FR3138808A1 - Device for reducing the electrical charge of a space vehicle - Google Patents

Abstract

According to one aspect, the present description relates to a device for reducing the electrical charge of a space vehicle comprising: a substrate (201) configured to be electrically connected to the structure of the space vehicle; a first layer (202) formed of a plurality of carbon nanotubes substantially oriented perpendicular to the substrate, said first layer (202) at least partially covering the substrate (201) and being in contact with the substrate (201); a second layer (203) at least partially covering the first layer (202) and comprising a dielectric material such as to acquire a more positive charge than the first layer (202) when the device is subjected to a flow of electrons, d ions and/or a flux of vacuum ultraviolet (VUV) type radiation. FIG. 2A

Description

Device for reducing the electrical charge of a space vehicle

The present description relates to a device for reducing the electrical charge of a space vehicle and a space vehicle comprising such a device. In addition, the present description relates to a method for reducing the electrical charge of a space vehicle.

State of the art

Many space vehicles such as satellites, launchers, landers, space stations, space probes and rovers (or “rover” according to the English expression) are intended to evolve in a space environment without atmosphere, also called “environment space loading”.

The charging space environment includes electrically charged particles that can interact with the vehicle. In particular, satellites are generally very sensitive to electrons from the charging space environment whose energy is between a few tens of electron volts and a few hundred kilo-electron volts.

Due to interaction with the charging space environment, vehicles acquire an electrical charge, in particular a negative electrical charge, which can lead to adverse consequences if not controlled, due to the appearance of leakage currents and electric arcs which could damage the space vehicle and/or cause failures.

Space vehicles generally comprise a conductive structure and different coatings arranged on the structure comprising materials with different electrical properties and which can be charged at different levels depending on their capacity to store and emit electrons when they undergo the impact of charging electrons and ions from the space environment. The electrical charge levels of the coatings also depend on the positions of the coatings on the space vehicle, including significant differences between coatings exposed to sunlight and coatings in shade because coatings exposed to sunlight re-emit a significant portion of their negative charge towards the charging space environment due to photoemission triggered by vacuum ultraviolet radiation (VUV, after the English expression “ Vacuum Ultra - Violet ” ).

The balance between electric currents on each coating and on the conductive structure of the satellite governs the evolution of the electric potentials of each element. When the potential difference between two elements reaches a critical threshold, electrical energy can be released spontaneously and sporadically in the form of an electrostatic discharge (or “ESD” according to the English expression “ electric static discharge ”). The severity of the discharge and its possible consequences on the space vehicle depend on the amplitude of the discharge, its temporal dynamics, its duration and the proximity of sensitive elements of the space vehicle.

In certain cases, the structure of the space vehicle and all the conductive elements connected to it may be negatively charged with respect to the space environment while an external coating arranged on the external surface of the space vehicle structure finds itself negatively charged, but less negatively than structure. In this particular configuration, called inverse potential gradient, the risks of ESD are especially increased due to the appearance of an electric field between the external coating and the structure of the space vehicle which lowers the potential barrier that the electrons must cross to escape the space vehicle. Thus, in an inverse potential gradient configuration, the emission of a surplus of electrons is favored at the point where the conductive material, the insulator and the charging spatial environment meet, called the triple point in the field of astronautics. Inverse potential gradient configurations are particularly common for space vehicle solar panels, in which an external protective glass covering the solar cells typically charges less negatively than the space vehicle structure.

In order to limit ESD problems linked to the acquisition of charges by a space vehicle, it is known to use an active electrical charge emission device.

US patent 6,362,574 [REF1] describes for example a device for emitting an electrical charge of the micro-tip type comprising a set of micro-tips made of conductive material configured to be in electrical contact with the structure of the space vehicle and a conductive grid. In this device, a voltage source imposes a potential difference between the gate and the set of micro-tips allowing the emission of a flow of electrons from the micro-tips towards the charging spatial environment. Such a device therefore makes it possible to reduce the negative electrical charge of the space vehicle.

However, such a microtip device has the disadvantage of being an active device which is complex to control and requires a voltage source consuming electrical energy. Furthermore, when using such a device, the emission of electrons must be stopped when the potential of the space vehicle is reduced to zero in order to prevent said potential from reaching positive values that could reattract the electrons. issued by the system. In some cases, the return of electrons can be in the form of a focused beam which can damage sensitive systems of the space vehicle.

