DEVICE FOR CONTROLLING THE ANGULAR VEHICLE OF A SPACECRAFT AND ASSOCIATED SPACECRAFT

Description

Scope of the invention

[0001] The field of the invention is that of attitude control of spacecraft, such as satellites.

[0002] The invention relates more particularly to an angular velocity control device for a decommissioned spacecraft.

[0003] The invention thus has applications, in particular, but not exclusively, for all spacecraft for which an end-of-life removal operation must be considered. Prior art and its drawbacks

[0004] Decommissioned spacecraft contribute to the accumulation of space debris. The presence of such debris in space is problematic because it constitutes pollution, as the debris follows trajectories that can intersect the orbits of operational spacecraft, creating a risk of collision. Furthermore, collisions between debris increase the total amount of debris, further exacerbating the risk of collision for operational spacecraft.

[0005] In this context, regulations stipulate that a satellite cannot remain in orbit for more than 25 years. If such a satellite is orbiting at an altitude greater than approximately 600 km, atmospheric drag is insufficient to bring it down to Earth. Therefore, either such a satellite is configured to descend under its own power, or, if it malfunctions before it can do so, another spacecraft must rendezvous with it to bring it back to Earth.

[0006] However, even if a satellite is in orbit low enough that atmospheric drag would cause it to fall to Earth, it is essential to verify that there are no risks associated with such a reentry. For example, if the satellite contains too many components likely to survive atmospheric reentry (steel, titanium, ceramics), this could pose a risk on the ground if the satellite were to re-enter passively (i.e., anywhere). In such cases, the satellite must be capable of a controlled re-entry, which requires significantly more propellant and more delicate operations.

[0007] Therefore, in order to capture and deorbit space debris such as a decommissioned satellite, spacecraft are known that are adapted to perform maneuvers such as docking with the debris to form a composite, such as deorbiting satellites like those described in applications EP2746163 and EP2671804. It is understood, however, that the rotational speed of the decommissioned satellite remains a limiting factor for the success of the capture phase in such missions. Indeed, it is common for a decommissioned satellite to have a high angular velocity, either due to a fatal failure that also interrupted the mission (propulsion failure, collision with debris), or due to the accumulation of weak external disturbances (solar radiation pressure) over long periods.Furthermore, even in the case of a successful capture, the immediate subsequent operations for controlling the composite are incompatible with high rotational speeds, particularly when the deactivated satellite is connected to the deorbiting satellite by flexible links, such as a harpoon or a net. Also known is patent EP3538441, which describes a projectile comprising an outer casing separated by a viscous fluid from a magnetized inner body. Document US9663250B1 discloses a device for controlling the angular velocity of a spacecraft, including a magnetic braking system.

[0008] There is generally a need to improve the control techniques of a decommissioned spacecraft. Description of the invention

[0009] The invention relates to an angular velocity control device for a decommissioned spacecraft, facilitating the active removal of the spacecraft as space debris. Such an angular velocity control device comprises a stator and a rotor movable about an axis of rotation relative to the stator. The stator is intended to be driven by the spacecraft to be stabilized, while the rotor is intended to orient itself according to the Earth's magnetic field. The stator comprises an electrically conductive and non-ferromagnetic body, while the rotor comprises a magnetized system configured to induce braking eddy currents in the stator, counteracting the relative motion of the rotor with respect to the stator and creating a magnetic moment in the Earth's magnetic field.The rotor further comprises one (or more) lifting magnet(s) designed to cooperate with a magnetic field generated by a source external to the device to induce magnetic lift of the rotor relative to the stator when the angular velocity control device is in Earth's gravity. The angular velocity control device is made of one or more non-ferromagnetic materials, at least within a region influenced by the magnetic field generated by said lifting magnet. Thus, the invention proposes a novel and inventive solution for controlling the attitude of a decommissioned spacecraft (i.e., one on which no power source is available). This is achieved by a passive magnetic damping device attached to the platform structure, where a rotor equipped with magnets is free to rotate within a non-ferromagnetic conductive stator (i.e., such that it does not become magnetized over time).The magnets of the magnetic system are positioned opposite the body, for example, an aluminum one. Even if the spacecraft rotates, the rotor remains aligned with the geomagnetic field: the differential angular velocity between the rotor and the platform creates eddy currents in the stator, thus dissipating the rotational kinetic energy and tending to stop the spacecraft's rotation relative to the Earth's magnetic field. Furthermore, the implementation of one (or more) lifting magnets allows for testing the angular velocity control device on the ground by simulating weightlessness through the interaction of the magnet(s) with the magnetic field generated by an external source. Conversely, the angular velocity control device does not include any ferromagnetic material(s), at least not within the area of ​​influence of the magnetic field generated by the lifting magnet(s).Thus, the presence of the lifting magnet (or magnets) 11 within the angular velocity control device does not disturb the rotation of the rotor relative to the stator once the device is in orbit. In some embodiments, the magnetic system comprises a plurality of braking magnets arranged in a plane perpendicular to the axis of rotation of the rotor.

