WO2025120165A1

WO2025120165A1 - Staged electrostatic thruster

Info

Publication number: WO2025120165A1
Application number: PCT/EP2024/085089
Authority: WO
Inventors: Lucas Matthias Steitner; Ian Alexander JUBY
Original assignee: Dalion BV
Current assignee: Dalion BV
Priority date: 2023-12-08
Filing date: 2024-12-06
Publication date: 2025-06-12
Anticipated expiration: 2026-06-08
Also published as: NL2036471B1

Abstract

An electrostatic thruster for producing thrust by charging gas and/or liquid particles using a high voltage potential, the electrostatic thruster comprises at least two thruster cells, wherein each thruster cell comprises: - at least one emitter, - at least one collector, wherein the at least one collector is spaced from the at least one emitter by a thruster cell gap, wherein the electrostatic thruster further comprises a power source electrically connected to the at least one emitter and the at least one collector of each thruster cell, wherein the power source is configured to apply a voltage between the at least one emitter and the at least one collector of each thruster cell, wherein the at least two thruster cells are positioned in parallel to form a thruster cell array, wherein the thruster cell array further comprises an intermediate electrode powered by a current source that generates a substantially constant current.

Description

Title: Staged Electrostatic Thruster

FIELD OF THE INVENTION

The present invention relates to an electrostatic thruster configured to produce thrust using high voltage potentials.

BACKGROUND OF THE INVENTION

For many years people demonstrated that a force or thrust can be produced by “asymmetrical capacitors” consisting of a very thin electrode wire and a larger second electrode. When high voltage is applied to the thin electrode wire, a force is produced into the direction of this wire.

In 1921, T. T. Brown discovered a force on a Coolidge (X-ray) tube which he could not explain. The force was observed when a high voltage was applied to the tube. This discovery led to the first asymmetrical capacitor with a very thin anode and a very large cathode which produces a force in the direction of the anode when a high voltage is applied to the anode. GB300311A (herein: D1) is the first patent of T. T. Brown which discloses a method and an apparatus for producing motion. The document presents a power-producing unit consisting of alternated insulating slab and conducting plates. The document also discloses an apparatus to produce rotary motion, wherein the slabs and plates are arranged radially.

EP1619123A2 (herein: D2) discloses an ion drive system for creating a propulsive force or thrust. The ion drive system comprises at least one stage with an emitter 10 and an attractor 12, wherein the attractor is spaced from the emitter by a gap D. The ion drive system further comprises a propellant source for introducing a propellant in the vicinity of the emitter and a power source 14. The power source creates a high intensity field in the vicinity of the emitter to ionize the dielectric media and creates a diffused field in the vicinity of the attractor to accelerate the ions away from the emitter. The attractor is also accelerated towards the high intensity field in the vicinity of the emitter. These accelerations combined create a propulsive force.

In a preferred embodiment of D2, the ion drive system comprises a plurality of stages. The additional stages are isolated to prevent reverse flow of oppositely charged particles. The additional stages are isolated due to a reverse polarity of adjacent emitter-attractor pairs and by positioning the subsequent emitter downstream of the prior stage diffused attractor field. One drawback of the device is that it requires a propellant source to produce sufficient propulsive thrust.

Another example of an implementation of an electrostatic thruster is disclosed in US2009159754A1 (herein: D3). D3 presents a rotary-wing system which generates a directed ion field to propel a fluid along a rotary-wing to control at least one boundary layer characteristic. A propeller system 10 comprises multiple propeller blades or rotary-wings 14. Each rotary-wing comprises emitter-collector pairs electrically connected to a high voltage source. The emittercollector pairs are positioned on an upper side and a lower side of each rotary-wing. Each emitter 18 operates as an ion source and each attractor 20 operates as an ion collector such that the emitter/attractor network may be utilized to create a directed ion field to create a thrust force.

A drawback of the electrostatic thruster of D3 is that the emitter-collector pairs on the lower side of a rotary-wing produce a thrust force perpendicular to the surface of the lower side of the rotary-wing. The thrust force is directed away from the rotary-wing and therefore counteracts the rotational movement of the propeller system.

WO2022086667A2 (herein: D4) discloses a low noise vertical take-off and landing (VTOL) unmanned air vehicle (UAV). The UAV 10 of D4 comprises an ion thruster 1 for providing thrust in a vertical direction and a thrust vectoring system to provide thrust in a horizontal direction. The ion thruster consists of three geometrically identical levels of electrode pairs 50. Each electrode pair comprises a top electrode 52 and a bottom electrode 54 with an opposite voltage potential to the top electrode. By applying a potential, thrust is generated in the direction of the top electrode. The UAV further comprises a rotating motor with impellers 5 to support the force produced by the ion thrusters.

A drawback of the UAV of D4 is that the force produced by the ion thrusters is not sufficient to lift the UAV from the ground. Additional rotating impellers are required to produce sufficient lifting force. It was recognized in the present invention that the distance between the electrode pairs is not sufficient to prevent that a level affects the performance of a subsequent level of electrode pairs. The overall size of the UAV becomes too large when the distance between the levels of electrode pairs is increased sufficiently.

The current invention solves major problems of existing ion thrusters: loss of performance when staging thrusters, loss of performance when placing thrusters close to each other and loss of efficiency when increasing the voltage to produce more thrust. OBJECTION OF THE INVENTION

It is an object of the present invention to provide an improved electrostatic thruster which takes away at least one of the drawbacks and limitations discussed above and in general to provide a more efficient electrostatic thruster device.

It is another object of the present invention to provide an electrostatic thruster which is relatively compact, and in particular uses less materials and will be less heavy.

SUMMARY OF THE INVENTION

At least one of the above mentioned objects is achieved with an electrostatic thruster 10 for producing thrust by charging gas and/or liquid particles using a high voltage potential, the electrostatic thruster comprises at least two thruster cells, wherein each thruster cell comprising: at least one emitter, at least one collector, wherein the at least one collector is spaced from the at least one emitter by a thruster cell gap, wherein the electrostatic thruster further comprises a power source electrically connected to the at least one emitter and the at least one collector of each thruster cell, wherein the power source is configured to apply a voltage between the at least one emitter and the at least one collector of each thruster cell, wherein the at least two thruster cells are positioned in parallel to form a thruster cell array, wherein the thruster cell array further comprises an intermediate electrode, wherein the intermediate electrode is positioned in an intermediate area between the emitters and the collectors of two adjacent ones of the thruster cells in the thruster cell array, wherein the intermediate electrode is electrically connected to the collectors of the thruster cell array via a current source configured to generate a substantially constant current.

A liquid and/or gas is ambient to the at least one emitter and the at least one collector. The liquid and/or gas may also be identified as a fluid, the fluid comprising a gas and/or a liquid. The emitter and collector are surrounded by the fluid. The fluid may be ambient (such as air or water) or may be dispensed by a dispenser in an area surrounding the at least one emitter and collector. The emitter may be understood as an electrode capable of emitting electrical charge, positive or negative, to thereby positively or negatively charge particles, such as molecules, of the gas and/or liquid surrounding the emitter. The collector may be understood as an electrode capable of collecting the charge from the charged particles. By having a power source applying a voltage between an emitter and a collector, electrically charged particles surrounding the emitter are produced. The charged particles and the collector attract each other creating a force on the electrostatic thruster in the direction of the emitter. The emission of charged particles by the emitter may be understood to include the emission of charged particles and/or the emission of electrical charge which electrically charges particles in the liquid and/or gas that surrounds the emitter, so as to form the charged particles.

The term parallel may be understood as parallel in respect of a direction of the force created, i.e., the thrust created. The term parallel may also be understood as parallel in respect of the direction from the emitter to the corresponding collector or vice versa. Similarly, the term in series may be understood as arranged in a direction of the force created, i.e., the thrust created by the electrostatic thruster. The power source may be an electrical power source and may be configured to apply any suitable voltage between the emitter and the collector. For example, the electrical voltage between the emitter and the collector may be a DC (direct current) voltage or a pulsed voltage. The electrical voltage may be positive (e.g., the emitter in operation being at a higher voltage than the collector) or negative (e.g., the emitter in operation being at a higher voltage than the collector).

The charged particles emitted in operation by the emitter have a same polarity as the polarity of the emitter. As a result of electrostatic forces, similarly polarized items repel each other while oppositely polarized items attract each other. Therefore, the charged particles that are emitted by the emitter of a thruster cell repel each other and are repelled by the emitter. The inventors have realized that two effects may play a role in the generation of thrust by the thruster. On the one hand, the emitted, charged particles may be attracted by the collector, which may result in an acceleration of the charged particles towards the collector to generate a flow towards the collector. As a result of drag effects, the charged particles may tend to drag other particles, such as non-charged particles, molecules, etc. which may enhance the flow. This so called “ion wind” may provide for some displacement, however the inventors have realized that the thrusting force to be generated as a result of the ion wind may be relatively low.

The inventors have realized that a further effect may be used to enhance thrust force, namely electrostatic force. In a prior art electrostatic thruster, the net electrostatic force may be low, hence a contribution of the electrostatic force to thrust may be low. The charged particles emitted by the emitters of the thruster cell array may form a sphere of charged particles around the emitters. A part of the charged particles may be emitted in a hemisphere away from the collectors of the thruster cells of the thruster cell array and another part of the charged particles may be emitted in a hemisphere towards the collectors of the thruster cells of the thruster cell array. Due to the electrostatic forces between the charged particles and the emitter, the charged particles emitted in the hemisphere away from the collectors of the thruster cells of the thruster cell array and the charged particles emitted in the hemisphere towards the collectors of the thruster cells of the thruster cell array may result in opposite electrostatic forces on the emitter, resulting in a relatively low net force in the prior art electrostatic thruster. The emitted charged particles may be attracted by the collector due to the electrostatic forces. In the hemisphere of the emitter facing away from the collector, such attractive force on the charged particle may may be low, due to the presence of the oppositely charged emitter. Thus, in the prior art electrostatic thruster, a net effect of the electrostatic force may be low.

