The US2003 / 046921 describes a Hall effect thruster naturally aspirated. Such thruster uses particles of the residual atmosphere in which it evolves to operate.

The thrusters naturally aspirated Hall are mainly used to propel observation satellites; these propellants are particularly useful in low orbit.

At this altitude, the residual atmosphere slows satellites, which limits their lifespan. Advantageously, the thrusters Hall aspirated help offset this drag, and thereby increase the life of the satellites.

However, given the scarcity of the atmosphere with altitude, these thrusters can not operate beyond an altitude of 100 km. They are therefore unusable altitudes above it, such as to allow the transfer of satellites to higher orbits.

Moreover, the document US2008 / 116808 describes a plasma thruster technology can be implemented on an external wall.

PRESENTATION OF THE INVENTION

The object of the invention is therefore to provide a propeller naturally aspirated Hall capable of operating at a higher altitude than traditional thrusters Hall.

A first aspect of the invention relates firstly to the Hall effect thruster comprising a channel (internal) for accelerating particles.

According to this first aspect of the invention, the objective mentioned above is achieved by means of a Hall effect thruster to develop a thrust along a thrust axis, the thruster comprising:

a channel for the collection, acceleration and ejection of particles by the propellant when the latter is in operation, the channel being radially delimited by an inner wall and an outer wall;

an electrical circuit comprising an anode, a cathode, and an electric voltage source for emitting electrons via the cathode and attract electrons through the anode;

a magnetic circuit for generating a magnetic field in the channel axially downstream of the anode, the magnetic field being directed in a substantially radial direction with respect to the axis of thrust; the thruster being characterized in that

the channel is open on an upstream side of the propeller and comprises a hub particles to collect the particles;

the shape of the hub is defined by a continuous contour in a plane perpendicular to the thrust axis and surrounding the latter;

over a major portion of the outline, namely at least 50% of the contour and preferably at least 75% of the contour, each section of the hub perpendicular to the contour is parabolic in shape and has a home belonging to the contour; and

the magnetic circuit is arranged to generate the magnetic field in the vicinity of the contour.

In known manner, the cathode is placed downstream of the anode. In addition, the electrical circuit is arranged such that the electric field is generated in a generally axial direction (that of the axis of thrust) between the anode and the cathode.

Generally, downstream of the concentrator channel further has a cylindrical or substantially cylindrical rear portion. Per part rear cylindrical 'here denotes a rear portion whose surface is generated by the movement in a direction of a closed contour; here, this direction is the thrust axis. The rear part of the channel is then used to channel and direct the particles during their acceleration and their ejection by the propellant.

This rear portion extends generally straight from the downstream limit of the concentrator.

The channel generally has an annular shape; it therefore has an inner wall and an outer wall. In one embodiment

preferential, the magnetic circuit comprises a plurality of link arm arranged to connect the inner wall and the outer wall of the channel.

The fact that the contour surrounds the thrust axis (naturally, in order along this axis) means that the contour goes around this axis with a view along the axis of thrust.

Moreover, the term 'voltage source' means in this way a broad document that can generate a voltage device. This tension does not have to be constant or even periodic in time. As a result, a current source configured to deliver a current of constant intensity is a voltage source within the meaning of the present invention.

In one embodiment, the voltage source is available: it is configured so that the voltage applied between its anode and (or) the cathode (s) may be reversed order. When reversing the roles of the anode and the cathode (or cathodes) in the electrical circuit are reversed.

This reversal allows to reverse the direction of the force applied by the propellant, and use thereof as a braking system, for example for braking a satellite during a re-entry into the atmosphere.

On the other hand, a second aspect of the invention relates to a specific configuration propellant, wherein the particles are accelerated not inside the channel indicated earlier, the heart of the propellant, but instead outside the -Cl, around the wall. Despite this important difference, the principle of the Hall effect thruster remains approximately the same as in previous propellants Hall.