US patent 8,511,616 [REF 2] discloses another type of micro-tip device in which the conductive grid is electrically connected to a large conductive plate exposed to the Sun and which emits a large quantity of electrons due to a photoemission effect induced by VUV radiation. In this configuration, the conductive grid does not need to be powered by a voltage generator. However, such a device only becomes effective if the conductive plate is sufficiently extended, which is bulky and takes up significant space on the space vehicle hosting the device, to the detriment of other installations such as photovoltaic cells.

On the other hand, patent US 8,014,121 [REF3] discloses a passive ESD prevention device comprising a conductive substrate electrically connected to the structure of a satellite, a conductive layer in electrical contact with the substrate, and a dielectric material placed on the conductive layer. In such a device, when the charging space environment comes to charge the satellite negatively, different levels of electrical charge are acquired by the conductive layer and by the dielectric material. In the same way as for an inverse potential gradient, an electric field then appears between the conductive layer and the dielectric material so that the emission of electrons from the conductive layer towards the charging spatial environment is favored at the point triple.

The applicant has observed that this device, although being passive, has disadvantages linked to an emission of electrons which depends on the asperities of the dielectric material and the conductive layer and therefore cannot be controlled, which can in particular lead to avalanche effects that could damage the device. The inverse gradient necessary to start the emission can in fact sometimes be too great, which can lead to high intensity ESD occurring on the device itself even before the device is put into operation, thus limiting the the usefulness of the device in reducing the negative charge of a space vehicle.

In this context, the present description describes devices for reducing the load of a space vehicle which solve all or part of the problems of the devices according to the state of the art.

As used herein, the term “include” means the same as “include” or “contain,” and is inclusive or open-ended and does not exclude other matters not described or depicted.

Furthermore, in the present description, the term "approximately" or "substantially" is synonymous with (means the same as) having a lower and/or higher margin of 10%, for example 5%, of the respective value.

According to a first aspect, the present description relates to a device for reducing the electrical charge of a space vehicle comprising:

- a substrate configured to be electrically connected to a conductive structure of the space vehicle;

- a first layer formed of a plurality of carbon nanotubes substantially oriented perpendicular to a plane of the substrate, said first layer at least partially covering the substrate and being in contact with the substrate;

- a second layer at least partially covering the first layer and comprising a dielectric material configured to emit electrons when said dielectric material is subjected to an external flow (ER) comprising electrons, ions and/or vacuum ultraviolet radiation (VUV ), so as to give the second layer a more positive charge than the first layer when the device is subjected to said external flow.

In the present description, the external flow (ER) can come from a charging spatial environment.

In the present description, “vacuum ultraviolet” radiation, or VUV, is electromagnetic radiation comprising a wavelength spectrum whose central wavelength is between approximately 140 nm and approximately 200 nm.

The applicant has shown that in such a device, the synergy between the first layer and the second layer allows a reduction in the load of the space device with very good efficiency.

In particular, the presence of carbon nanotubes tends to increase the electric field at the upper surface of the first layer and therefore to reduce the potential barrier that the electrons present in the substrate must cross to be evacuated from the substrate, in particular by tunneling or by field effect.

In addition, the presence of the second layer tends to further increase the electric field at the upper surface of the first layer, and therefore, again, to reduce the potential barrier that the electrons present in the substrate must cross to be evacuated. of the substrate.

Furthermore, the carbon nanotubes of the first layer produce a multitude of peak effects favoring regular and homogeneous electron emission and adapting at each moment to the most favorable local conditions, so that the avalanche effects are avoided.

Thus, such a device allows, under the influence of the charging spatial environment, an evacuation of electrons from the substrate, which leads to a reduction in the negative electric charge of the substrate, and a reduction in the potential difference between the second layer and the substrate. Since the substrate is electrically connected to the conductive structure of a space vehicle, it has the same electrical charge as the structure of the space vehicle. Thus, the emission of electrons from the substrate to the charging space environment tends to jointly reduce the negative charge of the substrate and the negative charge of the space vehicle to which the substrate is connected.

