SPACECRAFT WITH AN ELECTRICAL DEVICE AND ALIGNMENT SYSTEM FOR THE ELECTRICAL DEVICE

Description

Technical field

[0001] The present invention relates to space systems and in particular to the arrangement of electrically powered devices such as ion engines on spacecraft. State of the art

[0002] In the space sector, some electrical devices, such as ion engines, require the use of large diameter electrical cables that can withstand high amperage and / or high voltage. It may be necessary to be able to orient certain electrical devices, particularly ion engines, to adjust the direction of their propulsion force.

[0003] A constraint in the space sector is that the constituent parts of a spacecraft must be able to withstand strong accelerations and vibrations that may occur during launch or release phases. In addition, in the space sector, the relative movements of the constituent parts of a spacecraft must generally allow repeatability over a period of several years, without it being possible to carry out maintenance operations. Space systems must therefore have a high level of reliability and robustness.

[0004] We know of document US 6,025,815 entitled “ drive unit for adjusting satellite components requiring orientation » which teaches an orientation system using linear actuators arranged in parallel and connecting rods.

[0005] US 2016 / 200456 and AT512487 disclose other orientation systems. Document US 2016 / 200456 discloses, according to the abstract, a chassis, a movable part and two rotation axes having a point of intersection. Presentation of the invention

[0006] The present invention aims to provide a spacecraft equipped with an electrical device, such as an ion engine, the orientation of which is adjusted by means of an improved orientation system.

[0007] To do this, the invention provides a spacecraft according to claim 1.

[0008] The invention therefore proposes a spacecraft equipped with an orientation system whose architecture combines two (or more) rotary motors, mounted in series via a junction piece, and at least one guide fork external to the junction piece.

[0009] The guidance of the electrical cables of the device to be oriented by the guide fork(s) makes it possible to keep the cables of the electrical device in a restricted space (the guide path), in order to prevent them from coming into contact with other equipment of the spacecraft arranged nearby. This confinement (keeping in a restricted space) of the cables is particularly useful during the launch and release phases of the spacecraft, during which the cables of the electrical device are subjected to strong vibrations which can go so far as to cause a cable to break or damage the surrounding equipment. This arrangement of the cables according to the invention makes the system resistant to significant vibrations and thrust forces.

[0010] Due to their stiffness (particularly in the case of large diameter cables), the cables exert resistive torques on the rotary actuators. While it is useful during the launch and release phases, the confinement of the cables could, on the contrary, be considered negative during operating phases (when the actuators are activated) in that it risks amplifying the torques exerted by the cables on the rotary actuators. The use of guide forks according to the invention makes it possible to overcome this drawback on the one hand by supporting the cables, by controlling their position and their curvature, and on the other hand by limiting the stresses and in particular the friction forces undergone by the cables or the torques exerted by the cables. In addition, since the cables extend outside the junction piece, the stresses they undergo are limited; the same therefore applies to the stresses that these cables impose on the actuators.

[0011] The use of one or more guide forks according to the invention thus makes it possible to maintain reduced resistive torques exerted by the cables on the rotary actuators. The power required for the rotary actuators is thus optimized. This results in significant weight savings and energy savings. In addition, a high level of reliability and robustness of the system is obtained, so that many repetitive movements can be performed without maintenance operations.

[0012] Another advantage of the invention is that the orientation system allows the direction of the axes of the electrical device to be varied at will and the device to be placed in any desired position. It allows the device to be rotated around two axes of rotation over significant angles, for example + / - 25° (relative to an initial position serving as a reference), and even up to 180° in both directions, the maximum angular amplitude not being limited by the architecture of the orientation system.

[0013] The orientation system according to the invention also makes it possible to resolve possible problems of conflicts between the electrical cables of the electrical device and the equipment located nearby and / or to free up spaces for the installation of other equipment, by limiting the volume in which said cables can move.

[0014] According to a possible characteristic of the invention, the guide fork(s) each comprise a fixing branch fixed to the junction piece by a first end; furthermore, the fingers are in the form of rods, which are secured, via one of their ends, to the second end of said fixing branch.

[0015] According to a possible characteristic of the invention, the electrical cables are free to slide relative to the fingers of each guide fork. In particular, no holding member limiting the movement of the cables in the longitudinal direction of said fingers is provided. Similarly, the cables are advantageously left free to slide relative to the fingers through the fork, in the direction of routing of said cables. This characteristic makes it possible to minimize the resistive torques exerted by the cables on the rotary actuators.

[0016] According to a possible characteristic of the invention, for one or each of the guide forks, the fingers of said guide fork are rectilinear and parallel to each other. On the other hand, the fingers of the guide forks may not be parallel from one fork to another. For example, the fingers of a first fork all extend in a first direction while the fingers of a second fork all extend in a second direction.