The inventors have devised that a thrust by the electrostatic force may be enhanced in that the charged particles, which are emitted by the emitters of the thruster cell array, are pulled into the gap, i.e. a space between the emitters and the collectors of the thruster cell array. In other words, the charged particles, emitted into the hemisphere away from the collectors and the hemisphere towards the collectors, may be pulled e.g. into the hemisphere towards the collectors, e.g. into the space between the emitters and the collectors of the thruster cell. By pulling the charged particles, emitted by the emitters into the area between the emitters and the collectors of the thruster cell, the charged particles may be subject to a net electrostatic force: on the one hand, the charged particles may exert a repelling force on the emitters, hence pushing the emitters away. On the other hand, the charged particles may exert an attracting force on the collectors, hence attracting the collectors. The repelling force on the emitters and the attracting force on the collectors may be in a same direction and may contribute to an electrostatic force.

The inventors have devised that the charged particles emitted by the emitters may be pulled towards the space between the emitters and the collectors of the thruster cell by an intermediate electrode. The intermediate electrode is electrically connected to the collectors of the thruster cell by a current source configured to generate a substantially constant electrical current. The current source may provide for a substantially constant discharge of charged particles into the intermediate electrode. Hence, an amount of discharge of the charged particles by the intermediate electrode may be well controlled. A voltage (an electrical potential) of the intermediate electrode may adapt itself according to the substantially constant current by the current source. The substantially constant current generated by the current source and drawn at the intermediate electrode, may effectively pull the charged particles emitted by the emitter into the space between the emitters and the collectors of the thruster cell, to draw the charged particles into the space where they may contribute to the electrostatic force on the emitters as well as on the collectors of the thruster cell array. On the other hand, the substantially constant current generated by the current source may limit a discharging of the charged particles at the intermediate electrode, and may provide that the electrical voltage on the intermediate electrode is self-adjusting: a voltage at the intermediate electrode may adjust itself to provide the discharging of charged particles according to the substantially constant electrical current.

The current source may for example be understood as a high impedance current control circuit, such as a current regulator circuit, a current limiting circuit, or a high series impedance. The current regulator may be configured to provide a substantially constant electrical current or an electrical current which is controlled to be proportional to the collector current. The current regulator may for example be configured to measure the collector current and control the substantially constant current to be a proportional to the measured collector current, thus enabling to adjust the substantially constant current as a thruster power of the electrostatic thruster is adjusted. As an example of the high series impedance, the current source may comprise a high impedance series resistor connected between the intermediate electrode and the collectors of the thruster cell array or a voltage source in series with a high impedance to provide a substantially constant electrical current. The current source may immediately be connected to the collectors of the thruster cell array or mediately be connected to the collectors of the thruster cell array, e.g. via the emitters of the thruster cell array and the power source connected between the emitters and the collectors of the thruster cell array.

An electrostatic thruster may be comprised in an aircraft or a watercraft. The gas and/or liquid in which the electrostatic thruster operates may hence be subject to change, such as a change in pressure or a change in water or moisture content. Hence, dielectric properties of the gas and/or liquid in which the electrostatic thruster operates may strongly vary. By powering the intermediate electrode by a current source configured to generate a substantially constant electrical current, the electrical voltage on the intermediate electrode may adapt according to the dielectric conditions of the gas and/or liquid, hence providing a desired pull on the emitted charged particles to bring the charged particles towards the space between the emitters and the collectors of the array in order to contribute to the electrostatic force, while avoiding a breakdown or undesirably large discharge by the intermediate electrode.

Accordingly, a high electrostatic thruster force may be generated at a variety of environmental conditions, in particular a variety of dielectric conditions of the (environmental) gas and/or liquid in which the thruster is to operate. As described above, the ion wind resulting from the movement of the charged particles towards the collector may generate some thrust. The electrostatic force as may be generated with the electrostatic thruster according to the invention may substantially increase an effective thrusting force of the electrostatic thruster.

As the intermediate electrode driven by the current source are configured to pull the emitted charged particles from the emitters into the space between the emitters and the collectors, the collectors may be positioned further away from the emitters and a potential difference between the emitters and the collectors may be kept well below a breakdown, which may enhance a reliability of the electrostatic thruster and an ability to operate under a variety of dielectric conditions of the gas and/or liquid. Moreover, due to the large distance between the emitters and collectors of a thruster cell array, a relatively large amount of charged particles may reside in the space between the emitters and the collectors of the thruster cell array, i.e. in the gap between the emitter and collectors of the thruster cell array, which large amount of charged particles may enhance the electrostatic thrust force on the collector. The power source may be configured to set the voltage between the emitter and the collector well below a breakdown voltage, e.g. below 90%, or below 80% of the breakdown voltage, causing a speed of travel of the charged particles towards the collector to be decreased, which may enable the particles to contribute to the electrostatic thrust force for a longer time before being collected by the collector. The decreased speed of the charged particles may increase a total charge of charged particles between the emitter and collector at a time, which may contribute to enhancing electrostatic thrust force. The electrostatic thrust force may pull the collector towards the charged particles between the emitter and the collector, a direction of the electrostatic thrust force may hence be the direction from the collector to the emitter. The increased distance between the emitter and collector, in combination with the intermediate electrode driven by a current source and the relatively low electric field strength between the emitter and collector, electrostatic thrust may be significantly increased. Moreover, as the intermediate electrode pulls the charged particles emitted by the emitter towards the gap between the emitter and the collector, the resulting increase in charged particles between the emitter and collector may further contribute to an increase in thrust due to ion wind.

The inventors have devised that the electrostatic thruster according to the invention may generate a thrust force which is largely caused by electrostatic thrust, the electrostatic force may be larger than the force caused by the ionic wind. For example, while prior art electrostatic devices mostly rely on the generation of ionic wind to produce a thrust force, the thruster according to the present invention may enable to generate an electrostatic thrust force which contributes approximately 70% - 90% to a total thrust, while a contribution of the ionic wind may be approximately 10% - 30%.

The intermediate electrodes are configured to distort the electrical field surrounding each emitter by pulling more charged particles on the outside of the thruster array inwards instead of repelling the charged particles. By doing so, emitters can be placed closer to each other before loss in performance occurs. Increasing the number of emitters per unit area, increases the generation of charged particles per unit area. This improves the performance of the electrostatic thruster.

The intermediate electrodes are also configured to create a stronger electric pull on the emitters of a thruster cell array, while keeping the thruster cell gap larger. The benefit of doing so is to optimize and control the generation of charged particles while the size of the thruster cell gap does not have to be on the edge of dielectric breakdown of the gas/l iquid, hence creating a more reliable electrostatic thruster. Secondly, the increased size of the thruster cell gap allows for more charged particles in this area, creating more electrostatic pull on the collectors, increasing the efficiency of the system. Alternatively, the use of intermediate electrodes allows thrusters with relatively low voltages to become more effective.

The intermediate electrodes are electrically connected to the collectors of the thruster cell array via a current source configured to generate a substantially constant current.

The current source regulates the voltage on the intermediate electrode, which is charged by the charged particles surrounding the emitter. By having a current source rather than an externally fixed voltage, the current source creates a fixed 'puli' on the emitter.

When the emitter is charged by the power source, the voltage on the intermediate electrodes may be 0V. This may create a direct dielectric breakdown, without intense arcing because of the limited, i.e. substantially constant, current through the intermediate electrode. The voltage on the intermediate electrodes may rise to a voltage potential as high as the charged particles from the emitter can charge it. The current source limits the voltage potential of the intermediate electrode. The voltage potential on the intermediate electrode therefore levels out as high as the charged particles can charge it. By increasing the (substantially constant) current of the current source, the number of produced charged particles may increase, as the intermediate electrode may pull the charged particles away from the emitter, causing a density of the charged particles surrounding the emitter to be reduced, which may promote the emission of charged particles by the emitter. As a result of the flow of charged particles to the intermediate electrode, the voltage on the intermediate electrode may fall back to the collector's potential when the current is increased too much, due to a maximum production of charged particles. This may result in constant dielectric breakdown between emitter and intermediate electrode. Therefore, the current source is able to control the production of charged particles by the emitter.

In some embodiments, the substantially constant current may be at least an order of magnitude lower than a collector current of the thruster cell array in operation. The term order of magnitude may be understood as a factor 10. The collector current of the thruster cell array may be understood as an electrical collector current due to absorption of charged particles by the collectors of the thruster cell array. A loss of efficiency of the electrostatic thruster may be kept low, as a discharging of charged particles at the intermediate electrode may be kept at least an order of magnitude lower than the discharging of the charged particles at the collectors of the thruster cell array.

In some embodiments, the substantially constant current may be lower than 3%, preferably between 1% and 3% of the collector current of the thruster cell array in operation. The substantially constant current lower than 3% of the collector current of the thruster cell array may further enhance efficiency. The substantially constant current between 1% and 3% of the collector current of the thruster cell array may provide a sufficient pull on the emitted particles to enhance the electrostatic force, while keeping efficiency of the thruster and efficiency of emitted charges particles high.

