Statement of the Technical Field
This document relates to compact antenna system structures, and more particularly, to a compact deployable antenna reflector structure.
Description of the Related Art
Various conventional antenna structures exist that include a reflector for directing energy into a desired pattern. One such conventional antenna structure is a radial rib reflector design comprising a plurality of reflector ribs joined together at a common cylindrical shaped hub. The reflector ribs provide structural support to a flexible antenna reflector surface attached thereto. A plurality of cords, wires, guidelines, or other tensile members couple the flexible antenna reflector surface to the reflector ribs. The wires or guidelines define and maintain the shape of the flexible antenna reflector surface. The radial rib reflector is collapsible so that it can be transitioned from a deployed position to a stowed position. In the deployed position, the radial rib reflector has a generally parabolic shape. In the stowed position, the reflector ribs are folded up against each other. As a result, the antenna reflector has a stowed height approximately equal to the reflector's radius.
Another conventional antenna structure is a folding rib reflector having a similar design to the radial rib reflector design described above. However, the reflector ribs include a first rib tube and second rib tube joined together by a common joint. In the stowed position, the first rib tubes are folded up against the second rib tubes. As such, the antenna reflector has a stowed height that is approximately half the stowed height of the radial rib reflector design. However, the stowed diameter of the folding rib reflector may be larger than the stowed diameter of the radial rib reflector design.
Another type of configuration is a hoop reflector where the reflector surface is attached to a circular hoop. In a hoop-type reflector, the hoop structure must have a certain amount of stiffness to prevent the hoop from warping. Typical of this design is U.S. Pat. No. 5,680,145. In this patent, the hoop consists of two rings, an upper and a lower. Both rings are made up of tube elements. As such, the single tube elements provide minimal bending stiffness, or ring stiffness, about the longitudinal axis of symmetry defined as the direction perpendicular to the circle defining the perimeter of the hoop. The limited ring stiffness allows the hoop to become non-circular and is easily deformed into an oval shape. Other hoop designs provide significant ring stiffness by creating a toroidal hoop with a triangular configuration of members. For example, such an arrangement is disclosed in U.S. Pat. No. 6,313,811. To shape the reflector into a parabolic surface, the hoop must also have a deployed thickness perpendicular to the plane defined by the perimeter of the hoop. The thickness of the hoop is measured in the direction of a central axis of the hoop when deployed. Moreover, this thickness must generally be greater than the depth of the parabolic surface in order to achieve a desired parabolic shape. The required out of plane thickness of the hoop and the need for bending stiffness can make it challenging to design a hoop structure which, when stowed, is sufficiently compact in length along the longitudinal direction defined by the hoop central axis. For example, a conventional hoop system having a sufficiently rigid hoop structure with a deployed thickness H can, when collapsed for stowage aboard a spacecraft, have an elongated length along the hoop center axis equal to 2H.
This document concerns a reflector antenna system. The system includes a hoop assembly which is comprised of a plurality of link elements which are rigid and extend between a plurality of hinge members. The hoop assembly is configured to expand between a collapsed condition wherein the link elements extend substantially parallel to one another and an expanded condition wherein the link elements define a circumferential hoop around a central axis. A reflector surface of the antenna system is comprised of a collapsible web and secured to the hoop assembly such that when the hoop assembly is in the expanded condition, the reflector surface is expanded to a shape that is configured to concentrate RF energy in a desired pattern.
The hoop assembly in the expanded condition is defined by a plurality of N sides, each defining a rectangle, including a top, a bottom, and two opposing edges aligned with the central axis. The N sides are disposed edge to edge circumferentially around a periphery of the hoop assembly such that each opposing edge extends substantially the full axial depth of the expanded hoop assembly in a direction aligned with the hoop central axis.
Each of the N sides is comprised of an X-member. Each X-member is comprised of a plurality of the link elements. These link elements include a first and a second link element respectively disposed on opposing diagonals of the rectangle in a crossed configuration. A pivot member is connected at a medial pivot point of the first and second link elements. The pivot member facilitates pivot motion of the first link element relative to the second link element on a pivot axis when the hoop assembly transitions between the collapsed condition and the expanded condition. The hinge members connect adjoining ones of the X-members associated with adjacent sides at the top and bottom corners associated with each edge.
