Abstract:
A boom assembly for a rocket-launched spacecraft, the boom assembly comprising a plurality of rigid sections and a plurality of elastic sections that pivotally connect each of the rigid sections together so as to enable the boom assembly to be folded into a storage configuration and so as to enable the boom assembly to be automatically unfolded into a deployed configuration that provides the spacecraft with a large rigid extending platform. At least one of the rigid sections is mounted to the spacecraft so as to secure the boom assembly to the spacecraft. In one embodiment, a plurality of extendable components, such as solar panels and radar antennae, are mounted to the rigid sections so as to allow for storing and deploying the extendable components. In another embodiment, there may be no components mounted other than a length of wire or a length of metal tape which will allow the boom to act as an antenna. In the storage configuration, the boom assembly is folded about the elastic sections and secured with a releasable tie-down device. This allows the rigid sections to be positioned adjacent each other in an accordion manner so as to enable the boom assembly to be stowed into a small space of a launch vehicle and so as to store elastic energy in the deformed elastic sections. After the spacecraft is launched, the tie-down device is released so as to release the stored elastic energy of the elastic sections, thereby urging the boom assembly into the deployed configuration.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to rocket-launched spacecraft and, in particular, relates to boom assemblies that deploy extendable components of the spacecraft. 
     2. Description of the Related Art 
     Rocket-launched spacecraft, which include orbiting satellites and deep space probes, perform increasingly complex tasks. In particular, telecommunication satellites enable vast amounts of information, including voice and data, to be sent and received around the globe. In other examples, satellites equipped with earth imaging devices enable weather forecasters to more accurately study and predict global weather patterns. Furthermore, since satellites are positioned outside of the earth&#39;s atmosphere, they provide an ideal platform for observing and studying the universe. Additionally, deep space probes equipped with increasingly advanced scientific instrumentation that are launched into a non-earthbound trajectory enable scientists to obtain heretofore unobtainable data about the solar system. 
     The rocket-launched spacecraft is launched into a preferred trajectory by rocket-propelled means that includes positioning the spacecraft into a relatively small capsule of a rocket-propelled vehicle. Thus, the typical spacecraft is required to be configurable between a storage configuration that enables the spacecraft to be positioned within the capsule of the rocket-propelled vehicle and a deployed configuration that enables the spacecraft to function in a desired manner while in outer space. 
     Thus, subsequent to the launching of the spacecraft, the spacecraft is typically configured for use by deploying an assembly of extendable components. For example, the assembly of extendable components may comprise an extended solar panel array that is used to convert collected solar radiation into electrical energy. In another example, the assembly of extendable components may comprise an extendable antenna assembly that is used to transmit and receive electromagnetic signals to and from a plurality of earth-based installations. 
     To deploy each assembly of extendable components, the typical spacecraft often utilizes a boom assembly. In particular, the assembly of extendable components is usually mounted to the extendable boom assembly which is adapted to fold-up in the storage configuration and fold-out in the deployed configuration. Furthermore, the boom assembly also serves as a support structure for supporting the assembly of extendable components while the boom assembly is in the deployed configuration. Moreover, although the spacecraft is often in a weightless environment, forces applied by rocket thrusters of the spacecraft that are sometimes used to correct the trajectory of the spacecraft may create considerable stress throughout the boom assembly. Therefore the boom assembly is required to be rigid and have sufficient structural integrity while in the deployed configuration. 
     As increasingly advanced types of spacecraft are being developed, it has become apparent that known types of boom assemblies provide insufficient capabilities. In particular, deep space probes currently being designed require boom assemblies that are capable of extending to unprecedentedly large sizes. Furthermore, the required boom assembly must be lightweight so as to reduce the amount of fuel that is needed to launch the spacecraft into the required trajectory, be reducible to a small size so as to enable the large boom assembly to fit into the small capsule, and have a high degree of strength when fully deployed. Moreover, since cost is a major consideration in the design of spacecraft, it is preferable for the boom assembly to have a simple design so as to reduce the manufacturing costs of the boom assembly. 