The emitters, collectors and intermediate electrode(s) of the thruster cell array may have a longitudinal shape, e.g. extend parallel to each other in a longitudinal direction substantially perpendicular to a direction from the emitters to the collectors of the thruster cell array, i.e. perpendicular to the direction of the electrostatic thruster force. The parallel arrangement and longitudinal shape may enable a high density of emitters and collectors, which may promote a high density of the electrostatic force.

In some embodiments, the power source may be configured to apply the voltage between the at least one emitter and the at least one collector of each thruster cell in the thruster cell array with a same polarity. In some of the embodiments, a first distance between the emitter and the intermediate electrode may be smaller than a second distance between the collector and the intermediate electrode.

By having the intermediate electrodes positioned closer to the emitters than to the collectors, it becomes possible to distort the electrical fields surrounding the emitters, while keeping the size of the thruster cell gap larger.

In some embodiments, seen along the direction of the thrust force, i.e. seen from the collectors in the direction of the emitters of the thruster cell array, the intermediate electrode may be offset in respect of respective straight lines between the emitters and collectors of the thruster cell array. As a result of the offset, the intermediate electrodes may on the one hand enhance a pull on charged particles emitted from the emitters in a hemisphere facing away from the collectors, which may enhance an amount of the charged particles between the emitters and the collectors where they may contribute to the generation of the thrust force, while lowering an amount of charged particles that remain at the hemisphere of the emitters facing away from the collectors of the thruster cel array. Moreover, a distance between the emitters and the intermediate electrodes may be enlarged due to the offset, which may further prevent arcing. The intermediate electrode may be offset by a half of a pitch between adjacent emitters of the thruster cell array, thus to provide a pull of the emitted charged particles emitted by both adjacent emitters simultaneously, hence promoting a compact arrangement where the emitters may be placed relatively close together. A high density of emitters, and thus collectors, may enable to increase an effective electrostatic thrust force.

In some embodiments, the electrostatic thruster may comprise at least two adjacent thruster cell arrays positioned in series, wherein a distance between the collectors of a first (upstream) thruster cell array and the emitters of a second (downstream) thruster cell array is smaller than a distance between the collectors of the first thruster cell array and the collectors of the second thruster cell array. For example, the distance between the collectors of the first thruster cell array and the emitters of the second thruster cell array may be less than 50%, more preferably less than 25% of the distance between the collectors of the first thruster cell array and the collectors of the second thruster cell array. The collectors of the first thruster cell array may accordingly be used to push the charged particles emitted by the emitters of the second thruster cell towards the gap between the emitters and collectors of the second thruster cell array, as described in more detail below. Alternatively or additionally, the emitters of the second thruster cell array may collect or repel charged particles emitted by the emitters of the first thruster cell array, hence to enhance an overall efficiency of the thruster cell arrays positioned in series.

In some embodiments, comprising at least two thruster cells in series, the power source may be configured to, for two adjacent thruster cells in series, apply the voltage between the at least one emitter and the at least one collector of a first thruster cell of the two adjacent thruster cells and the voltage between the at least one emitter and the at least one collector of a second thruster cell of the two adjacent thruster cells in series with opposite polarities.

In this way, the polarity of the collector of the first thruster cell array may be equal to the polarity of the emitter of the second thruster cell array. This prevents that charged particles generated by the emitter of the second thruster cell array are attracted by the collector of the first thruster cell array. Instead, the collector of the first thruster cell array is configured to work as a repellent for the charged particles generated by the emitter of the second thruster cell array. The second thruster cell array will benefit from the repellent property of the collector of the first thruster cell array to enhance the generation of the electrostatic thrusting force as described above. The pulling force by the intermediate electrodes on the charged particles emitted by the emitters of the second thruster cell array may hence be complemented by a repelling force by the collectors of the first thruster cell array, in particular in case the distance between the collectors of the first thruster cell array and the emitters of the second thruster cell array is less than 50%, more preferably less than 25%, more preferably less than 10% of the distance between the collectors of the first thruster cell array and the collectors of the second thruster cell array, as the relatively nearby collectors of the first thruster cell array push the charged particles emitted by the emitters of the second thruster cell array towards the gap between the emitters and collectors of the second thruster cell array, hence contributing to electrostatic thrust force generation. Charged particles emitted by the emitter of the first thruster cell array that may have passed the collector of the first thruster cell array may be attracted by the emitter of the second thruster cell array to be discharged, which may avoid that these particles diminish an electrostatic force in the second thruster cell array, due to their opposite charge compared to the charged particles emitted by the second thruster cell array. Therefore, two adjacent thruster cell arrays according to this method may result in more than twice the thrust of a single thruster cell array. The collectors of the first thruster cell array may comprise blunt edges facing the emitters of the second thruster cell array, to enable that the collectors of the first thruster cell array reflect charged particles emitted by the emitters of the second thruster cell array, and to reduce or suppress emission of charged particles by the collectors of the first thruster cell array.

Adjacent thruster cell arrays with equal polarity need to be spaced sufficiently far from each other to prevent attraction between the collectors of the first thruster cell array and the emitters of the second thruster cell array. Opposite polarities allow reducing the distance between two adjacent thruster cell arrays. This provides the possibility to decrease the overall size and weight of the electrostatic thruster or to increase the number of thruster cells in a specific volume.

In some embodiments, each collector may have a blunt leading edge directed to the emitter of the corresponding thruster cell.

The blunt leading edge prevents the generating of charged particles surrounding the collector. These charged particles would attract the emitter and thereby generated a thrust force in the opposite direction.

In some embodiments, each collector may have a blunt trailing edge.

In some embodiments, the collector may have a sharp trailing edge, wherein the sharp trailing edge is configured to generate charged particles, and wherein the sharp trailing edge of the collector is the emitter of an adjacent thruster cell array.

The generated charged particles surrounding the sharp trailing edge of the collector attract the collector of the adjacent thruster cell array to generate the required thrust force. This eliminates the need for a separate emitter for the adjacent thruster cell array, reducing the number of parts required for the electrostatic thruster.

In some embodiments, the positive or negative high voltage potential applied to the collector may be at least 30kV, and more in particular at least 40kV, in order for the collector to work as a repellent for the next thruster cell array.

In some embodiments, comprising at least two thruster cells arrays in series, a distance between the emitters of the first thruster cell array may be larger than the distance between the emitters of each thruster cell array that follows after the first thruster cell array. Having a greater distance between the emitters of the first thruster cell array reduces the strength of the electric field lines surrounding the thruster cell array. Strong electric field lines cause a relatively large part of the charged particles to be repelled away from the thruster in an opposite direction, producing a counteracting force which goes against the intended force of the electrostatic thruster and therefore reduces its efficiency. The strength of the electric field lines surrounding the thruster cell array is reduced by the collectors acting as repellent reflectors for the charged particles, reducing the part of charged particles that are repelled away from the thruster cell array. This improves the performance of the electrostatic thruster.

The above-described embodiment may also be employed in other electrostatic thrusters. For example, according to a second aspect of the invention, there is provided an electrostatic thruster 10 for producing thrust by charging gas and/or liquid particles using a high voltage potential, the electrostatic thruster comprises at least two thruster cells, wherein each thruster cell comprising: at least one emitter, at least one collector, wherein the at least one collector is spaced from the at least one emitter by a thruster cell gap, wherein the electrostatic thruster further comprises a power source electrically connected to the at least one emitter and the at least one collector of each thruster cell, wherein the power source is configured to apply a voltage between the at least one emitter and the at least one collector of each thruster cell, wherein the at least two thruster cells are positioned in parallel to form a thruster cell array, wherein the electrostatic thruster comprises at least two of the thruster cell arrays and wherein a distance between the emitters of a first thruster cell array of the thruster cell arrays is larger than the distance between the emitters of each thruster cell array of the thruster cell arrays that follows after the first thruster cell array.

The above mentioned technical effects of the first aspect of the invention and this embodiment also apply to the second aspect of the invention. Further embodiments may also be combined with the second aspect of the invention.

In some embodiments, at least one electrical reflector may be positioned in front of the at least one emitter of the first thruster cell array, wherein each electrical reflector has a conductive surface and is smooth, wherein each electrical reflector is electrically connected to the power source, and wherein the power source is configured to: apply a high voltage potential to each emitter, apply substantially the same high voltage potential to each nearby electrical reflector.

Applying substantially the same high voltage potential to each nearby electrical reflector means that the voltage does not need to be exactly the same level, however, should at least have a same polarity to effectively repel the charged particles in the direction of the collectors.

In some embodiments, each electrical reflector may have a relatively large surface area compared to the surface area of each nearby emitter.

The smooth, relatively large surface area and conductive surface prevent any corona discharge or ion generation. The electrical reflectors allow the emitters in the first thruster cell array to be placed closer together while minimizing the loss of efficiency due to the electric field lines surrounding the thruster cell array. The electrical reflectors prevent that charged particles are repelled away from the thruster cell array in an opposite direction. Being able to place the emitters closer together provides the ability to create a relatively compact design for the electrostatic thruster.

