Abstract:
A hinge for a boom associated with a spacecraft antenna or other payload. The boom hinge includes two hinge bodies and at least three links, where one of the links is a drive link. The resulting hinge is an N+4 bar linkage. An actuator rotates the drive link so that the other links wrap around it, and the next link in the series of links acts as a drive link as the links get wrapped around the primary drive link. At the end of the deployment, the hinge precisely emulates the classic four-bar over-center latch behavior. This allows any hinge-offset distance between the hinge bodies when stowed in a larger hinge rotation angle without structural compromises.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates generally to a hinge fora spacecraft boom for an antenna or other payload and, more particularly, to a boom hinge for a spacecraft antenna or other payload, where the boom hinge includes at least three links to form a five or more bar linkage.  
         [0003]     2. Discussion of the Related Art  
         [0004]     Spacecraft usually employ various types of structures, such as reflectors, antenna arrays, sensors, etc., that must be deployed away from the spacecraft on a boom when the spacecraft is on orbit or in space. These booms typically employ one or more hinges that allow the boom and the structure to be folded or stowed into the spacecraft envelope or fairing during launch, and then be unfolded in space to the deployed position. In certain designs for larger structures, such as antenna reflectors, the boom and hinges are very robust to provide the desired pointing stiffness so that the structure remains pointed in the proper direction for a particular mission requirement. The hinges for these types of boom designs typically are “preloaded” in the deployed position so that disturbances on the spacecraft or boom do not affect the linearity of the pointing of the structure. Various techniques are known in the art for unfolding or deploying the boom, including the use of motors, preloaded springs and other types of actuators.  
         [0005]     A certain class of boom hinges are “clam-shell” designs that include two hinge halves. These boom hinges typically autonomously rotate from the stowed position when the antenna is in the spacecraft for launch to the deployed position when the spacecraft is in space. This requires very high deployed preloads that are applied centrally between the hinge halves. This typically requires a mechanism separate from the deployment actuator that will redundantly latch and provide the needed preload, such as some type of high-force latch. The known two-link over-center or “suitcase latch” type design can be configured to both centrally drive and latch the two halves of a clam-shell type hinge. The result is a simple four-bar linkage that is completely reversible in a direction of operation.  
         [0006]     The above-described antenna boom hinge has a problem in that if the boom hinge has a large rotation angle, for example 180°, from the stowed position to the deployed position, the links have to be so long that they need to pass through slots provided in the boom and hinge body wall when they are rotated through the deployment sequence. These slots reduce the structural integrity of the hinge, possibly to an unacceptable level. Also, the length of the links must be further increased with a corresponding decrease in efficiency if the boom pieces need to be spaced apart when stowed, i.e., if there is a significant offset between the hinge line and the boom and hinge center line. It would be desirable to provide a hinge for a spacecraft boom that provided the structural integrity and robustness in a compact and deployable design beyond those hinges currently existing in the art.  
       SUMMARY OF THE INVENTION  
       [0007]     In accordance with the teachings of the present invention, a hinge for a boom associated with a spacecraft antenna or other payload is disclosed. The boom hinge includes two hinge bodies and at least three links, where one of the links is a drive link. The resulting hinge is an N+four bar linkage. An actuator rotates the drive link so that the other links wrap around it. The next link in the series of links acts as a drive link as the links get wrapped around the primary drive link. At the end of the deployment, the hinge precisely emulates the classic four-bar over-center latch design. This allows any hinge offset distance between the hinge bodies when stowed in a larger hinge rotation angle without structural compromises.  
         [0008]     Additional advantages and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a perspective view of a spacecraft including a deployed reflector on a boom, where the boom includes at least one boom hinge, according to an embodiment of the present invention;  
         [0010]      FIGS. 2-6  are cross-sectional views of a boom hinge applicable to be used in the spacecraft shown in  FIG. 1  between a stowed position in  FIG. 2  and a deployed position in  FIG. 6 ; and  
         [0011]      FIGS. 7-10  are cross-sectional views of a boom hinge applicable to be used in the spacecraft shown in  FIG. 1  between a stowed position shown in  FIG. 7  and a deployed position shown in  FIG. 10 . 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0012]     The following discussion of the embodiments of the invention directed to a hinge for a boom on a spacecraft is merely exemplary in nature and is in no way intended to limit the invention or its applications or uses. For example, the hinge may have other applications beyond spacecraft applications.  
         [0013]      FIG. 1  is a perspective view of a communications spacecraft  10  including a spacecraft body  12  and solar arrays  14  and  16  mounted to the body  12  that have been extended or deployed. The spacecraft  10  further includes an antenna system having an array of antenna feeds  20  mounted to the spacecraft body  12 . The antenna system further includes an antenna reflector  18  configured on a truss  22 , and connected to the spacecraft body  12  by a boom  24 . Signals from earth received by the reflector  18  are directed to the antenna feeds  20 , and signals transmitted by the antenna feeds  20  are directed towards the reflectors  18  to be transmitted to earth. The operation of a communications satellite of this type is well understood in the art, and need not be discussed in detail here for a proper understanding of the invention.  