According to this second aspect of the invention, the objective of the invention mentioned above is achieved by means of a Hall effect thruster to develop a thrust along a thrust axis, the thruster comprising:

a magnetic circuit for generating a magnetic field;

an electrical circuit comprising an anode, a first cathode, and a voltage source for emitting electrons at least via the first cathode and attract electrons through the anode;

the thruster being characterized in that

. the propeller is arranged within a wall formed around the axis of thrust;

. the magnetic circuit and the electric circuit are arranged to generate magnetic and electric fields around the wall; and

. in any section parallel to the thrust axis and perpendicular to the wall:

the magnetic circuit has an upstream and a downstream magnetic pole magnetic pole, disposed substantially on the surface of the wall remote from each other, and

the magnetic circuit is arranged such that the magnetic field is oriented in a substantially radial direction (and thus perpendicular) with respect to the thrust axis at right upstream magnetic pole;

the anode and the first cathode are located on either side of the upstream magnetic pole;

. the wall comprises a hub particles serving to concentrate the particles;

the shape of the hub is defined by a contour (or curve) closed in a plane perpendicular to the thrust axis and going around the wall;

over a major portion of the outline, namely at least 50% of the contour and preferably at least 75% of the contour, each section of the hub perpendicular to the contour is of parabolic shape and having a focal point belonging to the contour;

the magnetic circuit being arranged to generate the magnetic field in the vicinity of the contour.

The previously mentioned wall is usually the outer wall of the housing of the spacecraft on which the propeller is mounted.

Downstream of the hub, this wall may further comprise a cylindrical rear portion or substantially cylindrical. Said rear portion constitutes a shield for protecting the rear of the ions ejected by the satellite thruster and other incident particles.

The characteristics set out above, either with reference to the first or second aspect of the invention, advantageously allow the propellant to have a sufficient supply particles and even if the spacecraft operates at high altitude.

Indeed, many of the particles that are on the trajectory of the spacecraft face the hub. It has a specific shape with its sections which have a parabolic shape (that is to say, a parabolic portion).

Due to this form, the particles impinging on the wall of the hub are all directed substantially in the same zone, namely towards the focus of the parabola.

As a result, the concentrator can concentrate all particles that collect in a relatively small volume. It follows that near that point, the particle density is well above and the particle density of the residual atmosphere.

It is thus possible advantageously in this zone to raise the density of particles at a value sufficient to power the Hall effect thruster (of the order of 10 20 particles per m 3 ).

It includes appropriate to dimension the diameter and more generally the dimensions of the walls of the hub so as to ensure that the particle density is reached, taking into account the altitude and speed at which it is expected to operate the satellite.

The particles concentrated near the focus of the parable is used as the propellant gas supply.

Due to the arrangement including its electrical circuit and its magnetic circuit, the propellant is configured to generate a cathode grid formed of electrons blocked by the magnetic field at the location or at least close to the focus of these parables.

The particles caught up in the spacecraft are therefore directed by the hub to the focus of the parabola and hence to the virtual cathode gate of the propellant. They are ionized and then accelerated towards the rear of the propellant under the effect of electric field generated between the anode and the cathode of the electrical circuit.

Thus, the arrangement of the propellant and in particular of its hub makes it possible to overcome the low density particles

high altitude, concentrating the particles on the satellite trajectory in a small area, in which they can be accelerated so as to generate a thrust to the spacecraft.

The propellant configured according to the second aspect of the invention optionally can comprise, as in the first aspect of the invention, a controllable voltage source whose poles can be reversed to allow use of the propellant such as brake system.

Whether following the first or second aspect, the invention can advantageously be implemented by integrating one or more of the following improvements: the contour from which the shape of the hub is defined may in particular be a circle, or an ellipse, or oval; the anode can be a portion of the wall or one of said walls; the anode may be formed by depressions in the wall or one of said walls.

Finally, the invention also relates to a spacecraft incorporating at least one Hall effect thruster as defined above.

As such, it relates to such a spacecraft incorporating at least one Hall effect thruster according to the first aspect of the invention, the spacecraft being configured to carry a payload disposed radially inside the inner wall of the channel the propellant.

In one embodiment of such a spacecraft, the contour may be a circle, or an ellipse, or an oval.

In one embodiment of such a spacecraft, the anode may be a portion of one of the propellant channel walls.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be well understood and its advantages appear better on reading the following detailed description of embodiments shown by way of non-limiting examples. The description refers to the appended figures in which:

- Figure 1 is a longitudinal section of a thruster for a spacecraft, according to the first aspect of the invention;

- Figure 2 is a perspective view of a satellite comprising the thruster of figure 1;

- Figure 3 is a longitudinal sectional spacecraft comprising a thruster according to the second aspect of the invention; and

- Figure 4 is a satellite perspective view of Figure 3.