The above-described embodiment may also be employed in other electrostatic thrusters. For example, according to a third aspect of the invention, there is provided an electrostatic thruster 10 for producing thrust by charging gas and/or liquid particles using a high voltage potential, the electrostatic thruster comprises at least one thruster cell, wherein the thruster cell comprises: at least one emitter, at least one collector, wherein the at least one collector is spaced from the at least one emitter by a thruster cell gap, wherein the electrostatic thruster further comprises a power source electrically connected to the at least one emitter and the at least one collector of the thruster cell, wherein the power source is configured to apply a voltage between the at least one emitter and the at least one collector of the thruster cell, wherein at least one electrical reflector is positioned in front of the at least one emitter of the thruster cell, wherein each electrical reflector has a conductive surface, is smooth and has a relatively large surface area compared to the surface area of each nearby emitter, wherein each electrical reflector is electrically connected to the power source, and wherein the power source is configured to: apply a high voltage potential to each emitter, apply the same high voltage potential to each nearby electrical reflector.

In some embodiments, each electrical reflector may have a relatively small surface area similar to the surface area of each nearby emitter, wherein the relatively small surface area is covered by a thin insulation.

The thin insulation is just sufficient to prevent emitting charged particles while at the same time providing a strong enough electrical field to repel nearby charged particles.

In some embodiments, the emitter may comprise a plurality of emitter electrodes positioned closely together, wherein the plurality of emitter electrodes are configured to act as a single emitter.

Positioning a plurality of emitter electrodes closely together will increase the particle charging property of the single emitter. A total charged particle emission may be enhanced. For example, the plurality of emitter electrodes may extend parallel to each other at a distance between the emitter electrodes is less than 1 millimetre, which may promote a high charged particle emission which may in turn promote the electrostatic thrust force. It can be beneficial to have a plurality of emitter electrodes configured to act as a single emitter when e.g., the first thruster cell array comprises less emitters than the following thruster cell arrays, to be able to produce a similar amount of charged particles in the first and following thruster cell arrays. The plurality of emitter electrodes may extend parallel to each other at a distance between the emitter electrodes of less than 1 millimetre, enhancing an overall emission while enabling the parallel emitters to act as a single emitter providing a high emission of charged particles.

The above-described embodiment may also be employed in other electrostatic thrusters. For example, according to a fourth aspect of the invention, there is provided an electrostatic thruster 10 for producing thrust by charging gas and/or liquid particles using a high voltage potential, the electrostatic thruster comprises at least one thruster cell, wherein each thruster cell comprises: at least one emitter, at least one collector, wherein the at least one collector is spaced from the at least one emitter by a thruster cell gap, wherein the electrostatic thruster further comprises a power source electrically connected to the at least one emitter and the at least one collector of the thruster cell, wherein the power source is configured to apply a voltage between the at least one emitter and the at least one collector of the thruster cell, wherein the emitter comprises a plurality of emitter electrodes positioned closely together, wherein the plurality of emitter electrodes are configured to act as a single emitter.

In some embodiments, the power source is configured to apply a pulsed voltage to each emitter to alternate the voltage between two or more adjacent emitters.

Alternating the voltage between two adjacent emitters may be understood as to applying the voltage to a first one of the adjacent emitters for a first part of a pulse repetition time, while applying a zero voltage, a lower voltage or no voltage to a second one of the adjacent emitters in the first part of the pulse repetition time. The power source is configured to apply, in a second, remaining part of the pulse repetition time, the voltage to the second one of the adjacent emitters and to apply the zero voltage, lower voltage, or no voltage to the first one of the adjacent emitters. This could be extended with different activations schemes to apply the voltage to the emitter of two or more adjacent emitters during different periods of time.

By providing low duty cycle pulses a similar number of particles can be charged as a higher current will flow through the dielectric fluid (air). On average, the power consumption is similar.

Another benefit of pulsing the emitter is that the repellent force is reduced as it is no longer a constantly present field. When multiple emitters are positioned close to each other, alternating the pulses between the emitters will ensure that the electric fields of nearby emitters hardly interfere, also resulting in more charged particles moving in the intended direction towards the collectors. This creates a more efficient electrostatic thruster which uses less materials and is less heavy.

The above-described embodiment may also be employed in other electrostatic thrusters. For example, according to a fifth aspect of the invention, there is provided an electrostatic thruster 10 for producing thrust by charging gas and/or liquid particles using a high voltage potential, the electrostatic thruster comprises at least two thruster cells, wherein each thruster cell comprising: at least one emitter, at least one collector, wherein the at least one collector is spaced from the at least one emitter by a thruster cell gap, wherein the electrostatic thruster further comprises a power source electrically connected to the at least one emitter and the at least one collector of each thruster cell, wherein the power source is configured to apply a voltage between the at least one emitter and the at least one collector of each thruster cell, wherein the at least two thruster cells are positioned in parallel to form a thruster cell array, wherein the power source is configured to apply a pulsed voltage to each emitter.

In some embodiments, each emitter and each collector may be elongate, and wherein the emitter comprises a longitudinal axis.

In some embodiments, the size of the thruster cell gap may vary in the direction of the longitudinal axis of the emitter. For example, the emitter may have a serrated edge facing towards the collector, the serrated edge extending along the longitudinal axis of the emitter. As another example, the emitter may be zigzag shaped.

The effective length of the emitter may be increased, e.g. by a zigzag shape of the emitter or a serrated edge of the emitter, without increasing the length of the collector, by alternating the size of the thruster cell gap along the direction of the longitudinal axis of the emitter. Because of this alternating distance and increased emitter length, charged particles are produced in a larger area and on average at a longer distance from the collector. Because of this more charged particles are located for a longer time at the intended side of the collector, resulting in increased thrust. At the same time this configuration results in lower input power for the same amount of thrust, hence the efficiency may be improved significantly. Furthermore, the zigzag shapes or serrated edge of the emitters of the thruster cell array, which zigzag shapes or serrated edges face the collectors of the thruster cell array may increase an effective distance between the emitter and collector in particular at recesses in the zigzag shape respectively in the serrations of the serrated edges. The zigzag shape or serrations may result in a maximum size of the gap which is 50% to 100% larger than a minimum size of the gap.

The above-described embodiment may also be employed in other electrostatic thrusters. For example, according to a sixth aspect of the invention, there is provided an electrostatic thruster 10 for producing thrust by charging gas and/or liquid particles using a high voltage potential, the electrostatic thruster comprises at least one thruster cell, wherein the thruster cell comprises: at least one emitter, at least one collector, wherein the at least one collector is spaced from the at least one emitter by a thruster cell gap, wherein the electrostatic thruster further comprises a power source electrically connected to the at least one emitter and the at least one collector of the thruster cell, wherein the power source is configured to apply a voltage between the at least one emitter and the at least one collector of the thruster cell, wherein each emitter and each collector may be elongate, and wherein the emitter comprises a longitudinal axis, and wherein the size of the thruster cell gap may vary in the direction of the longitudinal axis of the emitter.

In some embodiments, a barrier of a non-conducting material may be positioned on an opposite side of the emitter, and wherein the barrier follows the shape of the emitter. A downside of having the emitter in a varying shape charged particles that are generated at the outside of the thruster cell are repelled harder in the wrong direction because there is more emitter nearby. To reduce this downside, a barrier made from nonconducting material should be positioned on the opposite side of the emitter, closely following its shape. The barrier repels the charged particles which are moving in the opposite direction and re-direct the charged particles in the intended direction of the collectors.

In some embodiments, a first side of the collector may comprise a non-conductive material which is directed to a second side of the collector of an adjacent thruster cell without the non-conductive material, wherein the second side is configured to attract charged particles, and wherein the first side is not configured to attract charged particles.

When charged particles move in between two equally conductive collectors, charged particles in the centre are equally attracted to both collectors and continue a straight path. Because of this they may pass beyond the collectors before losing their charge, creating a backwards pull on the collector and therefore reducing the efficiency of the thruster. In case one side of each collector comprises a non-conductive material, charged particles are pulled towards the conductive side of the adjacent collector. This reduces the amount of charged particles which pass beyond the collectors.

The above-described embodiment may also be employed in other electrostatic thrusters. For example, according to a seventh aspect of the invention, there is provided an electrostatic thruster 10 for producing thrust by charging gas and/or liquid particles using a high voltage potential, the electrostatic thruster comprises at least two thruster cells, wherein each thruster cell comprising: at least one emitter, at least one collector, wherein the at least one collector is spaced from the at least one emitter by a thruster cell gap, wherein the electrostatic thruster further comprises a power source electrically connected to the at least one emitter and the at least one collector of each thruster cell, wherein the power source is configured to apply a voltage between the at least one emitter and the at least one collector of each thruster cell, wherein the at least two thruster cells are positioned in parallel to form an thruster cell array, wherein a first side of each collector comprises a non-conductive material and a second side of each collector is without the non-conductive material, wherein the first side of the collector of a thruster cell is directed to the second side of the collector of an adjacent thruster cell, wherein the second side is configured attract charged particles, and wherein the first side is not configured to attract charged particles.

In some embodiments, the thruster cell may comprise a first collector and a second collector having the same voltage potential as the first collector, wherein the first collector and the second collector are spaced by a collector gap, and wherein the first collector is positioned between the at least one emitter and the second collector.

In some embodiments, the second collector is mechanically disconnected from the first collector.

Because the second collector share the same potential as the first collector any opposite electrical field caused by charged particles passing by the first collector while remaining charged is cancelled by the second collector. Therefore, charged particles passing by the first collector cannot counter act the intended force of the thruster. When a negative or positive voltage is applied to the first and second collector, the collectors would also repel each other, further increasing the net force and efficiency. This is especially beneficial in applications like accelerating lift off or persistent hovering above a fixed collector system.