[0017] According to a possible characteristic of the invention, for one or each of the guide forks, the fingers of said guide fork are coplanar. Preferably, the fixing branch of the guide fork also extends in the same plane as the fingers. All the fingers of the fork are for example in a transverse plane which is orthogonal to the axial direction of the junction piece at the point where the plane of the fork intersects the junction piece, that is to say at the level of the first end of the fixing branch of the guide fork. Note that the axial direction of the junction piece may not be rectilinear: it may for example follow a curve which starts from the axis of rotation of one of the actuators while being tangent to this axis, and joins the axis of rotation of the other actuator, tangentially to it.

[0018] According to a possible characteristic of the invention, for each of the guide forks, the fingers of said guide fork protrude relative to the cables so as to prevent said cables from leaving their guide path. In other words, if we consider the assembly formed by the cables received between two consecutive fingers of a fork and we call "width" the dimension that this assembly of cables has in the longitudinal direction of the fingers of the fork, the length of the fingers is greater than the width of the assembly of cables, with a sufficient margin so that, whatever the positions of the rotary actuators, all the cables remain positioned between the fingers of the fork even if the cables are left free to slide relative to the fingers.

[0019] According to the invention, the axes of rotation of the rotary actuators are sequential; they intersect at a point called the center of intersection. This architecture has the advantage of compactness.

[0020] According to the invention, at least one or each of the guide forks has a main axis which passes through the center of intersection of the axes of rotation of the rotary actuators. In use, under the effect of the rotation of the actuators activated to adjust the position of the electrical device, the electrical cables of the device which extend between the frame and said device are displaced; as the actuators rotate, the amplitude of displacement of the cables describes a sort of wave. The arrangement of the fork(s) so that their main axis passes through the center of intersection of the axes of rotation of the actuators makes it possible to minimize the height of this wave. In addition, such an arrangement makes it possible to minimize the movements of the cables transversely to the fingers.

[0021] According to a possible characteristic of the invention, the guide fork(s) are configured to receive at least two superimposed layers of electrical cables, the cables in each of the layers being arranged side by side. Preferably, when the cables are thus organized into two superimposed layers, at least one—or preferably each—of the forks comprises three fingers, delimiting two intervals, each interval receiving one of the two layers of cables. It is not excluded to provide, as a variant, that one (or possibly several) of the forks comprises only two fingers, that is to say a single interval receiving the two layers placed one on top of the other.The embodiment using three-finger forks is however preferred because the separation of the two plies into two distinct intervals eliminates friction between the plies in favor of friction between each ply and the fingers surrounding it, which friction between the plies and the fingers is easier to control (and therefore to minimize).

[0022] According to a possible characteristic of the invention, in an embodiment which comprises several guide forks, these are regularly along the axial direction of the cables, so as to have, for each cable, cable sections of substantially the same length between two support points.

[0023] This allows the weight of the cables to be better distributed over the junction piece and therefore optimizes its design and sizing.

[0024] More particularly, if the system comprises only one fork, it is desirable that said fork be located substantially in the middle of the cables, that is to say on average substantially equidistant from the two ends of the cables (of course, depending on the positions of the actuators, the middle of the cables may pass on one side or the other of the fork, which is why we speak of "average").

[0025] If the system comprises three or more forks, again, the forks may be arranged so as to be regularly distributed along the entire length of the cables. Alternatively, it may be preferred that the forks be regularly distributed along the junction piece, regardless of the distances existing on the one hand between the electrical device and the junction piece and on the other hand between the frame and the junction piece. In this variant, for the same given cable, the cable sections located between two forks will have similar lengths, but there may be, on the side of the electrical device or on the side of the frame, a first cable section possibly larger or smaller than the cable sections between two forks.

[0026] Typically, each rotary actuator comprises a rotor and a stator, and each actuator has a power and control harness connected to its stator. According to a possible feature of the invention, the junction piece is fixed on the one hand to the stator of the actuator which is connected to the electrical device (the rotor of this actuator being connected to the electrical device) and on the other hand to the rotor of the rotary actuator which is connected to the frame of the spacecraft (this actuator being consequently connected to the frame by its stator). This feature advantageously makes it possible to optimize the positions of the actuators relative to their power harness. Indeed, the rotation of the actuator which is connected to the frame does not cause any force on the power and control harness of said actuator since this harness extends between the frame and the stator of the actuator and said stator is directly fixed to the frame (the harness therefore extends between two fixed parts).The actuator power and control harness that is connected to the electrical device extends between the spacecraft frame and the stator of said actuator. Choosing to connect the actuator stator to the junction piece (and the actuator rotor to the electrical device) makes it possible to limit the path traveled and the forces exerted by the harness on the actuator that is arranged between the electrical device and the junction piece.

