Abstract:
A synchronously deployable tetrahedral truss beam with orthogonally-hinged diagonals, having uniquely-connected transverse members and folding chordal members, where a plurality of bays can extend and retract in a coordinated manner without need for a deployment canister mechanism or other assembling means. The triangular cross-section truss can be adapted to deploy pre-attached panels or nodally-attached payload components. These triangular beams can be mounted side-by-side with a common chord to create a synchronously deployable trapezoidal cross-section beam or space-frame. Both the triangular and trapezoidal configurations can be adapted to deploy with a prescribed curvature of the longitudinal axis, and form perimeter trusses which can be post-tensioned for maximum structural performance.

Description:
RELATED APPLICATION 
     This application claims the benefit of and priority to U.S. Provisional Application Ser. No. 60/711,670, filed Aug. 29, 2005, the contents of which are incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to deployable triangularly-shaped truss systems, and more particularly discloses triangular truss systems having joints that allow for uniform and synchronous retraction and extension of triangularly shaped truss beams. 
     BACKGROUND OF THE INVENTION 
     There have been many attempts to design a practical, compact, folding or flexible truss system which can transition easily between retracted and extended states when the truss system is situated in varying operating environments. Prior art truss systems were designed to exhibit specific characteristics including low size/volume ratio; high kinematic stability; simplicity and reliability; high compactability; or high structural efficiency in terms of weight, complexity, auxiliary mechanism requirements, manufacturing costs, speed of operation or operating costs. Typically, truss systems disclosed in the prior art lack an optimal combination of features. Further, some prior art trusses have undesirable characteristics including undue complexity; inability to move in a coordinated and synchronous manner; requirements for a dedicated deployer; lack of compactability, reconfigurability, and multi-functional uses; and high costs. Relatively few designs have appeared in the marketplace that have been able to incorporate desirable design features, avoid undesirable features, and reduce the complexity of the chordal and section members of the truss system. Fewer still are capable of multiple uses and of deployment in multiple gravitational or operational environments. 
     For example, U.S. Pat. No. 3,783,573 to Vaughn (“Vaughn”) discloses many of the desired characteristics listed above but also includes some of the undesirable characteristics. Vaughn discloses frame sets and frame bays in a parallelogram configuration that includes extra chords and members that make the design overly complex, increasing the number of components that could fail to extend or retract. Further, Vaughn discloses that collapsing the structure requires the disconnection of the structural bays from each other and the collapse of each bay separately. Thus, Vaughn&#39;s system fails to act in a continuous and synchronous manner. 
     One advance in the art is represented in U.S. Pat. No. 7,028,442, to Merrifield, (the “442 patent”), the teachings of which are incorporated herein by reference. The &#39;442 patent discloses a deployable square or rectangular configured truss with many desirable characteristics. The &#39;442 patent does not disclose, however, the triangular configuration of the present invention, which possesses distinct characteristics and advantages. 
     There is a continuing need for improved deployable triangular truss systems that achieve synchronous coordinated motion of all members while extending or retracting, are stable, and do not require dedicated auxiliary mechanisms and structures to function, so that the overall deployable system remains compactable and low in weight, and has both reduced complexity and cost. 
     SUMMARY 
     Accordingly, the present invention is directed to deployable triangular truss beam systems with orthogonally-hinged folding diagonal members that substantially eliminate one or more of the limitations and disadvantages of the related art. 
     An object of the present invention is to provide an apparatus and method in which triangular, and double triangular trusses can be expanded from a compact form. 
     Another object of the present invention is to provide three-dimensional triangular trusses having few complex parts, wherein the trusses can be deployed and retracted in a stable, synchronous manner in a variety of combinations to form load bearing beams, masts, platforms, frameworks or other structures while reducing the number of folding chords and chordal members that are required. 
     Still another object of the present invention is to provide a means for the formation of either linear or curved triangular trusses, wherein the trusses have rectangular or planar faces useful for optional deployment of panels to serve a specified function. 
     Yet another object of the present invention is to create a triangular truss configuration which can be erected or deployed readily into curved beams or perimeter trusses, wherein the perimeter trusses can be post-tensioned for preloading and high stiffness without preloading of the individual joints for trusses of linear or curved segments. 
     It is still another object of the invention to permit triangular truss beams to be mounted side-by-side with a common chord to form a double triangular truss configuration. 
