Abstract:
A deployable truss having multiple rigid transverse sections, forming triangles, rectangles or other shapes, where adjacent transverse sections are connected by multiple three-piece longerons hinged together and to the transverse sections. In a folded configuration, the each longeron has a central link that maintains spacing between adjacent transverse sections, providing stowage space for load modules such as stacks of deployable panels. The longeron structure also ensures that deployment of the truss proceeds in a linear fashion and that the deployed truss is relatively rigid. Multiple stay wires coupling adjacent transverse sections further enhances structural rigidity.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates generally to deployable space structures and, more particularly, to truss structures that are essentially rigid when deployed, but which are foldable for compact stowage in a launch vehicle. As used in architecture, the term “truss” is usually applied to an assemblage of structural members that supports a load at two principal points, acting like a beam but reducing the size and weight that would be required if a single beam member were used. More generally, the term “truss” may also be applied to cantilevered structures supported at one end, as in the boom of a crane, or a boom attached to a space vehicle and carrying a load of some kind, such as an antenna or an array of panels.  
         [0002]     A deployable truss typically consists of multiple rigid members connected by hinges in such a way as to be deployable into a relatively rigid truss structure, and to be foldable for compact stowage in a launch vehicle. Deployable trusses for use in space have two major requirements, in addition to being foldable to a compact configuration for launching. First, the truss must deploy in a predictable and preferably linear fashion when commanded to do so and, second, the truss in its deployed configuration should be relatively stable and rigid in order to perform its desired function. For many applications of deployable trusses, there is a third requirement. Ideally, the truss in its launch configuration should provide adequate room for stowing modules that will be carried by the deployed truss. For example, if the truss is to carry an array of flat panels, space should ideally be provided for stacks of these panels, disposed in such a manner that facilitates their deployment when the truss is deployed. The present invention satisfies or exceeds all of these requirements.  
       SUMMARY OF THE INVENTION  
       [0003]     The present invention resides in a deployable truss that provides for linear and predictable deployment and, in the folded configuration, provides room for stowing other deployable components between adjacent sections of the truss. Briefly, and in general terms, the deployable truss of the invention comprises a plurality of similar transverse sections, each comprising multiple members joined to form a rigid, generally coplanar structure, the transverse sections being arrayed in a parallel spaced relationship along a longitudinal axis generally perpendicular to the transverse sections. Located between adjacent transverse sections is a plurality of foldable longerons connected by hinges to the transverse sections. The longerons are deployable from a folded configuration that minimizes spacing between adjacent transverse sections of the truss and a deployed configuration that maximizes the spacing and forms a rigid truss structure with the transverse sections.  
         [0004]     Each of the foldable longerons has three connected sections, including two longeron arms and an intermediate longeron link. Each of the longeron arms has first and second ends and is connected by its first end to a hinge point on one of the adjacent transverse sections. The longeron link is connected to the second ends of the longeron arms by additional hinges. On full deployment, each longeron has its three sections aligned and locked in position. In the folded configuration, each longeron arm is pivoted into the plane of the transverse section to which it is connected, and the longeron links maintain a minimum spacing between adjacent transverse sections.  
         [0005]     In one disclosed embodiment of the invention, each transverse section of the truss is rectangular and four foldable longerons are connected between corresponding corners of adjacent rectangular transverse sections of the truss. In another disclosed embodiment of the invention, each transverse section of the truss is triangular and three foldable longerons are connected between corresponding corners of adjacent triangular transverse sections of the truss.  
         [0006]     The truss may further comprise means for urging the transverse sections apart from each other along the longitudinal axis, unfolding the longerons to their fully extended position, in which the truss is said to be deployed. Preferably, the truss also comprises a plurality of stay wires disposed between and connected to adjacent transverse sections. The stay wires enhance the structural rigidity of the deployed truss.  
         [0007]     It will be appreciated from the foregoing that the present invention provides a significant advance in the field of deployable trusses. In particular, the truss of the invention deploys in a linear and predictable manner and is constructed to leave a minimum spacing between adjacent transverse sections in the folded configuration. Other aspects and advantages of the invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1A  is a perspective view depicting a rectangular truss in accordance with the invention, shown in a folded configuration and having just two transverse sections by way of illustration.  
         [0009]      FIGS. 1B and 1C  are views similar to  FIG. 1A , but showing the rectangular truss in two different intermediate stages of deployment.  
         [0010]      FIG. 1D  is a view similar to  FIG. 1A , but showing the rectangular truss fully deployed.  
         [0011]      FIG. 2  is an enlarged perspective view similar to  FIG. 1A , but showing a rectangular truss with three transverse sections, in the folded configuration.  
         [0012]      FIG. 3A  is a perspective view of a triangular truss having four transverse sections, shown in a folded configuration.  
         [0013]      FIG. 3B  is a view similar to  FIG. 3A , but showing the triangular truss in a partially deployed configuration.  
         [0014]      FIG. 3C  is a view similar to  FIG. 3A , but showing the triangular truss in a fully deployed configuration. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]     As shown in the drawings for purposes of illustration, the present invention is concerned with deployable trusses suitable for use in space applications. Deployable trusses of the prior art have not always been deployable in a stable and linear fashion and have not provided adequate space in the folded configuration for stowage of load modules that will be carried on the deployed truss.  
         [0016]     In accordance with the present invention, a deployable truss includes a plurality of transverse sections, each of which has multiple members connected in a rigid polygonal shape, and a plurality of double hinged longerons connecting corresponding points on adjacent transverse sections.  
