Angular velocity control device of a spacecraft and corresponding spacecraft.

Abstract

Angular velocity control device for a spacecraft and corresponding spacecraft. The invention relates to a device (1) for controlling the angular velocity of a decommissioned spacecraft, comprising: - a stator (3) and a rotor (4) movable about an axis (A21) of rotation relative to the stator. The stator (3) comprises an electrically conductive and non-ferromagnetic body (6), while the rotor (4) comprises a magnetized system (7) configured to induce, in the stator (3), braking eddy currents of a relative motion of the rotor (4) with respect to the stator (3); - a levitation magnet (11) intended to cooperate with a magnetic field generated by an external source to induce magnetic levitation of the rotor (4) with respect to the stator (3). The device (1) is made of one or more non-ferromagnetic materials in a zone (11ZI) influenced by the magnetic field generated by the levitation magnet. SAMPLE FIGURE: [Fig.4]

Description

Title of the invention: Angular velocity control device of a spacecraft and corresponding spacecraft. 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 envisaged. Prior art and its drawbacks

[0004] Decommissioned spacecraft contribute to the accumulation of space debris. The presence of such space 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 must not remain in orbit for more than 25 years. If such a satellite is flying at an altitude greater than approximately 600 km, atmospheric drag is insufficient to bring it down to Earth. Thus, either such a satellite is configured to descend under its own power, or, if it malfunctions before it can do so, another spacecraft will have to rendezvous with it to bring it down to Earth.

[0006] However, even in the case of a satellite in orbit low enough that atmospheric drag is sufficient to cause it to fall to Earth, it is necessary to verify that no risks are 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 reenter passively (i.e., anywhere). In such cases, the satellite must be capable of a controlled reentry, which requires significantly more propellant and more delicate operations.

[0007] Also, in order to capture and deorbit space debris such as a decommissioned satellite, spacecraft adapted to perform maneuvers such as docking with the debris, so as to form a composite, are known, for example, deorbiting satellites such as those described in applications EP2746163 and EP2671804. It is understood, however, that the rotational speed of the defunct satellite remains a limiting factor for the success of the capture phase in such missions. It is indeed common for a defunct 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 a high rotational speed, particularly when the defunct satellite is connected to the deorbiting satellite by flexible links, such as a harpoon or a net.

[0008] We also know of patent EP3538441 which teaches a projectile comprising an external enclosure separated by a viscous fluid from an internal magnetized body.

[0009] There is generally a need to improve control techniques for a decommissioned spacecraft. Description of the invention

[0010] 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, and 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 levitation 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 zone of influence of the magnetic field generated by said lifting magnet.

[0011] 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 inside a non-ferromagnetic conducting stator (i.e., so as not to become magnetized over time). The magnets of the magnetized system are positioned opposite the The body, for example, could be made of aluminum. 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 levitation 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 placed in orbit.

[0012] 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.

[0013] In certain 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.

[0014] Such a configuration makes it possible to combine the compass function and the current induction function.

[0015] In certain embodiments, the magnetic moments of several of the braking magnets are substantially perpendicular to the plane perpendicular to the axis of rotation of the rotor, such that their magnetic field passes through the plane perpendicular to the axis of rotation of the rotor 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 axis of rotation of the rotor. The stator, for example, has a U-shaped profile around and on either side of the ring.

[0016] Thus, the quantity 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).

[0017] In certain 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.

[0018] Such a configuration makes it possible to combine the compass function and the doubling of induced currents.

[0019] In certain embodiments, the levitation magnet (or magnets) includes a south pole and a north pole arranged along the axis of rotation.

[0020] Thus, the force generated in the presence of a magnetic field generated by a source external to the angular velocity control device is maximized in the direction of the axis of rotation.

[0021] In some embodiments, the rotor is guided in at least two housings of the stator centered along the axis of rotation, according to a mechanical contact of the sphere against plane type.

[0022] In certain embodiments, the two housings each comprise 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 along the axis of rotation are configured to cooperate with the two housings.

[0023] Thus, the rotor is adjusted 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).