The hoop assembly also includes at least one top cord which extends along the top of the side between top ends of the first and second link elements, and at least one bottom cord which extends along the bottom of the side between bottom ends of the first and second link elements. Each of the top cord and the bottom cord are exclusively tension elements. Further, first and second edge tension elements extend respectively along the two opposing edges of the side. At least one deployment cable provides a force needed to transition the hoop assembly from the collapsed condition to the expanded condition by reducing a length of each opposing edge.
In the system described herein, each of the first and second link elements includes a top end which extends to a top corner of the rectangle defined by the side, and a bottom end which extends to a bottom corner of the rectangle defined by the side. The first link element of each X-member is connected at the top end to the second link element of a first one of the X-members associated with a first adjacent side. The first link element is also connected at a bottom end to the second link element of a second one of the X-members associated with a second adjacent side.
The second link element is comprised of a plurality of elongated structural members which extend in parallel respectively on an inner and outer side of the first link element. The pivot member pivotally connects each of the plurality of elongated structural members to the first link element. The plurality of elongated structural members which comprise the second link element are connected to a top hinge at a top end of the second link element, and connected to a bottom hinge at a bottom end of the second link element.
The deployment cable extends along a length of each of the edge tension elements, and diagonally along the length of the first link element of the side. Top and bottom cord guide elements are respectively disposed at the top and bottom ends of the first link element. These top and bottom cord guide elements are configured to transition an alignment of the deployment cable from directions aligned with the opposing edges of each side, to a diagonal direction aligned with the first link element. At least one latching element is configured to latch the X-members in a fixed pivot position after the hoop assembly is in the expanded condition. Consequently, a force applied to the first link element by the deployment cable can be reduced while maintaining the hoop assembly in the expanded condition.
The reflector antenna system also includes at least one actuator configured to vary a length of the opposing edges of the side by controlling the extended length of the deployment cable extending around a periphery of the hoop assembly. A resistance mechanism is advantageously provided to resist the transition of the hoop assembly from the collapsed condition to the expanded condition. The force generated by the resistance mechanism serves to control the deployment rate and position of hoop as it transitions from the collapsed to the expanded condition.
This disclosure is facilitated by reference to the following drawing figures, in which like numerals represent like items throughout the figures, and in which:
It will be readily understood that the components of the systems and/or methods as generally described herein and illustrated in the appended figures could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description, as represented in the figures, is not intended to limit the scope of the present disclosure, but is merely representative of certain implementations in various different scenarios. While the various aspects are presented in the drawings, the drawings are not necessarily drawn to scale unless specifically indicated.
The required out of plane thickness of a hoop-type reflector antenna, and the need for a minimal level of bending stiffness, can make it challenging to design a suitable hoop structure. For example, it can be difficult to design such an antenna that, when stowed, demonstrates sufficient compaction in length in the longitudinal direction defined by the hoop central axis. The hoop-type reflector antenna disclosed herein is rigid and lightweight. But when collapsed for stowage (e.g. stowage aboard a spacecraft) the antenna structure will have an elongated length along a hoop center axis which is 1.4 t, where the distance t is a thickness of the antenna structure along the longitudinal hoop center axis when the reflector is in a deployed condition. This represents a significant improvement over conventional designs which when collapsed for stowage have an elongated length along the hoop center axis equal to 2 t.
A deployable reflector system (DRS) 100 will now be described with reference to
In the stowed condition, the hoop assembly can be sufficiently reduced in size such that it may fit within a compact space (e.g., a compartment of a spacecraft or on the side of a spacecraft). The hoop assembly 102 can have various configurations and sizes depending on the system requirements. In some scenarios the hoop assembly 102 can define a circular structure as shown in
The hoop assembly 102 is comprised of a plurality of link elements which are disposed about a central, longitudinal axis 108. The link elements can comprise two basic types which are sometimes referred to herein as a first link element 110, and a second link element 112. The link elements are elongated rigid structures which extend between hinge members 114, 116 disposed on opposing ends of the link elements. For example, in some scenarios the link elements can be comprised of elongated rigid tubular structures formed of a rigid lightweight material. Exemplary materials which can be used for this purpose include metallic or a Carbon Fiber Reinforced Polymer [or Plastic] (CFRP) composite material.