[0010] In some embodiments, the magnetic moments of the braking magnets sum up according to a non-zero component in the plane perpendicular to the axis of rotation of the rotor so that the braking magnets also allow an orientation of the rotor according to the Earth's magnetic field.

[0011] Such a configuration allows the compass function and the current induction function to be combined.

[0012] In some embodiments, the magnetic moments of several of the braking magnets are substantially perpendicular to the plane perpendicular to the rotor's axis of rotation, such that their magnetic field passes through the plane perpendicular to the rotor's axis of rotation to induce eddy currents in at least two areas of the stator body located opposite each other on either side of the plane perpendicular to the rotor's axis of rotation. The stator, for example, has a U-shaped profile around and on either side of the ring.

[0013] Thus, the amount of currents induced by a rotor magnet is doubled compared to an implementation in which the magnetic moment of the magnet is substantially parallel to the plane of rotation of the rotor (i.e. perpendicular to the axis of rotation of the rotor).

[0014] In some embodiments, the magnetic moments of several of the braking magnets form an oblique angle with respect to said plane perpendicular to the axis of rotation of the rotor.

[0015] Such a configuration allows combining the compass function and the doubling of induced currents.

[0016] In some embodiments, the lifting magnet (or magnets) includes a south pole and a north pole arranged along the axis of rotation.

[0017] Thus, the force generated in the presence of a magnetic field from a source external to the angular velocity control device is maximized in the direction of the axis of rotation. In some embodiments, the rotor is guided in at least two stator housings centered along the axis of rotation, via a sphere-to-plane type mechanical contact.

[0018] In some embodiments, each of the two housings comprises a closed plain bearing, opposite the rotor, by a flat end-of-stroke partition arranged transversely to the bearing. Two spherical heads integrated into the rotor and centered on the axis of rotation are configured to cooperate with the two housings.

[0019] Thus, the rotor is fitted to the stator with high precision (e.g. with a clearance of less than 1 mm) while minimizing friction during rotor rotation (e.g. the friction is preferably less than a fraction of the magnetic torque driving the rotor).

[0020] In some embodiments, the lifting magnet (or magnets) is permanently fixed to the rotor.

[0021] In some embodiments, the lifting magnet (or magnets) is temporarily attached to the rotor.

[0022] Thus, the lifting magnet (or magnets) can be attached to the rotor only during the ground testing phase. This makes the angular velocity control device lighter for orbital insertion.

[0023] In some embodiments, the support magnet (or magnets) is in an annular shape.

[0024] Thus, the force exerted by the lifting magnet(s) in the presence of a magnetic field generated by a source external to the angular velocity control device is collinear with the axis of rotation. This minimizes the horizontal gradient to avoid generating a lateral force (i.e., perpendicular to the axis of rotation during the test).

[0025] The invention also relates to a system comprising: an angular velocity control device as described above (according to any one of the aforementioned embodiments); and a device for testing the angular velocity control device. The test device includes at least one magnetic field source intended to cooperate with the lifting magnet(s) to induce magnetic lift of the rotor relative to the stator under Earth's gravity.

[0026] In some embodiments, the magnetic field source includes a permanent magnet or an electromagnet.

[0027] The invention also relates to a ground testing method for an angular velocity control device as described above (according to any one of the aforementioned embodiments), by implementing a test device comprising one (or more) magnetic field source(s) designed to cooperate with the lifting magnet(s) to induce magnetic levitation of the rotor relative to the stator under Earth's gravity. Such a method comprises: a relative adjustment of the control device and the test device, including a fine adjustment of the magnetic field generated by the magnetic field source(s) so that the magnetic field cooperates with the levitation magnet(s) of the angular velocity control device to induce magnetic levitation of the rotor relative to the stator; a functional test of the adjusted control device.

[0028] In some embodiments, the magnetic field source includes an electromagnet. The process includes at least one activation of the electromagnet to generate the magnetic field.

[0029] The invention also relates to a spacecraft comprising one or more angular velocity control devices as described above (according to any one of the aforementioned embodiments).

