FR2502404A1 - Articulated mounting for satellite sub-assembly - uses output from inertial detector to control step or torque motor to move support arm for stabilisation - Google Patents

Abstract

A sub-assembly (10e) is moved through small angles by a step or torque motor (29) located between the bracket support on a platform (12e) on a satellite. The motor rotates an arm (16e) about an axis (18e). The arm is coupled to the sub-assembly by pivot points (30). The motor is driven from an electronic control unit which receives inputs from an inertial detector system or where the sub-assembly is an antenna then the radio frequency signal is used. Motor assemblies in the other planes allow the sub-assembly to be positioned with two or three degrees of freedom. A passive damping element attenuates the vibration of the sub-assembly and provides a return force to return the sub-assembly to a natural balance condition.

Description

Articulated mounting device, in particular a subassembly of artificial satellite
The present invention relates to the hinged mounting devices of a subassembly for rotating the subset of small angles, which is not more than 100 times more particularly useful in the satellite field where it is frequently used. necessary to orient subsets to correct their position or to ensure energy absorption.

Among the functions that require such rotations include the following
on an attitude-controlled satellite, of the type stabilized along three axes or with permanent relative rotation (a type commonly called "Dual Spin"), the independent reorientation of an antenna reflector to maintain the orientation of a beam microwave provided by the antenna to a target, regardless of the movements of the reflector support and the integral horn of the main body of the satellite in a small angular range, or even the overall reorientation of an antenna, including the reflector primary and possibly a secondary reflector and a horn
- in the case of a satellite whose body is in permanent rotation, said "spinned", or of a satellite of the preceding kind, the setting in sinusoidal movement of a clock of frequency tuned on a cyclic movement of the structure for to dissipate the energy associated with this cyclic motion, such as nutation in the case of a spinned satellite or provided with an internal kinetic moment, the vibration in the case of flexible structures.

 We already know such devices. In particular, some have been used to orient antennas or antenna reflectors of telecommunications satellites and to absorb the nutation or vibration energy of a satellite. Mention may be made in particular of double-gimbal mechanisms and rigid or elastic ball-and-socket mechanisms for antenna reorientation devices. Mention may also be made of mechanical pendulums with a pivot, of the type of knife balance flail, as well as pendulums mounted on pivots constituted by crossed flexible blades, pendulums intended for damping devices.

 All these mechanisms have a common characteristic: the articulation axes around which the subsets rotate are real axes, contained in the envelope of the mechanism itself. This results in constraints, different depending on the intended application, but still annoying.

 For example, in the case of reorientation of a subset of satellite 1 this property leads to give the device a large footprint and has an adverse effect on the dimensioning of the displacement actuators of the subset. In the case of a damping function, we find the problems associated with a large footprint and there is added the need for a high pendulum mass to obtain the desired resonance and constraints on the geometric location of the pendulum in the satellite.

 The present invention aims to provide a device that responds better than those previously known to the requirements of the practice, in particular in that it allows for a virtual axis of rotation remote from the device itself.

 For this purpose, a device according to a first aspect of the invention comprises two connecting means each articulated around a fixed axis and an axis connected to the subassembly, all the axes being parallel, means capable of low angular deflections. around a rest position1 the extensions of the segments each connecting a fixed axis and a linked axis defining the virtual axis by their intersection at rest.

 An articulated mounting device of a subassembly around at least one virtual axis, according to a second aspect of the invention, comprises two connecting means each articulated around a fixed axis and an axis connected to the subassembly. said means each having a plurality of successive elements capable of taking a small relative angular displacement about intermediate axes, all the axes being parallel.

 The articulated connection means can rotate around axes of very diverse nature. In particular, these axes of actual articulation can be materialized by flexible pivots, deformable cross-blade pivots, grease bearings or smooth. The connecting means can also be realized by systems using the bending of cables stretched between a fixed support and a plate belonging to the subassembly. By giving the cables a slight longitudinal elasticity, it is possible to maintain the tension of the cables for all the positions of the subassembly in the nominal angular operating range.

