EP0044241A1 - Collapsible antenna reflector - Google Patents

Abstract

According to the invention, this reflector comprises an articulated structure (11, 13) on which a reflective cap (15) can be mounted, the shape of which is adjustable thanks to tension links (16). Equipment of artificial satellites.

Description

The present invention relates to an antenna reflector, in particular of large dimensions, for example intended to equip a telecommunications or direct television satellite.

• - les dimensions du réflecteur en configuration opérationnelle excèdent de beaucoup les valeurs autorisées par le stockage du satellite sous la coiffe du lanceur ;
• - les tolérances permises sur la forme du réflecteur pendant toute la durée de la mission sont très faibles (+ ou - quelques dixièmes de mm par rapport à un profil théorique qui peut être une portion d'un paraboloide de révolution) ;
• - la surface du réflecteur est constituée d'un matériau électriquement conducteur, par exemple un tissu dont les mailles sont inférieures à un maximum spécifié (quelques dixièmes de mm), dans le cas d'un réflecteur déployable.

We know that, in this case, the main constraints imposed by the mission on such a reflector are:

• - the dimensions of the reflector in operational configuration greatly exceed the values authorized by the storage of the satellite under the launcher cap;
• - the tolerances allowed on the shape of the reflector during the entire duration of the mission are very low (+ or - a few tenths of a mm compared to a theoretical profile which can be a portion of a paraboloid of revolution);
• - The surface of the reflector is made of an electrically conductive material, for example a fabric whose meshes are less than a specified maximum (a few tenths of a mm), in the case of a deployable reflector.

Already known, in particular from American patent No. 3,224,007, an antenna reflector comprising an electrically conductive flexible cap made of a wire mesh. Most of the embodiments described therein comprise a rigid structure supporting said cap and tensioning members, for example cables, between the cap and the structure. Thus, by adjusting the length and the tension of said members, it is possible to adjust the shape of the flexible cap to the desired shape and to comply with the tolerances imposed. However, in this known embodiment, the rigid structure is fixed and the reflector cannot be adapted for use on board a of a satellite. Also, when the antenna of the American patent N ° 3 224 007 must be used for a spatial application, the author of the said patent has to remove the rigid structure, the flexible cap then being rotated around its axis, so that, under the action of centrifugal forces, it retains its shape as a reflector. Such a reflector cannot be excited in offset (off center), and inertia problems make it difficult to control the attitude of the carrier satellite.

In addition to the fact that such a rotation requires drive means increasing the dimensioning, the mass and the cost of the assembly, the rotation generates a certain floating of the cap. Furthermore, it becomes impossible to use tension members to adjust the shape of the cap, since the rigid structure serving to anchor said members is eliminated.

Deployable reflectors such as those described in US Pat. Nos. 3,496,687, No. 3,508,270 and No. 3,521,290 are also known.

US Patent No. 3,496,687 describes a reflector deployable using arms and pantographs. This assembly therefore includes numerous joints, the play of which, in addition, adversely affects the precision of the reflector. It also has a fairly large folded size.

US Patent No. 3,508,270 describes a deployable reflector produced using wires stretched by an inflatable bladder stiffened by cables stretched using a mast.

Such a reflector has the advantage of a relatively small folded up space, but is not suitable for very high frequency emissions, because of the dimensions meshes formed by stretched threads, the number of which must be restricted.

The US patent. No. 3,521,290 describes a deployable reflector of the "parasol" type, the frames of which support rigid elements constituting parts of the reflector, which is formed, after deployment of said frames, by the juxtaposition of said rigid elements. Such an arrangement provides good precision of the reflected surface. healthy, but has a very large folded footprint and a fairly high mass.

The present invention relates to an antenna reflector satisfying the constraints mentioned above and overcoming the drawbacks of known embodiments.

In particular, it occupies in its folded form an extremely reduced volume.