The applicant has shown that the technical effect results from a plurality of mechanisms. A first part of the electrons is emitted directly from the first layer towards the charging space environment, for example via a field effect. A second part of the electrons is emitted indirectly from the first layer towards the charging space environment, via the second layer. In the second case, an electron propagates from the first layer to the second layer, for example by tunneling. Said electron is then accelerated by the electric field from the junction between the first layer and the second layer towards the second layer, which results in ionizing collisions of said electron with molecules included in the second layer. This results in the emission of one or more electrons, called secondary electrons, from the second layer towards the charging space environment.

Advantageously, such a device operates passively and therefore does not need to be powered by an energy source such as, for example, a voltage or current source. It is the interaction between the charging spatial environment and the device which produces the electric field favoring the emission of electrons from the substrate.

Furthermore, such a device is efficient while being compact and the device does not require a conductive plate as may be the case in state-of-the-art passive devices of the microtip type.

According to one or more examples, the device further comprises a resistive component having an electrical resistance greater than or equal to 10 kΩ configured to electrically connect the substrate to the conductive structure of the space vehicle.

Such a resistance, called protection resistance in the present description, prevents too high an electron current from being emitted by the device and then damaging the device, for example in the case of a strong external flux.

According to one or more examples, the protective resistor comprises a sheet of dielectric materials.

According to one or more examples, the first layer and/or the second layer is divided into several blocks.

According to one or more examples, the first layer is divided into several blocks, that is to say into several subsets of carbon nanotubes of the same nanotube density, but separated from each other laterally.

The applicant has observed that the block structuring of the nanotubes makes it possible to promote adhesion of the second layer to the assembly formed of the first layer and the substrate. In addition, structuring the plurality of CNTs into several blocks makes it possible to increase the number of side walls of the first layer, and therefore to increase the number of CNTs located on the side walls. The applicants have shown that the emission of electrons by field effect in a device according to the present description results from the electric field generated by the individual tips of the CNTs and from the electric field generated, on a larger scale, by the upper edges of the walls. lateral of the first layer; such a structuring into blocks therefore improves the emission of electrons by field effect.

According to one or more examples, the first layer is divided into a number of blocks between 2 and 9.

According to one or more examples, the second layer is divided into several blocks, that is to say several parts separated from each other laterally.

The applicant has observed that structuring the second layer makes it possible to produce a greater number of triple points on the side walls of the second layer, at the level of the junction between the first layer, the second layer and the loading environment. Thus, the electric field is increased, which increases the emission of electrons by field effect at said side walls.

According to one or more examples, the second layer is divided into a number of blocks between 2 and 9.

According to one or more examples, the second layer completely covers the first layer and comes into contact with the substrate.

The applicant has observed that such an arrangement makes it possible to promote adhesion of the second layer to the assembly formed of the first layer and the substrate. Such an arrangement is particularly advantageous when the second layer is deposited by a physical vapor deposition technique.

According to one or more examples, the dielectric material of the second layer is one of: alumina, magnesium oxide (MgO), silica, quartz, polydimethylsiloxane (PDMS), polyetheretherketone (PEEK).

The applicant has observed that such dielectric materials are particularly advantageous for acquiring a more positive charge than the first layer, when the device is exposed to an external flow.

In particular, it has been observed that such dielectric materials have a good capacity to generate multiple electrons following the impact of a photon or electron coming from the charging space environment and/or following an impact of an electron. from the first layer.

Thus, on the one hand, said second layer tends, under the effect of the charging spatial environment, to become positively charged on the surface exposed to said charging spatial environment. This results in the creation of an advantageously high electric field between the second layer and the first layer, which thus promotes the emission of electrons from the first layer towards the second layer, for example by tunneling effect.

On the other hand, when the second layer tends to generate multiple secondary electrons when electrons propagate in the second layer. Each secondary electron can then in turn lead to the generation of other electrons. This therefore leads to self-sustaining the emission of electrons, even in the case where the external conditions are not conducive to positively charging the second layer, for example in the case where the device finds itself sheltered from a large part of the radiation from the charging space environment.

According to one or more examples, the second layer has a thickness of approximately 4 micrometers to approximately 6 micrometers.

According to one or more examples, the second layer has a thickness of approximately 5 micrometers.

According to one or more examples, the second layer has a thickness strictly greater than the thickness of the first layer.

According to one or more examples, the second layer comprises at least one sheet of conductive materials.

According to one or more examples, said at least one sheet of conductive materials is arranged to separate the second layer into two superimposed parts.

