WO2014127813A1

WO2014127813A1 - Deployable support structure

Info

Publication number: WO2014127813A1
Application number: PCT/EP2013/053342
Authority: WO
Inventors: Giovanni-Lorenzo SCIALINO; Julian B. SANTIAGO-PROWALD; Cornelis Van't Klooster
Original assignee: Esa European Space Agency
Priority date: 2013-02-20
Filing date: 2013-02-20
Publication date: 2014-08-28

Abstract

The present invention relates to deployable support structures for space applications, such as deployable reflector antennas, solar reflectors, or concentrators. A deployable support structure comprising a polyhedron truss is proposed. The polyhedron truss comprises multi-bar linkages and is convertible from a deployed state into a first folded state and vice versa. In the deployed state, the polyhedron truss has an upper polygonal base of articulated bars (15) and a lower polygonal base of articulated bars (16), wherein the upper and lower polygonal base are perpendicular to a longitudinal center axis and interconnected by lateral bars (14) that are pivotably coupled to the articulated bars (15, 16) of the upper and lower polygonal base. The polyhedron truss is configured to be convertible from the deployed state into the first folded state such that in the first folded state, the bars of the upper and lower polygonal base are pivoted around the lateral bar to which they are pivotably coupled until being in a slightly inclined or parallel state to a longitudinal axis of the lateral bar, and the lateral bars are converged towards the center axis of the upper and lower polygonal base. The polyhedron truss is further configured to be convertible from the first folded state into a second folded state and vice versa such that in the second folded state, a lower part (10b) of the polyhedron truss is folded up against an upper part (10a) thereof, wherein a group of bars comprising one of the lateral bars and bars of the lower polygonal base (16) that are pivotably coupled to the one of the lateral bars (14) rotate around a common secondary hinge axis (22).

Description

DEPLOYABLE SUPPORT STRUCTURE

The present invention relates to deployable support structures for space applications, such as deployable reflector antennas, solar reflectors, or concentrators.

In particular, the present invention is related to foldable structures used on space vehicles to support flexible membranes in the deployed condition and that must be folded in a compact volume to be accommodated inside a launch vehicle together with the spacecraft.

A typical application is for large deployable reflectors, either with a metallic mesh radio frequency (RF) reflecting membrane kept in a parabolic profile by a set of nets and tensioners, or with an elastically foldable shell, or with a planar reflect- array multilayer membrane. Other applications include solar concentrators in which the flexible membrane is tensioned in a prescribed shape and is reflecting the solar energy in a desired direction or solar sails in which the membrane is stretched in a planar fashion and collects the energy of the solar wind in order to provide translational force to the spacecraft.

Large deployable reflectors are known in the art. The ones already used in flight applications have the following architectures for the foldable structure that supports the RF reflective mesh: flexible ribs folded by wrapping around a central hub; structures made by radial rods folded in radial planes, with associated tensioning wires and scallops structures to support and shape the mesh in between the rods; modular deployable structures connected in series each with foldable radial rods with associated tensioning wires and nets to tension and shape the mesh in between the rods; expandable ring structure with symmetric nets connected by ten- sioners in order to keep the parabolic profile and the RF reflecting mesh connected to one of the nets.

The flexible ribs architecture requires a complex deployment mechanism and has the disadvantage of a large diameter and relatively thick stowed package. The other approaches described above have the disadvantage that the stowed volume of the support structure usually has a length much bigger than the thickness of the reflector in deployed configuration. By way of example, a low weight, compactly deployable support structure has been disclosed previously as W02012/065619 Al, which is hereby incorporated by reference. This deployable structure comprises articulated struts arranged in a conical-shaped module when deployed, which can be either unique or multiply connected in a complex structure. One of the aspects of this deployable structure is the deployment actuation within all of the hinged struts (V-folds) forming the upper and lower chords of the cell or ring. This actuation can be either elastically or electrically motorized. This deployable support structure enables a flexible modular architecture for building large apertures. As the required aperture size or number of reflectors per space-deployed communication site increases, the availability of lightweight, compactly packaged antenna structures that can be compactly stowed for transport on a spacecraft is a key prerequisite for the usage of such large apertures.

In view of the above problems of the prior art, the present invention seeks to pro- vide an improvement to the architecture of such large annular deployable structures, like the ones of the reflectors for antennas, in order to reduce the length of the package in stowed configuration compared to the prior art.

This object is accomplished by the subject-matter according to the subject-matter of the independent claim 1. The dependent claims refer to preferred embodiments of the invention. In accordance with an aspect of the invention, a deployable support structure for space applications is proposed. The deployable support structure comprises a polyhedron truss. The polyhedron truss comprises multi-bar linkages of articulated members. Preferably, the members are articulated struts or bars and are of a light- weight, yet rigid material. The polyhedron truss is convertible from a deployed state into a first folded state and vice versa. Thus, the kinematics of the deployable support structure is reversible.

