Abstract:
An antenna reflector for satellites or space vehicles having a number of hexagonal individual reflectors ( 1 ) which can be arranged around a rigid central element ( 2 ). The reflectors ( 1 ) are connected to the central element ( 2 ) by a support structure ( 3 ) that can collapse to hold the reflectors in a compact storage state or be extended to deploy the reflectors. The reflectors ( 1 ) are folded like an umbrella in a transport state when the reflectors are collapsed and at the place of use, they are brought into their operating positions and spread out, so that they collectively form a reflector surface. Each reflector ( 1 ) has a foldable surface structure connected by a multiple number of ribs ( 11 ) to a rigid, central structure ( 12 ).

Description:
FIELD OF THE INVENTION 
     The present invention relates to a reflector and a reflector element for antennas for use in outer space. 
     BACKGROUND 
     Antenna reflectors for satellites or space vehicles must fulfill a number of requirements. For example, they must be lightweight and have a high accuracy. It is important that they can be stowed in a very small space when transported into space. 
     For this purpose, reflectors have been developed, which are folded together during transport into orbit and are then deployed in space. Conventional mechanisms, however, are often susceptible to jamming together, which often leads to failure of the reflector to be utilized after it is transported into space. In addition, known reflectors only have a limited size, which is additionally limited, for example, by requirements for accuracy. Further, there is the problem that the reflectors are subjected to high stresses due to thermal effects and by radiation, which in the case of known reflectors often leads to a delay and to a consequent inaccuracy of the reflector surface. Specific requirements are placed on the reflector, depending on the type of application, and thus, the development and manufacture of individual reflectors is associated with high cost. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a reflector for use in space, which can be easily transported into space, can be safely and simply deployed, has a large surface with a high shape stability and can be used for multiple purposes. 
     According to one aspect of the invention, a reflector is provided for antennas for application in space, which comprises: 
     a plurality of individual reflector elements, 
     a rigid central element, 
     a support structure connecting said individual reflector elements to said central element, said support structure having collapsed and extended states which provide respective collapsed and deployed states for said reflector elements, 
     said reflector elements in said deployed state adjoining one another to collectively form said reflector. 
     In this way, it is achieved that the reflector can be stowed in a very small space, and after deployment has a large reflector surface, which is stable and has a high contour accuracy. The reflector returns to its original unfolded state when deployed in the operating state, i.e., without application of external force whereas conventional deployable reflectors are stressed to reach their operating position. 
     Preferably, the central element is itself a reflector, which forms a part of the overall reflector surface in the operating position. The individual reflectors are preferably hexagonal at their perimetral edges and arranged circumferentially around the central element in the operating position. In this way, a particularly large effective reflector surface is obtained in the operating position. 
     Preferably, the support structure has rigid support arms, on which flexible elastic elements, such as springs or leaf-spring elements, are arranged to form pivotal connections. In this way a freedom of play of the mechanical elements is achieved, which increases the stability and the surface accuracy of the reflector. The reflector preferably has a securing mechanism such as a clamping device for attaching the individual reflectors in the folded position at one or both sides of the central element. In this way, space is saved, and a self-actuating deployment of the reflector can be obtained without external actuators by virtue of a pre-stress in the pivotal connections when the reflectors are folded. 
     The number of individual reflectors is variable, whereby, additional individual reflectors can be used, in order to form a modular system. In this way, the reflector size can be expanded and the reflector can be adapted in a simple way to specific requirements. In addition, costs are saves, since the individual reflector elements are preferably identical and the overall reflector is constructed according to a building-block principle. 
     Preferably, the individual reflectors are folded up like an umbrella and have an approximately cylindrical or truncated-conically shaped outer periphery in the folded state. In this way, the individual reflectors in the folded state can be stored with their longitudinal axes aligned essentially parallel to one another and/or parallel to a surface of the central element. In this way transport into orbit is made possible with a minimum space requirement. 
     The reflector can be mounted on a main support arm in such a way that it can be displaced on the main support arm in the folded state. 