[0030] In some embodiments, the spacecraft further includes three-axis attitude control means adapted to stabilize the attitude of the spacecraft in operation. The angular velocity control device(s) of the spacecraft when out of service act simultaneously with the attitude control means of the spacecraft in operation and exert a negligible effect compared to these attitude control means of the spacecraft in operation. In some embodiments, each angular velocity control device is arranged such that the rotor's axis of rotation forms an angle of 45° or less with an axis of greatest inertia of the spacecraft, such that the out-of-service spacecraft tends toward a rotational motion about this axis of greatest inertia.

[0031] A primary advantage of the invention is that it allows for the reduction of the angular velocity of the satellite to be captured, prior to its capture, thereby facilitating the capture process. The present invention thus prevents a defunct satellite from exhibiting a high angular velocity, whether due to a fatal failure that caused mission interruption, such as a propulsion failure or a collision with debris, or due to the accumulation of weak external disturbances caused, for example, by solar radiation pressure, over extended periods. A second advantage of the invention is that it allows for the testing of the angular velocity control device on the ground, while simultaneously simulating weightlessness through the interaction of the lifting magnet(s) with the magnetic field generated by an external source. List of figures

[0032] Other objects, features and advantages of the invention will become more apparent upon reading the following description, given by way of simple illustration and not limitation, in relation to the figures, among which: [ Fig.1 ] represents an angular velocity control device for a spacecraft according to an embodiment of the invention; [ Fig. 2 ] represents an angular velocity control device for a spacecraft according to another embodiment of the invention; [ Fig. 3a ] represents a configuration of the braking magnets of a spacecraft angular velocity control device according to an exemplary embodiment of the invention; [ Fig. 3b ] represents a configuration of the braking magnets of a spacecraft angular velocity control device according to another embodiment of the invention; [ Fig. 4] represents a detailed view of an axial portion of a spacecraft angular velocity control device and a test device for the control device according to an exemplary embodiment of the invention; Fig. 5 ] represents the steps of a ground test procedure for a spacecraft angular velocity control device according to an exemplary embodiment of the invention; [ Fig. 6 ] represents a simplified model of a spacecraft's angular velocity control device that allows for the prediction of the spacecraft's derotation time constant; [ Fig. 7 ] represents a spacecraft equipped with two angular velocity control devices according to an exemplary embodiment of the invention. Detailed description of embodiments of the invention

[0033] The general principle of the invention is based on a device for controlling the angular velocity of a spacecraft, particularly for facilitating the removal of the spacecraft as space debris. Such a device comprises a stator and a rotor that rotates about an axis relative to the stator. The stator is designed to be driven by the spacecraft to be stabilized, while the rotor is designed to orient itself according to the Earth's magnetic field. The stator comprises an electrically conductive and non-ferromagnetic body, while the rotor comprises a magnetized system configured to induce braking eddy currents in the stator, counteracting the relative motion of the rotor with respect to the stator and creating a magnetic moment in the Earth's magnetic field (compass function).The rotor behaves like a compass needle thanks to a magnetic moment bias brought about by an asymmetrical arrangement of the polarities of the braking magnets or thanks to dedicated orientation magnets.

[0034] Thus, even in the absence of a power source on board the spacecraft, the rotor remains aligned with the Earth's magnetic field (compass function). The differential angular velocity between the rotor and the spacecraft creates eddy currents in the stator, dissipating the rotational kinetic energy and tending to stop the spacecraft's rotation relative to the Earth's magnetic field. The spacecraft's rotational speed is therefore controlled.

[0035] Furthermore, the rotor includes one (or more) lifting magnets designed to work with a magnetic field generated by a source external to the angular velocity control device to induce magnetic levitation of the rotor relative to the stator when the angular velocity control device is in Earth's gravity. Moreover, the stator is made of a non-ferromagnetic material within the region influenced by the magnetic field generated by the magnet(s). Thus, the angular velocity control device can be easily tested on the ground, as the presence of the magnet(s) allows for the simulation of weightlessness.

[0036] We now present, in relation to the [ Fig.1 ] an angular velocity control device 1 of a spacecraft 2 according to an example of an embodiment of the invention.

[0037] As described further below in relation to the [ Fig. 7The device 1 according to the invention makes it possible, in particular, to control the angular velocity of the spacecraft 2 when the latter is out of service. This makes it possible, for example, to facilitate the active removal of the spacecraft 2 as space debris.