When in the deployed state, the polyhedron truss comprises an upper polygonal base of articulated bars and a lower polygonal base of articulated bars. In accordance with an aspect, the upper polygonal base and the lower polygonal base are perpendicular to a common longitudinal center axis and interconnected by lateral bars that are pivotably coupled to the articulated bars of the upper and lower polygonal base. The bars of the upper and of the lower polygonal base and the lateral bars are coupled to each other by hinges. These hinges are hereinafter referred to as primary hinges, as these hinges are configured to enable rotation of the bars when converting the polyhedron truss from the deployed state into the first folded state and vice versa. In accordance with this aspect, the polyhedron truss is configured to be convertible from the deployed state into the first folded state. In the first folded state, the bars of the upper and lower polygonal base are pivoted around the lateral bar to which they are pivotably coupled by the primary hinges until being in a slightly inclined or parallel state to a longitudinal axis of the lateral bar. In the first folded state, the lateral bars may be converged towards the center axis of the upper and lower polygonal base forming a compact "cylindrical" pack- age.

Thus, a first folding mechanism or first folding means is provided to convert the polyhedron truss from a deployed state into an intermediate folding configuration by rotating the bars of the polyhedron truss around the primary hinges. In the in- termediate folding configuration, the diameter of the support structure may be reduced since the bars that have been rotated around the primary hinges are in a parallel or in a slightly inclined state to the other bars of the polyhedron truss. The terms "bars", "rods", and "struts" are used synonymously.

In accordance with an aspect of the invention, the polyhedron truss is further con- figured to be convertible from the first folded state into a second folded state and vice versa such that in the second folded state, a lower part of the polyhedron truss is folded up against an upper part thereof. Thus, a second folding mechanism is provided that significantly reduces the axial length of the support structure compared to the intermediate folding configuration.

Preferably, when converting the polyhedron truss from the first folded state into the second folded state, a group of bars comprising one of the lateral bars and bars of the lower polygonal base that are pivotably coupled to the one of the lateral bars by means of one of the primary hinges rotate around a common second- ary hinge axis when being folded up against the upper part of the support structure. The term "group of bars" as used herein refers to a set of bars of the polyhedron truss that rotates around a common axis (secondary hinge axis) when the polyhedron truss is converted from the first folded state into the second folded state and vice versa. It will be appreciated that the terms "upper" and "lower" as used herein are used for convenience only, and the actual relative positions of the first or upper part of the polyhedron truss and the second or lower part of the polyhedron truss may be varied.

In order to avoid interference of adjacent groups of bars during the transition from the first folded state to the second folded state and vice versa, each group of bars may have a different common secondary hinge axis and all secondary hinge axes may be located in the same plane such that the lower part of the polyhedron truss is folded up radially outboard against an upper part thereof. By way of example, the plane of the secondary hinge axes may be perpendicular to the longitudinal center axis of the polyhedron truss and the secondary hinge axes may be arranged along a circumferential direction of the cylindrical package of folded bars in the first folded state. Preferably, angles between adjacent secondary hinge axes are identical or substantially identical. This advantageously maximizes the distance between adjacent groups of bars during the folding from the first folded state to the second folded state and vice versa. In accordance with a further aspect, each of the lateral bars and the bars of the lower polygonal base may comprise a hinge for the secondary folding from the first folded state into the second folded state and vice versa. Hereinafter, these hinges are referred to as secondary hinges. The term "secondary hinge" is used to highlight the aspect that this hinge is used for the secondary folding from the first fold- ed state into the second folded state and vice versa. A secondary hinge segments a bar into two members. In accordance with this aspect, the secondary hinges of each group of bars may be positioned on the common hinge axis for each group of bars during the folding up of the lower part of the polyhedron truss against the upper part thereof. In other words, the bars of each group of bars may have co- aligned secondary hinges.

It is beneficial to arrange the secondary hinges at an end portion of the bars of the lower polygonal base, e.g., close or adjacent to a primary hinge, in order to reduce the axial length of the folded support structure in the second folded state.

Likewise, it is beneficial to configure the secondary hinges to enable a rotation of elements of the bars of the lower part of the polyhedron truss outboard of the longitudinal center axis in order to avoid any unintended interference of adjacent groups of bars during the unfolding from the second folded state to the first folded state and vice versa.