 The device will frequently be "active": it will then include a torque or force generator acting either around the axis or virtual axes, or around at least one of the real axes to provide the desired orientation. Means for measuring relative angular orientation around at least one real or virtual axis (or even the virtual center of rotation if the subassembly is linked to its support via two devices allowing cross angular deflections) ) will then generally be provided.

 This angular orientation measurement can be replaced by an absolute linear or angular acceleration measurement and / or absolute speed or angular deviation. In the case of satellites, it is possible, in particular, to use integrating accelerometers or gyrometers and / or means for measuring orientation with respect to a reference external to the satellite, such as a radio frequency source, the terrestrial horizon, the light emission of a star.

 Whatever the measurement carried out, it will generally result in an electrical signal, in analog or digital form, which will then be processed in an electronics controlling the actuators to perform a specific function, such as dissipation of movement energy or precise orientation of the subassembly in a desired direction.

 For some applications, the device will be passive and without actuator. This case will in particular be one where the subassembly is constituted by a dead mass and where the device is provided with elastic return means which give the subassembly a position of natural balance. Among the applications of such a passive device is the damping of the nutation or vibration of a structure. The device will then be given a natural oscillation frequency close to the natural nutation or vibration frequencies to be damped, and the device will be provided with a system for dissipating energy.

 The active devices according to the invention are capable of numerous applications, among which the following can be cited in particular, as simple examples.

 The sub-assembly to be pointed in a limited angular range may be a microwave antenna reflector, in which case the device will generally be made so that the axis or the virtual center of rotation is close to the emitter horn associated with the reflector.

 The sub-assembly to be pointed may also consist of a large antenna of flexible structure: in this case, the axis or the virtual center of rotation of the device will advantageously be close to the center of mass of the satellite carrying the antenna.

The invention will be better understood on reading the following description of devices which constitute particular embodiments thereof, given by way of non-limiting examples. The description refers to the accompanying drawings in which
FIGS. 1 and 2 are diagrams of devices for rotating around an axis,
FIGS. 3 and 4 show possible embodiments of the connection means of the device,
FIGS. 5 and 6 are detailed views of FIG. 3,
FIGS. 7 and 8 show embodiments of motor actuators of the device,
FIGS. 8a and 8b are detailed views showing two variants of the actuator of FIG. 8,
FIG. 9 shows the assembly which can be considered as inverse to that of FIG. 8,
FIGS. 10 and 11 schematically show two actuator assemblies constituted by jacks,
FIGS. 12 to 14 show three embodiments of devices with two axes of rotation,
FIG. 15 schematically shows an actuator that can be used in the devices of FIGS. 12 to 14,
FIG. 16 shows an example of a device with three axes of rotation,
FIG. 17 shows another possible embodiment of a device with three axes,
FIG. 18 is a detailed view of an actuator that can be used in the device of FIG. 17,
FIGS. 19 to 21 show schematically the use of the device on a satellite to drive an antenna,
- Figures 22 to 24 show a temporary locking system of the device and details of this system.

 FIGS. 25 and 26 show a device and associated electronics constituting another variant.

 The principle implemented by the invention is shown schematically in Figure 1 which shows a subassembly 10 to be mounted on a support 12 which is constituted for example by the platform of a satellite. The mounting device shown is intended to allow the angular displacements of the subassembly 10 about an axis of oscillation 14 placed at a distance from the support 12 and the real pivots of the system.

For this purpose, the device comprises two articulated connection means 16 of similar constitution. Each of these means connects the support 12 to a point 17 of the subassembly 10 and is constructed to allow the point 17 to move in a circle whose center is placed on an axis 18 of articulation of the corresponding means on the support 12. The hinge pins 18 are obviously parallel. It can be seen that, for low angles of rotation around the rest position, the movement given to the subset 10 is comparable to a virtual rotation about an axis 14. The assimilation of the displacement to a rotation around the 14 axis is better than the clearance angle a is smaller and the lever arms 18-17 are larger when the direction 18-17 is opposite direction 14-17. it is not necessary, however, that the axes 18 are opposite the axis 14 relative to the subassembly: one can also use hinge pins located on the same side, for example 19 (Figure 1) .