According to one or more examples, the second layer comprises a plurality of conductive particles and/or at least one sheet of conductive materials, said at least one sheet of conductive materials being arranged to separate the second layer into two superimposed parts.

According to one or more examples, the sheet of conductive materials comprises one or more materials chosen from: gold, silver, copper, aluminum.

According to one or more examples, the second layer comprises a plurality of conductive particles.

According to one or more examples, the conductive particles are arranged in the second layer to form a two-dimensional mesh parallel to the surface of the second layer.

According to one or more examples, the conductive particles are arranged in the second layer to form a three-dimensional mesh. The density of such a three-dimensional mesh can be uniform or non-uniform in the volume of the second layer.

According to one or more examples, the conductive particles comprise one or more materials chosen from: gold, silver, copper, aluminum.

According to one or more examples, the device further comprises:

- a measurement unit configured to measure a current delivered by the device, that is to say a current of electrons emitted from the device towards the charging spatial environment.

Such an arrangement makes it possible to know the current due to the emission of electrons by the device. The applicant observed that this makes it possible to verify that the current remains in value ranges ensuring that the elements of the device such as the first layer and the second layer are operational and do not suffer irreversible damage. Furthermore, this device makes it possible to inform and alert on the appearance of a significant electrostatic charge on the surface of the satellite due, for example, to the charging space environment or to the activation of a satellite system. The device can for example be used to alert satellite operators of the risk incurred by satellites in the vicinity of said satellite due to the loading space environment or to adapt the use of satellite systems.

According to one or more examples, the device further comprises:

- a voltage generator configured to bring, in operation, the substrate to a negative electrical potential relative to the conductive structure of the space vehicle;

- a measurement unit configured to determine the electrical potential of the space vehicle; And

- a control unit configured to activate the voltage generator when the electric potential determined by the unit of measurement is, in absolute value, greater than or equal to a set value.

Such an optional arrangement, which makes the device active, makes it possible to improve the reduction of the negative electrical charge of the space vehicle by bringing the substrate to a negative electrical potential relative to the structure of the space vehicle, which promotes the emission of electrons from the substrate.

According to a second aspect, the present description relates to a space vehicle comprising a conductive structure and a device for reducing the electrical charge of a space vehicle according to the first aspect, in which the substrate of the device is electrically connected to the conductive structure of the vehicle spatial.

Such a space vehicle subjected to radiation present in the charging space environment sees its negative electrical charge reduced via the emission of electrons by the device, which avoids the destructive effects of electrostatic discharges.

According to one or more examples, the space vehicle further comprises:

- a light source capable of emitting ultraviolet type radiation from a vacuum; wherein the light source is configured to positively charge the second layer of the device relative to the substrate.

Such a light source replaces or acts as a complement to the charging space environment so that the negative charge reduction device of the space vehicle continues to operate when the charging space environment does not sufficiently interact with the device to charge positively the second layer relative to the substrate. Such an eventuality may occur, for example, when the device is in the shadow of the space vehicle or a celestial object.

According to one or more examples, the light source is configured to be activated continuously or on demand.

According to a third aspect, the present description relates to a method for reducing the electrical charge of a space vehicle using a device according to the first aspect, the method comprising:

- the electrical connection of the substrate of the device to the conductive structure of the space vehicle.

- exposure of the space vehicle to an external flow (ER) of a charging space environment comprising electrons, and/or ions, and/or vacuum ultraviolet radiation (VUV).

According to one or more examples, the method further comprises,

- the emission of an alert signal by the device when the electrical charge of the space vehicle reaches a predetermined threshold value.

Brief description of the figures

Other advantages and characteristics of the invention will appear on reading the description, illustrated by the following figures:

, represents a diagram of a satellite comprising examples of a device for reducing the electrical charge of a space vehicle according to the present description;

, represents a first embodiment of a device for reducing the electrical charge of a space vehicle according to the present description.

, represents a second embodiment of a device for reducing the electrical charge of a space vehicle according to the present description;

, represents a third embodiment of a device for reducing the electrical charge of a space vehicle according to the present description;

, represents a fourth embodiment of a device for reducing the electrical charge of a space vehicle according to the present description;

, represents a fifth embodiment of a device for reducing the electrical charge of a space vehicle according to the present description;

, represents a diagram illustrating an operating principle of a device for reducing the electrical charge of a space vehicle according to the present description;

, represents several configurations of a device for reducing the electrical charge of a space vehicle according to the present description.