     When employed in a single embodiment, these objects create a stable triangular truss that achieves a synchronous, coordinated motion of its members while extending and retracting. The triangular truss in such an embodiment also preferably does not require dedicated auxiliary mechanisms to function, and is therefore lower in weight, compactable, and low in both complexity and cost. 
     These and other objects are preferably accomplished by providing a deployable triangular truss beam with proximal and distal ends, comprising a plurality of framesets, each frameset having a first diagonal side member, a second diagonal side member, and a transverse member, each of said diagonal side members and said transverse member having a first and a second end, said first diagonal side member being hingedly connected at its first end adjacent to the first end of said second diagonal side member at a primary joint and the second end of said first diagonal side member being hingedly connected to the first end of said transverse member at a first secondary joint, the second end of said transverse member being hingedly connected to the second end of said second diagonal side member, at a second secondary joint, a plurality of framebay subassemblies, each framebay subassembly comprising a first and second frameset, one of said framesets being connected to another of said framesets by a diagonal member connecting the second end of said second diagonal member at its connection to the second end of said transverse member to the primary joint of a first frameset, and said one of said framesets also being connected to another of said framesets by a diagonal member connecting the second end of said first diagonal member at its connection to the first end of said transverse member to the last mentioned primary joint thereby forming a framebay subassembly. A plurality of framebays, each framebay comprising a framebay subassembly, is provided having a first primary chord connected to the primary joints of the framesets comprising the framebay subassembly, a first secondary chord connected to the second ends of said first diagonal side members of the first and second framesets comprising the framebay subassemblies at their points of connection to the first ends of said transverse members, and a second secondary chord connected to the second ends of said second diagonal side members of the first and second framesets comprising the framebay subassemblies at their points of connection to the second ends of said transverse members. All of the joints are separable into two interconnected mating parts and have hinge means thereon for folding said chords and said diagonal members from a first deployed position to a second retracted position. 
     Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of at least one embodiment of the invention. 
       In the drawings: 
         FIG. 1  is a side view of a fully extended triangular truss beam with two identical framebays (bays). 
         FIG. 2  is a top view of the fully extended triangular truss beam of  FIG. 1 . 
         FIG. 3  is a front perspective view of the fully extended triangular truss beam of  FIGS. 1 and 2 . 
         FIG. 4  is an end view of the truss beam of  FIGS. 1 to 3 . 
         FIGS. 5A-5C  illustrate deploying of a curved truss beam embodiment from its compacted or retracted state to its fully formed, curved state. 
         FIG. 6A  is a top view of a primary joint in accordance with the teachings of the invention. 
         FIG. 6B  is a side view of the joint of  FIG. 6A . 
         FIG. 7A  is a view of a secondary joint in accordance with the teachings of the invention, taken along lines  7 A- 7 A of  FIG. 2 . 
         FIG. 7B  is a right end elevation view of the joint of  FIG. 7A , parts thereof being omitted for convenience of illustration. 
         FIG. 8A  is a view of a secondary joint in accordance with the teachings of the invention taken along lines  8 A- 8 A of  FIG. 2 . 
         FIG. 8B  is a right side view of the joint of  FIG. 8A . 
         FIG. 9  is a perspective view illustrating how  2  triangular truss beams, as in  FIGS. 1 to 3 , can be connected in a side-to-side relationship to form a double triangular truss beam. 
         FIG. 10  is a perspective view illustrating the interconnection of  4  framesets as shown in  FIG. 3 . 
         FIG. 11  is a side view of a folding hinge. 
         FIG. 12  is a top plan view of joint  802  of  FIG. 9 . 
         FIG. 13  is a view similar to  FIG. 4  illustrating the formation thereof from a frameset in the &#39;442 patent. 
         FIG. 14  is a view similar to  FIG. 4  showing the truss retracted. 
         FIG. 15  is a perspective view of two bays in the retracted state. 
         FIG. 16  is a perspective view illustrating the formation of the triangular truss beam of the invention into a perimeter truss configuration. 