 In general, it will be advantageous to give the articulated connection means 16 a symmetrical arrangement and arrangement, as shown in FIG. 2, where the actual position of the subassembly 10 has been indicated at 10a after a determined change of orientation, in where the position which would result from a rotation about the axis 14a.

 As indicated above, the hinge pins 17 and 18 can be made in a variety of ways, given that the angles of movement <x are always low.

 The embodiment illustrated in FIG. 3 (where the members corresponding to those of FIG. 1 are designated by the same reference number assigned to the index b) differs essentially from the previous one in that the articulated connection means 16b each comprise several axes of true rotation arranged in cascade.

In this case, it is possible to improve the approximation sought, especially since the characteristics of the means make it possible to approach for each of them the condition (in the case of two intermediate axes).

 In the formula above, 1 denotes the distance between the virtual center 14b and the points 17b for fixing the linking means articulated on the subassembly 10b, d is the rest length of the connecting means, 6i and 62 are the rotations around successive axes. As in the previous case, the axes of rotation can be materialized in very different ways.

In particular, it is possible to use known solutions, such as ball bearings, grease bearings, plain bearings without lubricant (or self-lubricating), elastic bearings with crossed blades whose elasticity is limited to a small area around each of the axes of joints. and flexible blades. It is also possible to use flexible blades embedded in the support and fixed to the subassembly so as to be rotatable about it about parallel axes.

The elasticity of the blades tends to return the subassembly to a rest position.

 Still another solution, illustrated in FIG. 4, consists in using, to form the connecting means, flexible cables 22, held in tension between the points 18c and 17c by resilient means such as springs 23. This last solution authorizes no only deflections around two parallel axes, each defined by two points 18c, but also deflections around two axes perpendicular to the previous ones, which globally results in a possibility of displacement of the subset 10c around two perpendicular virtual axes, which can be defined to cut themselves and thus to define a virtual center of rotation.

 Instead of springs 23 each associated with a cable 22, it is possible to use elastic means of any kind, which must simply be mounted so as to keep the cables 22 in permanent tension.

It can especially be a compressed spring between the support and the table.

 Finally, the functions of connection and elastic return can be fulfilled by the same members, for example constituted by elastic rods replacing the cables 22 of FIG. 4.

In practice, the intermediate axis means of the kind shown diagrammatically in FIG. 3 can be produced by means of recessed blades, cut to form elementary strips. FIG. 5 shows, by way of example, a possible constitution of these means which comprise, for each axis 18d, two identical blades 23 and 24. These blades each comprise two lateral parts 25 of width d1, delimited by slots and connected, at their end remote from the recess in the support 12d, to an intermediate strip 26 connecting with a central strip 27. If we designate dl, d2 and d3 the width of the strips 25, 26 and 27, the condition (1) mentioned above is fulfilled in accordance with the conditions
2d1 = d3
d1 = Û d2 / 2
This relation obviously supposes that the blade is homogeneous and of constant thickness. It is moreover clear that the condition (1) could be respected with blades of other nature, not symmetrical. Moreover, it is possible to associate with each axis not two blades 23 and 24, but a single cut blade 28, as illustrated in FIG.

 The devices which have just been described can be realized in passive form or in active form.

If they are passive, they may have either a specific equilibrium position (case of Figures 4, 5 and 6) or an indifferent equilibrium (case of Figure 1). To be active, they must be equipped with actuators which will now be described some types, as non-limiting examples.

