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CA-3071022-C - FIELD EMISSION PROPULSION SYSTEM AND METHODS FOR CALIBRATING AND OPERATING A FIELD EMISSION PROPULSION SYSTEM

CA3071022CCA 3071022 CCA3071022 CCA 3071022CCA-3071022-C

Abstract

The invention relates to a field emission propulsion system (1) for spacecraft, comprising: a control unit (4); a propulsion assembly (2) with a plurality of field emission propulsion units (23) that comprise an ion source with a plurality of ion emitters (222) and extraction electrodes (24), associated with said ion emitters (222) and arranged in a field arrangement; and a plurality of extraction electrode voltage sources (43), each associated with the extraction electrodes (24) to operate same, controlled by the control unit (4), using an individual extraction electrode voltage.

Inventors

  • Daniel Bock
  • Martin Tajmar
  • Philipp Laufer

Assignees

  • TECHNISCHE UNIVERSITAT DRESDEN

Dates

Publication Date
20260505
Application Date
20180716
Priority Date
20170731

Claims (20)

  1. Claims 1. A field emission propulsion system for a spacecraft, the system comprising: - a control unit; - a propulsion assembly including a plurality of field emission propulsion units arranged in a field arrangement, each of the plurality of field emission propulsion units comprising: an ion source having a plurality of ion emitters; and extractor electrodes associated with the plurality of ion emitters and electrically insulated from one another; - a plurality of extractor electrode voltage sources, which are each assigned to the extractor electrodes, configured to control the extractor electrodes by the control unit with an individual extractor electrode voltage; and - an extraction plate supporting the extractor electrodes and formed from nonconductive material.
  2. 2. A field emission propulsion system according to claim 1, the system including a current measuring unit which is configured to measure an electric current flowing from the plurality of ion emitters and an electric current flowing into the extractor electrodes.
  3. 3. A field emission propulsion system according to claim 1, the system including a current measuring unit which is configured to measure an electric current flowing from the plurality of ion emitters or an electric current flowing into the extractor electrodes.
  4. 4. A field emission propulsion system according to any one of claims 1 to 3, wherein the control unit is configured to control a field strength of an electric field between the 16 plurality of ion emitters and the respective associated extractor electrode 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, by measuring a current-voltage characteristic of the respective field emission propulsion unit by measuring an emitter current through the corresponding said ion emitter, with other said field emission propulsion units 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 sets itself to correspond to the predetermined level of the ion current.
  5. 5. A field emission propulsion system according to any one of claims 1 to 4, wherein at least one of the extractor electrodes is formed with at least two extractor electrode segments electrically insulated from each other, which together form an annular shaped extractor electrode, wherein the corresponding said extractor electrode voltage source is formed in order to provide the extractor electrode segments with individual segment voltages such that, in use, a predetermined direction of the ion beam is controlled..
  6. 6. A field emission propulsion system according to claim 5, wherein separate segment voltage sources are provided for a plurality of the extractor electrode segments in order to provide the plurality of extractor electrode segments with individual segment voltages such that, in use, the predetermined direction of the ion beam is adjusted.
  7. 7. A field emission propulsion system according to any one of claims 1 to 4, wherein at least one of the extractor electrodes is formed with at least two extractor electrode 17 segments electrically insulated from each other, which together form an annular shaped extractor electrode, wherein separate segment voltage sources are provided for a plurality of the extractor electrode segments in order to provide the plurality of extractor electrode segments with individual segment voltages such that, in use, a predetermined direction of the ion beam is adjusted.
  8. 8. A field emission propulsion system according to any one of claims 5 to 7, wherein one of an adjustable series resistor or an adjustable voltage divider is assigned to one of each part of the extractor electrode segments or to each of the extractor electrode segments in order to generate the individual segment voltages from the extractor electrode voltage assigned to the respective extractor electrode or another predetermined voltage.
  9. 9. A field emission propulsion system according to any one of claims 1 to 8, wherein a neutralizer is provided to output an electron current of controllable magnitude.
  10. 10. A field emission propulsion system according to any one of claims 1 to 9, wherein the ion source of the propulsion assembly comprises a fuel tank for a liquid or liquefiable electrically conductive fuel, wherein the fuel is ejectable for field ionization at a tip of the ion emitter facing the respective extractor electrode.
  11. 11. A field emission propulsion system according to any one of claims 1 to 10, wherein the extractor electrode have central openings which are arranged concentrically to an extension direction of the plurality of ion emitters. 18
  12. 12. A field emission propulsion system according to any one of claims 1 to 4, wherein each said extractor electrode is annularly-shaped.
  13. 13. A field emission propulsion system according to any one of claims 1 to 7 or any one of claims 9 to 12 when depending from claims 1 to 7, wherein the extractor electrode voltage sources each comprise an adjustable voltage divider to provide an adjustable extractor electrode voltage.
  14. 14. A field emission propulsion system according to claim 8 or any one of claims 9 to 12 when depending from claim 8, wherein the adjustable voltage divider is configured to provide an adjustable extractor electrode voltage.
  15. 15. A field emission propulsion system according to any one of claims 1 to 14, wherein one or more of the extractor electrodes comprises, along a full or partial circumference, an electrically conductive first shielding structure projecting in the direction of the plurality of ion emitters.
  16. 16. A field emission propulsion system according to any one of claims 1 to 14, wherein one or more of the extractor electrodes comprises, along a full or partial circumference, an electrically conductive shielding structure projecting in the direction facing away from the plurality ion emitters.
  17. 17. A field emission propulsion system according to claim 15, wherein one or more 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 plurality of ion emitters. 19
  18. 18. A spacecraft comprising a field emission propulsion system according to any one of claims 1 to 17.
  19. 19. A method for calibrating the field emission propulsion system according to any one of claims 1 to 17, wherein a field strength of an electric field between the plurality of ion emitters and the respectively 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, wherein the extractor electrode voltage results 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, the method comprising the following steps: - for each of the field emission propulsion units, measuring a current-voltage characteristic by measuring an emitter current through the ion emitter thereof, with remaining said field emission propulsion units 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 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.
  20. 20. A method of operating a field emission propulsion system according to any one of claims 1 to 17, wherein a field strength of an electric field between the plurality of 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 currentvoltage characteristic and the predetermined ion current to be adjusted of a respective one of the plurality of field emission propulsion units, the method comprising: - adjusting a predetermined thrust vector of the field emission propulsion system by driving 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.

Description

1 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 2 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 a method of calibrating a field emission propulsion system as herein described, and a method of operating a field emission propulsion system as herein described. 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 3 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 sim