[0024] In some embodiments, the support magnet (or magnets) is permanently fixed to the rotor.

[0025] In some embodiments, the support magnet (or magnets) is temporarily fixed to the rotor.

[0026] Thus, the lifting magnet (or magnets) can be attached to the rotor only during the ground testing phase. The angular velocity control device is therefore lighter for orbital insertion.

[0027] In some embodiments, the support magnet (or magnets) is in an annular shape.

[0028] 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).

[0029] The invention also relates to a system comprising:

[0030] - an angular velocity control device as described above (according to one any of the aforementioned embodiments); and

[0031] - a test device for the angular velocity control device. The device test 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 in Earth's gravity.

[0032] In some embodiments, the magnetic field source includes a permanent magnet or an electromagnet.

[0033] 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) intended to cooperate with the lifting magnet(s) to induce magnetic lift of the rotor relative to the stator in Earth's gravity. Such a method comprises:

[0034] - a relative adjustment of the control device and the test device, comprising a fine adjustment of the magnetic field generated by the magnetic field source(s) so that the magnetic field cooperates with the lifting magnet(s) of the angular velocity control device to induce magnetic lift of the rotor relative to the stator;

[0035] - a functional test of the adjusted control device.

[0036] In some embodiments, the magnetic field source includes an electromagnet. The method includes at least one activation of the electromagnet to generate the magnetic field.

[0037] 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).

[0038] In certain embodiments, the spacecraft further comprises 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.

[0039] In certain embodiments, each angular velocity control device is arranged so that the rotor's rotation axis forms an angle less than or equal to 45° with an axis of greatest inertia of the spacecraft, such that the out-of-service spacecraft tends towards a rotational movement about this axis of greatest inertia.

[0040] A first advantage of the invention is that it allows the angular velocity of the satellite to be captured to be reduced prior to its capture, thereby facilitating the capture process. The present invention thus makes it possible to prevent a defunct satellite from having a high angular velocity, either due to a fatal failure that caused the mission to be interrupted, 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 long periods.

[0041] A second advantage of the invention is to allow the testing of the angular velocity control device on the ground, while simulating weightlessness via the cooperation of the levitating magnet(s) with the magnetic field generated by an external source. exterior. List of figures

[0042] Other objects, features and advantages of the invention will become more apparent upon reading the following description, given by way of simple illustrative, and not limiting, example, in relation to the figures, among which:

[0043] [Fig-1] represents an angular velocity control device for a spacecraft according to an example of an embodiment of the invention;

[0044] [Fig.2] represents an angular velocity control device for a spacecraft according to another example of the realization of the invention;

[0045] [Fig.3a] represents a configuration of the braking magnets of a spacecraft angular velocity control device according to an example of an embodiment of the invention;

[0046] [Fig.3b] represents a configuration of the braking magnets of a spacecraft angular velocity control device according to another embodiment of the invention;

[0047] [Fig.4] represents a detailed view of an axial part of a control device angular velocity of a spacecraft and a test device for the control device according to an example of an embodiment of the invention;

[0048] [Fig.5] represents the steps of a ground test procedure for an angular velocity control device of a spacecraft according to an example of an embodiment of the invention;

[0049] [Fig.6] represents a simplified model of a spacecraft angular velocity control device allowing the prediction of the spacecraft's derotation time constant;

[0050] [Fig.7] represents a spacecraft equipped with two speed control devices angular according to an example of an embodiment of the invention.

[0051] Detailed description of embodiments of the invention

[0052] 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 movable about an axis of rotation relative to the stator. The stator is intended to be driven by the spacecraft to be stabilized, and 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 (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 orientation magnets. dedicated.

[0053] 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 and thereby dissipates the rotational kinetic energy, tending to stop the spacecraft's rotation relative to the Earth's magnetic field. The spacecraft's rotational speed is thus controlled.

[0054] Furthermore, the rotor includes one (or more) lifting magnet(s) designed to cooperate 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 in a region influenced by the magnetic field generated by the magnet(s). Thus, the angular velocity control device can be easily tested on the ground, the presence of the magnet(s) allowing weightlessness to be simulated.