DETAILED DESCRIPTION OF THE INVENTION

Two embodiments of the invention corresponding to the first and the second aspect will now be presented through the examples of two satellites 1 and 101, respectively comprising a propeller 10 and a propeller 110, both according to the invention .

These satellites 1 and 101 are satellites that are destined to evolve into Earth's atmosphere remaining between 100 and 300 km altitude.

Advantageously, this height is relatively low, allowing some equipment (communication equipment, cameras, etc.) have a size and therefore a relatively low mass. Conversely, at this altitude the Earth's atmosphere offers little resistance, but not zero, the satellite pass. It is therefore necessary to compensate for the induced drag.

The function of Hall effect thruster that comprises each of these satellites is provide thrust to the satellite capable of maintaining it in operation at the desired altitude.

It also ensures that any changes or corrections of orbits.

Advantageously, a propellant according to the invention such as those installed on board these satellites, coupled to means for electrical power supply such as solar panels, is able to provide over very long periods the thrust required to maintain the altitude satellite.

The first embodiment illustrates the first aspect of the invention in connection with Figures 1 and 2.

Figures 1 and 2 show the thruster 10 of the satellite 1 (an example of a spacecraft), which is a Hall effect thruster naturally aspirated.

The propellant 10 generally has a shape of revolution about a thrust axis X. It is arranged within a housing 20 of substantially cylindrical shape of axis X. The upstream end 22 of the housing is opened with the other end 26 (downstream end) is partially closed by a substantially flat base 25 perpendicular to the axis X. the base 25 is, however, passes through an annular passage 28 for ejecting particles.

The bottom 25 has a generally disc-shaped perpendicular to the axis X. Due to the presence of passage 28, the bottom 25 is constituted by a disk 56, and an annular ring 58 located radially around the annular passage 28. The ring 58 is formed integrally with the rest of the casing 20.

Inside the housing 20, the propellant 10 has a channel 30 of generally annular shape about the axis X. More generally, this channel 30 can also be axisymmetric. However, non-axisymmetric shapes may alternatively be envisaged, for example, oval cross section or racetrack.

The channel 30 is generally annular and includes a radially outer wall 34 and a radially inner wall 32, which are concentric about the axis X.

The channel 30 is essentially constituted by a hub particles 36, which opens the upstream side (left in FIG 1) of the satellite 1 and is used to collect particles on the satellite track.

The downstream side, the hub 36 opens the annular passage 28, which is itself open at the downstream side of the satellite 1 to permit ejection of the particles accelerated by the propellant 10.

According to the invention, the shape of the hub 36 is defined by a continuous Cl contour. In this embodiment, this Cl outline is a circle located in a plane perpendicular to the thrust axis. Cl circle is centered on the axis X (and therefore it surrounds this axis).

In any plane perpendicular to the circle Cl (that is to say, in this embodiment, in any meridian plane), the section of the concentrator is that shown in Figure 1: It has a parabolic shape S, whose focus Fl belongs to circle Cl (Only part of the S parabola used to define the shape of the hub 36).

Cl circle is positioned so as to be located axially at the annular passage 28.

The upstream side, the propellant 10 further comprises link arms 24 which provide a mechanical connection between the inner and outer walls 32 and 34 of the channel 30. Between the arms 24 are formed four apertures 25 through which the particles penetrate into the P channel 30.

The propellant 10 includes a magnetic circuit 50 and an electric circuit 60.

The magnetic circuit 50 includes: the housing 20 itself, which is made of ferromagnetic material and thus forms an external magnetic core; funds 24 and 25, made of ferromagnetic material; and a central magnetic core 54 shaped shaft which extends along the axis X. The disc 56 which constitutes part of the bottom 25 forms the downstream end of the shaft 54.

All the elements of the magnetic circuit 50 indicated above is arranged to allow a movement without loss of a magnetic field through the magnetic circuit.

To protect from wear the downstream part of the channel and contain the electron cloud formed in the air gap of the magnetic circuit, the axially downstream portions of the walls 32 and 34 are formed by ceramic material rings 82 and 84 positioned at the annular passage 28.

The magnetic circuit 50 further comprises an internal annular bobbin 70 and an outer annular coil 72, which serve to generate the magnetic field B required to operate the Hall effect thruster. Both coils are formed concentrically about the axis X. These are substantially cylindrical coil form, each of the turns is substantially a circle of axis X.