         FIG. 17  is an end view of  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
       FIGS. 1-4  disclose the general configuration of an embodiment of a two-bay portion of a basic single triangular deployable truss beam in an extended or deployed state. In the embodiment illustrated in  FIGS. 1 to 4 , the deployed portion of truss beam  100  is comprised of a series of planar trusses in a Warren pattern. The illustrated embodiment provides a triangle-shaped truss wherein three truss chords, Chord A, Chord B, and Chord C (see  FIG. 2 ), form longitudinal chords. Chord A is a chord that connects base joints  120  of individual truss segments as illustrated in  FIGS. 1-4 . Chord A, also referred to herein as the “Apex chord”, can also connect to an end mount frame (not shown) as discussed in U.S. Pat. No. 7,028,442. The two other longitudinal chords, Chords B and C, are also oriented substantially along the truss beam&#39;s longitudinal axis and each chord connects secondary joints  125 B,  125 C for the truss segments (joints  125 B for Chord B and joints  125 C for Chord C). Chords B and C can also connect to the end mount frame (not shown). 
     Chords A, B and C can be comprised of component members, referred to as primary chordal members  101  (Chord A) and secondary chordal members  102  (Chords B &amp; C). Primary chordal members  101  and secondary chordal members  102  may be compression structures or tension structures depending on the structural needs and compacting requirements of the truss system. Compression chord members may be rigid members that are affixed to the truss after extension or deployment or hinged to fold during truss retraction. Tension chord members can be flexible, hinged, pressure formed or use cables. For the purposes of clarity, it is assumed herein that Chords A, B and C use folding members. However, it should be apparent to one skilled in the art that alternative member arrangements can be substituted therefor without departing from the spirit or the scope of the invention. 
     Thus, triangularly shaped truss beam  100  is shown in  FIG. 1  in the deployed state and comprised of a primary Chord A and  2  secondary Chords B and C. Each Chord A, B and C is comprised of a plurality of chordal members. Thus, Chord A is comprised of a plurality of primary chordal members  101  and Chords B and C are comprised of a plurality of secondary chordal members  102 . 
     In  FIGS. 1 and 2 , diagonal members  108  connect primary joints  120  to secondary joints  125 B,  125 C, as illustrated. Transverse members  106  connect secondary joints  125 B and  125 C as illustrated. Chordal members  102  connect like secondary joints. For example, chordal members  102  in secondary chordal member C in  FIG. 2  connect secondary joint  125 C at top left to secondary joint  125 C at the top middle, then to secondary joint  125 C at top right. Chordal members  102  in secondary chordal member B connection secondary joint  125 B (bottom left) to bottom middle secondary joint  125 B, then to the end second joint  125 B (bottom right). Chordal members  101  in primary chordal member A connect primary joints  120  as seen in  FIG. 2 . Thus, all chordal members  101 ,  102  connect like joints; that is, secondary joint  125 B connects to another secondary joint  125 B, secondary joint  125 C connects to another secondary joint  125 C, primary joint  120  connects to another primary joint  120 , etc. 
     As shown in  FIGS. 1 and 2 , certain of the chordal members  101 ,  102  are hinged at chordal hinges  111 , as shown. Also, as will be discussed, certain of the joints, such as at the ends of the structure shown in  FIGS. 1 and 2 , may terminate in ½ of a joint for subsequent connection to a mating joint half on another truss bay. 
     Transverse members  106  ( FIG. 2 ) act as struts, increasing the structural stability of truss beam  100 . Transverse members  106  are preferably situated perpendicular to the truss longitudinal axis to further increase the structural stability of truss beam  100 . Primary chordal members  101  and secondary chordal members  102  can also be attached in the longitudinal axis of truss beam  100  via the various joints. All chordal members can be knife-edge (male clevis end) configured for better load transfer. 
     In an alternative embodiment, as seen in  FIG. 3 , secondary joints  125 B and  125 C may also be connected by flexible cross-diagonals  200  for increased torsional rigidity. Flexible cross-diagonals  200  are preferably coplanar with Chords B and C. The flexible cross-diagonals  200  are preferably connected from one secondary joint, such as secondary joint  125 B, to a diagonally opposite secondary joint  125 C. Moreover, given the flexible nature of the cross-diagonals  200 , they should preferably collapse in a scissor pattern when truss beam  100  retracts. 
     Secondary joints  125 B and  125 C may also optionally have preloaded features to enable higher stiffness with zero free play. During extension, the triangularly shaped bays preferably remain aligned to each other by the action of the joints, as described below. In this embodiment, the hinge axes of secondary joints  125 B and  125 C are orthogonal with respect to primary chordal members  101  and secondary chordal members  102  when comparing truss beam  100  in its retracted and deployed states. The use of compression chordal members permits bidirectional beam moment loading. 
       FIG. 4  also illustrates a single frameset with two diagonal members  108  connected to joints  125 A and B, respectively. These diagonal members  108  extend to and are connected to primary joint  120 . 