     According to another aspect of the invention, a reflector or reflector element is produced for antennas for use in space, which has a heat-stable foldable surface structure, which serves as a reflector surface, the reflector element having a multiple number of ribs for supporting the surface structure and a rigid central structure, which is connected to the ribs by pivotal connections, so that the surface structure can be deployed by pivoting the ribs outwards. 
     Thus, the reflector element can be stowed in a very small space, and can easily be deployed. The ribs can be aligned essentially parallel to one another in the folded state and they are pivoted in the deployed state, preferably essentially radially outwards from the central structure. 
     The surface of the reflector is made from CFK. In this way, a high stability is obtained relative to thermal stresses and radiation pressure. The surface can be provided with an RF-effective layer, for example, a metalized Kapton foil. The surface structure is preferably subdivided into individual pre-shaped segments of part-parabolic or part-spherical shape, which can each be held by two ribs and they are arranged, circumferentially around the central part. Preferably, the ribs are connected to the surface structure by means of an elastic joint. This elastic joint can include an intermediate rib element and a slitted profile member to enable a good and easy adaptation to the curvature of the reflector. 
     The pivotal connections are preferably made of flexible, elastic elements, such as, coil springs or leaf-springs, which are preferably form-stable and have, in particular, a defined buckling direction. The reflector element can also have a detachable clamping device for holding the reflector element in its folded state. In this way, a deployment is possible without an actuator, due to a pre-stressing of the pivotal connections. 
     According to yet another aspect of the invention, a reflector is provided which comprises one or more reflector elements according to the invention as the individual reflectors as described above. 
     The process for deployment a reflector according to the invention comprises the steps of: 
     outwardly swinging a multiple number of folded individual reflectors joined to a central element, from a transport position into an operating position, 
     deploying the individual reflectors in the operating position so that the individual reflectors adjoin one another to collectively form the overall reflector surface. 
     The individual reflectors can be moved in pairs into the deployed or operating position. Preferably, the reflectors are released under pre-stress after a securing mechanism is released. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a preferred embodiment of a reflector according to the invention in the deployed state. 
     FIG. 2 shows the reflector according to the invention schematically in a stowed or compacted state. 
     FIGS. 3 a  to  f  show various phases of a deployment operation of the reflector. 
     FIG. 4 shows a reflector element according to the invention in the folded state. 
     FIG. 5 shows a portion of the back side of the folded reflector element. 
     FIG. 6 shows a portion of the back side of the deployed reflector element. 
     FIGS. 7 a  and  7   b  show different phases of the deployment of the reflector element. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a preferred embodiment of the reflector of the invention in its deployed state. The reflector is constructed from a number of umbrella-type individual or partial reflectors  1  that can be deployed, which are circumferentially arranged around a rigid central reflector  2 , which forms a central support element of the reflectors  1 . The individual reflectors  1  and the central reflector  2  are connected together by a support structure  3 , which is collapsible to provide a compact, folded state of the reflector (FIG.  2 ). In the open or deployed state shown in FIG. 1, the reflector is in its operating position. 
     The central reflector  2  and the partial reflectors  1  are connected together by support arms  3   a , which form part of support structure  3 . Support arms  3   a  of partial reflectors  1  are formed as rolled carbon-fiber tubes having a laminate structure designed to be heat-stable and resistant to bending. Hinge joints  4  are provided on arms  3   a  to achieve a horizontal pivotal capability of arms  3   a  relative to central element  2  as well as relative to partial reflectors  1  in order to bring each reflector from its folded state (FIG. 2) to its operating position shown in FIG.  1 . The hinge joints are spring biassed in a direction to open the reflector to its unfolded state as will be explained later. 
     A main support arm  5  of the support structure  3  is connected to a mounting base  6  which can be the satellite itself or a separate housing by a hinge  7 . Ribs  11  extend radially outward from a central member  12  of each reflector  1  and support the reflector at its back side. Each reflector  1  has a hexagonal outer contour as does the central support element  2 . In the deployed position shown in FIG. 1, the reflectors  1  abut one another and the central support element  2  to collectively form the overall reflector surface. Accordingly, the central support element is, itself, formed as a reflector. Each individual reflector  1  is divided into twenty four individual sectors  10   a  arranged radially around the respective central part  12 . 