The appended figures are schematic and are not necessarily to scale, they aim above all to illustrate the principles of the invention. From one figure (fig.) to another, identical elements (or parts of elements) are identified, when possible, by the same reference signs.

Detailed description of the invention

There represents a satellite-type space vehicle 100 subjected to an external flow (ER) originating from a charging space environment surrounding the satellite 100. The satellite 100 has a main body 103 and two solar panels 101, 102 and comprises an internal conductive structure. Each of the solar panels has two faces 110, 111. The body 103 and the faces of the solar panels 101, 102 of the satellite 100 are covered with various coatings.

When the satellite 100 is subjected to the external flow (ER), the coatings tend to charge positively or negatively with respect to the conductive structure internal to the satellite which is not exposed to the external flow (ER); however, electrostatic discharges are avoided because the excess electrons from the conductive structure are evacuated by devices 200 for reducing the electric charge arranged on the satellite and conforming to the present description.

The location of the devices 200 for reducing the electrical charge can be adapted to the specificities of the space vehicle, and is only shown as an example on the . For example, the devices 200 can be arranged on masts deployed from the body of the space vehicle.

Although in the example illustrated on the the devices 200 for reducing the electrical charge are only visible on the visible faces of the solar panels, one or more devices can be arranged on the hidden faces of the solar panels.

Although in the example illustrated on the several devices 200 for reducing the electrical charge are arranged on the body 103 and on the solar panels 101, 102, according to other examples the devices can be arranged differently. In particular, according to certain examples, the body 103 and/or the solar panels 101, 102 may comprise only one device 200.

THE , , , And represent devices for reducing the load of a space vehicle according to several embodiments.

In all these embodiments, the device comprises a substrate 201, a first layer 202 arranged on the substrate and a second layer 203 arranged on the first layer 202. The second layer 203 can be at least partially in contact with the substrate 201 ( see in particular the described later).

The substrate 201 comprises a conductive or semiconductor material and is configured to be electrically connected to a conductive structure of a space vehicle. In particular, the substrate may comprise a metal plate, for example a stainless steel plate, or a semiconductor plate, for example a silicon plate.

The first layer 202 comprises a set of carbon nanotubes (CNT), said set preferentially occupying a surface substantially centered relative to the substrate.

The set of CNTs, also called forest of CNTs in the present description, comprises carbon nanotubes substantially oriented perpendicular to a plane of the substrate 201.

The forest of CNTs preferably comprises several sheets of CNTs forming a layer having a substantially uniform height of between approximately 5 micrometers and approximately 150 micrometers. The substantially uniform nature of the height means that the height distribution of the CNTs of the CNT forest has a dispersion less than or equal to approximately 10%.

In certain examples, the forest of CNTs can be divided laterally into several blocks or subsets of carbon nanotubes, separated from each other laterally, in order to promote the adhesion of the second layer 203 on the assembly formed of the first layer 202 and substrate 201. For example, the forest of CNTs can be divided into 9 blocks arranged in 3 rows of 3 blocks.

The blocks occupy, on the substrate 201, surfaces included in square or circular zones having sides or diameters between approximately 1 mm and approximately 2 mm, for example square or circular zones with sides or diameters equal to approximately 1.5 mm.

When the forest of CNTs is divided into blocks, said blocks are preferentially separated by distances of between approximately 1 mm and approximately 10 mm, for example distances equal to 5 mm.

The second layer 203 is an insulating layer at least partially covering the first layer 202. The second layer 203 may comprise an alumina deposition carried out for example by physical vapor deposition or "PVD" according to the English expression "Physical Vapor Deposition". ".

In some examples, the second layer 203 can also be divided into several blocks.

Thus, in the examples illustrated on the and on the , the forest of CNTs of the first layer 202 only includes a single block, that is to say that the first layer 202 is “monoblock”.

In the example illustrated on the , the second layer 203 completely covers the upper surface of the first layer 202 (that is to say the surface opposite the substrate 201) whereas in the example illustrated on the , the second layer 203 comprises two blocks 203a, 203b each covering a distinct part of the first layer 202.