As may be observed in
The reflector surface 106 is advantageously formed of a thin highly flexible sheet or web material. The reflector surface is likewise comprised of a material which is highly reflective of radio frequency signals. For example, in some scenarios the reflector surface can be comprised of a reflective film or a conductive metal mesh. Reflective films and conductive metal meshes used for this purpose are well-known in the art and therefore will not be described here in detail. However, due to their highly flexible nature, these materials are inherently collapsible, such that they can be compactly stowed when the hoop is in the collapsed condition. For example, the mesh material in some scenarios can be stored in a collapsed or folded condition within the circumference of the hoop assembly when folded or collapsed for stowage. The conductive mesh material is advantageously secured at attachment points 107 along its periphery to the hoop assembly 102. The mesh material is also attached at various locations to shaping/support cords 109 disposed within the periphery of the hoop assembly. Consequently, when the hoop assembly is in the expanded condition, the reflector surface is expanded to a shape that is intended to concentrate RF energy in a desired pattern. For example, the reflector surface can be controlled so as to form a parabolic surface when the hoop assembly is in the expanded or deployed condition. To enhance the clarity of the disclosure herein, the reflector surface 106 and the shaping/support cords 109 are not shown in
It may be noted that in order to shape the reflector 106 into a parabolic surface (or other reflecting surface shape), the hoop assembly 102 will necessarily need to have a thickness t which extends in the longitudinal direction aligned with the central axis 108. As such, the hoop assembly 102 will include structural elements which extend some predetermined distance out of a plane defined by the peripheral edge of the reflector surface. This distance is usually greater than the depth of the reflector as measured along the axis 108. It will be appreciated the hoop assembly as described herein must also have a degree of bending stiffness to allow the reflector to conform to the required shape. For a system using symmetric optics where RF energy is focused along the longitudinal axis of the reflector 108, the structure 102 will be circular when deployed. For systems requiring an ‘offset’ configuration where the RF energy is focused on a line parallel to the longitudinal axis 108 but located outside the perimeter of the hoop, the structure 102 is elliptical in shape.
Referring now to
As shown in
In some scenarios, the top and bottom edges 502, 504 can be aligned with a top cord 202 and a bottom cord 204 when the hoop assembly is in a deployed condition. Likewise, the two opposing vertical edges 506, 508 can be aligned with aligned with side edge tension elements 206. Such a scenario is illustrated in
As may be observed in
Each of the N sides is defined in part by an X-member 500 which is comprised of a first and second link element 110, 112. As shown in
A pivot member 518 is connected at a pivot point of the first and second link elements. The pivot point is advantageously located intermediate of the two opposing ends of each link element. For example, the pivot point is advantageously disposed at approximately equal distance from the opposing ends of the first link element, and at approximately equal distance from the opposing ends of the second link element. As such, the pivot point can located approximately at a midpoint of each element.