To this end, according to the invention, the antenna reflector comprising a flexible conductive cap and a rigid structure supporting said cap, is remarkable in that said structure consists, on the one hand, of a plurality of members converging towards the axis of the reflector and distributed around said axis, the ends of said members close to this axis being articulated about axes tangent to a circle orthogonal to said axis of the reflector, so as to be able to assume a folded position along said axis of the reflector and a deployed position transverse to the latter axis in the manner of the branches of an umbrella, and, on the other hand, of a plurality of arms, each of which is articulated at the end of a member remote from the axis of the reflector, so that, when said members are in the deployed position, said arms are angular rement arranged projecting relative thereto so that said structure forms a kind of cradle, in the concavity of which is disposed said deployed flexible cap, and that, when said members are in the folded position, said arms are also folded along the side of said frames inside the cradle, so that said structure then forms a sort of small diameter beam enclosing the folded flexible cap.

Thus, a foldable and deployable antenna is obtained which does not require rotation drive means and avoids any floating of the deployed cap, but requires an actuation mechanism with a limited operating time. Furthermore, it is possible to use tensioning members allowing the shape of the reflector to be adjusted. Indeed, the connection between the flexible cap and the structure can be achieved, on the one hand between the periphery of the cap and the free ends of said articulated arms and, on the other hand, by tensioning members arranged between the convex surface of the cap and said members.

• - une calotte souple conductrice qui constitue la surface réfléchissante du réflecteur ;
• - une structure rigide articulée et déployable assurant les fonctions suivantes :
  • . en configuration de lancement : assurer à l'ensemble une géométrie compatible avec l'espace laissé disponible par le satellite à l'intérieur de la coiffe du lanceur
  • . en configuration orbitale : constituer un solide de référence par rapport auquel sera située la calotte souple.
• - Un jeu de fils tendeurs ajustables reliant la calotte souple à la structure rigide, et dont la tension et la longueur sont réglées de façon à approcher au mieux la face réfléchissante de la calotte du profil théorique souhaité.

The reflector according to the invention therefore consists of three parts:

• - a flexible conductive cap which constitutes the reflecting surface of the reflector;
• - a rigid articulated and deployable structure ensuring the following functions:
  • . in launch configuration: ensure that the geometry is compatible with the space left available by the satellite inside the launcher cap
  • . in an orbital configuration: constitute a reference solid with respect to which will be located the flexible cap.
• - A set of adjustable tensioning wires connecting the flexible cap to the rigid structure, and the tension and length of which are adjusted so as to best approach the reflective face of the cap of the desired theoretical profile.

In addition to the advantages mentioned above, thanks to its design, the antenna reflector according to the invention has that of having a rigid structure to which. flexible caps of different diameters and curvatures can be adapted. Thus, one can use the same rigid structure to obtain reflectors of different focal lengths, or even off-center reflectors and / or excited in offset.

Each frame can be in one piece or on the contrary be made up of several foldable and deployable sections.

In the case where the members are in one piece, they advantageously have a trapezoidal section so that, the diameter of the circle to which their articulation axes are tangent being chosen accordingly, they can, in the folded position, come into contact with each other another, so that said bundle has a closed outer surface, at least substantially cylindrical. It is then advantageous that said arms also have a trapezoidal section so that, in the folded position, they form an at least substantially cylindrical block, determining the internal diameter of said beam. Thus, in the folded position of the structure, the members and the arms form a closed enclosure for the folded cap, which is thus protected.

It is therefore easy to imagine that a satellite equipped with at least one reflector according to the invention, in the folded state, can be mounted inside the casing of its launcher. After putting said satellite into orbit, it is then necessary to deploy said reflector. To this end, any known drive means can be provided (spring, electric screw jack, pneumatic jack, etc.) controlling the opening of the structure by means of, for example, a link system. Whatever the drive means chosen, it can actuate a movable member sliding along the axis of said reflector and to which all of said links are connected. Thus, the opening of the members is simultaneous.

Furthermore, to connect the reflector according to the invention to the satellite or to an articulated arm on the satellite, it is advantageous to provide a hollow base, coaxial with the axis of the reflector, on which said members are articulated, and with the inside of which is located at least partially housed the opening mechanism of the reflector.