Figures 7 and 8 show devices comprising an actuator acting around a real axis of rotation 18e. In the case of FIG. 7, this actuator is constituted by an electric motor, which may notably be a stepper motor or a torque motor, interposed between brackets carried by the support 12e and one of the connecting means 16e. shown as an arm rotatable in bearings 30 attached to subassembly 10e, shown as a tray. Since the angular deflections required around the real axes are very small, we can adopt, for the actuator, a very simple constitution, for example that shown schematically in Figure 8 where the actuator is reduced to a finger 30 carried by the arm 16 and cooperating with a coil 31.A such actuator, whose travel is limited to a small angle, can have the constitution of detail shown in Figure 8a or Figure 8b. In FIG. 8a, the finger 30 terminates in a fork equipped with permanent magnets giving two opposite intensity flows.
B flanking a coil 31 carried by the support 12e. Such an actuator is of the differential type and exerts a force equal to 2 Bilai being the current flowing through the coil 31 and 1 being the width of the magnet.

 In the case illustrated in FIG. 8b, the actuator comprises a core 32 carried by the finger 30 and cooperating with a coil 33 fixed to the support.

 In the embodiment shown in Figure 9, the actuator 34 is mounted to exert a torque tending to rotate the subassembly 10f around the virtual axis 14f. The actuator 34 itself may have a constitution similar to that shown in Figure 8a, the finger 30f being simply fixed on the structure instead of being fixed on the arm 16f. The magnets fork terminating the finger can obviously have a shape adapting to the rotation around the axis 14f rather than a straight form. The coil 31f can of course be fixed to the support 12f in an orientation perpendicular to that indicated in FIG. 9. The coil may then have an outer shape in cylinder portions centered on the virtual axis of rotation of the device.

 The electromagnetic actuators shown in FIGS. 7 to 9 may be replaced by actuators of other types, for example by fluid, rotary or linear cylinders. By way of example, FIGS. 10 and 11 show two possible arrangements of fluid pressure cylinders.

 When security requires redundancy of the actuators, this can be achieved by various means. When it comes to an electric motor that can drift when it is not powered, the redundancy can be ensured by doubling the motor itself or simply its coils. When the actuators are on the contrary constituted by irreversible or self-locking motors, this same redundancy can be ensured by the addition of an engine disengaging device or a differential action device taking advantage of the fact that the deflections are always very small. Such a device makes it possible, when the engine failed is not very far from the median position, to perform the actions with a second motor, identical to the first. In the case of linear cylinders of the type illustrated in FIG. 11, this redundancy can be ensured by substituting, with the single cylinder 35, two jacks 36 associated by a rocker 37, as indicated by dashes.

 As indicated above, the invention finds an important application in the field of the dissipation of the vibration energy or nutation of a satellite.

In this case, it will be possible to use an active device or a passive device. In the first case, the device will be supplemented by detector means and control electronics (not shown). The detector means may be an inertial detector, such as an accelerometer or a gyrometer, or a resolver for measuring rotations around a real axis or the virtual axis of rotation.

Some detector assemblies (as indeed the actuator) are moreover such that one can not really determine if it is the rotation around a real axis or the virtual axis. The control electronics will use the output signals of the detectors to control actuators which may in particular have one of the constitutions defined above. The subset will consist of a mass. Depending on whether the center of gravity of this mass will be centered on the foot of the perpenicular lowered from the virtual axis on the plane of the actual axes of articulation or will instead be off-center, the device will not be or will be sensitive to any solicitation in the plane perpendicular to the axes of rotation.

 If the dissipation device is passive, it must obviously include an energy dissipating member operating without external power supply. It may especially be a dissipator current Foucaud whose assembly may be similar to one of those defined above for the engines.

 All embodiments shown so far, with the exception of that of Figure 4, to achieve a virtual axis of rotation. In many cases, it is necessary to carry out two perpendicular or even three virtual axes of rotation, whether concordant or not.

 Many provisions relating to successive sets of connecting means can be adopted. FIG. 12 shows a particularly simple arrangement, comprising a first set of connecting means 16g interposed between the support 12g and an intermediate plate 18 which in turn supports a plate 39 by a set of connecting means 40, whose axes are crossed. with those means 16g.