     Hence, there is a continuing need for extendable boom assemblies for spacecraft that are lightweight and are readily foldable into a compacted storage configuration for launch of the spacecraft. The boom assembly should also be readily deployable into an extended configuration upon the spacecraft reaching a desired trajectory and have sufficient strength to maintain spacecraft components in a desired deployed configuration. 
     SUMMARY OF THE INVENTION 
     The aforementioned needs are satisfied by the spacecraft boom assembly of the present invention comprised of an elongate boom having at least one opening formed at a location along the boom. In particular, the at least one opening defines at least one folding region so as to permit the elongate boom to be folded about the at least one folding region to thereby reduce the length of the elongate boom. Furthermore, the elongate boom is formed of a resilient material so as to store elastic energy when the elongate boom is in the folded configuration to thereby bias the folded elongate boom into an unfolded deployed state. 
     In another aspect of the invention, the aforementioned needs are satisfied by the spacecraft boom assembly of the present invention having a storage and a deployed configuration. In particular, the assembly comprises a first and a second mounting member and a foldable interconnection connected between the first and the second mounting members. Furthermore, the foldable interconnection is formed of an elastic material that is biased into a deployed configuration wherein the first and second mounting members are maintained in a deployed configuration such that the foldable interconnection rigidly maintains the first and second mounting members in a desired orientation with respect to each other such that the length of the boom assembly is a deployed length. Moreover, the foldable interconnection is adapted to permit release from the deployed configuration so that the first and second mounting members can be positioned in a storage configuration wherein the first and second mounting members are positioned so as to reduce the length of the boom assembly. 
     In another aspect of the invention, the aforementioned needs are satisfied by the elongate structural support member for a spacecraft comprising a first rigid member having a first and a second end, a second rigid member having a first and a second end, and a foldable connecting member integrally attached to the first ends of the first and second rigid members so as to interconnect the first and second rigid members. In particular, the foldable connecting member is bendable so as to allow the first and second rigid members to be positioned substantially adjacent each other substantially along the lengths of the first and second rigid members in a storage configuration. Moreover, the foldable connecting member is biased towards a deployed configuration wherein the first rigid member is rotated about the connecting member with respect to the second rigid member so that the first and second rigid members extend outward from the foldable connecting member. 
     In another aspect of the invention, the aforementioned needs are satisfied by the boom assembly for a spacecraft comprising a first boom sub-assembly having a first and a second rigid section with a folding section interposed therebetween. In particular, the folding section enables the first and second rigid sections to be folded about the folding section to thereby reduce the length of the first boom sub-assembly in a storage configuration. Furthermore, the folding section is biased so as to urge the first boom sub-assembly into a deployed configuration. The boom assembly further comprises a second boom sub-assembly having a first rigid section and a folding section wherein the second boom sub-assembly is mounted to the second rigid section of the first boom sub-assembly. Moreover, the folding section of the second boom sub-assembly enables the first rigid section of the second boom sub-assembly to be folded with respect to the second rigid section of the first boom sub-assembly to reduce the length of the second boom sub-assembly with respect to the first boom sub-assembly. 
     In another aspect of the invention, the aforementioned needs are satisfied by the structural support member for a spacecraft boom assembly, the support member comprising a plurality of rigid sections that include a first, a second, and a third rigid section and a plurality of foldable sections that interconnect the plurality of rigid sections. In particular, the plurality of foldable sections include a first foldable section that interconnects the first and second rigid sections and a second foldable section that interconnects the second and third rigid sections. Furthermore, each of the foldable sections is formed of a resilient material having a shape that is biased into a rigid unfolded state such that the foldable sections rigidly interconnect the rigid sections so as to maintain the structural support member in a rigid deployed configuration. Moreover, each of the foldable sections is configurable into a strained folded state so as to enable the plurality of rigid members to be positioned substantially adjacent each other substantially along the lengths of the plurality of rigid members so as to place the structural support member in a storage configuration having a reduced size. Additionally, the first and second rigid sections are able to fold and unfold with respect to each other along a first plane and the second and third rigid sections are able to fold and unfold with respect to each other along a second plane such that the first and second planes intersect each other. 