     The reflector shown in FIG. 1, is constructed as a module from the individual reflectors  1  and has a diameter of approximately  3  meters in the preferred embodiment. Larger reflectors can also be produced, however, in a simple way due to the modular construction. Individual reflectors  1  are made of foldable, form-stable CFK (carbon-fiber-reinforced plastic) structures, with a porous CFK surface, such as, for example, Triax fiber or the like, which is supported on the ribs  11  of the respective reflectors  1  and is folded or deployed in the manner of an umbrella. When it is deployed, the small central part  12  of each reflector  1  remains fixed in position. The reflector surface is shaped with high precision, whereby a metallized Kapton foil can be provided as an RF-effective layer in a particular embodiment. The configuration of the reflector surface as a fiber network structure provides a reduction in the degree of radiation. Support arms  3   a  are foldable, structurally stable rods, which securely hold the reflectors  1  in their final position. 
     FIG. 2 shows the reflector according to the invention in the folded state, suitable for transport into orbit. Two pairs of individual reflectors  1   a ,  1   b  are folded together and are fixed and positioned in respective pairs by a securing mechanism  8 . The pairs of reflectors la and lb are arranged at the back side of central reflector  2 . The respective securing mechanisms  8  enclose two individual reflectors and hold them under pre-stress against the back side of central reflector  2 . In this position, the longitudinal axes of the folded individual reflectors  1   a ,  1   b , are aligned parallel to the back side of central reflector  2 . 
     Each individual reflector  1  is secured in its umbrella-like folded state by a closure device  9 , which is comprised of two retainer straps. Two folded individual reflectors  1   c  are arranged at the front side of central reflector  2  in this embodiment. Hinge joints  4  enable the individual reflectors  1   a ,  1   b ,  1   c  to be brought from the folded position shown in FIG. 2 to the operating position shown in FIG. 1 under the bias of the hinge joints  4 . 
     In a preferred embodiment, the hinge joints  4  are formed as elastic, form-stable leaf-spring elements. They are free of play and they make possible a horizontal pivotal movement around respective horizontal axes. The elements of joints  4  are concave in cross-section and are produced from CFK. In the position shown in FIG. 2, joints  4  are pre-stressed, whereby the individual reflectors  1  are brought automatically into the operating position by releasing the securing mechanism  8 . The hinge joints  4  can also be formed by conventional springs which are compressed when the reflectors are collapsed to provide a bias to urge the reflectors out to their operative positions. 
     FIGS. 3 a  to  3   f  shown the deployment of the reflectors  1  in different stages. 
     FIG. 3 a  shows the stage in which after pivoting arm  5  from a position adjacent to base  6  to the position shown in FIG. 3 a , the securing mechanism  8  of the first pair of individual reflectors la (securing mechanism  8  is not shown in FIG. 3 a ), is released and the individual reflectors la swing out to their respective operating position. The expulsion of the reflectors la is produced by the pre-stress of the hinge joints  4 , which cause a self-actuated positioning of the two individual reflectors la, which are still folded, due to their defined pre-stress and defined hinge axis. 
     The two individual reflectors la are shown in FIG. 3 b  in the obtained operating position. The longitudinal axes of the individual reflectors la are aligned perpendicular to the surface of central reflector  2  in this position. 
     In the next stage of deployment shown in FIG. 3 c , the pair of individual reflectors  1   c  arranged at the front side of central reflector  2  are moved to their final position when the associated securing mechanism  8 , is released. The expulsion and the positioning are again produced by the spring action of the hinge joints  4 . 
     The two pairs of individual reflectors la,  1   c  are shown in their obtained final position in FIG. 3 d . Next the securing mechanism  8  of the two individual reflectors  1   b  at the back side of central reflector  2  is released, whereby these two individual reflectors are brought to their final position relative to central reflector  2  (FIG. 3 e ). Then the connection arm  5  is pivoted around hinge  7  on base  6  to move central reflector  2  together with the individual reflectors  1   a ,  1   b ,  1   c , to an upstanding position as shown in FIG. 3 f.    
     The sequential deployment of the reflector is thus carried out in the following steps: 
     1. outwardly pivoting the reflector system away from casing  6 , 
     2. swinging out individual reflectors  1  of respective pairs, 
     3. pivoting of connection arm  5  to its final position, and 
     4. opening the individual reflectors  1  to their final deployed positions. 
