Patent Description:
Concurrently, advances in miniaturizing technology have allowed spacecraft to shrink in size and weight while maintaining capabilities rivaling that of much larger traditional satellites and crafts. However, the sensitivity and resolution of radar antenna detection depends directly on the area of the antenna receiver or dish. So, while other spacecraft components such as high-speed processors, high energy density batteries, solar cells, inertial measurement units, divert and attitude control systems, etc. have shrunk in size and weight in today's smallsats and nanosats, the antenna area must remain large to provide the required performance.

This demand for large area has resulted in new concept designs for RF antennas that maintain large area while allowing for highly compactable storage during launch into space. The antenna must be able to be folded into a small volume in a rocket payload, and, once in space, deploy to its full extent while maintaining an accurate parabolic reflective surface quality and shape that permits the collection of undistorted radio wave information from light years away.

Conventional stowable antennas include pre-formed rigid structures that include discrete positions that permit the segments to fold into a collapsed configuration. By extending the structure by unfolding and locking these joints, the structures defines a desired deployed configuration. For example, rigid sheets may include hinges between sheets to permit the antenna to unfold from a stowed configuration to a deployed configuration. Similarly, a support frame of an antenna structure may include rigid segmented rods that form foldable links. The support frame may be folded at discrete positions in the stowed configuration and unfolded and locked in a deployed configuration.

Conventional stowable antennas that do not include static, pre-formed shapes may include inflatable structures. These structures are essentially balloons in the shape of the desired final form. These systems, however, require additional components for storing and applying the inflation gas or substance to deploy the structure. Therefore, these structures may provide a benefit in not requiring a specific or static stored configuration mandated by preformed and static structures. However, these structure require additional space and weight be dedicated to deployment of the structure.

<CIT> discloses a reflector assembly including a frame centered about a longitudinal axis and having a first height along the axis. A curved body extends from the frame and has a second height along the longitudinal axis which could be greater than the first height. A stretchable membrane has an electromagnetically reflective surface and is secured to the curved body.

<CIT> discloses an architecture deploying an energy-directing mesh so as to conform with a prescribed surface including a plurality of radially extending support structures. Cords extend between the support structures in a generally circumferential fashion, and have attachment locations for the energy-directing material offset from the support structures. Each of a plurality of outermost intercostal cords is retained in tension between the support structures and is configured to substantially conform to the perimeter of the prescribed surface. Flexible intercostal compression reactor members are arranged to be placed in tension in a generally arcuate shape between adjacent support structures. Flexible radial compression members are placed in compression between the intercostal compression reactor members and the outermost intercostal cords, so that the outermost cords substantially conform with the perimeter of the prescribed surface. The outermost intercostal cord is supplemented by at least one, and preferably a plurality of, additional, auxiliary cords installed between each pair of support structures. These plural cords are attached to intercostal and radial compression members in a manner that fills in the scallop-shaped gaps of the conventional architecture with an auxiliary mesh attachment structure for conforming the perimeter of the mesh surface with its intended geometrical shape. The combination of these additional intercostal cord sets and their associated radial compression members provides for a more accurate mesh attachment geometry and improved stability.

<CIT> discloses a method and apparatus for making a mesh reflector that may be used to produce a shaped reflector. The mesh reflector may be an umbrella-style deployable mesh reflector capable of approximating both parabolic and arbitrarily shaped reflecting surfaces, including those with regions of reversed curvature. The reflecting surface may be provided by a soft mesh attached to a highly pre-tensioned net composed of two sets of substantially parallel chords forming a plurality of parallelogram-shaped facets. The net/mesh may be made to conform to the desired shape by pulling and/or pushing on it at each of its facet corners via a set of finely adjustable tension ties and/or compression rods, the distal ends of which react against a set of pre-tensioned catenary-shaped chords disposed on the aft side of the mesh. The net/mesh and the aft catenaries may be supported and pretensioned by a set of substantially stiff radial ribs connected to a central hub by a means capable of providing high deployment torque and a means for controlling and coordinating the deployment of the ribs so that they reach their fully deployed positions nearly simultaneously. Methods for fabricating the mesh and attaching it to the net are also provided.

<CIT> discloses a collapsible conductive material including a generally mesh-configured, collapsible surface, that defines the intended reflective geometry of an antenna. A distribution of tensionable cords and ties form radial truss elements with a plurality of inflatable radially extending ribs and posts of a support structure. The antenna is fully deployed once the support structure is inflated to at least a minimum pressure necessary to place the ties and cords in tension so that the reflective surface acquires a prescribed (e.g., parabolic) geometry, which is stably maintained by the radial truss elements.