     The spacecraft boom assembly of the present invention is formed from an improved structural element that is both bendable and compressible so as to enable the boom assembly to be easily folded into a storage configuration so that the boom assembly can be stowed within the relatively small payload space of a launching vehicle. Furthermore, since the foldable sections of the structural element are formed of a resilient material, the elastic energy stored within each of the folded foldable sections provides each of the foldable sections with a bias that urges the boom assembly to self-extend from the storage configuration to the deployed configuration. Moreover, the structural element, when in the deployed configuration, provide sufficient rigidity so that the boom assembly is capable of supporting extending components of the spacecraft. Additionally, the extendable structural element is relatively inexpensive to manufacture, is lightweight, and is capable of extending into relatively large sizes. These and other objects and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an perspective view of a typical spacecraft in a launched state; 
     FIG. 2A is a side view of an alternative spacecraft having a boom assembly of the present invention which illustrates the boom assembly in the storage configuration; 
     FIG. 2B is a side view of the spacecraft of FIG. 2A which illustrates the boom assembly extending between the storage configuration and a deployed configuration; 
     FIG. 2C is a side view of the spacecraft of FIG. 2A which illustrates the boom assembly in the deployed configuration; 
     FIG. 3A is a perspective view of a structural support member of the boom assembly of the spacecraft of FIG. 2A which illustrates the structural support member in the deployed configuration; 
     FIG. 3B is a magnified perspective view of the structural support member FIG. 3A which illustrates a foldable section of the structural support member in greater detail; 
     FIG. 3C is an alternative perspective view of FIG. 3B; 
     FIG. 3D is a cross-sectional view of the foldable section of FIG. 3B in the deployed configuration; 
     FIG. 3E is a cross-sectional view of the foldable section of FIG. 3B in a flattened state which illustrates how the foldable section is adapted into the storage configuration; 
     FIG. 3F is a perspective view of the foldable section of FIG. 3B in a partially folded state; 
     FIG. 3G is a perspective view of the foldable section of FIG. 3B in the storage configuration; 
     FIG. 4 is a perspective view of one embodiment of the boom assembly of FIG. 2A which forms a part of a solar panel array; 
     FIG. 5A is a perspective view of one embodiment of the foldable section of FIG. 3B which further includes a torsion stiffening assembly; 
     FIG. 5B is an alternative perspective view of FIG. 5A; 
     FIG. 6A is a schematic diagram of one embodiment of a structural support member having a plurality of laterally extending rigid sections and a plurality of longitudinally extending rigid sections which generally illustrates the structural support member in the deployed configuration; 
     FIG. 6B is a schematic diagram of the structural support member of FIG. 6A which generally illustrates the structural support member in a partially folded state; and 
     FIG. 6C is a schematic diagram of the structural support member of FIG. 6A which generally illustrates the structural support member in the storage configuration. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made to the drawings wherein like numerals refer to like parts throughout. FIG. 1 illustrates a typical spacecraft  30  in a launched state. In particular, the spacecraft  30  is representative of many different types of space vehicles that include orbiting satellites and deep space probes. Furthermore, the spacecraft  30  is configured into the launched state in a launch phase that involves stowing the spacecraft  30  in a launch vehicle, such as a manned space shuttle or an unmanned rocket. 
     As shown in FIG. 1, the typical spacecraft  30  comprises a housing assembly  32  and a plurality of extending components  34  that extend from the housing assembly  32 . In particular, the housing assembly  32  encloses a plurality of components that may include, for example, electronic instrumentation, scientific instrumentation, and electrical power assemblies. 
     As shown in FIG. 1, the extending components  34  may comprise a solar array assembly  36 . In particular, the solar array assembly  36  having a plurality of solar array panels  38  is adapted to generate electrical power by converting solar radiation captured by the panels  38  into electrical energy. Furthermore, the solar array assembly  36  includes a first boom assembly  40  that extends the solar array assembly from a storage configuration (not shown) to the deployed configuration of FIG. 1 subsequent to the launch phase and provides a rigid structure so as to support and maintain the solar array panels  38  in the deployed configuration of FIG.  1 . 
