Patent Application
20070094847
1. Field of the Invention
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.
2. Discussion of the Related Art
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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
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.