[0055] We now present, in relation to [Fig.1], a device 1 for controlling the angular velocity of a spacecraft 2 according to an example of an embodiment of the invention.

[0056] As described further below in relation to [Fig. 7], the 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.

[0057] Returning to [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.

[0058] 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.

[0059] This gives rise to 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.

[0060] The body 6 of the stator 3 is electrically conductive and non-ferromagnetic so as not to become magnetized over time. The body 6 is, for example, made of aluminum or copper.

[0061] Furthermore, according to the embodiment shown in [Fig. 1], the magnetic system 7 comprises, on the one hand, braking magnets 18 and, on the other hand, magnets 19 orientation. 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).

[0062] We now present, in relation to [Fig.2] an angular velocity control device 1 according to another embodiment of the invention.

[0063] According to the embodiment example in [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.

[0064] More particularly, 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.

[0065] 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.

[0066] We now present, in relation to [Fig.3a] a configuration of the braking magnets 18 according to an example of an embodiment of the invention.

[0067] More particularly, 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.

[0068] In such a radial configuration, the radius of the trajectory of the induced eddy currents is maximized in the body 6. The energy dissipation is thus also maximized.

[0069] 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 [Fig.2].

[0070] 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).

[0071] Furthermore, the stator housing 3 can be made of any material, for example plastic, with simply a track 6 made of a non-ferromagnetic material (e.g., aluminum or copper) forming a recess or arranged in a recess made in the stator 3, opposite the magnets 18. This recess extends, for example, around the stator with a U-shaped profile. The stator includes, for example, a cylindrical ring coming to this accommodation.

[0072] We now present, in relation to [Fig.3b] a configuration of the braking magnets 18 according to another embodiment of the invention.

[0073] 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.

[0074] Thus, the magnetic field of the braking magnets 18 passes through the plane P20 to induce eddy currents in at least two areas of the stator body 6 3 located opposite each other on either side of the aforementioned plane P20. The eddy currents thus induced are potentially doubled compared to a radial configuration of the braking magnets 18 as described above in relation to [Fig. 3a]. However, in the normal configuration of the braking magnets 18 in [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 therefore necessary, for example, orienting magnets 19 as described above in relation to [Fig. 1].

[0075] 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 [Fig. 3a]. This results in a mixed configuration with some braking magnets 18 in a normal configuration and some braking magnets 18 in a radial configuration.

[0076] 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. Moreover, 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).

[0077] We now present, in relation to [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.

[0078] In practice, the rotor 4 must be adjusted to the stator 3 with sufficient precision so that the braking magnets 18 typically move less than 1 mm from the body 6 of the stator 3 without ever touching. Furthermore, the adjustment means of the The interaction between rotor 4 and stator 3 must induce as little friction as possible, so that rotor 4 is always free to rotate. Preferably, the friction should be less than a fraction of the magnetic torque driving rotor 4. To this end, rotor 4 is guided in two corresponding housings 10a, 10b of stator 3 via a sphere-to-plane mechanical contact. For this purpose, each of the two housings 10a, 10b includes, for example, a closed plain bearing, opposite rotor 4, with a flat end-of-stroke partition arranged transversely to the bearing. Two spherical heads 9a, 9b, integrated into rotor 4 and centered around the axis of rotation A21, are configured to cooperate with the two housings 10a, 10b. With this pivoting technology, the resistive torque obtained during the rotation of rotor 4 relative to stator 3 is very low, particularly in orbital conditions (i.e., in the absence of perceived gravity).

[0079] However, in order to carry out the ground tests, additional means are implemented to recreate the operational conditions of the angular velocity control device 1 in orbit.

[0080] More 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.

[0081] More specifically, the external source to the angular velocity control device 1 is provided here by the test device 20. Such a test device 20 comprises one (or more) magnetic field source(s) 21 intended to cooperate with the lifting magnet(s) 11 to induce magnetic lift of the rotor 4 relative to the stator 3 in Earth's gravity. For example, the magnetic field source(s) 21 comprises a permanent magnet or an electromagnet.

