Apparatus for Unfolding an Antenna Netting Reflector

The present application is based on German Ser. No. P 31 24 907.8, filed in the Federal Republic of Germany on June 25, 1981. The priority of the German filing date is claimed for the present application.

The present invention relates to an apparatus for unfolding an antenna netting reflector. Such reflectors comprise stiff ribs which are pivotally supported and which extend radially outwardly from a center in the unfolded condition of the antenna netting reflector. The netting of the reflector is secured to the ribs and suspended between the ribs.

Such antenna reflectors are primarily used in space travel because it is essential in space vehicles that the payload is as large as possible having regard to the limited transport volume. Thus, these antennas are initially folded when the space vehicle travels towards its intended orbit. Only when the intended orbit has been reached, will the antenna be unfolded. Several different constructions are known in the art for such folding antennas. These prior art structures comprise various types of unfolding mechanisms adapted to particular requirements, see for example the publication "Zeitschrift fuer Flugwissenschaft und Weltraumforschung", Number 4, 1980, Volume 5, pages 255 to 267. A so-called "offset" reflector is disclosed in this reference among others. Such reflector may be unfolded and has the above mentioned features. The unfolding takes place in two sequential phases. In the first unfolding phase flexible cross connectors are effective which are secured between the rib ends. These flexible cross connectors are kept under tension during the folded condition of the reflector. When these flexible cross connectors are released they start the unfolding of the reflector by spreading the radial ribs. The full unfolding takes place in the second phase which also provides for a locking in the unfolded position. Such locking is necessary to assure a defined surface configuration of the reflector netting. Such locking requires an additional drive means because during or along the last portion of the unfolding displacement a counteraction is required for opposing the increasing tension in the reflector netting. The prior art structure provides for this purpose an adjustment motor which operates block and tackle means. However, the structural details of such block and tackle means are not described in the above mentioned reference.

The flexible cross connectors which are secured to the rib ends in the prior art reflector construction are exposed to extraordinarily high mechanical tensions, especially when the ribs are in their folded condition resting closely next to one another. Moreover, during the starting or launching of a space vehicle, vibrational energy is introduced into the reflector structure which must be taken up additionally by said cross connectors. These extraordinarily high loads are a source of trouble or danger because they may cause one or the other cross connectors to break even before the unfolding operation begins, whereby a proper unfolding is not assured anymore.

In view of the above it is the aim of the invention to achieve the following objects singly or in combination:

to construct an unfoldable antenna netting reflector in such a manner that it is capable of handling high mechanical loads while nevertheless assuring a proper unfolding at any time;

to avoid two separate unfolding phases by assuring a proper unfolding in one sequence;

to assure the required locking in the unfolded condition;

to make sure that the entire reflector netting is uniformly unfolded so that the desired unfolded shape is obtained; and

to keep the ribs, even in the folded condition, as far apart as possible so as to make the unfolding as easy as possible while simultaneously efficiently using the available space.

The unfoldable netting antenna reflector according to the invention comprises at least one lever which connects two adjacent ribs at its two ends. Each lever has two sections capable of buckling in but one direction and locking into a stretched out position when it is in the unfolded condition. Cables forming a block and tackle arrangement are secured to the knuckle or knee joint of the lever sections.

This type of construction according to the invention makes sure that the unfolding operation takes place in a single sequence by the actuation of the cables which are arranged to be effective on the levers buckled substantially radially outwardly in the folded condition, but are substantially radially inwardly effective under the influence of the cables when the cables pull the levers into a stretched out position in which the levers are locked. This type of arrangement makes sure that the unfolding proceeds without any trouble and that the required locking takes place automatically at the end of the unfolding. In their folded condition the levers are not subject to any load and are thus able without any difficulties to withstand the loads that may occur during the transport of these antennas.

The arrangement of the block and tackle means may be such that the cables which cooperate with a plurality of levers are operable in unison. This feature makes sure that the entire reflector may be unfolded uniformly so that localized tension loads in the reflector netting are avoided. The levers which are essential for the unfolding operation are preferably secured to the ribs with a spacing from the radially outer rib ends. Thus, it is possible to make these levers shorter than would be necessary if they are secured to the radially outer rib ends. Additionally, spacing the levers from the radially outer end of the ribs has the advantage that the angle between the two arms of the lever in their folded condition is larger which facilitates the beginning of the unfolding operation. The unfolding, especially the beginning of the unfolding, is also facilitated by providing spacers between the ribs so that the ribs cannot contact each other in the folded condition. The larger the initial spacing is between the ribs, the larger the lever angle will become so that the initiation of the unfolding operation becomes ever easier.