The above-described embodiment may also be employed in other electrostatic thrusters. For example, according to an eighth aspect of the invention, there is provided an electrostatic thruster 10 for producing thrust by charging gas and/or liquid particles using a high voltage potential, the electrostatic thruster comprises at least one thruster cell, wherein the thruster cell comprises: at least one emitter, at least one collector, wherein the at least one collector is spaced from the at least one emitter by a thruster cell gap, wherein the electrostatic thruster further comprises a power source electrically connected to the at least one emitter and the at least one collector of the thruster cell, wherein the power source is configured to apply a voltage between the at least one emitter and the at least one collector of the thruster cell, wherein the thruster cell comprises a first collector and a second collector wherein the power source is configured to apply a same voltage potential at the first collector and the second collector of the thruster cell, wherein the first collector and the second collector of the thruster cell are spaced by a collector gap, and wherein, in the thruster cell, the first collector is positioned between the at least one emitter and the second collector.

In some embodiments, the power source may be configured to apply a voltage difference between each emitter of the first thruster cell array and each collector of the second thruster cell array, and wherein the electrostatic thruster comprises at least one electrical reflector configured to bend the electrical field of adjacent thruster cell arrays, wherein the electrical reflector is positioned between the thruster cell arrays, and wherein the distance between the second thruster cell array and the electrical reflector is smaller than the distance between the first thruster cell array and the electrical reflector.

In some embodiments, the power source may be configured to apply the same voltage potential to the emitter and to the corresponding electrical reflector.

In some embodiments, each electrical reflector may be insulated to reduce charged particle production.

In some embodiments, the surface area of an electrical reflector may be larger than the surface area of an emitter.

The above-described embodiment may also be employed in other electrostatic thrusters. For example, according to a ninth aspect of the invention, there is provided an electrostatic thruster 10 for producing thrust by charging gas and/or liquid particles using a high voltage potential, the electrostatic thruster comprises at least two thruster cells, wherein each thruster cell comprising: at least one emitter, at least one collector, wherein the at least one collector is spaced from the at least one emitter by a thruster cell gap, wherein the electrostatic thruster further comprises a power source electrically connected to the at least one emitter and the at least one collector of each thruster cell, wherein the power source is configured to apply a voltage between the at least one emitter and the at least one collector of each thruster cell, wherein the at least two thruster cells are positioned in parallel to form an thruster cell array, wherein the electrostatic thruster comprises at least two of the thruster cell arrays, wherein the power source is configured to apply a voltage difference between each emitter of a first one of the thruster cell arrays and each collector of a second one of the thruster cell arrays, and wherein the electrostatic thruster comprises at least one electrical reflector configured to bend the electrical field of adjacent thruster cell arrays, wherein the electrical reflector is positioned between the thruster cell arrays, and wherein the distance between the second thruster cell array and the electrical reflector is smaller than the distance between the first thruster cell array and the electrical reflector.

The invention further relates to an aircraft, in particular an airplane or Unmanned Arial Vehicle, comprising the electrostatic thruster of any of the preceding claims.

The invention further relates to a spacecraft, in particular a small satellite, comprising the electrostatic thruster of any of the preceding claims.

The above mentioned advantages of the presented features also apply to an airplane, an Unmanned Arial Vehicle or a small satellite. An aircraft or spacecraft with a smaller, lighter and more efficient electrostatic thruster would significantly improve the operational freedom of an aircraft or spacecraft. It would increase the operational range, would increase the maximum allowable payload and would make the aircraft or spacecraft better sustainable for the future.

The invention further relates to an electrostatic wing thruster (100) for providing a thrust force to a wing which is configured for a movement through a fluid, wherein the electrostatic wing thruster comprising: the wing, wherein the wing comprising: o a front part, wherein the front part comprises at least one front emitter, o an upper part, wherein the upper part comprises at least one collector positioned at an upper surface of the wing, o a lower part, wherein the lower part comprises at least one lower reflector positioned at a lower surface of the wing, a power source electrically connected to the at least one emitter, the at least one reflector and the at least one collector, wherein the power source is configured to: o apply a high voltage potential to each front emitter and to each reflector, o apply an opposite high voltage potential or a neutral voltage potential to each collector, wherein each emitter is configured to generate charged particles, and wherein each reflector is configured to repel the charged particles and each collector is configured to attract the charged particles.

Fluid (air) flow causes charged particles to move along the bottom of the wing, passing the at least one reflector with identical polarity will repel the wing upwards and the at least one reflector will repel the charged particles downwards, creating a high pressure below the wing. Charged particles moving along the top of the wing (by fluid flow and electrostatic force) will be attracted to the at least one collector there, while the at least one collector and the wing are attracted upwards towards the charged particles, creating a low pressure above the wing. This provides the ability to control upward or downward motion of the wing.

In some embodiments, each front emitter may be spaced from a front surface of the wing by a front gap.

In some embodiments, the lower part of the wing may comprise at least one lower emitter which is spaced from the lower surface of the wing by a lower gap, wherein each lower emitter is electrically connected to the power source, and wherein the power source is configured to apply the high voltage potential to the each lower emitter.

The invention further relates to an aircraft, in particular an airplane or Unmanned Arial Vehicle, comprising the electrostatic wing thruster of any of claims 26-28.

The invention further relates to a watercraft, in particular a submarine or hydrofoil, comprising the electrostatic wing thruster of any of claims 26-28. The above mentioned advantages of the presented features also apply to an aircraft or a watercraft comprising the electrostatic wing thruster 100. The electrostatic wing thruster 100 would significantly improve the controllability of the device.

SHORT DESCRIPTION OF THE FIGURES

Figures 1a - 1b show an isometric view of an embodiment of the electrostatic thruster with intermediate electrodes.

Figure 2 shows a schematic view of a thruster cell array with intermediate electrodes.

Figures 3a - 3b show a schematic view of two thruster cells in series.

Figure 4 shows an isometric view of a thruster cell.

Figures 5a - 5b show an isometric view of the electrostatic thruster.

Figure 6a shows a schematic view of a thruster cell array.

Figure 6b shows a schematic view of two thruster cell arrays in series.

Figures 7a - 7b show an isometric view of the electrostatic thruster with electrical reflectors.

Figure 8 shows a schematic view of two thruster cell arrays with electrical reflectors.

Figure 9 shows an isometric view of a thruster cell array with a plurality of emitter electrodes.

Figure 10 shows a schematic view of a thruster cell array with pulsating voltage source.

Figure 11 shows a side view of a thruster cell.

Figures 12a - 12b show a schematic view of the collectors of a thruster cell array.

Figure 13 shows an isometric view of an electrostatic thruster.

Figure 14 shows an isometric view of a thruster cell with additional collector.

Figure 15 shows a schematic view of two thruster cells with electrical reflectors.

Figures 16a - 16b show a cross-sectional view of an electrostatic wing thruster.

DETAILED DESCRIPTION OF THE FIGURES

Turning to figures 1a - 1b and 4, an electrostatic thruster 10 for producing thrust by charging gas and/or liquid particles using a high voltage potential is shown. The electrostatic thruster 10 uses the Coulomb force and accelerates gas and/or liquid particles in the direction of the electric field. The electrostatic thruster 10 comprises at least two thruster cells 20. Each thruster cell 20 comprises at least one emitter 22 and at least one collector 24. At least two thruster cells 20 are positioned in parallel to form a thruster cell array 40. The parallel thruster cells may be arranged along a direction perpendicular to the direction of the electric field between the emitters and the collectors. The parallel thruster cells may also be arranged in different, non-parallel, configurations like triangle, square or hexagon configurations.

The electrostatic thruster 10 further comprises a power source 30 which is electrically connected to the at least one emitter 22 and the at least one collector 24. The power source 30 is configured to apply a direct current (DC) voltage between the at least one emitter 22 and the at least one collector 24 of each thruster cell 20. By having a power source 30 applying a voltage between an emitter 22 and a collector 24, charged particles 5 surrounding the emitter 22 are generated. The charged particles 5 and the collector 24 attract each other creating a force on the electrostatic thruster 10 in the direction of the emitter 22. The emitters of a thruster cell may be vertically above the collectors of the thruster cell, providing that the force generated by the electrostatic thruster acts in vertical direction, i.e., thrusts the thruster upwards.

The emitters 22 have a relatively small surface area compared to the surface area of the collectors 24. The smaller surface area provides ionization of a fluid, such as a gas and/or a liquid surrounding the emitter 22. This is called corona discharge. The collectors 24 have a relatively large surface area to prevent any ionization which would otherwise result in oppositely charged particles 5. These oppositely charged particles 5 would be attracted by the emitter 22 of the corresponding thruster cell 20, resulting in a thrust force in the opposite direction. The power source is configured to generate the voltage to be sufficiently high to generate the ionization in the ambient fluid around the emitter, such as at least 5 kV, preferably 20 - 40 kV in air. In other gasses or liquids the voltages could be very different, which is directly related to the gas/liquid's dielectric strength. The emitters and collectors may be formed by electrically conductive structures, such as metal structures which may at least partly be in a direct contact with the ambient fluid in order to charge particles of the ambient fluid, such as at the emitter, and to discharge the charged particles in the ambient fluid, such as at the collector.

The force comprises two main components. The first component is caused by the attraction of the collectors 24 in the direction of the charged particles 5 surrounding the emitter 22. The other component is caused by charged particles 5 which move in the direction of the collector 24 and thereby push gas and/or liquid particles in the surrounding medium to create a thrust force in the direction of the emitter.