[0082] However, in order that the presence of the levitation magnet (or magnets) 11 within the angular velocity control device 1 does not interfere in orbit with the pivoting technology described above, 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 (or magnets). Thus, the levitation magnet (or magnets) 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.

[0083] According to the present embodiment, the levitation magnet (or magnets) 11 It comprises a south pole 11S and a north pole 1IN arranged along the rotation axis A21 (e.g., the magnetic moment of the support magnet(s) 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.

[0084] According to some implementations, the lifting magnet (or magnets) 11 is permanently fixed to the rotor 4.

[0085] 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.

[0086] The remanence of the lifting magnet (or magnets) 11 is chosen according to 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, according to the weight of the rotor 4 and according to the magnetic field source 21. For example, it is preferable to minimize the horizontal gradient so as not to generate a lateral force (i.e., perpendicular to the axis of rotation A21 during the test).

[0087] Thus, according to certain 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 about the axis A21 of rotation. 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 A21 of rotation. This makes it possible, for example, to avoid biasing the ground test of the angular velocity control device 1 by adding a lateral force on the rotor with respect to the axis A21 of rotation.

[0088] 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.

[0089] For example, the choice of the characteristics of the magnet(s) 11 supporting 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.

[0090] The steps of a test procedure are now presented in relation to [Fig. 5]. ground of the angular velocity control device 1 according to an example of an embodiment of the invention.

[0091] More particularly, such a test method implements a test device 20 as described above (according to any one of the embodiments described above).

[0092] 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.

[0093] 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 levitation 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 makes it possible to optimize the value of the magnetic field generated by the source 21 of the test device 20 as perceived by the levitation magnet(s) 11 of the angular velocity control device 1.Alternatively, when the magnetic field source 21 includes an electromagnet, step E500 includes, for example, step E500a of switching on the electromagnet to generate the magnetic field, and then, if necessary, 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.

[0094] 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, makes it possible to test the functionality of the angular velocity control device 1 under conditions simulating weightlessness.

[0095] A simplified model of the angular velocity control device 1 is now presented in relation to [Fig.6] according to an example of an embodiment of the invention.

[0096] More particularly, such a model makes it possible to estimate the derotation time constant of a spacecraft to which an angular velocity control device according to the present technique would be attached.

[0097] As a simplifying assumption, a braking magnet 18 is considered here 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 rotor 4

[0098]

[0099]

[0100]

[0101]

[0102]

[0103]

[0104]

[0105]

[0106]

[0107]

[0108] cylindrical of infinite length along its axis (y-axis) and of radius R. The braking magnet 18 moves at an assumed infinitesimal distance ê (= air gap) from a cylindrical metal casing, also of infinite length along the axis of the cylinder, modeling the stator 3. 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 at its surface approaches the asymptotic value, characterized by the remanence, Br, of the material: [Math.l] Br B = -2 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: [Math.2] dB VXE = ——-dt reduces to a single differential equation: [Math.3] dEv dB, dBz dx dt dx with R the radius of the cylinder and as the angular velocity of rotation of the cylinder around its axis. Since the electric and magnetic fields are negligible at infinity, integrating equation [Math.3] along x is straightforward. It follows that the axial electric field is proportional to the radial magnetic field according to the following relationship: [Math.4] Br Ey = -B ■ Rû) ■ Rœ The electrical power P dissipated per unit volume V of the stator housing 3 (considering a material of resistivity P) for a single magnet 18 is then: [Math.5] dP 1 ., B? „ ^^-E^ -E- dV p 5 4p In order to obtain the total electrical power P dissipated, the previous relation must be integrated over the volume where the phenomenon occurs, assumed to be exaxb (where e is the thickness of the stator housing 3, a is the width of the magnet in the tan- direction gentielle, b is the actual and finite length of the magnet along y). We thus obtain:

[0109] [Math.6] ^2 P = ~~ • eab • R2a)2 4p

[0110] When considering a rotor 4 with n braking magnets 18, 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 be stabilized and the rotor remains oriented according to the Earth's magnetic field, the total electrical power P dissipated actually corresponds to a loss of kinetic energy of the satellite ε” = feA with the inertia of the spacecraft 2 to be stabilized around the axis of the cylinder. We thus obtain: [YES] [Math.7] B2, 2. nP ~ / mm =--neab • R m" 4p