[0027] It is of course possible to arrange the rotary actuators differently, i.e. for example to fix each of the two actuators to the junction piece by its stator, or vice versa by its rotor.

[0028] In one possible version of the invention, the electrical device to be oriented (relative to the spacecraft frame) is an ion engine. Brief description of the figures:

[0029] The invention, according to an exemplary embodiment, will be well understood and its advantages will appear better on reading the detailed description which follows, given for information purposes and in no way limiting, with reference to the appended drawings, in which: [ Fig. 1 ] There figure 1 is a schematic perspective view of a first embodiment of an orientation system according to the invention. Fig.2 ] There figure 2 is a schematic side view of a second embodiment of an orientation system according to the invention. Fig.3 ] There figure 3 is a schematic top view of the second embodiment of the figure 2 .

[0030] Identical elements shown in the above figures are identified by identical reference numerals. Detailed description:

[0031] There figure 1schematically represents a spacecraft 100 according to the invention, comprising a mobile ion engine 1 and an orientation system making it possible to orient said ion engine along two axes Δa and Δb relative to a frame 4 of the spacecraft 100. The ion engine may be, for example, a grid ion engine or a Hall effect thruster.

[0032] The orientation system could also be applied to another electrical device installed on the spacecraft, such as a solar panel or an antenna.

[0033] The orientation system comprises two rotary actuators 2a and 2b and a junction piece 5 which, in the embodiment of the figure 1, has a beveled sleeve shape. Each rotary actuator comprises a rotor and a stator. The junction piece 5 has two interfaces for its connection to the rotary actuators 2a, 2b, in this case two openings each equipped with a peripheral rim 50a, 50b, which may be circular as illustrated in the fig.1 . The opening 50a rigidly receives the stator of the rotary actuator 2a, while the opening 50b rigidly receives the rotor of the rotary actuator 2b. Each rotor or stator of a rotary actuator is for example fixed on the peripheral rim of the opening with which it is associated.

[0034] Furthermore, the stator of the rotary actuator 2a is rigidly connected to the ion engine 1, while the stator of the rotary actuator 2b is rigidly connected to the frame 4 of the spacecraft. The ion engine 1 can thus be oriented, relative to the frame of the spacecraft, around two axes of rotation Δa and Δb according to angular deflections 3a and 3b.

[0035] Rotary actuator motors can be, for example, DC motors, AC motors, stepper motors, brushed or brushless motors. The two motors can be of the same type (e.g., two brushless motors) or different types (e.g., one brushed motor and one brushless motor).

[0036] The connecting piece 5 comprises for example a cylindrical portion, the axis of which coincides with the axis of rotation Δa of the rotary actuator 2a. The cylindrical portion 5a is truncated at a bevel on one side and normally to its axis on the other side. The end truncated normally to the axis has a circular section forming the opening 50a which receives the stator of the rotary actuator 2a.

[0037] The junction piece 5 comprises a second planar portion 5b, which extends in the extension of the beveled end of the cylindrical portion 5a. This second planar portion 5b is orthogonal to the axis of rotation Δb of the other rotary actuator 2b. This second planar portion 5b may be parallel to the axis of the truncated cylindrical portion 5a, in which case the axes of rotation Δa and Δb of the actuators are orthogonal. A circular cutout is provided in the planar portion 5b to form the opening 50b which receives the rotor of the rotary actuator 2b.

[0038] In the connecting piece 5, the circular openings receiving the rotors or stators are for example arranged with their central axis arranged respectively in two transverse directions relative to each other. In the illustrated example, the axes of rotation Δa and Δb of the rotary actuators are perpendicular (i.e. orthogonal and coplanar). They could, alternatively, only be sequential with any angle (i.e. coplanar without necessarily being perpendicular). These axes could also be orthogonal without being coplanar (and therefore not sequential).

[0039] According to the invention, one or more guide forks are also associated with the connecting piece 5. The figure 1 illustrates an embodiment comprising only one fork 6, while the figures 2 And 3represent an embodiment comprising two forks 6a, 6b. Except for the number of forks used, the principles set out remain the same for these two embodiments. For reasons of clarity, the cables have not been shown in the figure 1 , while the actuators and the ion engine were not represented in the figures 2 And 3 .

[0040] As shown in the figure 1 , the fork 6 may comprise three rectilinear fingers 9a, 9b, 9c, coplanar and parallel to each other, carried by a central fixing branch 15.