In accordance with a further aspect of the invention, the secondary hinge axes may be arranged at a height that does not interfere with the struts of the upper and lower polygonal base when parallel to the lateral bars in the first folded state. In accordance with this aspect, the secondary folding mechanism would not require additional secondary hinges, since the folding line would not encounter any of the two lateral struts in each group of bars. In accordance with a further aspect of the invention, a lateral facet of the polyhedron truss may comprise a diagonal inclined member, wherein inclined members in adjacent lateral facets are arranged in an alternate inclination.

In accordance with this aspect, the lower and upper polygonal base may comprise an alternate sequence of joints with three converging bars and joints with five converging bars. By way of example, a joint with three converging bars of the lower polygonal base comprise a lateral bar and two bars of the lower polygonal base, whereas a joint with five converging bars comprises a lateral bar and two bars of the lower polygonal base and two diagonal inclined members. Joints of the upper polygonal base may be configured in an analogous manner with the exception that bars of the upper polygonal base are used. In accordance with an aspect of the invention, in the deployed state, the polyhedron truss may be configured to have a cylindrical shape with rectangular lateral facets, wherein the lateral facets comprise a bar of the upper polygonal base, a bar of the lower polygonal base, two lateral bars, and a diagonal inclined member. A lateral facet is a lateral flat face on the polyhedron truss comprising opposing lateral bars and one or more bars of the upper polygonal base and one or more bars of the lower polygonal base.

In accordance with an aspect, the inclined member may comprise a secondary hinge and each group of bars may comprise two inclined members, wherein all secondary hinges of the same group of bars are co-aligned in the first folded state.

In accordance with an aspect of the invention, the inclined member may be telescopic having its minimal length in the deployed state. In accordance with this aspect, the inclined telescopic member comprises an inner element and an outer element, and the secondary hinge of the inclined member may be provided on the outer element. In accordance with a further advantageous aspect, it is proposed that in the first folded state, the inner member has moved out of an area of the secondary hinge such that only the outer element is folded up against the upper part of the polyhedron truss when converting the polyhedron truss from the first folded state to the second folded state. In accordance with a further aspect of the invention, means for actuating said primary and secondary hinges may be provided to deploy the folded support structure from the fully folded state (i.e., the second folded state) via the intermediate folded configuration (i.e., the first folded state) to the fully deployed state. Said means for actuating cause said bars of the polyhedron truss to pivot around the primary hinges when moving between said deployed and first folded states, and cause said group of bars to pivot around the secondary hinge axes when moving between said first folded state and second folded state. The deployment actuation of the primary and secondary hinges can be either elastically or electrically motorized using actuation means known in the art. By way of example, it is proposed that each secondary hinge comprises a spring-driven actuation system for driving the rotation of the folded bars during an unfolding process from the second folded state into the first folded state which provides a reliable, light-weight actuation means suitable for space applications. In order to constrain the rods in the aligned position at the end of the unfolding rotation process, each secondary hinge may comprise a latching system.

In accordance with a further aspect of the invention, the deployable support structure may comprise means for constraining the rods in the adjacent configuration when converting the polyhedron truss from the first folded state to the second folded state and vice versa. The adjacent configuration is the state wherein the bars of the upper and lower polygonal base are pivoted around the lateral bar to which they are pivotably coupled such that they remain in a slightly inclined or parallel state to a longitudinal axis of the lateral bar.

In accordance with another aspect, a lateral facet of the polyhedron truss may comprise a six-bar linkage and the six-bar linkage may comprise two bars of the upper polygonal base arranged in series and coupled by a primary hinge, two bars of the lower polygonal base arranged in series and coupled by a primary hinge and two lateral bars, wherein each lateral bar is coupled to a bar of the lower polygonal base and a bar of the upper polygonal base by a primary hinge, respectively.

In accordance with this aspect, in the deployed state, the polyhedron truss may form a truncated pyramidal or cylindrical ring structure. By way of example, the six- bar linkage may have a trapezoidal shape and the polyhedron truss is forming a truncated hexagonal pyramidal ring structure.

In accordance with an aspect of the invention, a deployable space antenna, a solar reflector or a solar concentrator is proposed comprising a deployable support structure according to any of the aspects described above. It is again noted that the kinematics of the deployable support structure is reversible so that the support structure can be converted from the fully folded state (i.e., the second folded state) via the intermediate folded configuration (i.e., the first folded state) to the fully deployed state. However, said means for actuating are typically configured to deploy the fully folded support structure, but not to fold the deployed assembly. By way of example, the deployable support structure is typical^¬ ly stowed in the fully folded state in a spacecraft.