The coil 70 is formed around the shaft 54 ​​inside (radially) of the wall 32 (that is to say, between the shaft 54 ​​and the wall 32). The coil 72 is formed on the inner face of the cylindrical housing 20, more precisely between the inner face and the outer wall 34 of the channel 30. The coils 70 and 72 are supplied by a not shown electric power source.

In the magnetic circuit 50, the central magnetic core 54 and the external magnetic core (the casing 20) are arranged so that their polarities are opposite.

The circuit 50 is arranged to generate a substantially radial magnetic field B in the annular passage 28, which thus constitutes the gap of the circuit 50. Thus, the downstream portion of channel 30 passes or extends into the air gap 28 circuit 50.

In the channel 30, the magnetic field B is maximum at (axially) of the annular passage 28.

On the other hand, as previously indicated the propellant 10 also comprises an electrical circuit 60.

This circuit includes an anode 62 located axially slightly upstream of the annular passage 28, a cathode 64 located at the most downstream part of the end 26 of channel 30 (and therefore downstream of the passage 28), and an electrical voltage source 68 connecting the anode 62 to the cathode 64.

In this embodiment, the voltage source 68 is controllable (although this is not shown in the figures): its electrical voltage may be reversed in order to reverse the thrust of the thruster.

The anode 62 forms a portion of the inner wall 34 of channel 30: it is thus incorporated into this channel, while being electrically isolated from the latter (and in particular of the wall 34).

In the vicinity of the anode 62, the magnetic field B generated by magnetic circuit 50 is attenuated by the inner and outer magnetic shields 77 formed respectively on the inner surface of the casing 20 and on the outer surface of the shaft 54. These screens 77 also serve to mechanically support the coils 70 and 72.

The cathode 64 is located outside of the open downstream end of the annular channel 28. In the embodiment of Figures 1 and 2, it is fixed on the disc 56, the outer side that is to say downstream of the shaft 54. in Figure 2, the cathode 64 is shown in dotted lines.

In another embodiment, the cathode 64 may be fixed not on the disc 56, but rather on the outer surface (the downstream or back side) of the ring 58. The cathode may then have such an annular shape, and not the form of pad illustrated in Figure 2.

The cathode 64 is connected to the voltage source 66 by a cable running inside the inner wall 32 of channel 30, more specifically, inside the shaft 54.

In the embodiment of Figures 1 and 2, the volume available inside (radially) of the wall 32 is arranged to accommodate a payload 35 of the satellite 1.

Thereof is disposed radially inwardly of the inner wall 32, as illustrated in Figures 1 and 2.

In another embodiment, the propellant may be specifically designed with an internal volume much greater inside the wall 32. A large part or all of the payload may then be disposed in this volume, in inside the inner wall 32 of the channel 30 of the thruster.

In this case, the propellant is arranged in practice as an annular structure disposed around the payload of the satellite, or more generally of the spacecraft.

The operation of the thruster 10 is described. This operation is essentially identical to that of the propeller described by US2003 / 0046921 Al.

When the satellite 1 travels at high speed in the atmosphere, particles on its trajectory are caught up in the concentrator 36 and penetrate therein.

As shown in Figure 1, when a particle P and penetrates into the hub 36, it hits most often one of the walls 32 or 34 thereof.

However, it was found that the particles bounce almost specularly on the walls satellites or spacecraft. In other words, collisions between a particle and a satellite wall appear to be without friction, that is to say that the angle of incidence and the particle ejection angle-vis vis the wall are equal.

Therefore, following this shock and because of the properties of the focus of a parabola, a P particle striking a wall 32 or 34 of the concentrator 36 is returned to the focus Fl, that is to say towards a point circle Cl.

Thus, the hub advantageously makes it possible to direct the particles caught up by the satellite 1 in a relatively small area in the vicinity of the circle Cl.

Cl circle that is positioned to be located where the radial magnetic field B generated by the magnetic circuit is most intense, that is to say at the annular passage 28.

More simultaneously, an electrical voltage, typically of the order of 150 to 800 V is established between the cathode 64 downstream of the downstream end of channel 30 and the anode 62. The cathode 64 emits electrons, therefore, which are largely trapped in a magnetic chamber 'formed by the magnetic field B. This magnetic enclosure is adapted to the desired performance and is typically of the order of 100 to 300 gauss. Electrons trapped in this magnetic enclosure thus form a virtual cathode grid 65, substantially forming a ring according to the Cl circle inside the channel 30.