     As seen in  FIG. 10 , which shows  4  framesets, without chords, with diagonal members  108  connecting one half of a secondary joint  125 B and one half of a secondary joint  125 C, respectively, with primary joint  120 . A first end of one diagonal member  108  is connected to one half of a secondary joint  125 B. The opposite end of that diagonal member  108  connects to the primary joint  120  of another truss segment or frameset at the primary joint of that other segment or frameset. Similarly, another diagonal member  108  is connected to base joint  120  and has an opposite end that connects to another truss segment or frameset at a secondary joint. Although not illustrated in  FIG. 10 , it should be apparent that a primary chordal member  101  can be used to join primary joint  120 . A secondary chordal member  102  can be used to join the respective secondary joints  125 B and  125 C. 
     Secondary joints  125 B and  125 C can connect to other components via lugs or equivalent connectors (e.g., an end frame or mount structure). The connectors preferably provide a hinge pin connection for the longitudinal chordal members such that, when truss beam  100  is in an extended position, the joint hinge pins in each chord are coplanar and lie on the chordal axis as discussed in Merrifield U.S. Pat. No. 7,028,442. Thus, 2 framesets form a frameset subassembly and the addition of Chords A, B &amp; C to a plurality of frameset subassemblies form a framebay such as shown in  FIG. 3 . 
     In its basic form the invention can be used as a beam, mast, or the framework for a wide variety of applications in low and zero gravity environments and at-normal gravity. As a beam, it may be cantilevered or may be supported or mounted at each end of the beam. As a mast, it is may be base-mounted with support from guy cables or equivalent. The truss system may also be used as the framework for larger structures that may be affixed to the truss beam. 
     The truss system can use power actuated folding chordal members to cause the continuous, synchronous motion of the truss system during extension and retraction. Hinged chordal members may also lock passively during extension of the truss system. The locking may be accomplished by a spring lock or equivalent manner. A minimum amount of force may be required to cause the unlocking and initial rotation of the joints prior to retraction of the full assembly. For a fully automated or semi-automated operation, there may be a need for actuators whose selection will be dependent on the specific requirements of a given truss beam application. 
     In some embodiments, if gravity loading is not present or if the truss frames are supported by rollers or equivalent, a method of deployment may include the application of an axial force at the end frame. The axial force will be used to extend or retract the truss system. At full extension of the truss system, the chordal members, if hinged, are spring locked. When a truss system is fully extended in the deployed position, for the system to retract, any hinged or locked chordal members need to be unlocked and given an initial force. 
     When extending and retracting the truss system on level or inclined surfaces, low friction caster wheels attached to the primary hinge joints may be used to support the truss frame. If there is no support surface to support the truss system, various cable and winch mechanisms may be utilized to aid in deployment and retraction of the truss system. 
     Truss systems may also be designed to cover a span, wherein multiple truss systems are configured having at least two separate trusses located at opposite ends of the span. Each truss deploys and extends from their side across the span. Once the chordal members lock, the ends of each truss maybe aligned and a locking mechanism located at the ends of each truss will fasten together the two trusses across the span. 
     As seen in  FIG. 5A , a triangularly shaped truss beam  100  with a plurality of bays is shown in a retracted position, associated with a surface  500 .  FIG. 5B  illustrates the deployed position of beam  100  along surface  500 .  FIG. 5C  illustrates the curvature of beam  100  with respect to surface  500 . That is, the truss beam  100  extends out in a linear fashion and conventional actuators, known in the art, located along the longitudinal chords of the truss beam  100 , react mechanically to curve truss beam  100  into an arc as illustrated in  FIG. 5C . 
     Primary joint  120  is shown in  FIGS. 6A and 6B . Joint  120  comprises two identical fitting halves  605 , each with  2  diagonal connector ends  601 ,  602 . Ends  601 ,  602  connect to diagonal members  108 , whereas chordal end fitting  603  with end connector  604  is connected to a primary chordal member  101 . Member  603  is pivotally connected to fitting half  605  at pivot pin  611  ( FIG. 6B ). 
     Fitting half  605  is hinged to an identical fitting half having diagonal connector ends  601 ,  602  extending outwardly at an angle as shown. Chordal end fitting  603  is pivotally connected at pivot pin  611  ( FIG. 6B ) and connected to a primary chordal member  101 . Ends  601 ,  602  connect to diagonal members  108  as shown in  FIG. 2 . 