     Shock forces due to the unfolding and deployment are minimized, since only small individual masses are moved to their final position. The steps can also be conducted in a different sequence. 
     In FIG. 4, an individual reflector  1  is shown in its folded state. A clamping device  9 , formed as a tightenable strap, encloses the periphery of the folded individual reflector  1  at its lower end and at its upper third. The outer periphery of the individual reflector  1  is shaped essentially cylindrically or as a truncated cone in the folded state. Reflector  1  has a surface structure  10 , which is subdivided into individual segments  10   a , which extend in the longitudinal direction around a longitudinal axis, i.e., the segments are folded parallel to the longitudinal axis A of the reflector. 
     A portion of a folded individual reflector  1  is shown in FIG. 5 in a view from the bottom. Each of the folded segments  10   a  is held rigidly between two ribs  11 , which are attached to the edges  101  of respective segments  10   a . Ribs  11  are aligned in the folded state essentially parallel to one another and extend outwards from edge  121  of the round, rigid central part  12 . Ribs  11  are connected to central part  12  by hinge joints  15 . Each joint  15  is comprised of CFK push-pull belt or leaf-spring elements, which have a curvature in their cross-section or are concavely shaped in order to resist transverse forces. A play-free operation of joints  15  is made possible by the configuration of joints  15  as elements of elastic material or elastic, concave spring joints. 
     FIG. 6 shows a portion of the back side of the individual reflector  1  in the deployed state. Ribs  11  form reflector arms, which support the foldable surface structure  10 , which is constructed as a heat-resistant, form-stable structure, for example, having carbon filaments or fibers at its surface. 
     The self-supporting, parabolic or spherically shaped surface segments  10   a  are respectively supported by two ribs  11 , which are connected to the structure of the segments by means of a foil joint  20  and a slitted L-profile member  21  adapted to the reflector contour. Namely, the rib  11  is secured to the reflector structure by means of an intermediate structure  11   a , which is adapted to follow the curved contour of the reflector segment when it is deployed. The intermediate structure  11   a  is comprised of two CFK plates, which are glued at one side to foil  20  and on the other side are connected to the slitted L-profile  21  of CFK, which forms the connection to the reflector structure. By slitting one leg of L-profile member  21 , a simple adaptation to the curvature of the reflector is possible. 
     Central part  12  comprises star-shaped CFK hollow profiles  12   a , which are adhered together in the center on the upper and lower sides by means of CFK disks  12   b . One of the CFK disks  12   b  forms the intersection to the connecting flexible joint  4  of the connecting arm  3   a  of the reflector, which is not shown in FIG.  6 . 
     The deployment of the individual reflectors  1  is shown schematically in FIGS. 7 a  and  7   b . Joints  15  which are pre-stressed in the folded state cause ribs  11  to open up radially outwardly around edge  121  of central part  12 , as shown by arrow B, when clamping devices  9  are released. The deployed final position is shown in FIG. 7 b.    
     By the distribution of joints  15  along a curved line formed by edge  121  of central piece  12 , the radial extension of ribs  11  in the deployed state is made possible. The distance between two adjacent ribs  11  is increased when the parallel alignment of ribs  11  in the folded state changes to the radial alignment in the deployed state. In this way, segments  10   a  are deployed and obtain their final contour. 
     Joints  4  and  15  are FLEX-BOOM-elements, i.e., structures, which are changed due to the elastic change of their cross-sectional geometry from a bearing structure that is easy to bend to one that is resistant to bending. Joining and locking functions are integrally united thereby. 
     The reflector according to the invention combines the advantages of a small mass of a large reflector surface with a high surface accuracy and stability. It is heat-stable, cost-favorable, and suitable for larger numbers of pieces due to the modular system and can be applied in various ways. The reflector is suitable not only for antennas, but is can also be used, for example, as energy collecting mirrors in outer space. 
     Although the invention is disclosed with reference to particular embodiments thereof, it will become apparent to those skilled in the art that numerous modifications and variations can be made which will fall within the scope and spirit of the invention as defined by the attached claims.