In order to provide a reflector structure which is especially stable or rugged in its unfolded and locked state, the rib ends are also interconnected by levers which lock into position when they are stretched out and which are capable of knuckling or folding only in one direction. These levers at the outer ends of the ribs may additionally be employed for facilitating or supporting the unfolding operation. This may be accomplished in a manner similar to that of the lever switch as spaced from the rib ends. For this purpose the knee or knuckle joints of the levers interconnecting the rib ends are also connected to cables of respective block and tackle systems.

In order that the invention may be clearly understood, it will now be described, by way of example, with reference to the accompanying drawings, wherein:

FIG. 1 illustrates an antenna netting reflector according to the invention in its unfolded state;

FIG. 2 shows the reflector according to FIG. 1 in the folded condition;

FIG. 3 illustrates a further example embodiment of an antenna netting reflector according to the invention in the unfolded state; and

FIG. 4, illustrates the reflector of FIG. 3 in its folded condition.

FIG. 1 illustrates schematically an antenna netting reflector 1 whereby only the left-hand half is shown in detail. The right-hand half is a mirrorsymmetrical image of the left-hand half. The reflector 1 comprises substantially a central rib 2 and a plurality of lateral ribs 3, 4 and 5, as well as outer ribs 6. The lateral ribs 3, 4 and 5 are arranged symmetrically on both sides of the central rib 2. For example, three lateral ribs 3, 4 and 5 may be used and one end rib 6 on each side. The ribs 2 to 5 are reinforced in the manner of a truss framework extending perpendicularly to the plane of the drawing substantially in the form of a two-dimensional frame work. The outer ribs 6 are also reinforced by a truss framework, however, in the form of a three-dimensional truss framework. The ribs are all secured to a central holding block 7 from which the ribs extend radially outwardly. The ribs 3 to 6 are pivoted to the holding block 7 and are preferably made of fiber reinforced synthetic material such as carbon fibers embedded in a resin matrix. Thus, these ribs are rather lightweight, yet they have a substantial strength.

A first and second inner lever 8 or 9 is provided between the ribs 2, 4 and 6. The lever 8 comprises two sections 8a and 8b forming a pair. The lever 9 comprises two sections 9a and 9b also forming a pair. The outer ends of the lever sections are connected by conventional pivots or journals 40 to the respective ribs 2, 4, 6. The inner ends of the sections 8a, 8b; 9a, 9b are connected to each other in pairs by conventional knee joints 8', 9' also referred to as knuckling or buckling joints 8' and 9' which take up a locked position when the levers 8 and 9 are in the stretched out position illustrated in FIG. 1. However, these knee joints or buckling joints 8', 9' may buckle radially outwardly. These knee joints as such are conventional machine elements. The radially outer end of the ribs 2 to 6 are interconnected by further outer levers 10, 11, 12 and 13 each also having two sections 10a, 10b; 11a, 11b; 12a, 12b; and 13a, 13b. These outer levers are also locked in the stretched out position and may be buckled radially outwardly by means of their conventional buckling joints 10', 11', 12', and 13' interconnecting their lever sections.

The outer ends of the lever sections 10a to 13b are pivotally connected by conventional pivots or journals 41 to the respective rib.

A total of three cables 14, 15 and 16 are operatively secured to the buckling joints 8' to 12' of the levers 8 to 12. The first cable 14 runs over a first compensating roller or sheave 17. The second cable 15 runs over a second compensating roller or sheave 18 and the third cable 16 runs over a third compensating roller or sheave 19. A fourth cable 20 is operatively secured to the compensating rollers 18 and 19. The fourth cable 20 runs over a fourth compensating roller or sheave 21 which in turn is operatively connected to a pulling cable 22 which may be subjected to a substantially radially inwardly directed tension force or pull which may, for example, be exerted by a power drive such as an electric motor. Additional guide rollers not provided specifically with reference numbers are located to guide the cables. The function of these guide rollers is quite clear from FIG. 2.