The invention is explained below in an exemplary manner with reference to the accompanying drawings, wherein

Figs. 1A to 1G show a series of transition states when converting a deployable support structure from the deployed state into the folded state according to an embodiment of the invention;

Figs. 2A and 2B show a joint with five rods of the polygonal base of a deployable support structure in the deployed and folded state according to an embodiment of the invention;

Figs. 2C and 2D show a joint with three rods of the polygonal base of a deployable support structure in the deployed and folded state according to an embodiment of the invention;

Figs. 3, 4, and 5 illustrate detailed views of an intermediate folding configuration of a deployable support structure according to embodiments of the invention;

Figs. 6A and 6B show a detailed view of a secondary hinge of the inclined member according to an embodiment in the deployed and folded configuration;

Figs. 7A to 7G show a series of transition states when converting a deployable support structure from the deployed state into the folded state according to a further embodiment of the invention;

Figs. 8A and 8B show a cut-out front and perspective view of a deployable support structure in the deployed configuration according to an embodiment of the invention; Figs. 9A and 9B show a cut-out front and perspective view of an intermediate folding state of a deployable support structure according to an embodiment of the invention; Figs. 9C and 9D show a cut-out perspective and top view of another intermedi^¬ ate folding state of a deployable support structure according to an embodiment of the invention; and

Figs. 9E to 9G show perspective views of further intermediate folding states of a deployable support structure according to an embodiment of the invention.

Fig. 1A shows a deployable polyhedron truss structure 10 according to an embod- iment. The structure has a longitudinal axis 13 illustrated by the dashed line 13 and a closed periphery centered on the longitudinal axis. The periphery is com^¬ posed by a structure of multi-bar linkages comprising two sets of members: an upper polygonal base 11 of articulated bars 15 and a lower polygonal base 12 of ar^¬ ticulated bars 16. The upper and lower polygonal bases are interconnected by lat- eral bars 14 that are pivotably coupled to the articulated bars 15, 16 of the upper and lower polygonal base. Thus, the two sets of members are connected by a set of lateral bars 14 such as to create a stiff and stable interconnection between the two peripheral edges. The lateral members 14 connecting the nodes of the edges are arranged as mem^¬ bers parallel to the longitudinal axis 13. The polyhedron truss comprises an even total number of lateral facets, wherein a lateral facet of the polyhedron truss comprises two opposing lateral bars 14, one bar 15 of the upper polygonal base 11, one bar 16 of the lower polygonal base 12, and an inclined member 20 as a diag- onal element of the lateral facets. Inclined members 20 of adjacent lateral facets have an alternate inclination. The inclined member 20 is telescopic and in the deployed configuration shown in Fig. 1A, it achieves its minimal length. Figs. 1A to 1G show a series of transition states when converting the polyhedron truss 10 from the deployed state shown in Fig. 1A into the fully folded state shown in Fig. 1G. According to a first folding mechanism, the polyhedron truss 10 is con- figured to be convertible from the deployed state shown in Fig. 1A into the first folded state shown in Fig. ID. The folding process is based on the rotation of the edge members 14, 15, 16 of the multibar-linkage and of the inclined ones 20 such as to become parallel or at least slightly inclined to the longitudinal axis 13. The rotation is made such as to elongate all the telescopic members 20 and to align them to the longitudinal axis 13. This rotation reduces the width of a lateral facet and hence reduces the diameter of the structure 10, since the bars converge towards the center axis 13.

The polyhedron truss is further configured to be convertible from the first folded state shown in Fig. ID into a second folded state illustrated in Fig. 1G and vice versa such that in the second folded state, a lower part 10b of the polyhedron truss is folded up against an upper part 10a thereof. The members 16 of the lower polygonal base 12 and the telescopic members 20 include each a secondary hinge 17 (shown in Figs 4, 5, 6A and 6B). The secondary hinge allows the folding of the members of the lower edge and of portion of the inclined members with a movement, contained in planes that extend radially from the longitudinal axis 13, first outboard as shown in Fig. IE and then such as to set the members parallel or slightly inclined to the ones of the upper polygonal base 11, as illustrated in Figs lF and lG.

The joints coupling the bars of the upper or lower polygonal base with the lateral bars have an alternate sequence of configurations. Joints with five converging rods are alternate to joints with three converging rods as shown in Figs. 2A to 2D along the circumferential edge of the upper polygonal base and along the circumferen- tial edge of the upper polygonal base of the polyhedron truss. Fig. 2A shows a joint 18 with five bars of the polygonal base, pivotably coupling two bars 15 of the upper polygonal base, two inclined members 20, and a lateral bar 14 with primary hinges 21. Fig. 2A shows the joint 18 when the polyhedron truss 10 is in the deployed state of Fig. 1A, whereas Fig. 2B shows the joint 18 when the polyhedron truss 10 is in the first folded state of Fig. ID. In the first folded state, the bars 15 of the upper polygonal base and the inclined bars 20 are pivoted around the lateral bar 14 to which they are pivotably coupled until being in a parallel or slightly inclined state to a longitudinal axis 14a of the lateral bar 14 and thus, also parallel to the longitudinal center axis 13.