 This relative arrangement having the disadvantage of being bulky, it can be substituted for more compact assemblies, such as those shown in Figures 13 and 14, where the members corresponding to those of Figure 12 have the same reference number.

 To constitute an active device from the assembly of FIGS. 12 to 14, it is possible to assign an actuator to each set of real axes, or to provide a single actuator capable of making movements in two directions.

 Figure 15 shows an actuator deriving from that shown in Figure 9 and is capable of moving in two directions. This actuator 41 comprises two coils 42 and 43 placed on a support having a spherical cap shape centered on the virtual center of rotation, represented by the intersection of the two virtual axes. The device can be completed to provide a third virtual axis: FIG. 16 shows such a device, which derives from that of FIG. 14 by adding a set of connecting means 44 and an intermediate frame 45. Additional blades may be provided at 46 to stiffen the joint perpendicular to the plate 47 which constitutes the suspended subset.

 It is also possible to produce a three-axis articulated mounting device more simply than by superposing sets of connection means, in particular by using the anisotropy of deformation of cables. Figure 17 shows a device of this kind. It can be seen that the plate 39h is connected to the support by two sets of cables 48 and 49. Two actuators 34g can be provided to ensure redundancy.

 The assembly of FIG. 17 obviously has a hyperstatic character. But, on the one hand, this hyperstatism is of little importance given the small deflections envisaged and, on the other hand, it is to a large extent corrected by the elasticity of the cables or the mounting of the end cables via springs 50. Return springs 51 may be provided to impose the device a specific rest position.

 With regard to redundancy, it should be noted that it is necessary to have three motors or coils if the permanent magnets are considered as providing the necessary reliability in the case of a system with two degrees of freedom, and four motors in the case of a three-degree system.

 We will now describe, as specific applications, antenna assemblies on telecommunication satellites.

 It should first be remembered that the currently known devices for pointing antenna reflectors whose horn is connected to the body of the satellite have a serious drawback: the horn does not remain on the axis of the reflector during a movement of the antenna. satellite or a change in direction of the area to be covered by the antenna, compensated by reorientation of the reflector. This results in deformation of the antenna lobe, even if the axis of the lobe is correctly pointed. It has been found on the existing satellites that the deformation is already sensitive for reflector tilts of the order of 0.50 and this deformation leads to oversize the nominal lobe, so the power consumes by the antenna. By mounting the reflector on a device according to the invention, to allow an orientation along two perpendicular axes, passing through the center of the horn (whose radiation can be considered isotropic), it is possible to rule out this difficulty.

 In the case where a large antenna has to be reoriented with respect to a satellite, a device of the kind shown in FIGS. 19 and 20 has hitherto been used.

FIG. 19 shows the relative disposition of the antenna 55 with respect to the body 56 of the satellite provided with solar panels 57. FIG. 20 shows that, during parasitic rotations of the body of the satellite 56 around its center of mass G, the devices antennas, which act via an arm 58, give the antenna a large translational movement when it is necessary to reorient the axis of the antenna by an angle 6 ( moving from the solid position to the dashed position). However, the large antennas, generally deployable when the satellite is in orbit, have a relatively flexible structure which, as a result of the translation movements imposed by the pointing device, results in a modification of the shape of the reflector luimeme.Le reflector then oscillates, resulting in changes of gain following an approximately sinusoidal law.

 This disadvantage can be ruled out when using the arrangement according to the invention, shown schematically in FIG. 21. The device according to the invention 10j and, in particular, the connecting means 16j, are then dimensioned so that the virtual center of rotation is approximately at the center of mass of the satellite 56. During angular oscillations of the body of the satellite, the antenna can be oriented without proper translation.

 One could obviously reject at infinity one or more virtual axes of rotation, by arranging the corresponding connecting means so that they are parallel to the rest: one can thus realize systems with n degrees of freedom, n being greater than 3 , allowing several simultaneous decoupling around parallel but not coincidental axes.