     As shown in FIG. 1, the extending components  34  of the spacecraft  30  further includes an extending antenna assembly  44 . In particular, the antenna assembly  44  is adapted to send and receive a plurality of signals  46  to and from a plurality of Earth-based communication stations  48 . Furthermore, the antenna assembly  44  includes a second boom assembly  50  that supports the antenna assembly  44  in a deployed configuration as shown in FIG.  1  and extends the antenna assembly  44  from a storage configuration (not shown) into the deployed configuration of FIG. 1 subsequent to the launch phase. 
     It will be appreciated that the support structure that maintains the solar array panel  38  and the antenna assembly  44  in the deployed configuration must be sufficiently rigid to maintain these structures in a precisely oriented deployed configuration. These and many other types of deployable structures on spacecraft must often be maintained in a desired deployed orientation while the spacecraft experiences different accelerations. Hence, not only must the support structures be able to be stowed for launch, they must also be capable of deploying and maintaining structures in a desired orientation. 
     Reference will now be made to FIGS. 2A-2C which illustrate another embodiment of a spacecraft  60  having a novel boom assembly  62  which is the same type of boom assembly as the assemblies  40  and  50 . As will be described in greater detail below, the boom assembly  62  is able to be stored in a compact storage configuration, is lightweight, is able to self-extend into a relatively large deployed configuration, and is relatively inexpensive to produce. Furthermore, the boom assembly  62  may self-extend into a variety of shapes that include, but are not limited to, a linear shape, an elongated planer shape, and a non-elongated planer shape. Consequently, the boom assembly  62  is able to support and extend a plurality of components that may include a solar array assembly or an antenna array assembly such as those illustrated above in FIG.  1 . 
     As shown in FIGS. 2A-2C, the spacecraft  60  comprises a housing assembly  61  and the boom assembly  62 . In particular, the housing assembly  61  is substantially similar to the housing assembly  32  of the known spacecraft  30  of FIG.  1 . Furthermore, the housing assembly  61  and the boom assembly  62  are coupled together as will be described in greater detail below. 
     As shown in FIG. 2A, the boom assembly  62  is comprised of a plurality of rigid members  54  that pivotally interconnect at a plurality of foldable members  56  so as to enable the boom assembly  62  to be placed in the storage configuration in an accordion manner. Furthermore, the rigid member  54  includes at least one mounting member  68  that mounts to the housing assembly  61  in a well-known manner so as to secure the boom assembly  62  to the housing assembly  61 . 
     As shown in FIGS. 2A-2C, the boom assembly  62  is adapted to extend from the storage configuration of FIG. 2A to the deployed configuration of FIG.  2 C. In particular, the foldable members  56  are adapted to store elastic potential energy when placed in the storage configuration of FIG. 2A so as to be biased into the deployed configuration. Thus, when the boom assembly  62  is allowed to extend, for example, by the release of a suitable latching mechanism  69 , the stored elastic potential energy of the foldable members  56  will urge the boom assembly  62  to extend into the deployed configuration of FIG.  2 C. 
     As shown in the embodiment of FIG. 2C, the boom assembly  62  extends into an elongated shape in the deployed configuration. However, in another embodiment, the boom assembly may be adapted to extend along multiple directions as will be described in greater detail below in connection with FIGS. 8A-8C. 
     As will be described below, the boom assembly  62  is comprised of at least one elongated extendable structural element, otherwise known as a boom, having a plurality of rigid sections and at least one foldable section integrally interposed between the rigid sections. In particular, the rigid sections of the extendable structural element form the rigid members  54  of the boom assembly  62  and the foldable sections of the extendable structural element form the foldable members  56  of the boom assembly  62 . 
     Reference will now be made to FIGS. 3A-3D which illustrate one embodiment of the extendable structural element  66  of the boom assembly  62 . In particular, FIG. 3A is a perspective view of the extendable structural element  66  that is adapted to extend into a linear shape. Furthermore, FIGS. 3B and 3C are magnified perspective views of FIG. 3A which illustrate the foldable section  63  in greater detail. Moreover, FIG. 3D is a cross-sectional view of the foldable section  63  of FIG. 3A in a rigid configuration showing a cross-sectional profile of an adjacent tubular wall  70  in phantom. 