Preferably, opening conjugation means are provided, such as cables and rollers connecting each frame and its associated arm, so that, when the actuation mechanism causes said frames to pass from their folded position to their deployed position, said arms pass automatically and gradually from their folded position along the inner side of the members to their angularly projecting position. So that the angularly projecting position of the arms is well determined with respect to the members, stop systems are provided between these elements.

Furthermore, the deployment of the assembly according to the invention is reversible, if only to carry out tests before the launch of the artificial satellite carrying said assembly. For this purpose, means are provided for returning to the folded position.

The figures of the appended drawing will make it clear how the invention can be implemented.

• La figure 2 est une vue de face correspondant à la figure 1, la coiffe du lanceur n'étant plus représentée.
• La figure 3 illustre, en coupe diamétrale, le réflecteur selon l'invention en position déployée.
• La figure 4 est une vue éclatée partielle d'un mode de réalisation du réflecteur selon l'invention, en position déployée.
• La figure 5 illustre schématiquement le déploiement des membrures et des bras.
• La figure 6 est une vue en bout agrandie selon la flèche F de la figure 5, de la structure du réflecteur selon l'invention, en position repliée. ;

Figure 1 illustrates schematically, in side view, the position and the launch and orbital configuration of a reflector according to the invention mounted on a satellite.

• Figure 2 is a front view corresponding to Figure 1, the cover of the launcher is no longer shown.
• FIG. 3 illustrates, in diametral section, the reflector according to the invention in the deployed position.
• Figure 4 is a partial exploded view of an embodiment of the reflector according to the invention, in the deployed position.
• Figure 5 schematically illustrates the deployment of the frames and arms.
• FIG. 6 is an enlarged end view according to arrow F in FIG. 5, of the structure of the reflector according to the invention, in the folded position. ;

In Figures 1 and 2, there is shown an artificial satellite 1 equipped with a small reflector 2 of fixed size and a deployable reflector 3 according to the invention, of large dimensions. l

During its launch, the satellite 1 is placed inside the cover 4 of a launcher and the reflectors 2 and 3 are then folded against the body of the satellite. In FIGS. 1 and 2, the folded position of the reflector 2 is not indicated, while that of the reflector 3, shown in dotted lines, bears the reference 3 '.

When the satellite is in its orbit (configuration illustrated in Figures 1 and 2), the reflectors 2 and 3 are unfolded and occupy the positions indicated in solid lines. It will be noted that for this purpose the reflector 2 is simply rotated about an articulation axis 5 connecting it to the body of the satellite, while the reflector 3, in addition to a rotation of its support arm 6 around an axis 7 allowing its spacing du. satellite body 1, undergoes deployment and rotation around an axis 8 connecting it to said support arm 6.

As illustrated better in FIGS. 3 and 4, the deployable reflector according to the invention has a structure preferably of revolution around its axis XX and comprises a massive base 9, fixed to the end of the arm 6 and on which are articulated , around axes 10, a plurality of radial members 11. At the end of the members 11 opposite the axes 10 are articulated, around axes 12 orthogonal to the members 11, arms 13 capable of pivoting between a position for which they are folded between said members and a position for which they are transverse thereto (see FIG. 5) this last position being determined for the cooperation of a stop 14 integral with said arms with the end of said members. A flexible reflecting cap 15 is made integral (directly or via tension links), by its periphery, with the free ends of the arms 13, while tension wires 16 are provided between the convex face of the cap 15 and the members 11 · A reversible actuation mechanism 17 makes it possible to control the deployment of the members 11 and of the arms 13.

The reflective cap 15 must be a good conductor of electricity, flexible, dimensionally stable, light, resistant and have a low coefficient of expansion. It can be produced, for example, in the form of a fabric or knitted fabric, the weaving or knitting characteristics of which give flexibility and the constituent materials of which determine stability, thermal expansion and conductivity. The materials used for the production of this fabric or of this knitted fabric may be either metallic (molybdenum, chromel R, etc.) or synthetic and coated in a known manner with a metallization (such as for example a polyester thread metallized with l The weaving or knitting yarn advantageously consists of a plurality of strands (up to 300) and it can be twisted to reduce its bending stiffness. Its diameter is preferably very small (of the order 50 µ) and the mesh diameter is compatible with the wavelength used.