[0038] Back to the [ Fig.1 The device 1 comprises a stator 3 and a rotor 4 movable about an axis A21 of rotation of the rotor 4 relative to the stator 3. The stator is, for example, fixed to the satellite frame. Depending on the application to controlling the angular velocity of the spacecraft 2, the stator 3 is intended to be driven by the spacecraft 2 to be stabilized. The rotor 4, for its part, is intended to orient itself according to the Earth's magnetic field 5.

[0039] Furthermore, the stator 3 includes an electrically conductive body 6, for example made of aluminum, while the rotor 4 includes a magnetized system 7 configured to induce, in the stator 3, braking eddy currents of a relative movement of the rotor 4 with respect to the stator 3.

[0040] This gives us a passive magnetic damping device intended to be fixed to the structure of the spacecraft 2, where the rotor 4 equipped with the magnetized system 7 is free to rotate inside a stator 3.

[0041] The body 6 of the stator 3 is electrically conductive and non-ferromagnetic so that it does not become magnetized over time. The body 6 is made, for example, of aluminum or copper.

[0042] Furthermore, according to the example of implementation of the [ Fig.1The magnetic system 7 comprises, on the one hand, braking magnets 18 and, on the other hand, orientation magnets 19. The braking magnets 18 are configured to induce, in the stator 3, the braking eddy currents of the relative motion of the rotor 4 with respect to the stator 3. The orientation magnets 19 are configured to create a magnetic moment in the Earth's magnetic field 5. This maintains the orientation of the rotor 4 with respect to the Earth's magnetic field 5 (compass function).

[0043] We now present, in relation to the [ Fig. 2 ] an angular velocity control device 1 according to another embodiment of the invention.

[0044] According to the example of implementation of the [ Fig. 2 ], the magnetic system 7 comprises a plurality of braking magnets 18a, 18b, 18c, 18d arranged in a plane P20 perpendicular to the axis A21 of rotation of the rotor 4 relative to the stator 3.

[0045] In particular, the magnetic moments M22a and M22b of the braking magnets 18a and 18b sum up with a non-zero component in the plane P20 so that the braking magnets 18a and 18b also allow an orientation of the rotor 4 according to the Earth's magnetic field 5.

[0046] Thus, in this embodiment, the braking magnets 18 perform the function of the orientation magnets 19 (compass function). The braking magnets 18 and the orientation magnets 19 are the same magnets.

[0047] We now present, in relation to the [ Fig. 3a ] a configuration of the braking magnets 18 according to an example of an embodiment of the invention.

[0048] In particular, the magnetic moments M22 of several braking magnets 18 are here substantially parallel to the plane P20 perpendicular to the axis A21 of rotation of the rotor 4.

[0049] In such a radial configuration, the radius of the trajectory of the induced eddy currents is maximized in body 6. Energy dissipation is thus also maximized.

[0050] Furthermore, the same braking magnets 18 can also be used to ensure the orientation function of the rotor 4 relative to the stator 3 as described above in relation to the [ Fig. 2 ].

[0051] According to such a configuration of the braking magnets 18, it is also easier to control the size of the air gap between the magnets 18 and the body 6 of the stator 3 (e.g. to address the problem of starting vibrations, of free play in the pivot of the rotor 4) or to house magnets 18 with a larger aspect ratio (e.g. a greater height of the magnets 18 allows a larger air gap).

[0052] Furthermore, the stator housing 3 can be made of any material, for example plastic, with simply a track 6 made of non-ferromagnetic material (e.g. aluminum or copper) forming a housing or arranged in a housing made in the stator 3, opposite the magnets 18. This housing extends for example around the stator with a U-shaped profile. The stator includes for example a cylindrical ring fitting into this housing.

[0053] We now present, in relation to the [ Fig. 3b ] a configuration of the braking magnets 18 according to another embodiment of the invention.

[0054] More specifically, the magnetic moments M22 of several braking magnets 18 are here substantially perpendicular to the plane P20. In other words, the magnetic moments M22 of the braking magnets 18 in question are here substantially parallel to the axis A21 of rotation of the rotor 4.

[0055] Thus, the magnetic field of the braking magnets 18 crosses the plane P20 to induce eddy currents in at least two areas of the body 6 of the stator 3 located opposite each other on either side of the plane P20 in question. The eddy currents thus induced are potentially doubled compared to a radial configuration of the braking magnets 18 as described above in relation to the [ Fig. 3a ]. However, in the normal configuration of the 18 braking magnets of the [ Fig. 3b ], the braking magnets 18 cannot simultaneously perform the function of orienting the rotor 4 relative to the stator 3. Additional magnets performing the function of orienting the rotor 4 relative to the stator 3 are required here, for example, orientation magnets 19 as described above in relation to the [ Fig.1 ].