[0041] The fixing branch 15 has a first end which is fixed to the junction piece 5. Said fixing branch 15 is for example arranged along an axis 17 (which corresponds to the main axis of the fork) passing through the center of intersection 16 of the axes of rotation Δa, Δb of the actuators 2a and 2b. The movements of the cables are then advantageously minimized on either side of this fork.

[0042] The three fingers 9a-9c are connected, by one of their ends, to the second end of the fixing branch 15 by means of a common transverse branch 18.

[0043] Alternatively, one could consider a two-finger fork or a four-finger fork or more.

[0044] The fingers of the fork are intended to receive electrical power and control cables for the ion engine 1, generally organized in the form of layers. For example, here we choose to maintain a single layer in each interval delimited by two consecutive fingers. The three-finger fork 9a-9c then allows the maintenance of two layers of cables; a two-finger fork allows the maintenance of one layer of cables, a fork with N fingers allowing the maintenance of N-1 layers of cables.

[0045] For example, the fingers are straight; alternatively, they could be curved. Whether they are straight or curved, the fingers of the same fork can be parallel to each other, or not.

[0046] The fork may have a generally planar shape extending transversely to the cables, that is to say that the fingers 9a, 9b, 9c and the fixing branch 15 are coplanar (as in the illustrated examples) and that the plane of the fork is crossed by the cables. Alternatively, it is possible to have coplanar fingers carried by a fixing branch which is inclined relative to the plane of the fingers, in particular for reasons of ease of construction. In addition, the fingers of the same fork may not be coplanar.

[0047] The fingers may be of circular cross-section. Alternatively, the fingers may be of polygonal cross-section. The fingers may include flat cable-supporting portions. The fingers do not necessarily have a constant cross-section along their entire length.

[0048] The cables are held between two consecutive fingers, that is, two fingers facing each other.

[0049] The cables held in the fork remain free to move in a transverse direction relative to the fingers, on either side of the fork, and in a longitudinal direction relative to the fingers.

[0050] As illustrated (see Fig. 2 And Fig. 3 ), the fingers 9a-9c preferably extend outwardly from the cable web, which makes it possible, for example, to hold the cables when they move longitudinally relative to the fingers. The freedom of movement transversely to the fingers, on either side of the fork, makes it possible to adjust the lengths between the cable support points.

[0051] Cables could also be considered to be held between the fingers of the fork(s) with restricted degrees of freedom. The torque exerted by the cables on each rotary actuator 2a, 2b remains lower than the torque capacity of the actuator in all circumstances, the torque capacity of an actuator being the maximum reaction torque that the actuator can withstand in operation.

[0052] The positioning of the fork(s) is carried out in such a way as to impose one or more bends on the cables. Increasing the number of forks thus increases the bends and the forces and torques exerted by the cables on the rotary actuators, while remaining within controlled and acceptable limits, i.e. while remaining lower than the torque capacity of each of the rotary actuators.

[0053] The number of forks will be chosen advantageously to optimize the spatial layout of the area reserved for the passage of the cables according to the available power of the actuators. The fork(s) allow the arrangement of the cables in a limited spatial area and thus make the orientation system resistant to vibrations or thrust forces.

[0054] There figure 2 represents, in a side view, layers 8a and 8b of electric cables held by two forks according to the invention. Each fork 6a or 6b comprises three fingers 9a-9c, 10a-10c respectively, and receives two superimposed layers 8a and 8b. The cables 7a, 7b, 7c, 7d and 7e in the same layer 8a are arranged side by side. The actuators are not shown; the junction piece 5 between the actuators, on which the guide forks 6a and 6b are fixed, appears very schematically and is only partially visible on the figure 3; it can be observed that it does not necessarily have the same shape as the junction piece of the first embodiment of the figure 1 .

[0055] Each cable 7a or 7f is fixed at its two ends 11a and 11b or 12a and 12b respectively to the frame 4 and to the electrical device 1 to be powered. As explained previously, the cables referenced 7a, 7f, can for example slide relative to the fingers 9a-9c, 10a-10c of the forks 6a and 6b. The cable will be able to slide relative to a fork in particular when the support point of the cable on the fork is not arranged on the axis of rotation resulting from the movement of the actuators. The length of the fingers makes it possible to hold the cable in the forks.

[0056] Controlling the cable positions and their curvatures thus makes it possible to control the torques exerted by these cables on the rotary actuators due to their stiffness, and in particular allows for a high level of reliability and robustness of the system. Thus, the rotating actuators are stressed within their operating range. Many repetitive movements can therefore be carried out without maintenance operations.