An electric field E is thus generated in channel 30, at the annular passage 28 (fig.l) and upstream thereof to the anode 62, especially at the virtual cathode grid 65.

A small portion of the trapped electrons, namely those which are the most energetic (typically 10-40 eV), however escape the magnetic enclosure and joining the anode 62.

As indicated above, the particles P which are captured by the satellite 1 are concentrated by the concentrator 36 in the vicinity of the circle Cl. They therefore fall within the virtual cathode grid 65 formed by the electrons trapped by the magnetic field B.

The impacts of these electrons and P particles ionize them. Due to their electrical charge, the ionized particles are accelerated toward the downstream end 26 of channel 30 by the electric field E. As the mass of ionised particles is several orders of magnitude higher than that of the electrons, the magnetic field does not confine these ions as it does for electrons. The propellant 10 thus generates a plasma jet which is ejected at an extremely high velocity through the downstream channel end 30. The propellant 10 produces a thrust and substantially aligned with the central axis X.

The second embodiment, which illustrates the second aspect of the invention, will now be presented in connection with Figures 3 and 4.

3 shows a satellite 101, a propellant 110 comprising Hall effect according to the invention.

The satellite 101 is arranged in an outer protective casing

120 which generally has a shape of revolution about an axis X. The propeller 110 is arranged inside of the outer wall 122 of the casing 120.

The thruster 110 has a structure axisymmetric about the axis X. The terms "upstream" and "downstream" in this context are defined with respect to the normal direction of movement of the satellite and therefore the propellant.

The wall 122 has two parts, namely a hub particles 136, which serves to concentrate the P particles on the satellite track 101 or in the vicinity thereof, and a rear portion 124 located downstream of the concentrator 136.

The shape of the hub 136 is defined by a continuous contour C2. As in the previous embodiment, the outline is a circle C2. It is located in a plane perpendicular to the axis X of thrust and goes around the wall 120.

In section in any plane perpendicular to the contour C2, the concentrator 122 has a parabolic shape with a focus F2 belonging to the contour C2.

The concentrator 136 and the rear portion 124 join at an edge forming a circle C3 (Fig.4).

The rear portion 124 of the wall 120 is of cylindrical shape of axis X; its shape is that generated by the movement of the circle C3 rearwardly in the direction of the axis X.

The thruster 110 includes a magnetic circuit 150 and electrical circuit 160.

The magnetic circuit 150 is arranged to create a substantially radial magnetic field at (axially, with reference to the axis X) of the upstream portion of the wall 122.

For this, it comprises a plurality of identical elementary magnetic circuits 132, distributed so axisymmetric about the axis X.

Each circuit 132 includes a soft iron core 134 in an axial section has a form of U. The ring 134 has a long rod 136 extending parallel to the axis X close to the wall 122 (and the inside thereof). It also comprises two bent portions 138 which are bent in a radial plane toward the wall 122, such that the end of these sections is disposed just under the surface of the wall 122. In view of these sections 138, the casing 120 includes rings 140 of non-magnetic material to allow the passage of the magnetic field. The rings 140 may for example be ceramic, polycrystalline cubic carbon (c'es ie diamond) or alumina.

Each circuit 132 also includes a coil 146 arranged forming a solenoid around the rod 136.

The terminals of the coils 146 of the circuits 132 are linked to those of a voltage source 144. This voltage source is chosen such that under the effect of the voltage applied to the coils 146, a steady magnetic field B can be created around the wall. A current source can also be used.

As a result, when a voltage is applied by the voltage source 144 to the coils 146, each magnetic circuit 132 generates a magnetic field B. This field is radiated by the circuit 132 to the outside of the satellite 101 in space in the vicinity the satellite. The formed field lines are shown in Figure 3. As this figure shows, the ends of the bent portions 138 thus form magnetic poles for the circuits 132, namely an upstream magnetic pole 170 and a downstream magnetic pole 172.

The right of an upstream magnetic pole 170, the magnetic field B is oriented in a substantially substantially radial direction with respect to the thrust axis (X) (that is to say perpendicular to this axis and passing by it this).