[0056] In other implementations, the additional magnets fulfilling the function of orienting the rotor 4 relative to the stator 3 are other braking magnets 18 in a radial configuration as described above in relation to the [ Fig. 3a This results in a mixed configuration with some 18 braking magnets in normal configuration and some 18 braking magnets in radial configuration.

[0057] In other implementations, the magnetic moments M22 of several braking magnets 18 form an oblique angle with respect to the plane P20 perpendicular to the axis A21 of rotation of the rotor 4. For example, the magnetic moments M22 in question form an angle with the axis A21 of rotation of the rotor 4 of between 10 degrees and 80 degrees, preferably between 30 degrees and 60 degrees. In such a configuration, eddy currents are also induced on both sides of the plane P20 in question. Furthermore, a non-zero component of the total magnetic moment of the braking magnets 18 can thus be obtained in the plane P20 in question. In this way, the braking magnets 18 also perform the function of orienting the rotor 4 with respect to the stator 3 (compass function).

[0058] We now present, in relation to the [ Fig. 4 ],the axial part of the angular velocity control device 1 and a test device 20 of the angular velocity control device 1 according to an example of an embodiment of the invention.

[0059] In practice, the rotor 4 must be fitted to the stator 3 with sufficient precision so that the braking magnets 18 typically move within 1 mm of the stator 3 body 6 without ever touching. Furthermore, the means for fitting the rotor 4 to the stator 3 must induce as little friction as possible, so that the rotor 4 is always free to rotate. The friction should preferably be less than a fraction of the magnetic torque driving the rotor 4. To this end, the rotor 4 is guided in two corresponding housings 10a, 10b of the stator 3 via a spherical-plane type mechanical contact. For this purpose, the two housings 10a, 10b each include, for example, a closed plain bearing, opposite the rotor 4, with a flat end-of-stroke partition arranged transversely to the bearing. Two spherical heads 9a, 9b integrated into the rotor 4 and centered along the axis of rotation A21 are configured to cooperate with the two housings 10a, 10b.According to such a pivoting technology, the resistive torque obtained during the rotation of the rotor 4 relative to the stator 3 is very low, especially in orbital conditions (i.e. in the absence of perceived gravity).

[0060] However, in order to perform ground tests, additional means are implemented to recreate the operational conditions of the angular velocity control device 1 in orbit. Specifically, the angular velocity control device 1 includes one (or more) lifting magnet(s) 11. The lifting magnet(s) 11 is intended to cooperate with a magnetic field generated by a source external to the angular velocity control device 1 to induce magnetic lift of the rotor 4 relative to the stator 3 when the angular velocity control device 1 is in Earth's gravity.

[0061] More specifically, the external source for the angular velocity control device 1 is provided here by the test device 20. Such a test device 20 includes one (or more) magnetic field source(s) 21 intended to cooperate with the lifting magnet(s) 11 to induce magnetic levitation of the rotor 4 relative to the stator 3 in Earth's gravity. For example, the magnetic field source(s) 21 may include a permanent magnet or an electromagnet.

[0062] However, in order to prevent the presence of the levitation magnet(s) 11 within the angular velocity control device 1 from interfering with the pivoting technology described above in orbit, the angular velocity control device 1 is made of one or more non-ferromagnetic materials, at least in a zone 11ZI influenced by the magnetic field generated by the levitation magnet(s). Thus, the levitation magnet(s) 11 does not exert any additional force on the rotor 4 when the angular velocity control device 1 is isolated from the test device 20, e.g., when the angular velocity control device 1 is in orbit.

[0063] According to this embodiment, the lifting magnet (or magnets) 11 comprises a south pole 11S and a north pole 11N arranged along the rotation axis A21 (e.g., the magnetic moment of the lifting magnet (or magnets) 11 is parallel to the rotation axis A21). In this way, the force generated in the presence of a magnetic field from a source external to the angular velocity control device 1 is maximized in the direction of the rotation axis A21. However, other arrangements are possible.

[0064] According to some implementations, the lifting magnet (or magnets) 11 is permanently fixed to the rotor 4.

[0065] However, according to other implementations, the lifting magnet (or magnets) 11 is temporarily attached to the rotor 4. Thus, the lifting magnet (or magnets) 11 can be removed from the angular velocity control device 1 after the ground testing phase. The angular velocity control device 1 is therefore lighter for orbital insertion.