         [0014]     When the spacecraft  10  is launched from earth in a rocket fairing or on the shuttle, the reflector  18  is folded or stowed into a launch envelope within a confined space. When the spacecraft  10  is on orbit, the reflector  18  is deployed on the boom  24  by the articulation of a plurality of hinges depending on the particular design. Particularly, the boom  24  typically includes one or more hinges  26  that provide the deployment, structural integrity, preloading and pointing stiffness necessary for the reflector  18 .  
         [0015]      FIGS. 2-6  are cross-sectional views of a five-bar linkage hinge assembly  32 , according to an embodiment of the present invention, applicable to be used for the hinge  26  to extend or deploy the boom  24 .  FIG. 2  shows the hinge assembly  32  in a stowed position during launch of the spacecraft  10 , and  FIG. 6  shows the hinge assembly  32  in a deployed position as it would be in  FIG. 1  in the on orbit position.  FIGS. 3-5  show the hinge assembly  32  in sequential states between the stowed position and the deployed position.  
         [0016]     The hinge assembly  32  includes a first hinge body  34  and a second hinge body  36  having side walls  28  and  30 , respectively, defining chamber halves  44  and  46  therein. When the hinge assembly  32  is in the deployed position, the hinge bodies  34  and  36  are closed so that the chamber halves  44  and  46  combine to define a single chamber in which the hinge links are enclosed, as will be discussed below. The hinge body  34  includes a hinge tab  38  extending from the sidewall  28  and the hinge body  36  includes a hinge tab  40  extending from the sidewall  30 . The hinge tabs  38  and  40  are pivotally coupled together by a hinge pin  42  that is aligned with inside surfaces  48  and  54  of the hinge bodies  34  and  36 , respectively, as shown. The hinge tabs  38  and  40  may be a series of spaced apart tabs along the length of the hinge bodies  34  and  36 , where the hinge pin  42  extends through all of the tabs  38  and  40 . The length of the tabs  38  and  40  or the distance between the link pin  42  and the respective hinge body  34  and  36  defines the “offset” of the hinge assembly  32 . Some hinge assembly designs for a particular application may require that the hinge offset be significantly large, which presents certain design problems, as will be discussed below.  
         [0017]     A boom piece (not shown) will be coupled to an end  50  of the hinge body  34  and a boom piece (not shown) will be coupled to an end  52  of the hinge body  36 , so that the boom pieces are adjacent to each other when the reflector  18  is in the stowed position. In one embodiment, the coupling between the hinge body and the respective boom piece is a “cup and cone” design, well known to those skilled in the art. The boom pieces can be made of any suitable material such as metal, graphite, composite, etc., and can be secured to the hinge bodies  34  and  36  by any suitable technique, such as rivets, bolts, adhesive, etc. Likewise, the hinge bodies  34  and  36  can be made of any suitable rigid material, such as aluminum, composites, etc.  
         [0018]     The hinge assembly  32  includes a short drive link  56  rotatably coupled to the hinge body  34  by a drive shaft  58 . The hinge assembly  32  further includes a first U-shaped link  60  pivotally coupled to an end of the drive link  56  opposite to the drive shaft  58  by a link pin  62 . The hinge assembly  32  further includes a second U-shaped link  64  pivotally coupled to an end of the first link  60  opposite to the link pin  62  by a link pin  66 , and pivotally coupled to the hinge body  36  by a link pin  68  opposite to the link pin  66 , as shown. The second link  64  is positioned against a support pin  70  mounted to the hinge body  36  when the hinge assembly  32  is in the stowed position. The combination of the three links  56 ,  60  and  64  and the two hinge bodies  34  and  36  define the five-bar linkage.  
         [0019]     When the reflector  18  is deployed, a motor (not shown), or some other suitable actuation device, rotates the drive shaft  58  in a counter-clockwise direction. As the drive link  56  is rotated, the first link  60  pivots on the link pins  62  and  66  so that the hinge body  34  pivots on the hinge pin  42  in a clockwise direction, as shown in  FIG. 3 . As the drive shaft  58  continues to rotate, the hinge body  34  will continue to rotate in a clockwise direction, and the second link  64  will lift off the support pin  70 , as shown in  FIG. 4 . As the drive link  56  continues to rotate, it will eventually contact the first link  60 , and be folded parallel to it, making the first link  60  the drive link, as shown on  FIG. 5 . Eventually, the first link  60  will fold inside of the second link  64  so that the drive link  56  is positioned between the links  60  and  64  and the hinge assembly  32  is in the deployed position, as shown in  FIG. 6 . The orientation of the link 2   102  and  106  is “over” top dead center in the deployed position to provide the preload. In the deployed configuration, the boom pieces would extend along a common axis.  