     As shown in FIG. 3A, the extendable structural element  66  is comprised of a plurality of rigid tubular walls  70  having a first end  65  and a second end  67  that form each of the rigid sections  64  of the extendable structural element  66 . Furthermore, the extendable structural element  66  further comprises the at least one foldable section  63  that extends between the first and second ends  65  and  67  of adjacent rigid sections  64 . 
     As shown in FIGS. 3B-3D, each of the foldable sections  63  comprises a pair of connecting strips  74  that each connect the rigid section  64   a  with the adjacent rigid section  64   b . In particular, each connecting strip  74  includes a first elongated side edge  84 , a second elongated side edge  86 , a first end  76  that extends from the rigid member  64   a , a second end  78  that extends from the rigid member  64   b  and a central portion  88  located midway between the first and second ends  76  and  78 . Furthermore, each connecting strip  74  is biased into a shape having a concave inner surface  80  (FIG. 3D) and a convex outer surface  82  so as to resist bending in a manner that results in the elongated side edges  84  and  86  of the connecting strips  74  forming a substantially nonlinear shape. 
     As shown in the embodiment of FIGS. 3A-3C, the connecting strips  74  of the foldable section  63  are positioned in a generally parallel manner so that the inner surfaces  80  of each of the connecting strips  74  face each other. Consequently, in the deployed configuration of FIG. 3A, the foldable section  63  provides the extendable structural element  66  with a relatively high degree of rigidity so as to resist bending along any axis that is perpendicular to the elongated axis of the deployed extendable structural element  66 . However, as will be described below, the connecting strips  74  are capable of being deformed into a flat shape so as to enable the foldable sections  63  to fold. 
     As best shown in FIG. 3B, the first and second ends  76  and  78  of each connecting strip  74  are constructed with a flared shape. In particular, both the first and second ends  76  and  78  extend toward the rigid sections  64  in a flared manner so that the flared first and second ends  76  and  78  join with the rigid sections  64  substantially along the entire circumference of the wall  70 . Thus, the central portion  88  is able to be deformed from the biased shape of FIG. 3D such that the resulting stress is more uniformly distributed along the length of the connecting strips  74  and such that the change in the curvature of the first and second ends  76  and  78  of the connecting strips  74  is relatively small. Consequently, the first and second ends  65  and  67  of the rigid sections  64  experience a reduced stress which reduces the likelihood that the rigid sections  64  will develop stress fractures as a result of the extendable structural element  66  being placed in the storage configuration. 
     In one embodiment, the extendable structural element  66  is manufactured in a process that involves fabricating an initial tubular structure having an extended tubular wall so as to form the rigid sections  64 . Furthermore, each foldable section  63  is integrally fabricated in the extendable structural element  66  by forming a pair of openings  58  in the tubular wall so that the remaining portion of the tubular wall adjacent the openings comprise the connecting members  74 . Moreover, the initial tubular structure is preferably manufactured of a resilient material that provides rigidity in a curved shape and flexibility in a flat shape. Additionally, the initial tubular structure is preferably lightweight and capable of withstanding a large degree of mechanical strain. In one embodiment, the initial tubular structure is formed of glass fiber in an epoxy matrix. 
     In one embodiment, the extendable structural element  66  is formed with twenty rigid sections  64  and nineteen foldable sections  63  interposed therebetween. In particular, each rigid section  64  is formed with a tubular cross-sectional shape having a length of 100 cm, an inner diameter of 38.0 mm, and an outer diameter of 38.5 mm. Furthermore, each of the foldable sections  63  comprise two connecting strips each having a length of 5 cm, an inner radius of curvature of 38 mm, an outer radius of curvature of 38.5 mm, and a width of 15 mm. Consequently, the extendable structural element  66  is capable of extending into the deployed configuration with a length of 2.095 m and folding into the storage configuration having a width of 60 mm, a length of 105 cm, and a depth of 15 cm. 