Similarly, Figs. 2C and 2D illustrate a joint 19 with three rods of the polygonal base. Fig. 2C shows the joint 19 when the polyhedron truss 10 is in the deployed state of Fig. 1A, whereas Fig. 2D shows the joint 19 when the polyhedron truss 10 is in the first folded state of Fig. ID

Figs. 3, 4, and 5 illustrate detailed views of an intermediate folding configuration of a deployable support structure according to embodiments of the present invention. According to the embodiment shown in Fig. 3, the rods 15, 16 of the upper and the lower polygonal base (also referred to as edge rods) as well as the lateral rods 14 parallel to the longitudinal axis 13 all have the same length. This implies that after the rotation of the edge rods 15, 16 and inclined rods 20 to achieve the intermediate folded configuration shown in Fig. ID and Fig. 3, the joints 18, 19 are aligned on three levels along an upper, lower, and one central line, as shown in Fig. 3 of the intermediate folding configuration. Fig. 3 shows that the joints 18 with five converging rods are aligned on an upper and lower level, whereas joints 19 with three converging rods are aligned on a central level.

The embodiment shown in Fig. 3 indicates that the periphery of the folded support structure in the intermediate folding position has a width determined in a first ap- proximation by the sequence of the width of the following rods 15, 16 of the upper and lower edges and of the inclined members 20, whereas the lateral rods 14 oc- cupy the space in between the other rods and, hence, do not contribute to the width of the periphery.

Fig. 4 further illustrates the secondary folding mechanism (not shown in Fig. 3). In order to convert the polyhedron truss 10 from the first folded state into the second folded state and vice versa, secondary hinges 17 are provided. In particular, for each of the lower group or set of five rods (i.e., two rods 16 of the lower polygonal base, two elongated members 20 and one lateral bar 14), a set of secondary hinges 17 is provided, which is illustrated by the dotted elliptical line 17b. The hinges 17 of the five rods are collinear in order to enable the folding and subsequent deployment around a common hinge axis 22. The secondary hinges 17 segments the five rods in two components. It is preferred to keep the secondary hinges 17 separate from the ones 18, 19 of the peripheral edges, as shown in Fig. 4.

The secondary hinge axis 22 changes from one set of five rods to the next such to allow the deployment radially outboard from the polyhedron truss. It is noted that the simplified illustration of Fig. 4 does not show that the secondary hinge axes 22 are arranged along a circumferential direction of the cylindrical package of the folded polyhedron truss in the first folded state, wherein angles between adjacent secondary hinges axes are preferably identical. This shift of the hinge axes 22 is shown, however, in Fig. 9D.

When converting the polyhedron truss 10 from the first folded state into the se- cond folded state, each group of bars rotate around a common secondary hinge axis 22, as indicated by the dotted elliptical line so that the lower part 10b of the polyhedron truss 10 is folded up against an upper part 10a thereof. The lower part 10b of the polyhedron truss 10 is below the secondary hinge axes 22. Fig. 5 illustrates an embodiment according to which the inclined member 20 is telescopic and comprises an external hollow tube 20a and an inner sliding solid element 20b. The inner sliding element 20b has a conical edge opposite to the hinged edge and a cylindrical body in between the two edges (not shown). The conical edge is used to avoid the jamming of the inner sliding element when moving across the joint of the external hollow tube 20a, as will be explained further below. When the initial step of the folding process is complete, leading to have all the rods of the upper and of the lower edges parallel to the longitudinal rods (first folded state), the length of the telescopic rods 20 have increased to about two times the length of the lateral rods 14. In this condition, the inner sliding element 20b has moved out of the secondary hinges 17 of the inclined member 20.

At this stage, it is possible to perform the folding rotation around the secondary hinges as depicted in Figs. IE to 1G. At the end of the folding rotation, the external rods may be constrained by belts (not shown) in order to keep the rods in folded configuration aligned to the longitudinal center axis 13 of the structure. A third constraint system (not shown) can be used to keep the structure against a satellite interface cradle during the launch. The arm (not shown) to interface the structure to the satellite will be connected to one lateral rod at its upper and/or lower edges. The arm will be connected to a lateral rod that is not involved in the secondary rotation process. The side towards the satellite will be connected to a joint with five rods and the side opposite to the satellite will be connected to the joint with three rods. The arm will be stabilized by two diagonal secondary rods that will connect the arm to the adjacent three rods joints, the secondary rods are terminated with spherical hinges on both sides.