         [0017]     As shown in  FIGS. 1A-1D , for example, the truss structure of the invention includes multiple rectangular (or square) transverse sections, two of which are indicated at  10   a  and  10   b.  Each of the rectangular sections  10   a  and  10   b  is rendered rigid by the nature of the connections of its four members, as well as by the interconnecting longeron structure now to be described. Connecting each corresponding pair of corners of the rectangular sections  10   a  and  10   b  is a three-piece longeron  12 , having two longeron arms  12   a  and  12   b  connected at one end by hinges to the rectangular sections  10   a  and  10   b,  respectively, and an intermediate longeron link  12   c,  connected by additional hinges to the other ends of the longeron arms. Thus, each longeron  12  has three sections  12   a,    12   b  and  12   c  connected together by hinges.  
         [0018]     In the folded configuration of  FIG. 1   a,  the four longeron arms  12   a  are folded into a position in which they are essentially in the same plane as the rectangular transverse section  10   a.  Similarly, the longeron arms  12   b  are folded into a position in which they are essentially in the same plane as the other rectangular transverse section  10   b.  The four longeron links  12   c  are aligned in a parallel configuration, perpendicular to the planes of the rectangular transverse sections  10   a  and  10   b.    
         [0019]     As the rectangular truss is deployed, the rectangular transverse sections  10   a  and  10   b  move further apart and the longeron arms  12   a  and  12   b  rotate away from the planes of the rectangular sections and toward an orientation aligned with the longeron links  12   c.  When deployment is complete, each longeron  12  has its sections  12   a,    12   b  and  12   c  in collinear alignment, as shown in  FIG. 1D . During the transition to the deployed configuration, the constraints imposed by the pin hinges connecting the longeron components, and connecting the longerons to the transverse sections, maintains the two transverse sections  10   a  and  10   b  parallel and ensures that the two sections move apart along a perpendicular axis. These relationships apply to each pair of adjacent transverse sections, so that deployment of a truss with multiple transverse sections is constrained to proceed in a completely linear fashion. Deployment energy is supplied by any conventional means, such as spring-loading one of more of the hinges, driving at least one pair of the transverse sections apart using a motor or other means. To enhance rigidity of the deployed structure, adjacent transverse sections may be interconnected by multiple stay wires. These are not shown in  FIGS. 1A-1D  but will be discussed with reference to  FIGS. 3A-3C .  
         [0020]      FIG. 2  depicts a truss in the folded configuration, with three rectangular transverse sections  10   a,    10   b  and  10   c.  The three-part longerons are again referred to by numerals  12   a,    12   b  and  12   c.  As can be seen in the figure, each longeron arm  12   a  and  12   b  is attached to one of the transverse sections  10   a,    10   b,    10   c  by a pin hinge, which permits the longeron arm to pivot about the pin in a plane of rotation that is perpendicular to the plane of the transverse section. Each longeron link  12   c  is hinged to the longeron arms  12   a,    12   b  making up the longeron, but means for pin hinges having pins or axes parallel to the pins in the hinges at the other end of the longeron arms  12   a,    12   b.  In other words, the three members of each longeron are constrained to move, during deployment, in the same plane. When any two adjacent transverse sections are moved apart, these constraints keep the sections  10  parallel and also keep the longeron links parallel with each other and with the longitudinal axis, as discussed with reference to  FIGS. 1A-1D . In general, the structure may be scaled to any larger number of sections, and deployment will still proceed in a linear fashion, either sequentially from section to section, or simultaneously for all the sections.  
         [0021]      FIG. 3A  shows truss with four triangular transverse sections  20   a,    20   b,    20   c  and  20   d,  and multiple longerons  22  interconnecting adjacent transverse sections. As in the rectangular truss, so with the triangular truss each longeron  22  has three sections, including two longeron arms  22   a  and  22   b  coupled by hinges to the respective triangular transverse sections, such as  20   a  and  20   b,  and a longeron link  22   c  coupled by hinges to the two longeron arms  22   a  and  22   b.  In the folded configuration shown in  FIG. 3A , the longeron links  22   c  effectively space adjacent transverse sections apart and provide stowage space for modules to be carried on the deployed truss. As shown in the drawings, these modules may be stacks of radiation panels  30 , for example.  FIG. 3B  shows the triangular truss of  FIG. 3A  when partially deployed, and  FIG. 3C  shows the triangular truss fully deployed.  
         [0022]     Interconnecting each adjacent pair of transverse sections, such as sections  20   a  and  20   b,  are six stay wires  32 . Each pair of stay wires  32  is connected between a point on one transverse section to two non-corresponding points on the adjacent transverse section. The stay wires enhance the rigidity, especially torsional rigidity, of the deployed truss.  
         [0023]     The deployable truss of the present invention is well suited for use in a variety of space missions, including civilian missions such as interplanetary orbiters, and military missions such as space based radar. The simplicity of deployment of the truss makes it useful for unmanned as well as manned missions.  
         [0024]     It will be appreciated that the deployable truss structure of the invention represents a significant advance in the field of deployable trusses. In particular, the truss of the invention is deployable stably and linearly, provides a desirably rigid structure once deployed, and provides stowage space for deployable components, such as panels, thereby facilitating their deployment with the truss. It will also be appreciated that, although specific embodiments of the invention have been described in detail for purposes of illustration, various modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention should not be limited except as by the appended claims.