Turning to figures 1b, 2 - 3b, the electrostatic thruster 10 may further comprise at least two adjacent thruster cell arrays 40a, 40b positioned in series. Adjacent thruster cell arrays 40 are thruster cell arrays 40 which are positioned next to each other without any thruster cell arrays being positioned between them. The series arrangement of the thruster cell arrays may be understood as the thruster cell arrays (each comprising at least two parallel arranged thruster cells) being arranged along the direction of the electric field, i.e., the direction of the force generated by the thruster. Figure 2 illustrates a single thruster cell array of the series. As seen in figure 3a, distance 41a between the collectors 24 of a first thruster cell array 40a and the emitters 22 of a second thruster cell array 40b is smaller than a distance 41b between the collectors 24 of the first thruster cell array 40a and the collectors 24 of the second thruster cell array 40b. Multiple thruster cell arrays 40 can be positioned in series. This would result in multiple lines of emitters 22 and collectors 24 following after each other as illustrated by the arrays 40a, 40b and 40c in figure 1b.

The power source 30 is configured to apply the voltage between the at least one emitter 22 and the at least one collector 24 of each thruster cell 20 in the thruster cell array 40 with a same polarity. This ensures that the adjacent thruster cells 20 in the thruster cell array 40 cannot interfere with each other, which may result in an undesired force in an opposite direction and/or dielectric breakdown when the distance between the thruster cell arrays is insufficient.

The at least one collector 24 is spaced from the at least one emitter 22 by a thruster cell gap 28. The thruster cell gap 28 is an important factor for the efficiency of the electrostatic thruster 10. Increasing the gap ensures that the charged particles 5 remain in the thruster cell gap 28 for a larger period of time, generating more thrust as the total amount of emitted charged particles between the emitter and the collector may increase. On the other side, a larger thruster cell gap 28 would also increase the device, which would require more material and would result in a heavier electrostatic thruster 10. The thruster cell array 40 further comprises an intermediate electrode 42. The intermediate electrodes are configured to distort the electrical field surrounding each emitter by pulling more charged particles on the outside of the thruster array inwards, i.e. into the space between the emitter and the collector, instead of repelling the charged particles. Moreover, by doing so, emitters can be placed closer to each other before loss in performance occurs.

The intermediate electrode 42 is positioned in an intermediate area 44 between the emitters 22 and the collectors 24 of two adjacent ones of the thruster cells 20 in the thruster cell array 40. A first distance 45 between the emitter 22 and the intermediate electrode 42 is smaller than a second distance 46 between the collector 24 and the intermediate electrode 42. For example, the first distance 45 may be 50% of the second distance 46 or less. The intermediate electrodes 42 may be arranged, seen from the direction of the thrust force, in respective centres between adjacent emitters of the thruster cell array, which may pull the charged particles emitted from both adjacent emitters, while avoid that the intermediate electrode is arranged in a main path of the charged particles from the respective emitter to the respective collector, in which main path the intermediate electrode would attract many charged particles (which would in turn raise the voltage of the current source driven intermediate electrode more closely towards the emitter voltage resulting in a reduced pull on the charged particles). The intermediate electrodes 42 are electrically connected to the collectors 22 of the same thruster cell array 40 via a current source 32. The current source 32 is configured to apply a constant current to the intermediate electrodes 42, providing that a defined amount of the charged particles, as generated at the emitter, are collected by the intermediate electrode, hence keeping a collection of charged particles by the intermediate electrode to a defined level. The intermediate electrodes may comprise electrically conductive structures, such as metal structures and may extend along the emitters and collectors of the thruster cell array. The intermediate electrodes 42 are offset in respect of respective straight lines between the emitters 22 and collectors 42 of the thruster cell array by a half of a pitch between adjacent emitters 22 of the thruster cell array to provide a pull of the emitted charged particles emitted by both adjacent emitters 22 simultaneously.

The current source 32 is configured to apply a current level in the range of 1 pA - 10 pA to each intermediate electrode 42. This is approximately 1-3% of the total current supplied to the electrostatic thruster. The current level depends on the dielectric strength of the gas or liquid surrounding the electrostatic thruster and the position of the intermediate electrodes with respect to the emitters and collectors of the electrostatic thruster. Ideally, the current level supplied to the intermediate electrodes should be a low percentage of the total current. A high percentage would indicate that too many charged particles are discharged before they reach the collector of the thruster cell.

The intermediate electrodes 42 are also configured to create a stronger electric pull on the emitters 22 of a thruster cell array 40, while keeping the thruster cell gap larger 28. The benefit of doing so is to optimize and control the generation of charged particles 5 while the size of the thruster cell gap 28 does not have to be on the edge of dielectric breakdown of the gas/liquid, hence creating a more reliable electrostatic thruster 10. Secondly, the increased size of the thruster cell gap 28 allows for more charged particles 5 in this area, creating more electrostatic pull on the collectors 24, increasing the efficiency of the system. Alternatively, the use of intermediate electrodes 42 allows thrusters with relatively low voltages to become more effective. The charged particles emitted by the emitters may be pulled towards the space between the emitters and the collectors of the thruster cell by an intermediate electrode. The intermediate electrode is electrically connected to the collectors of the thruster cell by a current source configured to generate a substantially constant electrical current. The current source may provide for a substantially constant discharge of charged particles into the intermediate electrode. Hence, an amount of discharge of the charged particles by the intermediate electrode may be well controlled. A voltage (an electrical potential) of the intermediate electrode may adapt itself according to the substantially constant current by the current source. The substantially constant current generated by the current source and drawn at the intermediate electrode, may effectively pull the charged particles emitted by the emitter into the space between the emitters and the collectors of the thruster cell, to draw the charged particles into the space where they may contribute to the electrostatic force on the emitters as well as on the collectors of the thruster cell array. On the other hand, the substantially constant current generated by the current source may limit a discharging of the charged particles at the intermediate electrode, and may provide that the electrical voltage on the intermediate electrode is self-adjusting: a voltage at the intermediate electrode may adjust itself to provide the discharging of charged particles according to the substantially constant electrical current.

In figures 3a - 3b, the power source 30 is configured to, for two adjacent thruster cells in series, apply the voltage between the at least one emitter 22 and the at least one collector 22 of a first thruster cell 20a of the two adjacent thruster cells 20 and the voltage between the at least one emitter 22 and the at least one collector 24 of a second thruster cell 20b of the two adjacent thruster cells 20 in series with opposite polarities.

In this way, the polarity of the collector 24 of the first thruster cell array 40a is equal to the emitter 22 of the second thruster cell array 40b. This prevents that charged particles 5 generated by the emitter 22 of the second thruster cell array 40b are attracted by the collector 24 of the first thruster cell array 40a. Instead, the collector 24 of the first thruster cell array 40a is configured to work as a repellent for the charged particles 5 generated by the emitter 22 of the second thruster cell array 40b. The second thruster cell array 40b will benefit from the repellent property of the collector 24 of the first thruster cell array 40a. Therefore, two adjacent thruster cell arrays 40a, 40b according to this method result in more than twice the thrust of a single thruster cell array 40a. The positive or negative high voltage potential applied to the collector 24 is at least 30kV, and more in particular at least 40kV, in order for the collector 24 to work as a repellent for the next thruster cell array 40.

Adjacent thruster cell arrays 40 with equal polarity need to be spaced sufficiently far from each other to prevent attraction between the collectors 24 of the first thruster cell array 40a and the emitters 22 of the second thruster cell array 40b. Opposite polarities allows reducing the distance between two adjacent thruster cell arrays 40. This provides the possibility to decrease the overall size and weight of the electrostatic thruster 10 or to increase the number of thruster cell arrays 40a, 40b, 40c in a specific volume.

Each collector 24 has a blunt leading edge 25 directed to the emitter of the corresponding thruster cell 20. The blunt leading edge 25 has a relatively large surface area compared to the surface area of an emitter 22. The blunt leading edge 25 also does not have any sharp corners. These features combined prevent the generating of charged particles 5 surrounding the collector 24. These charged particles 5 would attract the emitter and thereby generated a thrust force in the opposite direction.

Furthermore, each collector 24 can have a blunt trailing edge 26 or a sharp trailing edge 27. The blunt trailing edge 27 provides the same advantage as the blunt leading edge 25. The sharp trailing edge 27 is, on the other side, configured to generate charged particles 5. The sharp trailing edge 27 comprises a relatively small surface area compared to the blunt leading edge 25, which allows corona discharge when a sufficiently high voltage is applied by the power source 30. The sharp trailing edge 27 of the collector 24 is the emitter of an adjacent thruster cell array 40.

The generated charged particles 5 surrounding the sharp trailing edge 27 of the collector 24 attract the collector 24 of the adjacent thruster cell array 40 to generate the required thrust force. This eliminates the need for a separate emitter 22 for the adjacent thruster cell array 40, reducing the number of parts required for the electrostatic thruster 10.

Turning to figures 5a - 5b, a part of an electrostatic thruster 10 is shown with a distance between the emitters 22 of the first thruster cell array 40a larger than the distance between the emitters 22 of each thruster cell array 40 that follows after the first thruster cell array 40a. The electrostatic thruster according to figures 5a and 5b may further comprise at least one intermediate electrode and current source, which have been omitted in the drawing for the sake of clarity. Turning to figures 6a - 6b, the effect of a larger distance between emitters 22 is shown. Having a greater distance between the emitters 22 of the first thruster cell array 40a reduces the strength of the electric field lines surrounding the thruster cell array 40. Strong electric field lines cause a relatively large part of the charged particles 5 to be repelled away from the thruster in an opposite direction, producing a counteracting force which goes against the intended force of the electrostatic thruster 10 and therefore reduces its efficiency, see the electric field lines of 6a. The strength of the electric field lines surrounding the thruster cell array 40 is reduced by the collectors 24 acting as repellent reflectors for the charged particles 5, reducing the part of charged particles 5 that are repelled away from the thruster cell array 40, see 6b. The electrostatic thruster according to figures 6a and 6b may further comprise at least one intermediate electrode and current source, which have been omitted in the drawing for the sake of clarity.