In an advantageous embodiment, a golden molybdenum wire, having a diameter of 50 μm and consisting of 3 twisted strands, is used to make the cap 15. This yarn is knitted in garter stitch, the stitches having a diameter of 0.7 mm.

In the flat knitting thus produced, pseudo-triangular strips are cut, which are assembled by sewing, gluing or welding to form the cap. This cap is stretched inside the cradle formed by the deployed structure 11, 13, for example by setting up tensioners (not shown) between points distributed around its periphery and the free end of the arms 13.

Said cap can also be made of a flexible, homogeneous and isotropic material metallized on the surface or internally by inclusion of conductive pulverulent charges.

For example, it can be carried out using an elastomer sheet loaded with gold or silver particles, or even using an aluminized "milar" sheet.

According to a particular embodiment of the invention, said cap may include in its central part a rigid dome of small diameter ensuring the continuity of the reflective profile and made integral with the base 9.

• - elle constitue un fond rigide au volume formé par le réflecteur replié, évitant ainsi à la peau conductrice de se trouver en contact avec les mécanismes de déploiement
• - elle stabilise géométriquement la partie restante de la calotte en lui assurant une position rigoureusement fixe en son centre par rapport aux membrures et aux bras, et remplace les fils de mise en forme du coeur du réflecteur
• - elle trouve facilement sa place à l'intérieur du cylindre formé par les membrures repliées
• - elle peut elle-même servir de support à une tour porte-source primaire, ou porte-réflecteur primaire si le système utilisé est du type "Cassegrain" ou "Gregory". Dans le dernier cas, elle supporte également la source primaire, dont l'ouverture est située sensiblement près de son sommet.

Said rigid dome is also made integral with the flexible part of said cap. It has the following advantages:

• - it constitutes a rigid bottom with the volume formed by the folded reflector, thus preventing the conductive skin from being in contact with the deployment mechanisms
• - it geometrically stabilizes the remaining part of the cap by ensuring a rigorously fixed position in its center with respect to the members and arms, and replaces the wires for shaping the core of the reflector
• - it easily finds its place inside the cylinder formed by the folded members
• - it can itself serve as a support for a primary source tower, or primary reflector holder if the system used is of the "Cassegrain" or "Gregory" type. In the latter case, it also supports the primary source, the opening of which is located substantially near its top.

The members 11 are rectilinear section beams closed. They can be made of carbon fibers and have a trapezoidal section to present a minimum bulk in the folded position (see FIGS. 5 and 6), and maximum inertias of bending and torsion. Thus, in this position, the beams 11 can form a faceted tube 18, the internal cavity 25 of which, determined by the cylinder 26 formed by the arms 13 folded, encloses the cap 15 (not shown in FIG. 5).

The arms 13 are produced in a similar manner to the members 11. Preferably, the deployments of the arms 13 are combined with those of the members. Such a combination of movements can be obtained by means of a cable system 27 and pulleys 28, said cable being anchored on the base 9.

Means for returning the arms 13 to the members 11 can be constituted by leaf springs, not shown in FIG. 3. Another means for returning the arms 13 to the members 11 can be obtained by doubling the cables 27 with cables of substantially equal length but along an opposite path relative to the joints 10 and 12 (Figure 5).

• - ouverture lente et régulière du réflecteur 11, 13, 15
• - énergie de fin d'ouverture importante pour assurer la tension de la calotte 15 et le verrouillage ou le maintien de l'ensemble en position de déploiement grâce à des moyens de verrouillage ou d'arrêt non représentés
• - fiabilité et reproductibilité du positionnement des membrures et des bras .