         [0020]     By providing more links in the hinge assembly  32  than the number of links used in the prior art, the deployed configuration of the links  56 ,  60  and  64  take up a smaller area, and are confined within the chamber defined by the chamber halves  44  and  46 . Thus, the links  56 ,  60  and  64  do not need to be as long, so that slots do not need to be formed in the sidewalls  28  and  30  of hinge bodies  34  and  36  or in the boom pieces to accommodate the folded link assembly.  
         [0021]     In alternate hinge designs according to the invention, the hinge offset may be required to be relatively large. This requires that the links be longer to accommodate the offset distance. In such a design, a five-bar linkage may not be enough because the links  60  and  64  may be too long where slots again would be required in the hinge bodies  34  and  36  and the boom pieces. Therefore, the present invention proposes other embodiments that are N+4 bar linkage designs.  
         [0022]      FIGS. 7-10  are cross-sectional views of a six-bar linkage hinge assembly  80 , according to another embodiment of the present invention, where  FIG. 7  shows the hinge assembly  80  in the stowed position and  FIG. 10  shows the hinge assembly  80  in the deployed position. The hinge assembly  80  includes a first hinge body  82  and a second hinge body  84  having sidewalls  76  and  78 , respectively, defining chamber halves  72  and  74 . The hinge body  82  includes a hinge tab  86  and the hinge body  84  includes a hinge tab  88 . The hinge tabs  86  and  88  are pivotally coupled together by a hinge pin  90  that is aligned with inside surface  92  of the hinge body  82  and inside surface  94  of the hinge body  84 , as shown. A spring  96  is wrapped around the hinge pin  90  to provide tension between the hinge bodies  82  and  84  that prevents an outside force other than the actuator from rotating the hinge body  82 .  
         [0023]     The hinge assembly  80  includes a drive link  98  rotatably coupled to the hinge body  82  by a drive shaft  100 . The hinge assembly  80  further includes a first U-shaped link  102  pivotally coupled to the drive link  98  by a link pin  104  opposite to the drive shaft  100 . The hinge assembly  80  further includes a second U-shaped link  106  pivotally coupled to an end of the link  102  opposite to the link pin  104  by a link pin  108 . The hinge assembly  80  further includes a third U-shaped link  110  pivotally coupled to an end of the link  106  opposite to the link pin  108  by a link pin  112 , and pivotally coupled to the hinge body  84  opposite to the link pin  112  by a link pin  114 . The link  110  is a more robust link to provide the structure required for the preload when the hinge assembly  80  is in the deployed position. The hinge body  82  includes nubs  120  and  122  that contact stops  124  and  126 , respectively, on the hinge body  84  when the hinge assembly  80  is in the deployed position.  
         [0024]      FIGS. 8 and 9  show the hinge assembly  80  in sequential states between the stowed position and the deployed position. When the motor rotates the drive shaft  100 , the drive link  98  rotates in a counter-clockwise direction so that the first link  102  pivots on the link pin  104  and the second link  106  pivots on the link  112 . Eventually, the drive link  98  will be positioned within and adjacent to the first link  102 , as shown in  FIG. 8 . As the drive shaft  100  continues to rotate, the first link  102  becomes the drive link, and the second link  106  is folded adjacent to the first link  102 , where the drive link  98  is positioned between the links  102  and  106 , as shown in  FIG. 9 . As the drive shaft  100  rotates to the deployed position as shown in  FIG. 10 , the first link  102  will be positioned adjacent to and within the third link  110 . The orientation of the third link  110  is “over” top dead center in the deployed position to provide the preload.  
         [0025]     By increasing the number of links it is not necessary to provide slots in the sidewalls  76  and  78  for larger hinge offsets, and therefore the torsional stiffness of the hinge assembly can be increased. This allows the hinge bodies to be preloaded in the deployed position better suitable for the pointing requirements. In one design, it is the cup and cone joints between the boom pieces and the hinge bodies that are preloaded. The structure of the hinge bodies are stressed by the preload as a result of the links.  
         [0026]     The hinge body  84  includes a stop  128 , such as a set screw, that prevents the third link  110  from rotating on the link pin  114  in a counter-clockwise direction. Further, the hinge body  82  includes a switch  130  that turns the motor off by contacting the link  102  when the hinge assembly  80  is in the deployed state shown in  FIG. 10 . The hinge body  84  also includes a threaded adjustment mechanism  132  that adjusts the position of the hinge pin  114  along the axis of the boom in the deployed position to provide the proper preload on the hinge assembly  80  by the link  110 .  
         [0027]     The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.