Figs. 6A and 6B show a detailed view of a secondary hinge 617 of the inclined member according to an embodiment in the deployed (Fig. 6A) and folded configuration (Fig. 6B). The inner sliding element 20b has an axial trough hole 24 in which a flexible tether 23 is routed that is running inside all the telescopic members 20 and is wound by a winch during the deployment process in order to create the expansion of the structure. By way of example, the length of the sliding element 20b is equal to 0.8 times the length of the lateral rod 14. By way of example, in the aligned configuration, the length of the external hollow structure 20a is about 1.4 times the length of the lateral rod 14. Each secondary hinge comprises a latching means 25 that constrains the rods in the aligned position at the end of the unfolding rotation process. Further, each secondary hinge 17 incorporates a spring-driven actuation system that will drive the rotation of the folded rods during the unfolding rotation process (not shown).

For illustrating purposes, the deployment process (reverse sequence from Fig. 1G to Fig. 1A) of a folded support structure 10 as described above may follow the steps listed hereafter:

- Release of the system that holds the structure constrained against the spacecraft;

- Deployment of the arm to locate the interface between the arm and the struc- ture in the operational position with regard to the spacecraft; .

- Release of the belts that keep the rotated rods aligned to the longitudinal axis of the structure. The release can be made by systems well known to the art; - As the folded rods are released from the belts, spring-driven rotators included in the secondary hinges may drive the rotation of the rods of the lower edge and of the portion of the telescopic members that include the inner sliding members, the rotation will proceed until the rods will become aligned with the longitudinal axis and the latches of each secondary hinge will become engaged and a spring connected to the tether will keep it from being trapped in the hinges;

- Once confirmed by telemetry that all secondary hinges have reached their latched aligned configuration, the primary belt system will be released to allow the expansion of the structure; - A motor driven winch will be activated to recover the tether, hence, actuating the shrinkage of the telescopic members and, as a consequence, the expansion of the structure. At the start of this sequence the conical edge of the inner element of the telescopic members will engage the joining area of the two halves of the external tube, the conical edge will avoid the risk of jamming during this movement; and

- Latches included in the telescopic struts will be activated when each telescopic member reaches its final prescribed length such to induce a stiffness of the structure.

Figs. 7A to 9G illustrate schematically the application of the secondary folding concept to another ring architecture, in particular, the truncated hexagonal pyramidal cell. Fig. 7A shows a perspective view of a polyhedron truss 30 having a trun- cated hexagonal shape in the deployed state according to another embodiment of the invention. Like numbers refer to like elements throughout. The polyhedron truss 30 comprises six-bar linkages in each of the lateral facets of the polyhedron truss 30. The six-bar linkage structure comprises six rigid members or articulated struts 34, 35, 36, each coupled to two others by a revolute joint 38 to form a closed loop. In other words, the struts are hinge-connected to one another in end-to-end fashion at hinge joints so as to define a closed loop structure. In the deployed state (Fig. 7A), the six-bar linkage structure is forming a trapezoid with two opposing parallel sides, each of the parallel sides being formed by two struts 35 (or two struts 36, respectively) arranged in series and coupled by a primary hinge 38 at the center of the upper and lower parallel sides. The non-parallel, quasi-vertical sides of the trapezoid in Fig. 7A are formed by one lateral strut which is pivotally coupled to a strut 35 by a revolute joint 38 and pivotally coupled to a lower strut 36 by another revolute joint 38. Similar to the embodiment shown in Fig. 1A, the polyhedron truss of Fig. 7A has a longitudinal axis illustrated by the dashed line 33 and a closed periphery centered on the longitudinal axis formed by the six-bar linkages. The upper struts 35 of the six-bar linkages form the upper polygonal base 31 of articulated bars and the low- er struts 36 of the six-bar linkages form the lower polygonal base 32 of articulated bars. The upper and lower polygonal bases are interconnected by the lateral bars 34 that are pivotably coupled to the articulated bars 35, 36 of the upper and lower polygonal bases. Figs. 7A to 7F illustrate schematically a folding sequence of the support structure 30 and a series of transition states when converting the deployable support structure from the deployed configuration (Fig. 7A) into the folded configuration (Fig. 7F) and vice versa. The distinction between the primary folding and secondary folding can be seen by following the figure sequence 7A, 7B, and 7C (primary folding) and 7D, 7E, and 7F (secondary folding).

The primary folding process is based on the retraction of the primary hinges 38 in the upper and lower polygonal bases 31, 32. The bars 35, 36 of the upper and lower polygonal bases 31, 32 are pivoted around the lateral bar 34 to which they are pivotably coupled (see Fig. 7B) until being in a slightly inclined or substantially parallel state to the lateral bar 34. Fig. 7C illustrates the end of primary folding, i.e. the first folded state. In this state, the lateral bars are converged towards the cen- ter axis 33 of the upper and lower polygonal base 31, 32 forming a cylindrical package with reduced diameter.