     As seen in  FIG. 6A , male clevis lug member  619  extends from fitting half  605  into a space formed between female clevis lugs  620 ,  621  extending from the opposing (second) fitting half. In like manner, a male clevis lug  619  extends from the second fitting half  605  into a space formed between  620 ,  621  on the first fitting half  605 . A hinge pin  625  ( FIG. 6B ) extends between each  619 ,  620 ,  621  couple, so that both fitting halves rotate about pin  625 . 
     Secondary joint  125 B is shown in  FIGS. 7A and 7B . Hinge fitting halves  628  and  632  are derived from the fitting halves of primary joint  120  just described ( FIG. 6A ). Half of each fitting half is removed, leaving what is shown in  FIG. 7A  as fittings  628  and  632 . Diagonal connector ends  634  and  635  are similar to those for joint  120  except that each connector incorporates rotation joints  634 ′ and  635 ′ for rotatable connection to diagonals  108  (as is taught in the 442 patent). Fitting halves  628  and  632  are hinged together through a clevis lug couple comprised of a male clevis lug  629  extending between spaced female lugs  630 ,  631 , the same as was described for primary joint  120 , and the chordal end fittings  626  having end connectors  627  are pivotally connected as for joint  120  at pins  640 . A principal difference is that joint  125 B connects one end  636  ( FIG. 7B ) of transverse member  106  to the main hinge pin  633 ′ through spherical bearing  633  mounted in the end of  106  as shown in  FIG. 7A , which allows necessary freedom of motion during truss extension and retraction. The end fitting member  636 , which contains spherical bearing  633 , is notched as shown in  FIG. 7B  to permit members  626  to fold parallel to transverse member  106  when the truss collapses/retracts. Thus, secondary joint  125 B can be derived from primary joint  120 , but provides for proper connection of transverse member  106 , and provides for rotatable connection of diagonals  108 . 
     Secondary joint  125 C is shown in  FIGS. 8A and 8B . The construction of this joint is similar to joint  125 B except that it is oriented 90 degrees to  125 B, does not provide for a spherical bearing connection to transverse member  106 , and does not require rotational connection of diagonals  108 . Like numerals refer to like parts of  FIGS. 7A and 7B . It provides for member  106  (at end  699 ) to be connected directly to main hinge pin  645  as shown in  FIG. 8B . Connectors  650 ,  651  do not rotate and fitting  699  is the end fitting for transverse member  106 . Chordal end fittings  626  having end connectors  627  are pivotally connected at pins  640  as in joint  125 B. 
     Folding hinge  111  is shown in  FIG. 11 . Each folding hinge  111  has a first chordal member connector  700  at one end integral with a female yoke portion  701 . A second chordal member connector  702  has a male extension portion  703  extending between yoke portion  701  and pivotally connected thereto by pivot pin  704 . 
     The triangular truss beam  100  of  FIGS. 1-4  can be uniquely combined to form a double triangular truss beam configuration  800  as shown in  FIGS. 9 and 17 , where two bays are shown. Like numerals refer to like parts of the configuration of  FIGS. 1 to 4 . This can be accomplished by mirroring one truss about its C chord such that both trusses use a common C chord. Where the  125 C joints are adjacent to each other, they are replaced by a  120  joint, modified to include end fittings  699  as in  FIGS. 8A and 8B , as used in the A chords (see  FIG. 6A ) but having the transverse members on either side connected to the main hinge pins  625 . This becomes the  802  joint of  FIG. 9  (see the detail in  FIG. 12  wherein like numerals refer to like numerals refer to like parts of  FIGS. 6A ,  6 B,  8 A and  8 B). For structural completeness, the Chord A  120  joints are connected by transverse members  107  (also shown in  FIG. 17 ) similar to members  106 , but where each end is connected to the respective main hinge pins  625  of the  120  joints. All other features of the single trusses  100  are retained. 
     The triangular truss beam described herein may be uniquely derived from the patented basic square/U-shaped truss beam in U.S. Pat. No. 7,028,442 (&#39;442 patent), the teachings of which are incorporated herein by reference. 