In the top plan view illustration the ribs appear to be straight. However, in reality the ribs 2 to 6 have a parabolic bend in a direction perpendicularly to the plane of the drawing for defining in a first approximation a parabolic reflector surface. A metallic netting, not shown, forming the reflector net is secured to the ribs. The netting is of a fine mesh type as is conventional. A second net of a larger mesh size may, for example, be arranged below the first netting for the purpose of adjustment by means of cross wires operatively and adjustably interconnecting both nettings, whereby a close approximation of a parabolically shaped configuration may be achieved.

The same structural components are provided in FIG. 2 with the same reference numbers as in FIG. 1. To further simplify the illustration the ribs 3 to 6 in FIG. 2 are shown by thin dashed lines, whereas the levers 8 to 13 are shown by thick dashed lines to provide a clearer overview. As shown, the ribs in FIG. 2 are not contacting each other in the folded condition since they are spaced from another by spacers not shown, keeping these ribs at a predetermined spacing from one another in the folded condition. Thus, the two inner levers 8 and 9 are not completely folded. This has the advantage that due to the angle enclosed by the lever arms of the levers, the unfolding operation may be easily started. The unfolding operation may be started, for example in that with the aid of the pull cable 22 a pulling force is exerted on the compensating roller or sheave 21 which pulling force extends substantially radially inwardly. This pulling force is transmitted to the compensating rollers 18 and 19, as well as 17 so that eventually a force is applied to the knuckling joints of the inner as well as of the outer levers 8 and 9 or 10 to 12 which force brings these levers into the stretched out position shown in FIG. 1. Simultaneously with the stretching of the levers the ribs are spread apart until the respective levers snap into a locked position in their fully out-stretched condition, whereby the entire reflector structure is locked in the unfolded condition. Thus, the reflector takes up the unfolded state as shown in FIG. 1.

The number and type of ribs shown in the example embodiment of FIGS. 3 and 4 correspond to those in FIGS. 1 and 2. Thus, the same reference numbers are used in FIGS. 3 and 4. The same applies to the inner and outer levers 8 and 9, or 10 to 13. The arrangement in FIGS. 3 and 4 differs from that of FIGS. 1 and 2 primarily in that the pulling force is applied to the inner levers only through one cable 23 connected to the respective knuckle joints 8' or 9'. The cable 23 runs over a compensating roller or sheath 24 and cooperates with a pulling cable 25 for exerting said pulling force.

The outer levers 10, 11 and 12 shown with heavy dashed lines are not actuated by a pull effective radially inwardly, but rather by a tensioning cable 26 which is peripherally arranged. Cable guides 27 to 30 are provided at the buckling joints of the outer levers 10 to 13 for the peripherally arranged tensioning cable 26. The cable guides 27 to 30 may be provided, for example in the form of hollow rails equipped with guide grooves which guide the tensioning cable 26 radially outwardly. Additionally, guide rollers 31 to 35 are pivoted to the radially outer ends of the ribs 2 to 6. These guide rollers 31 to 35 guide the tensioning cable 26 in the radially inward direction. The tension or pulling cables 25 and 26 may, for example, be subjected to tension by means of a motor drive winding apparatus 36 and 37. The details of such a winding apparatus are not essential. These winding devices are actuated if it is intended to bring the reflector from the folded condition shown in FIG. 4 into the unfolded and locked condition shown in FIG. 3.

The illustration in FIG. 4 corresponds to that in FIG. 2, while the reference numbers correspond to that of FIG. 3 as mentioned. In order to unfold the reflectors a pull is simultaneously applied to both tensioning or pulling ropes 25 and 26. However, it would actually be sufficient to bring the levers 8 and 9 into the straightened out position merely by actuating the tensioning cable 25. Further, the unfolding operation is facilitated and accelerated by the additional actuation or tensioning of the tension cable 26.

The compensating rollers 21 and 24 as well as 17, 18 and 19 shown in FIGS. 1 to 4, make sure that the tension applied on the tension cables 22 or 25 are transmitted uniformly to the buckling joints of the respective levers so that the unfolding operation also takes place as uniformly as possible to avoid any jamming.

Both example embodiments shown in the drawings represent reflectors of the so-called "offset type". However, the invention is not limited to this type of reflector. Rather, the invention is applicable without any problems to reflectors of the centrally symmetric type.

Although the invention has been described with reference to specific example embodiments, it will be understood, that it is intended to cover all modifications and equivalents within the scope of the appended claims.