In this particular embodiment, the secondary folding involves groups (sets) of three struts, wherein the axes 22 of the secondary folding rotation of the three struts are co-aligned in order to make the movement kinematically compatible. Each set of three struts is composed by one of the quasi-vertical struts 34 and the two adjacent folding struts 36 belonging to the lower polygonal base 32. By way of example, Fig. 7D shows a folding state of the secondary folding phase, wherein two sets of three struts are folded around co-aligned secondary hinges (not shown) so that a lower part 30b of the polyhedron truss is folded up against an upper part 30a thereof. The upper and lower hexagonal dashed lines 38a in Figs. 7D to 7F illustrate the position of an outer end portion of the polyhedron truss in the first folded state comprising some of the primary hinges 38. The hexagonal dashed line with the reference numeral 22 illustrates the locations of the secondary hinge axes 22 and of the secondary hinges (see also Fig. 9D).

Fig. 7E shows a folding state of the secondary folding phase, wherein two further sets of three bars are folded around aligned secondary hinges. Fig. 7F shows the second folded state wherein all sets of three struts are fully folded against the upper part 30a of the assembly. It is appreciated that all groups of three struts may also be folded up at the same time against the upper part 30a of the assembly.

Figs. 8A and 8B show a detailed perspective view of two facets of a deployable support structure in a starting position of the two facets of the polyhedron truss in a deployed state. Figs. 8A and 8B additionally show the secondary hinges 37 that are not shown in the schematic representation of the folding sequence of Figs. 7A to 7F.

Each bar 36 of the lower polygonal base and each lateral bar 34 comprises a secondary hinge 37. The secondary hinges 37 of the bars 36 are preferably provided at an end portion thereof, close to the primary hinge 38 that is coupling the bars 36 of the lower polygonal base arranged in series. This will reduce the axial length of the folded support structure in the second folded state.

Figs. 9A and 9B illustrate the folding state of the primary folding sequence already shown in Fig. 7B that is based on the retraction of the primary hinges 38 in the upper and lower polygonal bases 31, 32. The bars 35, 36 of the upper and lower polygonal bases 31, 32 are pivoted around the lateral bar 34 to which they are pivotably coupled until being in a slightly inclined or substantially parallel state to the lateral bar 34, as shown in Figs. 9C and 9D.

Figs. 9C and 9D show the end state of the primary folding, wherein the polyhedron truss 30 is folded to a cylindrical package. All struts are parallel in this stage. In Figs. 9C and 9D, only one full set of three struts belonging to the functional set that is synchronically folding in the secondary phase is visible, illustrated by the dotted elliptical line 37a. These struts have co-aligned secondary hinges 37 aligned on a common secondary hinge line 22, as shown in Fig. 9D. The adjacent groups of bars (only two bars of the adjacent groups are shown in Figs. 9C and 9D) have different common secondary hinge lines 22.

Figs. 9E to 9G then illustrate a secondary folding sequence of two sets of three bars. The groups of bars below the secondary hinge lines 22 form the lower part 30b of the polyhedron truss that is folded up radially outboard against an upper part 30a thereof. After completion of the secondary folding, the package length is almost half the original length.

Features, components and specific details of the structure of the above-described embodiments of the present invention may be exchanged or combined to form further embodiments optimized for the respective application. As far as those modifications are already apparent for an expert skilled in the art, this shall be disclosed implicitly by the above description, without specifying explicitly every possible combination, for the sake of conciseness of the present description.

In particular, it will be appreciated that the present invention is not limited to the particular cell structure or polyhedron truss described in the exemplary embodiments. By way of example, the secondary folding mechanism could also be provided for a deployable polyhedron truss comprising a six-bar linkage structure in a lateral facet of the polyhedron truss. In accordance with this aspect, the six-bar linkage structure of each lateral facet is convertible from a folded state into a deployed state, wherein the six-bar linkage structure comprises two first bars and four second bars, each bar being coupled to two others by a hinge to form a closed loop. In the deployed state, the six-bar linkage structure has substantially a quadrilateral shape. The two first bars are located at opposite sides of the quadrilateral and, thus, represent two opposing sides of the quadrilateral shape of the six-bar linkage when in the deployed state. Two second bars are arranged in series on each of the other two opposing sides of the quadrilateral in the deployed state. In the folded state, the second bars are pivoted around the first bars. In the folded state, the two second bars arranged in series are also pivoted relative to each other around their coupling hinge forming a V-shape (also referred to as V-fold bar). In the folded state, the first bars are arranged so that the end portions of two adjacent first bars are located side by side.

