission propulsion system (1) according to one of the preceding claims, wherein one, at least one or each of the extractor electrodes (24) comprises, along a full or partial circumference, an electrically conductive first shielding structure (242) projecting in the direction of the ion emitters (222), and/or wherein one, at least one or each of the extractor electrodes (24) comprises, along a full or partial circumference, an electrically conductive second shielding structure (245) projecting in the direction facing away from the ion emitters (222).
- 12. Method for calibrating the field emission propulsion system (1) according to one of the preceding claims, wherein a field strength of an electric field between the ion emitters (222) and the respectively associated extractor electrode (24) is adjustable for each of the plurality of field emission propulsion units (23) to an extractor electrode voltage corresponding to a predetermined ion current to be adjusted, wherein the extractor electrode voltage result from a current-voltage characteristic and the predetermined ion current to be adjusted of a respective one of the plurality of field emission propulsion units (23), comprising the following steps:- for each of the field emission propulsion units (23), measuring a currentvoltage characteristic by measuring an emitter current through the ion emitter (222) of the field emission propulsion unit (23), with remaining field emission propulsion units (23) simultaneously deactivated or operated with constant current at different extractor electrode voltages;- controlling the extractor electrode voltages for each of the field emission propulsion units (23) depending respectively on the current-voltage characteristic and the predetermined ion current so as to produce an emitter current of the respective field emission propulsion units (23) corresponding to the predetermined ion current to be adjusted.
- 13. Method of operating a field emission propulsion system (1) according to any one of claims 1 to 11, wherein a field strength of an electric field between the ion emitters (222) and the respective associated extractor electrode (24) is adjustable for each of the plurality of field emission propulsion units (23) to an extractor electrode voltage corresponding to a predetermined ion current to be adjusted resulting from a currentvoltage characteristic and the predetermined ion current to be adjusted of a respective one of the plurality of field emission propulsion units (23),TUD3108WO wherein a predetermined thrust vector of the field emission propulsion system (1) is adjusted by driving each of the field emission propulsion units (23) with an individual extractor electrode voltage such that the predetermined thrust vector results as the sum of the ion currents from the field emission propulsion units (23).
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE102017117316.1A DE102017117316B4 (en) | 2017-07-31 | 2017-07-31 | Field emission drive system and method for calibrating and operating a field emission drive system |
| DE102017117316.1 | 2017-07-31 | ||
| PCT/EP2018/069251 WO2019025174A1 (en) | 2017-07-31 | 2018-07-16 | Field emission propulsion system and method for calibrating and operating a field emission propulsion system |
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| AU2018312508A1 true AU2018312508A1 (en) | 2020-01-30 |
| AU2018312508B2 AU2018312508B2 (en) | 2024-05-23 |
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| AU2018312508A Active AU2018312508B2 (en) | 2017-07-31 | 2018-07-16 | Field emission propulsion system and method for calibrating and operating a field emission propulsion system |
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| EP (1) | EP3662160B1 (en) |
| JP (1) | JP7171699B2 (en) |
| AU (1) | AU2018312508B2 (en) |
| CA (1) | CA3071022A1 (en) |
| DE (1) | DE102017117316B4 (en) |
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| LT (1) | LT3662160T (en) |
| WO (1) | WO2019025174A1 (en) |
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| EP3604805B1 (en) | 2018-08-02 | 2024-04-24 | ENPULSION GmbH | Ion thruster for thrust vectored propulsion of a spacecraft |
| DE102022103408B4 (en) | 2022-02-14 | 2024-02-08 | Technische Universität Dresden, Körperschaft des öffentlichen Rechts | Electron emitters for space applications |
| CN115355145B (en) * | 2022-07-25 | 2024-05-14 | 北京控制工程研究所 | Micro-bovine-grade variable thruster based on gas field ionization enhancement |
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| JPS5944754A (en) * | 1982-09-06 | 1984-03-13 | Jeol Ltd | Charged particle source |
| US5269131A (en) | 1992-08-25 | 1993-12-14 | The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration | Segmented ion thruster |
| US5947421A (en) * | 1997-07-09 | 1999-09-07 | Beattie; John R. | Electrostatic propulsion systems and methods |
| JP3906549B2 (en) | 1998-02-19 | 2007-04-18 | 三菱電機株式会社 | Liquid metal ion thruster |
| AT500412B8 (en) * | 2002-12-23 | 2007-02-15 | Arc Seibersdorf Res Gmbh | LIQUID METAL ION SOURCE |
| JP4107391B2 (en) | 2005-05-17 | 2008-06-25 | 独立行政法人 宇宙航空研究開発機構 | Solid propellant thruster for space |
| US7690187B2 (en) | 2006-09-26 | 2010-04-06 | The Aerospace Corporation | Modular micropropulsion device and system |
| US8453426B2 (en) * | 2009-04-06 | 2013-06-04 | Raytheon Company | Current controlled field emission thruster |
| US10330090B2 (en) * | 2013-03-01 | 2019-06-25 | Michigan Technological University | Generating electrospray from a ferrofluid |
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2017
- 2017-07-31 DE DE102017117316.1A patent/DE102017117316B4/en active Active
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| DE102017117316B4 (en) | 2020-04-02 |
| JP2020532671A (en) | 2020-11-12 |
| EP3662160B1 (en) | 2021-05-26 |
| AU2018312508B2 (en) | 2024-05-23 |
| LT3662160T (en) | 2021-09-27 |
| CA3071022A1 (en) | 2019-02-07 |
| DK3662160T3 (en) | 2021-08-23 |
| WO2019025174A1 (en) | 2019-02-07 |
| DE102017117316A1 (en) | 2019-01-31 |
| WO2019025174A8 (en) | 2019-04-18 |
| JP7171699B2 (en) | 2022-11-15 |
| EP3662160A1 (en) | 2020-06-10 |
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