     Thus, as seen in  FIG. 13 , the side diagonal  109 ′, shown in dotted lines, and its joint  109 ″, is removed. Folding primary and secondary chordal members  101 ,  102  are added to the end joints as shown. In the preferred embodiment, transverse members  106  are added, oriented perpendicular to the truss beam longitudinal axis. Optional end frames, not shown, as in the &#39;442 patent, may be used as end close-outs with half-bay end chordal members in the primary chordal member. Optionally, for torsional rigidity, the joints  125 B and joints  125 C may be connected by flexible cross-diagonal members  200  as previously discussed (see  FIG. 3 ). 
     A retracted triangular truss bay is shown in  FIG. 14 . When two or more such bays are retracted, as seen in  FIG. 15 , the folded truss bays nest in parallel fashion, as disclosed in the &#39;442 patent, with a retracted length of about 1/10th to 1/30th of the extended or deployed length. During extension, the pyramidally shaped bays align to each other by the constraint action of the  125 B orthogonal joint hinges. With the use of folding chords, the truss motion is fully synchronous as taught in the &#39;442 patent. Without folding chords, the motion is synchronous if the joints adhere to a prescribed contour, e.g., a flat surface, or if the folding chords are powered. The truss may be extended into linear or curved beams, as in  FIGS. 5A to 5C , or with circular, parabolic, or other contour, and as a closed ring or ellipse (see ring  900  in  FIG. 16 ). The truss can be curved as shown in  FIGS. 5A to 5C  by minor modification of only joints  125 B and having the vertex chordal members longer or shorter than the “b” and “c” chordal members. Trusses can be connected laterally ( FIG. 13 ) to form linear or curved dual truss beams, in which case additional transverse struts are used to connect the primary joints  120 . 
     Thus, the invention herein expands the utility of the basic invention in the &#39;442 patent by enabling simplified formation of either linear or curved structures, where the structures have a wide face useful for optional deployment of flat panels to serve a specified function. 
     A truss geometry is created which can be readily used to efficiently form planar area platforms by lateral mating of linear trusses. 
     The number of folding chords required is minimal. A perimeter truss as seen in  FIG. 16 , can be post-tensioned with only one set of primary folding chordal members. 
     Truss configurations are created which can be erected/deployed readily into curved beams or perimeters. As closed perimeters, they can be post-tensioned for joint preloading without preloading of individual joints as for trusses of linear or open curved segments. 
     Referring to  FIGS. 1 and 13 , there are three orthogonal joint configurations, which connect the framesets defined in  FIG. 3 . Each joint&#39;s main hinge pin axis remains orthogonal to the truss longitudinal axis at all times during extension and retraction. 
     The joint  120 , shown in  FIGS. 5 ,  6 A and  6 B, is functionally the same as the primary joint in the &#39;442 patent (See FIG. 5 of the &#39;442 patent) and connects 6 truss members. They hingedly connect 2 pairs of diagonals which fold parallel to each other when the truss is retracted. This is shown clearly in  FIG. 15 . 
     The joints  125 B replace the primary joints in the truss in the patent &#39;442. They have two hinged fittings, which can be derived geometrically by splitting the hinged fittings of joints  120  down their centerlines. These joints are defined as including the end fittings of the chordal struts and transverse members. The latter incorporate spherical bearings to allow 2-axis freedom about the main hinge pin of the hinged fittings when the truss folds. These hinged fittings each connect to a side diagonal, through a rotational joint to permit the necessary orthogonal joint action as in the &#39;442 patent. The diagonals fold parallel to each other as shown in  FIG. 15 , and the chordal strut fittings and members fold into the same transverse space as the diagonals. 
     The joints  125 C are shown in  FIGS. 8A and 8B . When deployed, their hinge pin axes are orthogonal to those of the joints  125 B. These joints, like the  125 B joints, connect the side diagonals of mating framesets and the ends of the chordal struts. They also connect one end of each transverse member co-linearly to the main hinge pin. 
     For the dual truss embodiment of  FIG. 9 , formed by mirroring a single truss about a common “c” chord, the two adjacent  125 C joints are replaced by a new joint identical to joint  120 . 
     As shown in  FIGS. 5 ,  5 A to  5 C, the hinge pin axes of the  120  and  125 C joints permit curvature along a prescribed path, typically circular. The  125 B joints orthogonally require an additional degree of freedom, which can be provided by a compliant bushing or a spherical bearing within the clevis geometry. This can permit formation of a full 360-degree ring truss if desired, as shown in  FIG. 16 . The perimeter truss can be preloaded by chordal length adjustment when its free ends are connected, as described above. Flexible cross-diagonals  200  (not shown in  FIG. 16 ) may be provided where desired. 
     While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.