Turning to figures 7a - 8, an electrostatic thruster 10 with electrical reflectors 21 is shown. The at least one electrical reflector 21 is positioned in front of the at least one emitter 22 of the first thruster cell array 40a. Each electrical reflector 21 has a conductive surface, is smooth and has a relatively large surface area compared to the surface area of each nearby emitter 22. Each electrical reflector 21 is electrically connected to the power source 30 which is configured to: apply a high voltage potential to each emitter 22, apply the same high voltage potential to each nearby electrical reflector 21.

The smooth, relatively large surface area and conductive surface prevent any corona discharge or ion generation. The electrical reflectors 21 allow the emitters in the first thruster cell array 40 to be placed closer together while minimizing the loss of efficiency due to the electric field lines surrounding the thruster cell array 40. The electrical reflectors 21 prevent that charged particles 5 are repelled away from the thruster cell array 40 in an opposite direction. The electrostatic thruster according to figure 7a - 8 may further comprise at least one intermediate electrode and current source, which have been omitted in the drawing for the sake of clarity. Turning to figure 9, an electrostatic thruster 10 with an emitter 22 with a plurality of emitter electrodes 23 is shown. Each emitter 22 comprises the plurality of emitter electrodes 23 positioned closely together. The plurality of emitter electrodes 23 are configured to act as a single emitter 22. The plurality of emitter electrodes may extend parallel to each other at a distance between the emitter electrodes of less than 1 millimetre which may promote that the parallel emitters in fact behave as a single emitter having a high emission. The electrostatic thruster according to figure 9 may further comprise at least one intermediate electrode and current source, which have been omitted in the drawing for the sake of clarity.

Turning to figure 10, an electrostatic thruster 10 of which the power source 30 is configured to apply a pulsed voltage to each emitter 22 is shown. By providing low duty cycle pulses a similar number of particles can be charged as a higher current will flow through the dielectric fluid (air). On average, the power consumption is similar. Another benefit of pulsing the emitter 22 is that the repellent force is reduced as it is no longer a constantly present field. When multiple emitters 22 are positioned close to each other, alternating the pulses between the emitters will ensure that the electric fields of nearby emitters hardly interfere, also resulting in more charged particles 5 moving in the intended direction towards the collectors 24. The electrostatic thruster as depicted in figure 10 may further comprise at least one intermediate electrode and current source, which have been omitted in the drawing for the sake of clarity.

Turning to figure 11 , an electrostatic thruster 10 in which each emitter 22 and each collector 24 are elongate is shown. The emitter 22 comprises a longitudinal axis 12. The size of the thruster cell gap 28 varies in the direction of the longitudinal axis 12 of the emitter 22. In the example as depicted, the emitter comprises a zigzag shape. The length of the emitter 22 may be increased without increasing the length of the collector 24, by alternating the size of the thruster cell gap 28 in the direction of the longitudinal axis 12 of the emitter 22. Because of this alternating distance and increased emitter length, charged particles 5 are produced in a larger area and on average at a longer distance from the collector 24. Because of this more charged particles 5 are located for a longer time at the intended side of the collector 24, resulting in increased thrust. The zigzag shape of the emitter may increase an effective distance between the emitter and the collector, in particular at the recesses of the zigzag shape, where the emitter is furthest away from the collector, i.e. where the gap exhibits a longest length. The increased effective distance between the emitter and collector may contribute to an increase in total charged particles, hence overall electrical charge, between emitter and the collector which charged particles contribute to the electrostatic thrust force. Thereto, the zigzag shape or serrations may for example result in a maximum size of the gap 28 which is 50% to 100% larger than a minimum size of the gap 28. The electrostatic thruster as depicted in figure 11 may further comprise at least one intermediate electrode and current source, which have been omitted in the drawing for the sake of clarity.

At the same time this configuration results in lower input power for the same amount of thrust, hence the efficiency is improved significantly. A barrier 29 of a non-conducting material is positioned on an opposite side 14 of the emitter 22, and wherein the barrier 29 follows the shape of the emitter 29.

Turning to figures 12a - 12b, two adjacent collectors 24 are shown. A first side 52 of the collector 24 comprises a non-conductive material 50 which is directed to a second side 53 of the collector 24 of an adjacent thruster cell 20 without the non-conductive material 50. The second side 53 is configured to attract charged particles 5, the first side 52 is not configured to attract charged particles 5.

When charged particles 5 move in between two equally conductive collectors 24, charged particles 5 in the centre are equally attracted to both collectors 24 and continue a straight path, this shown in figure 12a. Because of this they may pass beyond the collectors 24 before losing their charge, creating a backwards pull on the collector 24 and therefore reducing the efficiency of the electrostatic thruster 10. In case one of side of each collector 24 comprises a non-conductive material 50, charged particles 5 are pulled towards the conductive side of the adjacent collector 24, as can be seen in figure 12b. This reduces the amount of charged particles 5 which pass beyond the collectors 24.

Turning to figure 13, an electrostatic thruster 10 with electrical reflectors 21 , intermediate electrodes 42 and collectors 24 with a non-conductive material 50 are shown. Figure 13 shows an embodiment wherein the technical effects of different features are combined in a single embodiment. This is a basic example of an embodiment with multiple features to improve the efficiency of the electrostatic thruster 10. Various other embodiments are possible wherein different features can be combined to form a single electrostatic thruster 10. Turning to figure 14, a thruster cell 20 with a first collector 24a and a second collector 24b is shown. The second collector 24b has the same voltage potential as the first collector 24a. The first collector 24a and the second collector 24b are spaced by a collector gap 16, The first collector 24a is positioned between the at least one emitter 22 and the second collector 24b. The second collector 24b is mechanically disconnected from the first collector 24a.

Because the second collector 24b share the same potential as the first collector 24a any opposite electrical field caused by charged particles 5 passing by the first collector 24a while remaining charged is cancelled by the second collector 24b. Therefore, charged particles 5 passing by the first collector 24a cannot counter act the intended force of the electrostatic thruster 10. When a negative or positive voltage is applied to the first and second collector 24a, 24b, the collectors would also repel each other, further increasing the net force and efficiency. The electrostatic thruster cells as depicted in figure 14 may further each comprise at least one intermediate electrode and current source, which have been omitted in the drawing for the sake of clarity.

Turning to figure 15, two thruster cells 40a, 40b in series are shown. The power source 30 is configured to apply a voltage difference between each emitter 22 of the first thruster cell array 40a and each collector 24 of the second thruster cell array 40b. The electrostatic thruster 10 comprises at least one electrical reflector 60, which is configured to bend the electrical field of adjacent thruster cell arrays 40. The electrical reflector 60 is positioned between the thruster cell arrays 40a, 40b, and wherein the distance between the second thruster cell array 40b and the electrical reflector 60 is smaller than the distance between the first thruster cell array 40a and the electrical reflector 60. The thruster cells as depicted in figure 10 may each comprise at least one intermediate electrode and current source, which have been omitted in the drawing for the sake of clarity.

The power source 30 is configured to apply the same voltage potential to the emitter 22 and to the corresponding electrical reflector 60. Each electrical reflector 60 is insulated or has a sufficiently large surface to reduce charged particle 5 production. The surface area of an electrical reflector 60 is larger than the surface area of an emitter 22. The electrostatic thruster 10 can be implemented in an aircraft, in particular an airplane or Unmanned Arial Vehicle.

The electrostatic thruster 10 can also be implemented in a spacecraft, in particular a small satellite, such as a microsatellite, a nanosatellite, a picosatellite, or a femtosatellite.

Turning to figures 16a -16b, an electrostatic wing thruster 100 for providing a thrust force 101 to a wing 110 which is configured for a movement 102 through a fluid 103 is shown. The electrostatic wing thruster 100 comprises the wing 110 and a power source 130. The wing 110 comprises a front part 112, an upper part 114 and a lower part 116. The front part 112 comprises at least one front emitter 120. The upper part 114 comprises at least one collector 122 positioned at an upper surface 115 of the wing 110 The lower part 116 comprises at least one lower reflector 124 positioned at a lower surface 117 of the wing 110.

The power source 130 electrically is connected to the at least one emitter 120, the at least one reflector 124 and the at least one collector 122. The power source 130 is configured to apply a high voltage potential to each front emitter 120 and to each reflector 124. The power source 130 is also configured to apply an opposite high voltage potential or a neutral voltage potential to each collector 122. Each emitter 120 is configured to generate charged particles 105. Each reflector 124 is configured to repel the charged particles 105 and each collector 122 is configured to attract the charged particles 105.

Each front emitter 120 may be spaced from a front surface 113 of the wing 110 by a front gap 111. The lower part 116 of the wing 110 comprises at least one lower emitter 126 which is spaced from the lower surface 117 of the wing 110 by a lower gap 127. Each lower emitter 126 is also electrically connected to the power source 130. The power source 130 is configured to apply the high voltage potential to each lower emitter 126.