     Reference will now be made to FIGS. 3E-3F which illustrate the pivoting characteristics of the foldable section  63 . In particular, the foldable section  63  can be induced to fold by applying an external pair of opposing lateral forces at the outer surface  82  of the central portion  88  of each of the connecting members  74  so as to flatten the shape of the central portion  88  of the connecting strips  74  as shown in FIG.  3 E. Thus, the foldable section  63  is subsequently able to be folded such that the inner surfaces  80  are flushly positioned adjacent each other in a parallel manner as shown in FIG. 3F to thereby reduce the length of the boom assembly  62 . Consequently, the connecting strips  74  are placed into a strained configuration such that the connecting strip  74   b  forms an outer bow  93  and the connecting strip  74   a  forms an inner bow  91  and such that the first and second ends  76  and  78  of the inner connecting strip  74   a  contact each other along the outer surface  82   a.    
     It will be appreciated that the foldable section  63  in the folded configuration of FIG. 3F possesses elastic potential energy that can subsequently provide a self-deployment mechanism. In particular, the formation of the inner and outer bows  91  and  93  result in intermolecular stretching of the material of the connecting strips  74 . Furthermore, the flushly adjacent first and second ends  76  and  78  of the inner bow  91  enable reactive forces to be applied therebetween so as to enable the stored elastic energy to be more readily converted into useful work that reorients the rigid sections  64   a  and  64   b  into the deployed configuration. Thus, the stored elastic potential energy will provide the bias that enables the extendable structural element  66  and, therefore, the boom assembly  62  to self-extend from the storage configuration upon release of the latching mechanism  69  of the boom assembly  62 . 
     Reference will now be made to FIG. 3G which illustrates a portion of the extendable structural element  66  in the storage configuration. In particular, with the foldable section  63  initially folded in the manner of FIG. 3F, the extendable structural element  66  is configured in the storage configuration by flushly aligning the rigid member  64   a  with the rigid member  64   b . Furthermore, the elastic characteristics of the tubular wall  70  of the rigid members  64  enable the rigid members  64  in this embodiment to be compressed into a shape having a reduced width as shown in FIG.  3 G. Thus, since the extendable structural element  66  is foldable along its length and compressible along its width, the extendable structural element  66  and, therefore, the boom assembly  62  is reducible in size. 
     Reference will now be made to FIG. 4 which illustrates a panel assembly  90 , such as a solar panel assembly, that comprises one embodiment of the boom assembly  62 . In particular, the panel assembly  90  comprises a plurality of flat rigid panels  94  that are mounted as part of the boom assembly  62  so as to store and deploy the panel assembly  90 . 
     As shown in FIG. 4, the boom assembly  62  comprises the first and second extendable structural elements  66   a  and  66   b  that are substantially similar to each other. In particular, the extendable structural elements  66   a  and  66   b  are positioned so as to be mutually aligned in a generally parallel manner so that the corresponding folding sections  63   a  and  63   b  are adjacent to each other. Furthermore, each rigid panel  94  mounts to the corresponding pair of rigid sections  64   a  and  64   b  along the opposing outer edges of the panel  94  so as to rigidly couple the rigid sections  64   a  and  64   b  of the extendable structural element  66   a ,  66   b  in a fixed relationship and so as to align the rigid sections  64   a  and  64   b  with the plane of the rigid panel  94 . Consequently, each opposing pair of rigid sections  64   a  and  64   b  mounted to the corresponding rigid panel  94  combine to form each of the rigid members  54  of the boom assembly  62 . 
     As shown in FIG. 4, the foldable sections  63   a  and  63   b  also combine to form the boom assembly  62  with each of the foldable members  56  having a pivot axis that extends between the foldable sections  63   a  and  63   b.  Thus, each of the panels  94  are capable of folding in an accordion manner so as to allow the panel assembly  90  to be placed in the storage configuration as shown in FIG.  2 A. 