 When using the device on satellite, it may be useful or even necessary to block the device during launch, given the constraints it is likely to undergo during the initial phases. Any of the many known blocking arrangements can be used. It is however advantageous to use a mechanism of the kind shown schematically in FIGS. 22 to 24. This mechanism uses a cable 49 stretched between levers 60 which, by means of articulations, lock rigid tabs 61 secured to the subassembly, schematized in the form of a 10k tray. We see that the efforts during the launch pass through the structure without soliciting the locking mechanism at the opening.

 Unlocking is eliminated by cutting the cable after launching: this cutting can in particular be performed by pyrotechnic means shown schematically at 62 in FIG. 24. When it is desired to be able to eliminate and reintroduce the locking at will, a motor can be used rather than pyrotechnic means.

 The basic constitution of the electronics to be incorporated by a satellite antenna reflector pointing device will now be described extremely succinctly and by way of example only. FIG. 25 shows the body of a stabilized 56k satellite along three axes of roll X, pitch Y and yaw Z. The horn 63 is secured to the satellite by a lattice structure. The reflector 55k must be maintained directed towards a radiofrequency tag 64, by orientation around a virtual center coinciding with the horn 63. For this purpose, the reflector is mounted on the body of the satellite by an antenna pointing device. , which will later be referred to as DPA to simplify.

 The mechanical part of the DPA is of the kind shown in FIG. 14 and the corresponding members carry the same assigned reference number of the index k. The plate 39k is integral with the reflector 55k and carries the permanent magnet of a visible actuator in FIG. 26. This actuator, capable of causing displacements in two orthogonal directions, comprises two crossed coils 42k and 43k. Each of these coils is associated with one of the axes of rotation provided by the antenna pointing device, which axes will usually be at 450 axes of roll and pitch.

 The electronic circuit intended to supply the coils 42k and 43k with the necessary regulation currents may have various constitution. That illustrated schematically in FIG. 26 uses an antenna pointing error detection by a multimode radio frequency detector incorporated into the antenna to be oriented, of the type itself well known.

 It can be considered that the electronic control circuit consists of the elements represented in the form of functional blocks in FIG. 26. These blocks will be successively described.

 The block 67 is intended for the processing of the microwave signal that it receives from the horn 63 and which comprises the payload and the signal coming from the radiofrequency tag 64. The circuit 67 supplies the usage signals on a payload output 68. I1 also comprises a microwave circuit for extracting the misalignment signals which appear on a second output 69.

These misalignment signals are applied to an electronics 70, of analog-digital type, processing of the misalignment signals making it possible to generate, on two outputs 71 and 72, signals representative of the deviations around the useful axes of control (roll deviation fm). and pitch difference em).

 As a general rule, the circuits 67 and 70 will be defined by the payload manufacturer, so that the design of the antenna pointing device will only require the realization of the downstream part of the electronics.

 This downstream part, which is the actual control electronics, can be regarded as comprising an electronics 73 for determining the control torques and an electronics 74 for determining the currents i1 and i2 to be passed through the coils. The control torques to be applied are calculated from the differences to be compensated and the mechanical characteristics of the mounting device.

dans lesquelles K1 et K2 sont des coefficients de gain assurant la correction géométrique de fain, définie par le rapport entre rotation du réflecteur et variation des écarts de pointage correspondants. K'1 et K'2 sont des coefficients de gain d'asservissement pour assurer la stabilité du pointage et la performance requise en bande passante. Le facteur sous forme de rapport, où a, T et p désignent respectivement un coefficient d'avance de phase, le temps et la transformée de Laplace, est fourni par un réseau correcteur proportionnelle-dérivée incorporé au circuit 73.These couples will have an expression of the kind

in which K1 and K2 are gain coefficients ensuring the geometrical correction of fain, defined by the ratio between rotation of the reflector and variation of the corresponding pointing differences. K'1 and K'2 are servo gain coefficients to ensure the stability of the score and the required bandwidth performance. The ratio factor, where a, T and p respectively denote a phase advance coefficient, the time and the Laplace transform, is provided by a proportional-derivative correction network incorporated in the circuit 73.