Fluid (air) flow causes charged particles 105 to move along the lower part 116 of the wing 110, passing the at least one reflector 124 with identical polarity will repel the wing 110 upwards and the at least one reflector 124 will repel the charged particles 105 downwards, creating an electrical high pressure below the wing 110. Charged particles 105 moving along the top of the wing 110 (by fluid flow and electrostatic force) will be attracted to the at least one collector 122 there, while the at least one collector 122 and the wing 110 are attracted upwards towards the charged particles 105, creating an electrical low pressure above the wing 110. This provides the ability to control upward or downward motion of the wing 110. The electrostatic wing thruster can be implemented in an aircraft, in particular an airplane or Unmanned Arial Vehicle or in a watercraft, in particular a submarine or hydrofoil.

While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting.

The terms “a” or “an”, as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising i.e. , open language, not excluding other elements or steps.

Any reference signs in the claims should not be construed as limiting the scope of the claims or the invention. It will be recognized that a specific embodiment as claimed may not achieve all of the stated objects.

The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

White lines between text paragraphs in the text above indicate that the technical features presented in the paragraph may be considered independent from technical features discussed in a preceding paragraph or in a subsequent paragraph.

Claims

1. An electrostatic thruster (10) for producing thrust by charging gas and/or liquid particles using a high voltage potential, wherein the electrostatic thruster comprises at least two thruster cells (20), each thruster cell comprising: at least one emitter (22), at least one collector (24), wherein the at least one collector is spaced from the at least one emitter by a thruster cell gap (28), wherein the electrostatic thruster further comprises a power source (30) electrically connected to the at least one emitter and the at least one collector of each thruster cell, wherein the power source is configured to apply a voltage between the at least one emitter and the at least one collector of each thruster cell, wherein the at least two thruster cells are positioned in parallel to form an thruster cell array (40), wherein the thruster cell array further comprises an intermediate electrode (42), wherein the intermediate electrode is positioned in an intermediate area (44) between the emitters and the collectors of two adjacent ones of the thruster cells in the thruster cell array, wherein the intermediate electrode is electrically connected to the collectors of the thruster cell array via a current source (32) configured to generate a substantially constant current.

2. Electrostatic thruster according to claim 1 , wherein the substantially constant current is at least an order of magnitude lower than a collector current of the thruster cell array in operation.

3. Electrostatic thruster according to claim 2, wherein the substantially constant current is lower than 3%, preferably between 1% and 3% of the collector current of the thruster cell array in operation.

4. Electrostatic thruster according to the preceding claim, wherein the power source is configured to apply the voltage between the at least one emitter and the at least one collector of each thruster cell in the thruster cell array with a same polarity.

5. Electrostatic thruster according to any of the preceding claims, wherein a first distance (45) between the emitter and the intermediate electrode is smaller than a second distance (46) between the collector and the intermediate electrode.

6. Electrostatic thruster according to any of the preceding claims, wherein the intermediate electrode is offset in respect of respective straight lines between the emitters and collectors of the thruster cell array, preferably by a half of a pitch between adjacent emitters of the thruster cell array.

7. Electrostatic thruster according to any of the preceding claims, comprising at least two adjacent thruster cell arrays (40a, 40b) positioned in series, wherein a distance (41a) between the collectors of a first thruster cell array (40a) and the emitters of a second thruster cell array (40b) is smaller than a distance (41b) between the collectors of the first thruster cell array and the collectors of the second thruster cell array.

8. Electrostatic thruster according to any the preceding claims, comprising at least two thruster cells in series, wherein the power source is configured to, for two adjacent thruster cells in series, apply the voltage between the at least one emitter and the at least one collector of a first thruster cell (20a) of the two adjacent thruster cells and the voltage between the at least one emitter and the at least one collector of a second thruster cell (20b) of the two adjacent thruster cells in series with opposite polarities.

9. Electrostatic thruster according to any of the preceding claims, wherein each collector has a blunt leading edge (25) directed to the emitter of the corresponding thruster cell.

10. Electrostatic thruster according to any of the preceding claims, wherein each collector has a blunt trailing edge (26).

11. Electrostatic thruster according to any of the preceding claims, wherein the collector has a sharp trailing edge (27), wherein the sharp trailing edge is configured to generate charged particles (5), and wherein the sharp trailing edge of the collector is the emitter of an adjacent thruster cell array.

12. Electrostatic thruster according any of the preceding claims, wherein the positive or negative high voltage potential applied to the collector is at least 30kV, and more in particular at least 40kV, in order for the collector to work as a repellent for the next thruster cell array.

13. Electrostatic thruster according to any of the preceding claims, comprising at least two thruster cells arrays in series, wherein a distance between the emitters of the first thruster cell array (40a) is larger than the distance between the emitters of each thruster cell array that follows after the first thruster cell array.

14. Electrostatic thruster according to any of the preceding claims, wherein at least one electrical reflector (21) is positioned in front of the at least one emitter of the first thruster cell array, wherein each electrical reflector has a conductive surface and is smooth, wherein each electrical reflector is electrically connected to the power source, and wherein the power source is configured to: apply a high voltage potential to each emitter, apply a substantially the same high voltage potential to each nearby electrical reflector.

15. Electrostatic thruster according to any of the preceding claims, wherein each electrical reflector has a relatively large surface area compared to the surface area of each nearby emitter.

16. Electrostatic thruster according to any of the preceding claims, wherein the emitter comprises a plurality of emitter electrodes (23) positioned closely together, wherein the plurality of emitter electrodes are configured to act as a single emitter, wherein preferably the plurality of emitter electrodes extend parallel to each other at a distance between the emitter electrodes is less than 1 millimetre.

17. Electrostatic thruster according to any of the preceding claims, wherein the power source is configured to apply a pulsed voltage to each emitter to alternate the voltage between two adjacent emitters.

18. Electrostatic thruster according to any of the preceding claims, wherein each emitter and each collector are elongate, and wherein the emitter comprises a longitudinal axis (12).

19. Electrostatic thruster according to the preceding claim, wherein the size of the thruster cell gap varies in the direction of the longitudinal axis of the emitter, the emitter preferably having a zigzag shape or a serrated edge facing towards the collector.

20. Electrostatic thruster according to any of the preceding claims, wherein a barrier (29) of a non-conducting material is positioned on an opposite side (14) of the emitter, and wherein the barrier follows the shape of the emitter.

21. Electrostatic thruster according to any of the preceding claims, wherein a first side (52) of the collector comprises a non-conductive material (50) which is directed to a second side (53) of the collector of an adjacent thruster cell without the non- conductive material, wherein the second side is configured attract charged particles, and wherein the first side is not configured to attract charged particles.

22. Electrostatic thruster according to any of the preceding claims, wherein the thruster cell comprises a first collector (24a) and a second collector (24b) having the same voltage potential as the first collector, wherein the first collector and the second collector are spaced by a collector gap (16), and wherein the first collector is positioned between the at least one emitter and the second collector.

23. Electrostatic thruster according to the preceding claim, wherein the second collector is mechanically disconnected from the first collector.

24. Electrostatic thruster according to any of claims 7-23, wherein the power source is configured to apply a voltage difference between each emitter of the first thruster cell array and each collector of the second thruster cell array, and wherein the electrostatic thruster comprises at least one electrical reflector (60) configured to bend the electrical field of adjacent thruster cell arrays, wherein the electrical reflector is positioned between the thruster cell arrays, and wherein the distance between the second thruster cell array and the electrical reflector is smaller than the distance between the first thruster cell array and the electrical reflector.

25. Electrostatic thruster according to the preceding claim, wherein the power source is configured to apply the same voltage potential to the emitter and to the corresponding electrical reflector.

26. Electrostatic thruster according to any of claims 24-25, wherein each electrical reflector is insulated to reduce charged particle production.

27. Electrostatic thruster according to any of claim 24-26, wherein the surface area of an electrical reflector is larger than the surface area of an emitter.

28. Aircraft (1), in particular an airplane or Unmanned Arial Vehicle, comprising the electrostatic thruster of any of the preceding claims.

29. Spacecraft (4), in particular a small satellite, comprising the electrostatic thruster of any of the preceding claims.

30. Electrostatic wing thruster (100) for providing a thrust force (101) to a wing (110) which is configured for a movement (102) through a fluid (103), wherein the electrostatic wing thruster comprising: the wing, wherein the wing comprising: o a front part (112), wherein the front part comprises at least one front emitter (120), o an upper part (114), wherein the upper part comprises at least one collector (122) positioned at an upper surface (115) of the wing, o a lower part (116), wherein the lower part comprises at least one lower reflector (124) positioned at a lower surface (117) of the wing, a power source (130) electrically connected to the at least one emitter, the at least one reflector and the at least one collector, wherein the power source is configured to: o apply a high voltage potential to each front emitter and to each reflector, o apply an opposite high voltage potential or a neutral voltage potential to each collector, wherein each emitter is configured to generate charged particles (105), and wherein each reflector is configured to repel the charged particles and each collector is configured to attract the charged particles.

31. Electrostatic wing thruster according to the preceding claim, wherein each front emitter is spaced from a front surface (113) of the wing by a front gap (111).

32. Electrostatic wing thruster according to any of claims 30-31 , wherein the lower part of the wing comprises at least one lower emitter (126) which is spaced from the lower surface of the wing by a lower gap (127), wherein each lower emitter is electrically connected to the power source, and wherein the power source is configured to apply the high voltage potential to the each lower emitter.

33. Aircraft (2), in particular an airplane or Unmanned Arial Vehicle, comprising the electrostatic wing thruster of any of claims 30-32.

34. Watercraft (3), in particular a submarine or hydrofoil, comprising the electrostatic wing thruster of any of claims 30-32.