     Furthermore, since the foldable sections  63   a  and  63   b  store a sufficient amount of elastic potential energy, the stored energy will therefore provide the bias that urges the solar panel assembly  90  to freely extend into the deployed configuration of FIG.  2 C. Moreover, since the foldable sections  63   a  and  63   b  are formed from resilient material that is capable of sustaining a high strain, the foldable sections  63   a  and  63   b  will recover their original curved shape so as to provide the deployed boom assembly  62  with a high degree of rigidity in the deployed configuration. 
     Thus, the solar panel assembly  90  is capable of folding in an accordion manner in the storage configuration such that the panels  94  are positioned adjacent to each other in a parallel manner so as to reduce the size of the panel assembly  90 . Furthermore, the panel assembly  90  is capable of extending into the deployed configuration such that the panels  94  are aligned in a common plane so as to increase the surface area of the panel assembly  90 . 
     Reference will now be made to FIGS. 5A and 5B which illustrate one embodiment of the extendable structural element  166  that includes a torsion stiffening assembly  102 . In particular, the extendable structural element  166  is substantially similar to the extendable structural element  66  except for the presence of the torsion stiffening assembly  102  at each folding section  163 . Furthermore, the extendable structural element  166  is adapted to replace the extendable structural element  66  in the boom assembly  62 . As will be described in greater detail below, the torsion stiffening assembly  102  provides the extendable structural element  166  with a greater resistance to deforming under the presence of torsional stress. 
     As shown in FIGS. 5A and 5B, the torsion stiffening assembly  102  comprises a plurality of stiffening elements  104 . In the embodiment of FIGS. 4A and 4B, the stiffening elements  104  comprise four stiffening elements  104   a,    104   b,    104   c  and  104   d.  Furthermore, the stiffening elements  104  are formed of a lightweight high strength high tension stretch resistant material, such as Kevlar or S-Glass fiber. 
     As shown in FIGS. 5A and 5B, when the extendable structural element  166  is placed in the deployed configuration, the stiffening elements  104   a  and  104   b  extend between the first elongated edges  184   a  and  184   b  of the connecting strips  174   a  and  174   b  in a taut diagonal manner. In particular, the stiffening element  104   a  rigidly couples the first end  176   a  of the first connecting strip  174   a  with the second end  178   b  of the second connecting strip  174   b . Furthermore, the stiffening element  104   b  rigidly couples the second end  178   a  of the first connecting strip  174   a  with the first end  176   b  of the second connecting strip  174   b . 
     As shown in FIGS. 5A and 5B, the stiffening elements  104   c  and  104   d  diagonally extend in a taut manner between the second elongated edges  186   a  and  186   b  of the connecting strips  174   a  and  174   b . Otherwise, the stiffening elements  104   c  and  104   d  attach between the connecting strips  174   a  and  174   b  in a substantially similar manner to that of the stiffening elements  104   a  and  104   b.    
     It will be appreciated that the torsion stiffening assembly  102  provides the extendable structural element  166  with increased torsional strength in the deployed configuration. In particular, since the stiffening elements  104  are diagonally mounted in a taut manner between the connecting strips  174   a  and  174   b  and since the stiffening elements  104  are resistant to stretching, the stiffening elements  104  will inhibit the first ends  176   a  and  176   b  of the connecting strips  176   a  and  176   b  from respectively being pulled away from the second ends  178   b  and  178   a.  Hence, the connecting strips  174  are inhibited from deforming under the presence of a torsional stress and the adjacent rigid members  164   a  and  164   b  of FIGS. 5A and 5B are inhibited from rotating with respect to each other about the elongated axis of the extendable structural element  166 . Consequently, the extendable structural element  166  will likely maintain a rigid shape even under the presence of torsional stress producing torques. Furthermore, when the extendable structural element  166  is placed in the storage configuration, the folding motion of the first and second rigid members  164   a  and  164   b  will place the torsion stiffening assembly  102  into a loose state so as to inhibit the torsion stiffening assembly  102  from interfering in the placement of the extendable structural element  166  between the deployed configuration and the storage configuration. 