[0112] From the previous relation, we can deduce a time constant T for the exponential decay of the angular velocity:

[0113] [Math. 8] m 4pl T = — = -------- m B2 R2 • neab

[0114] By way of example, a time constant T of 28 days is obtained for the following values ​​of the parameters of equation [Math.8]:

[0115] - Number of magnets 18, n: 8;

[0116] - width of a magnet 18 in the tangential direction, a: 3 mm;

[0117] - actual length of the magnet along y, b: 15 mm;

[0118] - thickness of stator housing 3, e: 1 mm;

[0119] - resistivity of the material, P: 2.7x10 8S7.m;

[0120] - radius of rotor 4, R: 2.5 cm;

[0121] - remanence of a magnet, Br: 1 T; and

[0122] - inertia of the spacecraft 2 to be stabilized around the axis of the cylinder, 1: 5000 kg.m2.

[0123] We now present, in relation to [Fig.7] a spacecraft 2 equipped with two angular velocity control devices 1 according to an example of an embodiment of the invention.

[0124] 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.

[0125] According to the present embodiment, two angular velocity control devices 1 are implemented in the spacecraft 2 to stabilize it 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, a deactivated 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 rotational axis A21 is strictly perpendicular to the principal axis of maximum inertia, residual angular rotation rates can be expected.

[0126] 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.

[0127] However, in other embodiments, the spacecraft 2 is equipped with only one angular velocity control device 1.

[0128] In some embodiments, the rotation axis A21 of the rotor 4 of the angular velocity control device(s) 1 forms an angle of less than or equal to 45° with the axis of greatest inertia of the spacecraft 2 (axis denoted “ “ in [Fig. 7]), such that the out-of-service spacecraft 2 tends towards a rotational movement around its 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 "fiat spin" in Anglo-Saxon terminology). Thus, an arrangement in which the rotational axis(es) A21 of the rotor(s) 4 of the angular velocity control device(s) 1 form an angle of 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.

[0129] The active spacecraft 2 further comprises 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.

[0130] In this way, 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

Demands

1. A device (1) for controlling the angular velocity of a decommissioned spacecraft (2) to facilitate the active removal of the spacecraft as space debris, comprising a stator (3) and a rotor (4) movable about an axis (A21) of rotation relative 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 itself 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), braking eddy currents of a relative motion 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 lifting magnet (11) intended to cooperate with a magnetic field generated by a source external to said device 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, and in that the angular velocity control device (1) is made of one or more non-ferromagnetic materials at least in a zone (11ZI) of influence of the magnetic field generated by said lifting magnet.

2. Angular velocity control device (1) according to claim 1, wherein said levitation magnet comprises a south pole (11S) and a north pole (UN) arranged along the axis (A21) of rotation.

3. Angular speed 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 sphere against plane type.

4. Angular speed control device (1) according to claim 3, wherein said two housings (10a, 10b) each comprise a closed plain bearing, opposite the rotor, by a flat end-of-stroke 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 levitation magnet is fixed permanently attached to the rotor.

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

7. Angular velocity control device according to any one of claims 1 to 6, wherein the levitating magnet is in annular form.

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 lift magnet to induce magnetic lift of the rotor (4) relative to the stator (3) in Earth's gravity.

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

10. A method for ground testing 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 lift magnet to induce magnetic lift of the rotor (4) relative to the stator (3) in terrestrial gravity, characterized in that it comprises: - a relative adjustment (E500) of the control device (1) and the test device, comprising a fine adjustment (E500b) of the magnetic field generated by said magnetic field source so that the magnetic field cooperates with said lift magnet of the angular velocity control device (1) to induce said magnetic lift of the rotor (4) relative to the stator (3); - a functional test (E510) of the adjusted control device (1).

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

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

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

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 greatest inertia of the spacecraft, such that the out-of-service spacecraft tends towards a rotational motion about this axis of greatest inertia.

Images