The actuation mechanism 17 must have the following characteristics:

• - slow and regular opening of the reflector 11, 13, 15
• - significant end of opening energy to ensure the tension of the cap 15 and the locking or maintaining of the assembly in the deployment position by means of locking or stopping means not shown
• - reliability and reproducibility of the positioning of members and arms.

• - ressort avec dispositif de régulation (non représenté)
• - vérin pneumatique 19 à double effet commandant les membrures 11 par l'intermédiaire de bielles 20 (voir figure 4)
• - moteur électrique réversible 21 entraînant en rotation une vis 22 sur laquelle se déplace un écrou 23,commandant les membrures 11 par l'intermédiaire de bielles 24 (voir figure 3)
• - cabestan électrique et câbles.

Depending on the dimensions of the reflector, different actuation mechanisms can be used:

• - spring with regulating device (not shown)
• - double-acting pneumatic cylinder 19 controlling the members 11 by means of connecting rods 20 (see FIG. 4)
• - reversible electric motor 21 driving in rotation a screw 22 on which a nut 23 moves, controlling the members 11 by means of connecting rods 24 (see FIG. 3)
• - electric capstan and cables.

The reflective surface of the cap 15 is shaped in accordance with the theoretical profile of the reflector by adjusting the length of the tensioning wires 16.

The wires 16 are stretched between points distributed judiciously, and for example uniformly, on the cap 15 and points distributed on the members 11, the structure 11, 13 being considered as very rigid in front of the fabric of the cap 15.

• - Fabrication des fils à longueur. Après mesures de la calotte et de la structure 11, 13 sous contrainte, la longueur de chaque fil 16 est déterminée par calcul. Une extrémité de chaque fil est collée sur la face convexe de la calotte 15, l'autre extrémité étant collée sur une membrure 11.
• - Ajustage par réglage : Sous les membrures 11 on monte des dispositifs de réglage non représentés (un par fil) permettant une mise à longueur précise du fil après contrôle global de la surface. Après réglage, le fil est collé sur la membrure , coupé entre le collage et le dispositif de réglage et ce dispositif est démonté.
• - Une solution mixte consiste à couper chaque fil avec une tolérance moyenne ( m 0,5 mm), puis à le régler très précisément, mais sur une faible plage (1 ou 2 mm).

The length of the wires 16 can be adjusted as follows:

• - Manufacture of threads to length. After measurements of the cap and the structure 11, 13 under stress, the length of each wire 16 is determined by calculation. One end of each wire is glued to the convex face of the cap 15, the other end being glued to a frame 11.
• - Adjustment by adjustment: Under the members 11, adjustment devices are not shown (one per wire) allowing precise length setting of the wire after overall control of the surface. After adjustment, the wire is glued to the frame, cut between the gluing and the adjustment device and this device is disassembled.
• - A mixed solution consists of cutting each wire with an average tolerance (m 0.5 mm), then adjusting it very precisely, but over a small range (1 or 2 mm).

In the folded position 3 ′, each member 11 occupies a position substantially parallel to the axis X-X and the corresponding arm 13 is folded against the face of said member facing this axis (see FIGS. 5 and 6). As a result, all of the members 11 form a quasi-cylindrical and tubular bundle 18, the internal diameter of which is determined by the arms 13 which are in contact with each other. The flexible cap 15 is then enclosed in the interior space 25 of the bundle 18, delimited by the members 11 and the arms 13. When the actuation mechanism 17 acts by moving a movable member such as 23 along the axis XX , the members 11 open in the manner of the branches of an umbrella under the action of the connecting rods 20 or 23 (see the right-hand part of FIG. 5), while the arms 13 gradually unfold by turning around the joints 10, under the action of the motion conjugation cables 27. In the maximum open position, the members form a substantially planar star, the arms 13 are in the erection position and the cap 15 is stretched.

Although in the assembly shown, the members 11 and the arms 13 are in one piece, it goes without saying that they could consist of a plurality of deployable sections, which would further increase the surface of the reflector according to the invention, for less bulk in the folded state.