[0066] The remanence of the lifting magnet (or magnets) 11 is chosen based on its volume (e.g., the remanence of the lifting magnet (or magnets) 11 of the angular velocity control device 1 is taken to be 1 Tesla). The volume is determined, in particular, based on the weight of the rotor 4 and the magnetic field source 21. For example, it is preferable to minimize the horizontal gradient to avoid generating a lateral force (i.e., perpendicular to the axis of rotation A21 during the test).

[0067] Thus, in some implementations, the lifting magnet (or magnets) 11 has an annular shape. For example, the lifting magnet (or magnets) 11 has an annular shape of revolution around the axis of rotation A21. In this way, the force exerted by the lifting magnet (or magnets) 11 in the presence of the magnetic field of the source 21 is collinear with the axis of rotation A21. This makes it possible, for example, to avoid biasing the ground test of the angular velocity control device 1 by adding a lateral force to the rotor with respect to the axis of rotation A21.

[0068] Similarly, the smaller the magnetic field source 21, the greater the horizontal gradient will be. Conversely, the larger the magnetic field source 21, the more uniform the field. In particular, a coil-type electromagnet makes it easy to create a relatively uniform magnetic field.

[0069] For example, the choice of characteristics of the magnet(s) 11 that support the angular velocity control device 1, as well as the characteristics of the magnetic field source 21, results from an iterative and empirical process. For example, the more physically extensive the magnetic field source 21 is, the finer its tuning must be.

[0070] We now present, in relation to the [ Fig. 5 ], the steps of a ground test procedure of the angular velocity control device 1 according to an example embodiment of the invention.

[0071] More specifically, such a test procedure implements a test device 20 as described above (according to any one of the embodiments described above).

[0072] Thus, during an adjustment step E500, the angular velocity control device 1 is adjusted relative to the test device. The adjustment step E500 includes a fine-tuning step E500b of the magnetic field generated by the magnetic field source 21 so that the magnetic field cooperates with the levitation magnet(s) 11 of the angular velocity control device 1 to induce magnetic levitation of the rotor 4 relative to the stator 3.

[0073] Such fine-tuning includes, for example, the relative positioning of the devices so that the magnetic field generated by the source 21 of the test device 20 cooperates with the levitating magnet(s) 11 of the angular velocity control device 1 to induce magnetic levitation of the rotor 4 relative to the stator 3. This is the case, for example, when the source 21 includes a permanent magnet. In such a case, the relative positioning of the devices optimizes the value of the magnetic field generated by the source 21 of the test device 20 as perceived by the levitating magnet(s) 11 of the angular velocity control device 1.Alternatively, when the magnetic field source 21 includes an electromagnet, the step E500 includes, for example, a step E500a of switching on the electromagnet to generate the magnetic field, and then, if necessary, the implementation of step E500b of fine-tuning the magnetic field generated by the magnetic field source 21 (e.g., via adjusting the current injected into the electromagnet) so as to obtain the desired effect of magnetic levitation of the rotor 4 relative to the stator 3.

[0074] During a test step E510, the functional test of the angular velocity control device 1 is performed. Due to the magnetic levitation of the rotor 4 relative to the stator 3, such a functional test, although carried out on the ground, allows the functionality of the angular velocity control device 1 to be tested under conditions simulating weightlessness.

[0075] We now present, in relation to the [ Fig. 6 ]a simplified model of the angular velocity control device 1 according to an example embodiment of the invention.

[0076] More specifically, such a model makes it possible to estimate the derotation time constant of a spacecraft to which an angular velocity control device would be attached according to the present technique.

[0077] As a simplifying assumption, we consider here a braking magnet 18 with a length b sufficiently large compared to its width a that it can be considered infinite. The braking magnet 18 is housed radially on the periphery of a cylindrical rotor 4 of infinite length along its axis (y-axis) and radius R The braking magnet 18 moves over a supposedly infinitesimal distance. ε (= air gap) of a cylindrical metal casing, also of infinite length along the axis of the cylinder, modeling the stator 3.

[0078] Magnet 18 is radially magnetized and its height h along the radial direction is sufficiently large compared to its width that it can also be considered infinite. Due to the infinite height of magnet 18, the magnetic field B generated by magnet 18 on its surface approaches the asymptotic value, characterized by remanence, Br of the material: B = B r 2

[0079] According to such a one-dimensional model, the electric field and currents have non-zero components only along the y-axis. This simplifies the analysis, because Maxwell-Faraday's law: ∇ × E = − ∂ B ∂ t reduces to a single differential equation: ∂ E y ∂ x = − ∂ B z ∂ t = − ∂ B z ∂ x Rω with R being the radius of the cylinder and ω the angular velocity of rotation of the cylinder around its axis. Since the electric and magnetic fields are zero at infinity, integration according to xThe solution to equation [Math.3] is simple. It follows that the axial electric field is proportional to the radial magnetic field according to the following relationship: E y = − B ⋅ Rω = − B r 2 ⋅ Rω