The pivot member 518 is configured to facilitate pivot motion of the first link element 110 relative to the second link element 112 about a pivot axis 520 in
The hinge members 114, 116, which are sometimes referred to herein as hinges, are disposed at opposing ends of the first and second link elements 110, 112 and connect adjoining ones of the X-members 500 at the top and bottom corners associated with each side. As shown in
As is best shown in
In a scenario disclosed herein, the plurality of elongated structural members 602a, 602b can be connected to a common or shared hinge 114 at a top end 512 of the second link element 112, and a common or shared hinge 116 at a bottom end 516 of the second link element. As such, the plurality of elongated structural members 602a, 602b can share a common top hinge 114 and a common bottom hinge 116. As shown in
In a hoop assembly as described herein adjacent ones of the sides 118 will necessarily be aligned in different planes. This concept is best understood with reference to
As best shown in
Referencing
Each rectangular side 118 comprising the hoop assembly is further defined by a plurality of tension elements (
To control the deployed position of each side of the expanded hoop, it is important that the top and bottom cords 202, 204 be stiff elements, meaning that they are highly resistant to elastic deformation when under tension. While slack in the collapsed state, these elements are selected to quickly tension at their expanded length. As such, they act as a ‘hard-stop’ to limit further hoop expansion by restricting the distance between hinges 114 at the top and 116 at the bottom. To effect ‘hard-stop’ behavior in these elements, the amount of stretch between the slack state and tension state should be small. For example, assume that the desired length of the top and bottom cord is Ld. In such a scenario, each cord will have length Ld when the hoop assembly is in its collapsed condition, with the top and bottom cords 202, 204 folded between the hinges 114, 116 in
In some scenarios, a separate top cord 202 can be provided between the link elements 110, 112 comprising each side 118. Similarly, each side 118 can be comprised of a separate bottom cord 204 which extends between the bottom ends of the first and second link elements. But in other scenarios it can be advantageous to use a single common top cord 202 which extends in a loop around the entire hoop assembly. Such a top cord 202 can then be secured or tied off at intervals at or near the top ends 510, 512 of the first and second link elements 110, 112. For example, the top cord 202 can be secured at intervals to securing hardware associated with each of the top hinge members 114. Consequently a portion or segment of the overall length of the single common top cord loop will define a top tension element for a particular side. A similar arrangement can be utilized for the bottom cord 204. Since the top and bottom cord have significant stiffness (resistance to elastic deformation) as explained above and are attached to opposing hinge elements at or near the top and bottom of each X-member, their length Ld will necessarily limit the maximum deployed or expanded rotation of the first and second link elements 110, 112 about a pivot axis 524.
Each side 118 is further defined by opposing vertical edge tension elements 206 which extend respectively along the two opposing edges of the side. In a scenario disclosed herein, the edge tension elements 206 can extend respectively along the two opposing vertical edges of each side. The edge tension elements 206 are configured for applying tension between the opposing top and bottom ends of the link elements 512, 514 and 510, 516 when they are in a latched condition.
Referring once again to
In each side 118, the control cable extends diagonally between the two opposing edges 506, 508, along the length of the first link element 110. For example, the deployment cable 604 in such scenarios can extend through a bore formed in the first link element 110, where the bore is aligned with the elongated length of the first link element. Of course, other arrangements are also possible and it is not essential that the deployment cable extend through a bore of the first link element. In some scenarios, the control cable could alternatively extend adjacent to the first link element through guide elements (not shown).
Cable guide elements are advantageously provided to transition an alignment of the deployment cable from directions aligned with the opposing edges 506, 508 of each side, to a diagonal direction aligned with the first link element 110. In a scenario disclosed herein, a top guide element 606 and bottom guide element 608 are respectively disposed at the top and bottom ends of the first link element 119. The cable guide elements can be simple structural elements formed of a low friction guiding surface on which the deployment cable can slide. However, it can be advantageous to instead select the cable guide elements to comprise a pulley that is designed to support movement and change of direction of a taught cord or cable. Details of a pulley type of cable guide element 606 can be seen in
As shown in
Substantial deployment cable tension force can be required in order to expand the hoop assembly to its fully deployed condition. However, a reflector antenna as described herein can remain deployed for long periods of time. Consequently, it can be desirable to provide at least one latching element which is configured to latch the X-members 500 in a fixed pivot or scissor position after the hoop assembly is in the expanded condition. The latch assembly can be configured to allow a force applied by the deployment cable to be reduced while maintaining the hoop assembly in the expanded condition.
In a scenario disclosed herein, the referenced latch assembly can be incorporated into the edge tension elements 206. Such a scenario is shown in
Eventually, a tip end 910 of the upper latch member 902 will be guided into a latch receptacle 912 of the lower latch member 904. The latch receptacle 912 in this example is a bore formed in an end portion of the lower latch member 904. The upper and lower latch members will then continue moving in directions 906, 908 until a notch 914 formed in the upper latch member is engaged by a nub 918 associated with a latching wings 916. In
Once the latch 900 is engaged, the tension force exerted by the deployment cable 604 on the first and second link elements 110, 112 can be removed. The tension force previously provided by the deployment cable 604 will be instead maintained by the side tension elements 206 since the edge tension elements 206 will have been transitioned to their latched condition. The hoop assembly 102 can then remain in the expanded condition, with the latches 900 engaged.