As can be seen in Figure 4, the upstream magnetic poles 170 of two elementary magnetic circuits 132 are formed adjacent so as to be close to each other, or even if possible to be in contact. The same goes for the magnetic poles 172. This downstream

allows that the magnetic circuit has an upstream and a downstream magnetic pole magnetic pole in any axial plane, which generate the magnetic field B. With this, the magnetic field B is generated substantially uniformly over the entire periphery of the wall 122.

The upstream magnetic poles 170 are formed at

(Axially) of the contour C2. Thus, the magnetic circuit 150 is arranged such that the magnetic field B generated at the upstream right magnetic pole is generated in the vicinity of the contour C2.

The thruster 110 also includes an electrical circuit 160. This circuit comprises an anode 162, a first cathode 164, a second cathode 166, a cathode 167 and a third voltage source 168 connecting the anode 162 to the first, the second cathode and third cathodes 164,166, 167. the anode 162 is located axially upstream of the upstream first magnetic pole 170. the cathode 64 is located downstream of the upstream magnetic pole 170 but in the immediate vicinity thereof and thus at a distance upstream of the downstream magnetic pole 172.

The second cathode 166 is located between the upstream magnetic pole 170 and the downstream magnetic pole 172. It is therefore downstream of the upstream magnetic pole 170, and upstream of the downstream magnetic pole 172.

The third cathode 167 is located downstream of the downstream magnetic pole 172.

Each of the cathodes 166 and 167 is located more near the downstream magnetic pole 172, and therefore at some distance downstream of the first cathode 164.

The anode 162 and the first, second and third cathode 164,166,167 are each ring-shaped. Each of these rings extending around the entire circumference of the wall 122 generally in a plane perpendicular to the axis X (or more specifically, between two close planes perpendicular to the axis X). Each of these cathodes is flush with the surface of the wall 122 and thus constitutes a portion of this wall.

The propellant 110 functions similarly to the thruster 10.

As the voltage source 68 in the foregoing embodiment, the voltage source 168 is controllable: the electrical voltage can be reversed in order to reverse the thrust of the thruster.

According to the meaning given to the voltage by the voltage source 168, the force generated by the propellant 110 may be in one direction or the other along the direction X; as appropriate, the propellant is therefore as engine system or as brake system.

The operating mode of the propeller described here is the motor mode:

When voltage is applied by voltage source 168 between the anode 162 and the cathodes 164, 166 and 167, an electric field E is formed in the space outside the satellite around the wall 122, substantially between the anode 162 and the first cathode 164. This field is substantially oriented in a direction parallel to the axis X.

In addition, under the effect of the electrical voltage established between the cathodes 164, 166 and 167 downstream and upstream anode 162, the cathodes 164, 166 and 167 begin to emit electrons. These are largely trapped in a magnetic enclosure formed by the magnetic field created by the magnetic circuit 150, adapted to the desired performance, and which can be typically of the order of 100 to 300 gauss. Electrons trapped in this magnetic enclosure will thereby forming a virtual cathode gate 165. However, some high-energy electrons (typically from 10 to 40 eV) escape the magnetic enclosure and joining the anode 62.

Due to the relative motion of the satellite 101 with respect to the atmosphere, every moment of particles enter the virtual cathode grid 165. impacts between electrons retained in the grid and the atoms of these particles cause ionization celles- this. The ionized particles under the influence of the electric field E created by the electrical circuit 160, are then accelerated toward the rear of the satellite. The propellant 110 thus generates a plasma jet which is ejected at an extremely high speed in the X direction, towards the back of the satellite, downstream of the wall 122. For reasons of symmetry, the generated thrust is substantially aligned with the central axis X.

As the propellant 110 is in operation, the second and third cathode 166 and 167 provide electrons with the particles

released downstream of the satellite 100, and thus ensure the electrical neutrality of these.

The use of the second cathode 166 is optional. It is mainly the third cathode 67, located downstream of the downstream magnetic pole 52, which provides the electrons necessary for the neutralization of the particles accelerated by the propellant 10.

Advantageously, the thruster of the invention requires no propellant gas supply, unlike most propellants Hall.

In addition, its arrangement on the outer wall of the satellite frees much of the satellite's interior space, allowing it to have a significant payload.

Note also that the electric field E generated by the electric circuit 160 is extremely small in the vicinity of the downstream magnetic pole 172. As a result, the force generated by the propellant 110 is formed in the vicinity of the upstream magnetic pole 170; in the absence of electric field E in the vicinity of the downstream magnetic pole 172, almost no reverse force is generated in the vicinity of that pole.