The configuration of the allows the first layer to be completely covered by the second layer and thus to protect the first layer from the external environment, including the charging space environment. In addition, the first layer covers all or almost all of the substrate, which increases the average density of carbon nanotubes per unit area and therefore, the electric field is increased by the presence of the carbon nanotubes over a larger area. surface.

The configuration of the makes it possible to produce triple points located at the junction between the first layer, the second layer and the external environment, which locally increases the electric field.

In the examples illustrated on the and on the , the forest of CNTs of the first layer 202 comprises two blocks 202a, 202b separated by a predetermined distance. Said predetermined distance is between approximately 1 millimeter and approximately 10 millimeters, for example distances equal to 5 mm.

In the example illustrated on the , the two blocks 202a, 202b of the first layer 202 are covered by a single second layer 203 which comprises a single block.

The configuration of the has the advantage of protecting the first layer from the external environment and of locally increasing the electric field at the periphery of the blocks of the first layer.

In the example illustrated on the , the two blocks 202a, 202b of the first layer 202 are each covered by one of the two blocks 203a, 203b of the second layer 203, respectively.

The configuration of the has the advantage of increasing the electric field at the periphery of the bocs of the first layer and at the triple points located at the junction between the first layer, the second layer and the external environment, which locally increases the electric field.

In the example illustrated on the , the forest of CNTs of the first layer 202 comprises two blocks 202a, 202b. In addition, the second layer 203 is arranged to cover both the upper surface of the two blocks 202a, 202b and the side walls of the two blocks 202a, 202b, so as to come into contact with the substrate 201. In this example, the second layer 203 can also be nested in the first layer 202 so that the CNTs are separated from each other by the dielectric material of the second layer 203.

In the example illustrated on the , the second layer is preferably a layer of alumina deposited, for example, by physical vapor deposition. The alumina layer preferably has a thickness of approximately 5 micrometers. The applicant has observed that such a thickness makes it possible to obtain good performance in terms of electronic emission.

In the example illustrated on the , the second layer 203 can also be a layer of PDMS deposited, for example by means of a syringe, on the substrate 201 and the first layer 202.

The applicant has observed that an alumina layer with a thickness of approximately 5 micrometers is also advantageous in the example devices illustrated in Figs. 2A-2B and Figs. 3A-3B.

The configuration of the makes it possible, in particular, to facilitate the adhesion of the second layer to the arrangement formed by the substrate and the second layer and to increase the electric field at the periphery of the blocks of the first layer, that is to say at the level of the side walls of the first layer.

Furthermore, in examples not illustrated, it is possible to have a device for reducing the load of a space vehicle comprising a first one-piece layer and a second layer which is arranged to cover both the upper surface of the first layer and the side walls of the first one-piece layer, so as to come into contact with the substrate in order to increase the surface area of the substrate which is covered by the first layer, which increases the average density of CNTs per unit surface area of the substrate .

In these examples, similarly to the device illustrated in the , the second layer can also be nested in the first layer so that the CNTs are separated from each other by the dielectric material of the second layer.

There represents, according to an example, the operating principle of a device for reducing the electrical charge of a space vehicle in the context of the example of device illustrated on the , that is to say a device comprising a first layer 202 with a single block and a second layer with two blocks 203a, 203b. The operating principle described nevertheless applies to the other examples of devices described in this description.

In the example shown in , external flows (ER) coming from a charging spatial environment interact with the first layer 202 and the second layer 203 of the device to cause, by impact of electrons or photons, the emission of impact electrons (IE ) and, by field effect, the emission of field effect (FE) electrons.

As illustrated on the , under the influence of the external flow (ER), the second layer 203a, 203b can emit one or more impact electrons (IE), represented by solid arrows. For this purpose, the second layer comprises a dielectric material having electrical properties giving it a strong capacity to emit electrons after impact of electrons or ions or photons coming from a charging space environment.

Thus, the external flow (ER) tends to produce a large quantity of positive charges on the part or parts of the second layer most exposed to the external flow (ER), in particular the upper surface of the second layer 203a, 203b, this which causes said part or parts to become more positively charged than the other parts of the second layer and the first layer.

The difference in charge between the different parts of the second layer and the first layer then results in the formation of an electric field (E) directed from the upper surface of the second layer 203a, 203b towards the first layer 202 and which promotes the field effect electron emission (F-E), represented by dotted arrows.