[0080] Electrical power P dissipated per unit volume V of the stator housing 3 (considering a resistivity material) P ) for a single magnet 18 is then: dP dV = 1 ρ ⋅ E y 2 = B r 2 4 ρ ⋅ R 2 ω 2

[0081] In order to obtain electrical power P Once the total value of the previous relation is dissipated, it must be integrated over the volume where the phenomenon occurs, assumed to be e × a × b (Or e is the thickness of the stator housing 3, a is the width of the magnet in the tangential direction, b is the actual, finished length of the magnet along y ). This gives us: P = B r 2 4 ρ ⋅ eab ⋅ R 2 ω 2

[0082] When considering a rotor 4 with n18 braking magnets, the total power dissipated is assumed to be proportional to n (assuming that the magnets 18 do not interact with each other). When the stator 3 is driven by the spacecraft 2 to stabilize it and the rotor remains oriented according to the Earth's magnetic field, the electrical power P The total dissipated energy actually corresponds to a loss of kinetic energy from the satellite. Ė = Iωω̇ , with / the inertia of the spacecraft 2 to be stabilized around the axis of the cylinder. We thus obtain: nP = Iω ω ˙ = B r 2 4 ρ ⋅ neab ⋅ R 2 ω 2

[0083] From the previous relationship, we can deduce a time constant. τ for the exponential decrease of angular velocity: τ = ω ω ˙ = 4 ρI B r 2 R 2 ⋅ neab

[0084] For example, a time constant τ 28 days is obtained for the following values ​​of the parameters of equation [Math.8]: Number of magnets: 18 n: 8; width of a magnet 18 in the tangential direction, a : 3 mm; actual length of the magnet along y , b : 15 mm; stator housing thickness 3, e : 1 mm; material resistivity, P: 2.7x10⁻⁸ Ω.m; rotor radius 4, R : 2.5 cm; remanence of a magnet, Br : 1 T; and inertia of the spacecraft 2 to be stabilized around the axis of the cylinder, I : 5000 kg.m 2< .

[0085] We now present, in relation to the [ Fig. 7 ] a spacecraft 2 equipped with two angular velocity control devices 1 according to an exemplary embodiment of the invention.

[0086] More specifically, the stator 3 of each device 1 is fixed to the spacecraft 2 so as to be driven by the spacecraft 2. The rotor 4 of each device 1 orients itself according to the Earth's magnetic field 5.

[0087] According to the present embodiment, two angular velocity control devices 1 are implemented in the spacecraft 2 to be stabilized when it is out of service. Indeed, an angular velocity control device 1 according to the present technique cannot theoretically dampen angular velocities normal to its axis. However, an out-of-service spacecraft 2 will naturally tend to follow a rotational motion about its principal axis of maximum inertia. Thus, if such an angular velocity control device 1 is not implemented so that its axis of rotation A21 is strictly perpendicular to the principal axis of maximum inertia, residual angular rotation rates can be expected.

[0088] Thus, if a single angular velocity control device 1 is theoretically sufficient to dampen the rotation of the spacecraft 2 around the 3 axes of inertia, it may be advantageous in practice to implement two or three angular velocity control devices 1 for redundancy purposes.

[0089] However, in other embodiment examples, the spacecraft 2 is equipped with only one angular velocity control device 1.

[0090] In some embodiments, the rotation axis A21 of the rotor 4 of the angular velocity control device(s) 1 forms an angle less than or equal to 45° with the axis of greatest inertia of the spacecraft 2 (axis denoted " I max » in the [ Fig. 7), such that the inactive spacecraft 2 tends towards a rotational movement around this axis of greatest inertia. Indeed, the rotation of spacecraft 2 will naturally tend towards a rotation around its axis of greatest inertia (a phenomenon known as "flat spin" in Anglo-Saxon terminology). Thus, an arrangement in which the axis(es) A21 of rotation of the rotor(s) 4 of the angular velocity control device(s) 1 form an angle less than or equal to 45° with the axis of greatest inertia of spacecraft 2 ensures the dissipation of the rotational kinetic energy of spacecraft 2 around its axis of greatest inertia, thereby slowing the rotation of the spacecraft.

[0091] The active spacecraft 2 further includes attitude control means along three axes adapted to stabilize the attitude of the active spacecraft. The angular velocity control device(s) 1 act simultaneously with the attitude control means of the active spacecraft but exert a negligible effect compared to these attitude control means of the active spacecraft.