Advantageously according to the invention, it is not necessary that the hub directs the particles that focuses precisely to the focus of the parabola defined by its wall (in the case of the propellant 10) or its walls (in the case of propellant 110). As a virtual cathode gate is formed in a certain volume surrounding the fireplace, it is sufficient that the particles caught up by the concentrator are directed inside this volume. This gives some tolerance as to the shape of the wall or walls of the concentrator.

CLAIMS

1. thruster (10) Hall effect to develop a thrust along a thrust axis, the thruster comprising:

a channel (30) for the collection, acceleration and ejection of particles by the propellant when the latter is in operation, the channel (30) being radially delimited by an inner wall (32) and an outer wall (34 );

an electrical circuit (60) comprising an anode (62), a cathode (64) and an electric voltage source (68) for emitting electrons via the cathode (64) and attracting electrons through the anode (62);

a magnetic circuit (50) for generating a magnetic field (B) in the channel (30) axially downstream of the anode, the magnetic field being directed in a substantially radial direction with respect to the thrust axis (X);

the channel (30) being open on an upstream side of the propeller and having a particle concentrator (36) for collecting particles (P);

the shape of the hub is defined by a continuous contour (C) located in a plane perpendicular to the thrust axis and surrounding the latter;

the thruster being characterized in that

over a major portion of the contour, each section of the hub perpendicular to the contour is parabolic in shape and has a focal point (Fl) belonging to the contour (C); and

the magnetic circuit (50) is arranged to generate the magnetic field (B) in the vicinity of the contour (Cl).

2. Propeller according to claim 1, wherein the magnetic circuit comprises a plurality of connecting arms (24) arranged to connect the inner wall (32) and the outer wall (34) of the channel, the channel having an annular shape .

3. thruster (110) Hall effect to develop a thrust along a thrust axis, the thruster comprising:

a magnetic circuit (150) for generating a magnetic field

(B) ;

an electrical circuit (160) comprising an anode (162), a first cathode (164), and a voltage source (168) for emitting electrons using at least the first cathode (164) and attracting electrons through the anode (162);

the thruster being characterized in that

. the propellant (110) is arranged inside of a wall (122) formed around the thrust axis (X);

. the magnetic circuit (150) and the electrical circuit (160) are arranged to generate magnetic fields (B) and electric (E) around the wall (122); and

. in any section parallel to the thrust axis (X) and perpendicular to the wall (122):

the magnetic circuit (150) has an upstream magnetic pole (170) and a downstream magnetic pole (172) disposed substantially on the surface of the wall remote from each other, and

the magnetic circuit (150) is arranged such that the magnetic field is oriented in a substantially radial direction with respect to the thrust axis (X) in line with the upstream magnetic pole (170);

the anode (162) and the first cathode (164) are located on either side of the upstream magnetic pole (170);

and in that :

. the wall (120) includes a hub particles (136) for focusing the particles (P);

the shape of the hub being defined by an outline (C2) closed in a plane perpendicular to the thrust axis and going around the wall;

over a major portion of the contour, each section of the hub perpendicular to the contour being parabolic in shape and having a focal point (F2) belonging to the contour (C2);

the magnetic circuit (150) being arranged to generate the magnetic field in the vicinity of the contour (C2).

4. Propeller according to any one of claims 1 to 3, wherein said contour (C1, C2) is a circle, or an ellipse, or an oval.

5. Propeller according to any one of claims 1 to 4, wherein the anode (62.162) constitutes a portion of the wall (122) or of one of said inner and outer walls (32,34).

6. Propeller according to any one of claims 1 to 5, wherein the anode (62.162) is formed recessed in the wall (122) or one of said inner and outer walls (32,34).

7. A spacecraft (1; 101) incorporating at least one propeller (10; 110) Hall effect according to any one of claims 1 to 6.

8. A spacecraft (1; 101) incorporating at least one propeller (10; 110) Hall effect according to claim 1 or 2, the spacecraft being configured to carry a payload disposed radially inwardly of the inner wall (32) of the channel (30).

9. A spacecraft according to claim 8, wherein said contour (Cl) is a circle, or an ellipse, or an oval.

10. A spacecraft according to claim 8 or 9, wherein the anode (62) constitutes a portion of one of said walls (32,34).