As illustrated on the , the second layer of the device according to the invention comprises materials capable of generating impact electrons (IE) in its own volume. In particular, when a field effect electron (FE) emitted due to the electric field (E) propagates in the second layer 203a, 203b, it is accelerated by the electric field (E) and generates, by ionizing collisions, positive (holes) and negative (IE impact electrons) free charge carriers. The electrons thus formed then move in turn in the second layer 203a, 203b under the effect of the electric field by carrying out new ionizing collisions or by recombining with the holes.

The second layer 203 of the device according to the invention comprises materials chosen to have a free charge carrier generation rate greater than the recombination rate such that a large part of the electrons generated following ionizing collisions can reach the upper surface. of the second layer 203 and be evacuated towards the charging spatial environment, thus making the charge of the second layer 203 more positive and increasing the electric field (E) even more.

This phenomenon allows self-maintenance of charge generation within the second layer even when external conditions no longer favor charge generation. The phenomenon therefore continues as long as the charge of the first layer 202 (and of the substrate 201) remains more negative than the charging spatial environment surrounding the device.

The applicant has observed that alumina is a particularly advantageous material which makes it possible to obtain the three effects mentioned above. Magnesium oxide is also a particularly advantageous material based on its known properties.

Furthermore, in the , FE electrons emitted towards the external environment by the first layer near the triple points located at the junction between the second layer, the second layer and the external environment collide with the surface of the second layer, which generates an emission of electrons by IE impact, which makes said impact surfaces more positive, in particular when a material having a high power of electron emission under electron impacts is chosen to constitute the second layer. This increases the electric field in the vicinity of the triple point and then increases the emission of electrons by field effect.

In addition, the applicant has shown that the presence of carbon nanotubes tends to increase the electric field (E) at the surface of the first layer, and therefore cooperates with the second layer to further reduce the potential barrier as the electrons present in the substrate must cross to be evacuated from the substrate, in particular by tunnel effect or by field effect.

Furthermore, the carbon nanotubes of the first layer produce a multitude of peak effects favoring regular and homogeneous electron emission and adapting at each moment to the most favorable local conditions, so that the avalanche effects are avoided.

There is a diagram illustrating more precisely three examples of configurations (306, 307, 308) for the implementation of a device 200 for reducing the load of a space vehicle 300 according to the present description. In all configurations, the device comprises a substrate 201, a first layer 202 formed of a plurality of carbon nanotubes, and a second layer 203 comprising a dielectric material conforming to the present description, and examples of which have been described below. above. These three configurations present in particular three ways of connecting the load reduction device to the space vehicle. Depending on the intended application and the resulting technical constraints, one or other of the configurations may be preferred.

In the example of the , the three configurations are possible with the same load reduction device arranged on a given space vehicle, for example a satellite, and a user can select one or the other of the configurations by means of an electrical circuit comprising a switch. In the example of the , the switch is in a position selecting configuration 306 but can, in the general case, be switched to select one of configurations 306, 307 or 308.

According to certain examples, the load reduction device only allows one of the three configurations, which is chosen according to the desired application.

In a first configuration 306, as illustrated in the , the substrate 201 is directly connected to the conductive structure 301 of the space vehicle 300. In this configuration, the device operates passively, and emits electrons (e-) under the action of the external flux ER without external power supply as has been described previously, for example by means of the . This configuration makes it possible to return electrons collected by the satellite to the external environment ER as soon as the satellite reaches a sufficiently negative potential. This configuration therefore limits the negative charge of the satellite. This configuration does not include a unit of measurement and is therefore particularly simple. This configuration is therefore particularly advantageous in the case where it is desired to limit the energy consumption of the device.

In a second configuration 307, the device comprises a substrate 201 which is connected to the conductive structure 301 of the space vehicle 300 via a measurement unit 305 configured to measure the electron current delivered by the device 200. In this second configuration, the device 200 also operates passively, and emits electrons (e-) under the action of the external flux ER. In addition, the current delivered by the device 200 is measured. The second configuration therefore makes it possible to know the current due to the emission of electrons by the device, which makes it possible to verify that the current remains in value ranges ensuring that the elements of the device such as the first layer and the second layer are operational and do not suffer irreversible damage. The second configuration 307 also makes it possible to inform a user about the possible occurrence of a significant electrostatic charge of the space vehicle, for example due to the charging space environment or the activation of a system on the space vehicle. Informing the user about the significant electrostatic charge can for example be carried out via the display of an alert signal by the measuring unit when the electrical charge of the space vehicle reaches a predetermined threshold value.