As the antenna structure deploys, the nominal tension in the deployment cable 604 is virtually zero as there are no resistive forces acting upon the structure. More particularly, there are no inwardly directed radial forces at hinges 114, 116 tending to push the structure towards its stowed position. Thus, as the structure deploys there is nothing to prevent the structure advancing more than the deployment cable windup would require. Due to the linked behavior of the collective set of X-members 500 the structure is synchronized. However, absent some type of biasing or limiting arrangement, the radius of the hoop assembly is possibly uncontrolled. Practically speaking, this means that if the deployment cable is lagging the structure position, there exists the possibility the extra slack in the deployment cable could allow disengagement of the cable from its pulleys. So it is advantageous that some minimal level of load be maintained on the deployment cable to preclude it ever becoming slack during the deployment.
To provide a mechanism to maintain deployment cable tension at all stages of deployment, the antenna system advantageously includes a resistance device that is configured to facilitate radially directed inward forces at hinges 114, 116 and or pivot members 518. In some scenarios, this can be implemented with a resistance cable that circumscribes the hoop assembly and is attached to all of the hinge elements 114, 116 and/or pivot members 518. This resistance cable is initially wound around a drum (not shown) in a similar fashion to the deployment cable 604 and is controlled in a fashion to maintain a prescribed level of tension on the deployment cable. The foregoing result is accomplished by letting the resistance cable out from the drum at a rate consistent with the deployment cable take-up rate. In this manner, the forces imposed by the resistance cable are reacted by the deployment cable, thereby maintaining the deployment cable at a prescribed minimal load to prevent the deployment cable from disengaging the pulleys.
In a scenario shown in
A further significant benefit of the resistance cable described herein is that it can serve as a re-stow cable to facilitate ground operations. Operation on-orbit usually does not require a full re-stow, as in most scenarios only a single deployment is required. However, partial re-stow on-orbit is an attractive feature to aid in over-coming anomalous conditions.
Of course other configurations for adding resistance to the antenna system during the deployment process are also possible and contemplated within the scope of the invention. For example, another method to implement the resistance function described herein can involve friction inducing devices that can be implemented in all or a subset of the hinges 114, 116 and/or pivot members 518. Friction inducing members associated with hinge or pivot elements are well-known in the art and therefore will not be described in detail. The friction inducing members as described are a passive mechanism available to maintain the deployment cable in tension and has the possible benefit of being a simpler approach in some scenarios. However it will be appreciated that the passive friction members described herein do not provide for any re-stow capability.
Finally, it may be noted that as the deployment of the antenna system progresses to the point where the surface 104 (
Reference throughout this specification to features, advantages, or similar language does not imply that all features and advantages that may be realized should be or are in any single embodiment. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with a particular implementation is included in at least one embodiment. Thus, discussions of the features and advantages, and similar language, throughout the specification may, but do not necessarily, refer to the same embodiment.
Furthermore, the described features, advantages and characteristics disclosed herein may be combined in any suitable manner. One skilled in the relevant art will recognize, in light of the description herein, that the disclosed systems and/or methods can be practiced without one or more of the specific features. In other instances, additional features and advantages may be recognized in certain scenarios that may not be present in all instances.
Reference throughout this specification to “one embodiment”, “an embodiment”, or similar language means that a particular feature, structure, or characteristic described in connection with the indicated embodiment is included in at least one embodiment. Thus, the phrases “in one embodiment”, “in an embodiment”, and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
As used in this document, the singular form “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art. As used in this document, the term “comprising” means “including, but not limited to”.
Although the systems and methods have been illustrated and described with respect to one or more implementations, equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In addition, while a particular feature may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Thus, the breadth and scope of the disclosure herein should not be limited by any of the above descriptions. Rather, the scope of the invention should be defined in accordance with the following claims and their equivalents.