It can therefore be seen that, according to the invention, a light and deployable structure 11, 13 is produced, which can be considered to be practically non-deformable under limited variations in stresses (creep) and in temperature. Such a structure allows the maintenance of a cap 15, the shape of which is independent of said structure and can be best adapted to the mission to be fulfilled, for example of parabolic shape. of centered revolution, or offset in the case of an antenna with offset illumination.

The invention therefore makes it possible to produce identical structures, for caps of different shapes.

Claims (13)

1 - Antenna reflector comprising a flexible reflecting cap and a rigid structure supporting said cap and consisting of a plurality of members converging towards the axis of the reflector and distributed around said axis, the ends of said members close to this axis being articulated around axes tangent to a circle orthogonal to said axis of the reflector, so as to be able to assume a folded position along said axis of the reflector and a deployed position transverse to the latter axis in the manner of the branches of an umbrella,
characterized in that said structure comprises a plurality of arms (13) each of which is articulated at 12 at the end of a frame (11) remote from the axis of the reflector, so that, when said frames ( 11) are in the deployed position, the said arms (13) are angularly projecting relative to the latter, so that the said structure forms a sort of cradle, in the concavity of which the said flexible cap (15) deployed, and that , when the members (11) are in the folded position, said arms (13) are also folded along the side of said members inside the cradle, so that said structure then forms a sort of beam (18) of small diameter enclosing said flexible cap folded up. 2 - Antenna reflector according to claim 1, characterized in that the connection between the flexible cap (15) and the rigid structure (11,13) is formed, on the one hand between the periphery of the cap (15) and the free ends of said articulated arms (11) either directly or by means of tensioners, and, on the other hand, by tensioning members (16) arranged between the convex surface of the cap (15) and said members (11), the latter constituting a stable dimensional reference. 3 - antenna reflector according to any one of claims 1 or 2,
characterized in that each frame (11) is in one piece. 4 - antenna reflector according to any one of claims 1 or 2,
characterized in that each frame (11) consists of several foldable and deployable sections. 5 - antenna reflector according to any one of claims 1 to 3,
characterized in that the members (11) are rectilinear and have a trapezoidal section so that, the diameter of the circle to which their articulation axes (10) are tangent being chosen accordingly, they can, in the folded position, come into contact with each other another, so that said bundle (18) has a closed outer surface, at least substantially cylindrical. 6 - Antenna reflector according to claim 5, characterized in that said arms (13) also have a trapezoidal section so that, in the folded position, they form an at least substantially cylindrical block, determining the internal diameter of said beam (18) . 7 - Antenna reflector according to any one of claims 1 to 6, comprising an actuating mechanism (17),
characterized in that said mechanism (17) comprises a movable member (19,23) sliding along the axis XX of said reflector and to which are connected a plurality of rods (20,24) each connected to one of said members ( 11). 8 - antenna reflector according to claim 7, characterized in that it comprises a hollow base (9), coaxial with the axis of the reflector and used for fixing said reflector, said frames (11) being articulated on said base (9), which serves at least partially to said actuation mechanism (17). 9 - antenna reflector according to any one of claims 1 to 8,
characterized in that it comprises opening conjugation means (27) connecting each member (11) to its associated arm (13), so that, when the members (11) pass from their folded position to their deployed position, said arms (13) automatically and progressively pass from their folded position along the inner side of the members to their angular projecting position. 10 - Antenna reflector according to any one of claims 1 to 9,
characterized in that the angularly projecting position of the arms (13) relative to the members (11) is determined by the cooperation of stops (14) between each member (11) and each arm (13). 11 - Antenna reflector according to any one of claims 1 to 10, characterized in that said actuating means (17) and conjugation (27) are reversible. 12 - Reflector according to any one of claims 1 to 11, characterized in that the central part of said cap is rigid and integral with said base (9). 13 - Reflector according to any one of claims 1 to 11, characterized in that said cap (15) has the shape of a portion of paraboloid, and in that the axis of said paraboloid is offset from the axis XX of said base (9).

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