From the signals representative of the pairs Css and Ce, the circuit 74 calculates the currents 11 and 12 to be applied by the formulas

C <SEP> i, <SEP> + <SEP> M <SEP> C
<tb><SEP> l <SEP> L <SEP> C <SEP> - <SEP> M <SEP> This
<tb><SEP> i2 = <SEP> e
<tb> where L and M are constants.

 The signals thus produced are applied to the current generators 75 and 76 respectively associated with the coils 43k and 42k.

 The invention is not limited to the embodiments which have been shown and described by way of example but extends to all variants remaining within the scope of this patent.

Claims (11)

claims  1. Articulated mounting device of a subset around at least one virtual axis, allowing the subset to rotate in a low angular range, typically not exceeding 100, characterized in that it comprises at least one set of two connecting means (16, 16b), each capable of rotating about an axis (18, 18b) on a fixed support (12, 12b) and an axis connected to the subassembly (10, 10b), all the axes being parallel and said means being capable of low angular deflections around a rest position, the intersection at rest of the extensions of the segments each connecting an axis to a fixed support and an axis connected to the subset defining a virtual axis away from the supnort.  2. Articulated mounting device of a subset around at least one virtual axis, allowing the subset to rotate in a low angular range, typically not exceeding 100, characterized in that it comprises at least one set of two connecting means (16, 16b), each rotatable about an axis (18a, 18b) on a fixed support (12, 12b) and an axis connected to the subassembly (10, 10b), and in that said means each comprise several successive elements making it possible to take a small relative angular displacement around intermediate axes, all the axes being parallel and  the intersection at rest of the extensions of the segments each connecting an axis to the fixed support and an axis connected to the subassembly defining a virtual axis of rotation of the subassembly.  3. Device according to claim 1 or 2, characterized in that at least some of the axes are embodied by flexible pivots, deformable cross-bar pivots, grease bearings or plain bearings.  4. Device according to claim 1 or 2, characterized in that the articulated connection means of a set comprises two flexible blades cut to generate a plurality of parallel real axes of articulation mounted in cascade.  5. Device according to any one of the preceding claims, characterized in that it comprises at least two sets of connecting means, the axes of rotation of the means of a game being orthononal to those of the means of the other game and the two games being advantageously provided so that the virtual axes of rotation associated with the two games are concurrent.  6. Active device according to any one of the preceding claims, characterized in that it comprises a torque or force generator acting around at least one virtual or real axis to ensure the orientation of the subassembly.  7. Device according to claim 6, characterized in that it further comprises means for measuring relative angular orientation around at least one real or virtual axis or means for measuring acceleration, speed or speed. absolute distance.  8. Device according to claim 7 for a satellite subassembly, characterized in that the measuring means comprise at least one accelerometer, integrating gyrometer or orientation measuring means with respect to a reference external to the satellite, such that a radio frequency source, the terrestrial horizon and the luminous emission of a star.  9. passive device for damping the nutation or vibration of a structure according to any one of claims 1 to 4, characterized in that, the subset consisting of a dead mass, the device is provided with resilient biasing means which give the subassembly a natural equilibrium position and a natural frequency of oscillation close to the eigenfrequencies of nutation or vibration to be damped.  10. Device according to any one of claims 1 to 8, characterized in that the subset to be pointed in a limited angular range being a microwave antenna reflector, said device is designed so that the axis or virtual center of rotation is close to the emitter horn associated with the reflector.  11. Apparatus according to any one of claims 1 to 8, characterized in that the subset pointer being constituted by a large antenna of flexible structure, the axis or the virtual center of rotation of the device will be advantageously close to the center of the support mass, typically a satellite, carrying the antenna.