[0057] Furthermore, whatever the position of the actuator(s), the cables are kept within a determined guidance volume, the other constituent elements of the spacecraft being able to be safely arranged outside this guidance volume.

[0058] There figure 3 represents, in top view, the layers of electric cables held by two forks according to the arrangement of the figure 2The fingers of each fork are parallel to each other and protrude beyond the external cable 7e, 7f of each layer, so as to prevent the cables from leaving their guide path, in the event of movement of the cables relative to the fingers.

[0059] The forks 6a and 6b are for example regularly distributed so as to have identical cable lengths between two support points. The term "support point" of a cable is understood to mean a point of attachment of the cable, for example at one of its ends, or a point of contact of the cable with a fork. The average length between two consecutive support points of a cable is, preferably, substantially the same along said cable. Of course, this length can vary according to the angular positions of the rotary actuators (hence the notion of average length). The length between two consecutive support points also varies from one cable to another, according to their position in the same layer or from one layer to another. For example, the average length between two support points of the internal cable 7a of the layer is less than the length of the external cable 7e of the layer and the variations in position of the external cable can be greater.

[0060] The arrangement of the forks can be optimized in many different ways, particularly depending on the constraints of each mission. The orientation system according to the invention is thus particularly adaptable to different space missions, for the orientation of one or more ion engines or other electrical devices to be powered.

Claims

1. A spacecraft (100) comprising - a frame (4), - an electrical device (1), - electrical cables (7a-7f) for powering and / or controlling said electrical device, - at least two rotary actuators (2a, 2b) for orienting the electrical device (1) about two non-parallel axes of rotation (Δa, Δb), - a junction member (5) between the two rotary actuators, one of the rotary actuators (2a) being connected on the one hand to the electrical device (1) and on the other hand to the junction member (5), the other rotary actuator (2b) being connected on the one hand to the junction member (5) and on the other hand to the frame (4), and - one or more guide forks (6, 6a, 6b), arranged outside the junction member, each of said guide forks being fastened to the junction member (5) and comprising fingers (9a, 9b, 9c; 10a, 10b, 10c) configured to support the electrical cables (7a-7f) and delimit between the fingers a guide path for said electrical cables (7a-7f), wherein each guide fork (6, 6a, 6b) is arranged so that, irrespective of the positions of the rotary actuators (2a, 2b), the electrical cables (7a-7f) exert, on each of the rotary actuators (2a, 2b), a torque that is lower than a torque capacity of the rotary actuator, wherein the axes of rotation (Δa, Δb) of the rotary actuators (2a, 2b) are secant at an intersection center (16) and at least one of the guide forks (6, 6a, 6b) has a main axis that passes through said intersection center (16).

2. The spacecraft according to claim 1, wherein each of the guide fork(s) (6, 6a, 6b) comprises a fastening branch (15) fastened to the junction member by a first end, the fingers (9a, 9b, 9c; 10a, 10b, 10c) being in the form of rods secured, via one of their ends, to the second end of the fastening branch (15).

3. The spacecraft according to claim 1, wherein the electrical cables (7a-7f) are free to slide relative to the fingers (9a, 9b, 9c; 10a, 10b, 10c) of each guide fork (6, 6a, 6b).

4. The spacecraft according to one of claims 1 or 2, wherein, for each guide fork (6, 6a, 6b), the fingers (9a, 9b, 9c; 10a, 10b, 10c) of said guide fork are rectilinear and parallel to each other.

5. The spacecraft according to one of claims 1 to 3, wherein, for each guide fork (6, 6a, 6b), the fingers (9a, 9b, 9c; 10a, 10b, 10c) of said guide fork protrude with respect to the cables (7a-7f) so as to prevent said cables from getting out of their guide path.

6. The spacecraft according to one of claims 1 to 5, wherein at least one of the guide forks (6a, 6b) comprises three fingers delimiting two intervals for receiving at least two superposed plies (8a, 8b) of electrical cables (7a-7f), the cables in each of the plies (8a, 8b) being arranged side-by-side.

7. The spacecraft according to one of claims 1 to 6, wherein the guide forks (6a, 6b) are evenly distributed along an axial direction of the cables so as to have, for each cable, cable sections having substantially the same length between two support points.

8. The spacecraft according to one of claims 1 to 7, wherein each rotary actuator comprises a rotor and a stator and wherein the junction member (5) is fastened on the one hand to the stator of the actuator (2a) which is connected to the electrical device (1) and on the other hand to the rotor of the rotary actuator (2b) which is connected to the frame (4) of the spacecraft.

9. The spacecraft (100) according to one of claims 1 to 8, wherein the electrical device (1) is an ion engine.