Claims

1. A employable support structure for space applications, comprising

a polyhedron truss (10; 30) comprising multi-bar linkages being convertible from a deployed state into a first folded state and vice versa;

in the deployed state, the polyhedron truss (10; 30) having an upper polygonal base (11;31) of articulated bars (15; 35) and a lower polygonal base (12; 32) of articulated bars (16; 36), wherein the upper and lower polygonal base are perpendicular to a longitudinal center axis (13; 33) and interconnected by lateral bars (14; 34) that are pivotably coupled to the articulated bars (15, 16; 35, 36) of the upper and lower polygonal base;

the polyhedron truss (10; 30) is configured to be convertible from the deployed state into the first folded state such that in the first folded state, the bars of the upper and lower polygonal base are pivoted around the lateral bar to which they are pivotably coupled until being in a slightly inclined or parallel state to a longitudinal axis (14a) of the lateral bar (14; 34), and the lateral bars are converged towards the center axis (13; 33) of the upper and lower polygonal base; and wherein

the polyhedron truss is configured to be convertible from the first folded state into a second folded state and vice versa such that in the second folded state, a lower part (10b; 30b) of the polyhedron truss is folded up against an upper part (10a; 30a) thereof, wherein a group of bars comprising one of the lateral bars and bars of the lower polygonal base (16; 36) that are pivotably coupled to the one of the lateral bars (14; 34) rotate around a common secondary hinge axis (22) .

2. Deployable support structure according to claim 1, wherein each group of bars has a different common secondary hinge axis (22), all secondary hinge axes being in a same plane such that the lower part (10b; 30b) of the polyhedron truss (10; 30) is folded up radially outboard against an upper part (10a; 30a) thereof.

3. Deployable support structure according to claims 1 or 2, wherein the lateral bars (14; 34) and the bars (16; 36) of the lower polygonal base (12; 32) comprise a secondary hinge (17, 617; 37), wherein during the folding up of the lower part (10b; 30b) of the polyhedron truss (10; 30) against the upper part (10a, 30a) thereof, the secondary hinges (17, 617; 37) of each group of bars are positioned on the common hinge axis (22) for each group.

4. Deployable support structure according to claim 3 wherein the secondary hinges (17, 617; 37) are configured to enable a rotation of elements (34b, 36b) of the bars of the lower part (10b; 30b) of the polyhedron truss (10; 30) outboard of the longitudinal center axis (13; 33).

5. Deployable support structure according to any of the preceding claims, wherein a lateral facet of the polyhedron truss comprises a diagonal inclined member (20), wherein inclined members (20) in adjacent lateral facets are arranged in an alter^¬ nate inclination.

6. Deployable support structure according to any of the preceding claims, wherein in the deployed state, the polyhedron truss (10) is configured to have a cylindrical shape with rectangular lateral facets, wherein the lateral facets comprise a bar (15) of the upper polygonal base (11), a bar (16) of the lower polygonal base (12), two lateral bars (14) and a diagonal inclined member (20).

7. Deployable support structure according to any of the claims 5 to 6, wherein the inclined member (20) comprises a secondary hinge (17) and each group of bars comprises two inclined members (20), wherein all secondary hinges (17) of the same group of bars are co-aligned in the first folded state.

8. Deployable support structure according to claims 5 to 7, wherein the inclined member (20) is telescopic having its minimal length in the deployed state.

9. Deployable support structure according to claim 8, wherein the inclined telescopic member comprises an inner element (20a) and an outer element (20b) and the secondary hinge (617) of the inclined member (20) is provided on the outer element (20b), wherein in the first folded state, the inner member (20a) has moved out of an area of the secondary hinge (617) such that only the outer element (20b) is folded up against the upper part (20a) of the polyhedron truss (10) when converting the polyhedron truss (10) from the first folded state to the second folded state.

10. Deployable support structure according to any of the preceding claims, wherein each secondary hinge (17, 617; 37) comprises a spring-driven actuation system for driving the rotation of the folded rods during an unfolding process from the first and/or second folded state into the deployed state.

11. Deployable support structure according to any of the preceding claims, wherein each secondary hinge (17, 617; 37) comprises a latching system.

12. Deployable support structure according to any of the preceding claims, further comprising means for constraining the bars of the polyhedron truss in the adjacent configuration during the folding process.

13. Deployable support structure according to any of claims 1 to 4, wherein a lateral facet of the polyhedron truss (30) comprises a six-bar linkage, the six-bar linkage comprises two bars (35) of the upper polygonal base (31), two bars (36) of the lower polygonal base (32), and two lateral bars (34).

14. Deployable support structure according to claim 13, wherein in the deployed state, the polyhedron truss (10) is forming a truncated pyramidal or cylindrical ring structure.

15. A deployable antenna or solar concentrator comprising a deployable support structure according to any of the preceding claims.