In a third configuration 308, the device comprises a substrate 201 which is connected to the conductive structure 301 of the space vehicle 300 via a measurement unit 304 configured to measure a current delivered by the device 200 and an electrical potential of the space vehicle 301. that, on the , the measurement unit 304 is represented as a current measurement unit, it is also suitable for measuring a voltage.

In addition, the substrate 201 is connected to the conductive structure 301 via a voltage generator 303 configured to, when in operation, bring the substrate 201 to a negative electrical potential with respect to the structure 301 of the space vehicle.

The voltage generator 303 is connected to a control unit 302 configured to activate the voltage generator 302 when the electrical potential determined by the measurement unit 304 is, in absolute value, greater than or equal to a set value.

The third configuration 308 makes it possible to improve the reduction of the negative electrical charge of the space vehicle by negatively charging the substrate relative to the structure of the space vehicle, which promotes the emission of electrons from the substrate.

Although described through a certain number of exemplary embodiments, the methods and devices for reducing the electrical charge of a space vehicle according to the present description include different variants, modifications and improvements which will be obvious to man. of the art, it being understood that these different variants, modifications and improvements form part of the scope of the invention as defined by the claims which follow.

Claims (11)

Device (200) for reducing the electrical charge of a space vehicle (100) comprising:
- a substrate (201) configured to be electrically connected to a conductive structure of the space vehicle;
- a first layer (202) formed of a plurality of carbon nanotubes substantially oriented perpendicular to a plane of the substrate (201), said first layer (202) at least partially covering the substrate (201) and being in contact with the substrate (202); And
- a second layer (203) at least partially covering the first layer (202) and comprising a dielectric material configured to emit electrons when said dielectric material is subjected to an external flow (ER) comprising electrons, ions and/or vacuum ultraviolet (VUV) radiation, so as to give the second layer a more positive charge than the first layer when the device is subjected to said external flow. A device according to claim 1, further comprising a resistive component having an electrical resistance greater than or equal to 10 kΩ configured to electrically connect the substrate (201) to the conductive structure of the space vehicle. Device according to any one of claims 1 to 2, in which the first layer (202) and/or the second layer (203) is divided into several blocks. Device according to any one of claims 1 to 3, in which the second layer (203) completely covers the first layer (202) and comes into contact with the substrate (201). Device according to any one of claims 1 to 4, wherein the dielectric material of the second layer (203) is one of: alumina, magnesium oxide (MgO), silica, quartz, polydimethylsiloxane (PDMS), polyetheretherketone ( PEEK). Device according to any one of claims 1 to 5, in which the second layer (203) comprises a plurality of conductive particles and/or at least one sheet of conductive materials, said at least one sheet of conductive materials being arranged to separate the second layer (203) in two superimposed parts. Device according to any one of claims 1 to 6 further comprising:
- a measurement unit (305) configured to measure a current delivered by the device. Device according to any one of claims 1 to 7, further comprising:
- a voltage generator (303) configured to bring, in operation, the substrate (201) to a negative electrical potential relative to the conductive structure (301) of the space vehicle;
- a measurement unit (304) configured to determine the electrical potential of the space vehicle; And
- a control unit (302) configured to activate the voltage generator (303) when the electric potential determined by the measuring unit (304) is, in absolute value, greater than or equal to a set value. Space vehicle comprising a conductive structure (301) and a device (200) for reducing the electrical charge of a space vehicle according to any one of the preceding claims, in which the substrate (201) of the device is electrically connected to the structure driver (301) of the space vehicle. Space vehicle according to claim 9, comprising:
- a light source capable of emitting ultraviolet type radiation from a vacuum; wherein the light source is configured to positively charge the second layer (203) of the device (200) relative to the substrate (201). A method of reducing the electrical charge of a space vehicle using a device according to any one of claims 1 to 8, the method comprising:
- the electrical connection of the substrate (201) of the device (200) to the conductive structure (301) of the space vehicle; And
- exposing the space vehicle to an external flow (ER) of a charging space environment comprising electrons, and/or ions, and/or vacuum ultraviolet radiation (VUV).