     Reference will now be made to FIGS. 6A-6C which schematically illustrate another embodiment of an extendable structural element  266  that is adapted to fold and extend in a multi-directional manner. In particular, the extendable structural element  266  may be used as part of a boom assembly of an antenna array assembly so as to enable the antenna assembly to be folded into a storage configuration and so as to enable the antenna assembly to be extended and supported in a deployed configuration. 
     As indicated in FIG. 6A, the extendable structural element  266  comprises a plurality of rigid sections  264  that are substantially similar to the rigid sections  64  of the extendable structural element of FIG.  3 A. Furthermore, the extendable structural element  266  comprises a plurality of foldable sections  263  that are substantially similar to the foldable sections  63  of FIG.  3 A. However, as indicated in FIG. 6A, the rigid sections  264  comprise a first plurality of rigid sections  124  and a second plurality of rigid sections  122  wherein each of the rigid sections  124  extends so as to be non-aligned with each of the extended rigid sections  122 . Moreover, the foldable sections  263  comprise a first plurality of foldable sections  126  having mutually parallel folding axes and a second plurality of foldable sections  128  having mutually parallel folding axes, wherein the folding axes of the sections  126  are substantially non-aligned with the folding axes of the sections  128 . 
     As indicated in FIG. 6A, the first rigid members  124   a  and  124   b  flexibly couple with a first end  130  of the second rigid member  122   a  such that the flexible members  126   a  and  126   b  are interposed therebetween. Furthermore, in this embodiment, the flexible members  126   a  and  126   b  are constructed so that their bending axes are perpendicular to the plane of FIG.  6 A. Thus, the first rigid members  124   a  and  124   b  are both able to be folded along a first plane that, in this embodiment, is the plane of FIG. 6B so that first rigid members  124   a  and  124   b  align with the second rigid member  122   a  as shown in FIG.  6 B. 
     As shown in FIG. 6A, the first members  124   c  and  124   d  flexibly couple with a first end  132  of the second rigid member  122   b  such that the flexible members  126   c  and  126   d  are interposed therebetween. Furthermore, in this embodiment, the flexible members  126   c  and  126   d  are constructed so that their bending axes are perpendicular to the plane of FIG.  6 A. Thus, the lateral rigid members  124   c  and  124   d  are both able to be folded along the first plane so that they align with the second rigid member  122   b  as shown in FIG.  6 B. 
     As shown in FIGS. 6A and 6B, the second rigid members  122   a  and  122   b  flexibly couple to each other such that the flexible member  128   a  is interposed therebetween. In particular, the flexible member  128   a  is constructed so that the bending axis is oriented from left to right along FIGS. 6A and 6B. Thus, the second rigid member  122   a  is able to be folded with respect to the second rigid member  122   b  along a second plane that, in this embodiment, is perpendicular to the plane of FIG. 6A such that the second rigid members  122  and the first rigid members  124  are compactly aligned adjacent to each other in a flush manner in the storage configuration as shown in FIG.  6 C. 
     It will be appreciated that the extendable structural elements described hereinabove enable the formation of the improved spacecraft boom assembly of the present invention. In particular, the extendable structural elements are bendable and compressible so as to enable the boom assembly to be easily folded into the storage configuration so that the boom assembly can be stowed within the relatively small payload space of the launching vehicle. Furthermore, since the foldable sections of the extendable structural elements are formed of a resilient material, the elastic energy stored within each of the folded foldable sections provides each of the foldable sections with a bias that urges the boom assembly to self-extend from the storage configuration to the deployed configuration. Moreover, the extendable structural elements, when in the deployed configuration, provide sufficient rigidity so that the boom assembly is capable of supporting extending components of the spacecraft. Additionally, the extendable structural elements are relatively inexpensive to manufacture, are lightweight, and are capable of extending into relatively large sizes. 
     Although the preferred embodiment of the present invention has shown, described and pointed out the fundamental novel features of the invention as applied to this embodiment, it will be understood that various omissions, substitutions and changes in the form of the detail of the device illustrated may be made by those skilled in the art without departing from the spirit of the present invention. Consequently, the scope of the invention should not be limited to the foregoing description, but should be defined by the appending claims.