[0092] Thus, the angular velocity control device(s) 1 have a negligible effect on the attitude control of the spacecraft 2 when it is in operation, but allow control of the angular velocity of the spacecraft 2 when it is out of service.

Claims

1. Device (1) for controlling the angular velocity of an out-of-service spacecraft (2) making it possible to facilitate the operations of active removal of the spacecraft as space debris, comprising a stator (3) and a rotor (4) movable about an axis (A21) of rotation with respect to the stator, the stator (3) being intended to be driven by the spacecraft (2) to be stabilized, the rotor (4) being intended to orient according to the Earth's magnetic field (5), wherein the stator (3) comprises an electrically conductive and non-ferromagnetic body (6) while the rotor (4) comprises a magnetic braking system (7) configured to induce, in the stator (3), eddy currents for braking a relative movement of the rotor (4) with respect to the stator (3) and to create a magnetic moment in the Earth's magnetic field (5), characterized in that the rotor (4) further comprises at least one magnetic-suspension magnet (11) intended to cooperate with a magnetic field generated by a source external to said device in order to suspend the rotor (4) magnetically with respect to the stator (3) when the angular velocity control device (1) is in the Earth's gravity, and in that the angular velocity control device (1) consists of one or more non-ferromagnetic materials at least in a zone (11ZI) of influence of the magnetic field generated by said magnetic-suspension magnet.

2. Angular velocity control device (1) according to claim 1, wherein said magnetic-suspension magnet comprises a south pole (11S) and a north pole (11N) disposed along the axis (A21) of rotation.

3. Angular velocity control device (1) according to claim 1 or 2, wherein the rotor (4) is guided in at least two housings (10a, 10b) of the stator (3) centered along the axis of rotation (A21), according to a mechanical contact of the counter-plane sphere type.

4. Angular velocity control device (1) according to claim 3, wherein said two housings (10a, 10b) each comprise a plain bearing closed, opposite the rotor, by a plane end stop partition disposed transversely to the bearing, two spherical heads (9a, 9b) integrated into the rotor (4) and centered along the axis of rotation (A21) being configured to cooperate with said two housings.

5. Angular velocity control device (1) according to any one of claims 1 to 4, wherein said magnetic-suspension magnet is permanently attached to the rotor.

6. Angular velocity control device (1) according to any one of claims 1 to 4, wherein said magnetic-suspension magnet is temporarily attached to the rotor.

7. Angular velocity control device according to any one of claims 1 to 6, wherein the magnetic-suspension magnet is in an annular shape.

8. System comprising: - an angular velocity control device (1) according to any one of claims 1 to 7; and - a device (20) for testing said angular velocity control device (1), the test device comprising at least one magnetic field source (21) intended to cooperate with said magnetic-suspension magnet in order to suspend the rotor (4) magnetically with respect to the stator (3) in the Earth's gravity.

9. System according to claim 8, wherein said magnetic field source (21) comprises a permanent magnet or an electromagnet.

10. Method for testing on the ground an angular velocity control device (1) according to any one of claims 1 to 7, by implementing a test device (20) comprising at least one magnetic field source (21) intended to cooperate with said magnetic-suspension magnet in order to suspend the rotor (4) magnetically with respect to the stator (3) in the Earth's gravity, characterized in that it comprises: - a relative adjustment (E500) of the control device (1) and of the test device, comprising a fine adjustment (E500b) of the magnetic field generated by said magnetic field source so that said magnetic field cooperates with said magnetic-suspension magnet of the angular velocity control device (1) in order to suspend said rotor (4) magnetically with respect to the stator (3); - a functional test (E510) of the adjusted control device (1).

11. Method according to claim 10, wherein said magnetic field source comprises an electromagnet, the method comprising at least one operation (E500a) of the electromagnet to generate said magnetic field.

12. Spacecraft (2) comprising at least one angular velocity control device (1) according to one of claims 1 to 7.

13. Spacecraft (2) according to the preceding claim, further comprising attitude control means according to three axes adapted to stabilize the attitude of the spacecraft in activity, said angular velocity control device (1) acting simultaneously with the attitude control means of the spacecraft in activity and exercising a negligible action with respect to these attitude control means of the spacecraft in activity.

14. Spacecraft (2) according to claim 12 or 13, wherein said angular velocity control device (1) is arranged so that the axis of rotation of the rotor forms an angle less than or equal to 45° with an axis of greater inertia of the spacecraft, such that the out-of-service spacecraft tends toward a rotational movement about this axis of greater inertia.