<CIT> discloses an antenna reflector intended to be capable of being packed and unfolded as automatically as possible, in particular for use in space. In order to avoid or to reduce the dependency on maintaining the correct pressure in the elements which are to be compressed, clamping rings, which can be folded and can be inflated, and space webs, which interact with them, as well as ribs, which are resistant to tension and folding, are provided in order to connect two membranes, which can be clamped on in mirror-image symmetry, in a manner to give the antenna its shape.

<CIT> and <CIT> disclose a deployable antenna, with a support structure including a shape memory composite having a remembered configuration, which is configured to deform along a length when a force is applied and is configured to return to the remembered configuration when heat is applied.

Exemplary embodiments are described herein for compactable antennas. Exemplary compactable antennas include a support structure and a reflector surface. The support structure may directly or indirectly define the reflector shape. Exemplary embodiments comprise deployable support structures to permit the compactable antenna to have a smaller volume stowed configuration and a larger volume deployed configuration.

The drawings and following associated descriptions are provided to illustrate embodiments of the present disclosure and do not limit the scope of the claims. Corresponding numerals indicate corresponding parts.

Embodiments of systems, components and methods of assembly and manufacture will now be described with reference to the accompanying figures, wherein like numerals refer to like or similar elements throughout. Although several embodiments, examples and illustrations are disclosed below, it will be understood by those of ordinary skill in the art that the inventions described herein extends beyond the specifically disclosed embodiments, examples and illustrations, and can include other uses of the inventions and obvious modifications and equivalents thereof. The terminology used in the description presented herein is not intended to be interpreted in any limited or restrictive manner simply because it is being used in conjunction with a detailed description of certain specific embodiments. In addition, embodiments of the inventions can comprise several novel features and no single feature is solely responsible for its desirable attributes or is essential to practicing the inventions herein described.

Although certain aspects, advantages, and features are described herein, it is not necessary that any particular embodiment include or achieve any or all of those aspects, advantages, and features. Some embodiments may not achieve the advantages described herein, but may achieve other advantages instead. Any structure, feature, or step in any embodiment can be used in place of, or in addition to, any structure, feature, or step in any other embodiment, or omitted. This disclosure contemplates all combinations of features from the various disclosed embodiments. No feature, structure, or step is essential or indispensable. Features may also be integrated or subdivided as necessary, such that the any combination of features, whether integrated, separated, removed, added, duplicated, or otherwise recombined fall within the scope of the instant disclosure.

Exemplary embodiments described may incorporate a shape memory composite defining a support framework, defining a support structure, or integrated into all or a portion of a non-structured collapsible antenna. Although embodiments described herein are in terms of a shape memory composite, exemplary antenna configurations may be novel by themselves. Therefore, the described structure may be made using any conventional deployable antenna material. Exemplary embodiments include two inventive designs for compactable RF antennas comprised of membrane reflectors. These designs are exemplary only and features may be recombined between them as necessary to achieve a given function. Although described in terms of radio frequency (RF) reflectors, exemplary embodiments may be used in other applications, such as reflectors for light or for transmitting/receiving other signals. Exemplary embodiments of the deployable structure may be used in other applications as well.

<FIG> illustrates an exemplary compactable membrane antenna. The antenna <NUM> includes a reflector <NUM> configured to receive an RF signal (dashed line) and direct the signal or wave to a collector <NUM>. The shape of the reflector <NUM> is important to position the reflective surface in a proper location relative to the collector such that the received signal can be properly positioned at the collector. As shown in <FIG>, a single reflector is used with a collector. However, any combination of reflectors may be used. For example, <FIG> illustrates a similar reflector, but the collector is an extended configuration in which a portion of the collector is positioned behind the reflector and a receiving portion is positioned in front of the reflector. Other dual reflector configurations, such as that illustrated in <FIG> may also be used. In this case, a primary reflector is similar to that of <FIG>, and a secondary reflector is positioned at the receiving location of the primary reflector. The secondary reflector is then configured to direct the received RF signals from the primary reflector to the collector. The collector may be positioned behind the primary reflector with a passage or hole in the primary reflector to permit the RF signal to pass from the secondary collector to the collector. Other reflector configurations may also be used, such as that of <FIG> in which the reflector includes an asymmetric configuration. This case may be used when the collector is positioned off axis from the reflector. As shown in <FIG>, the ribs <NUM> may extend across substantially an entire chord length from one side of the reflector to the other. As illustrated any configuration of one or more reflectors and collector may be used according to embodiments described herein. The illustrated reflector configurations are exemplary only and not intended to be limiting.

Exemplary reflectors include a support structure such as outer frame <NUM>, ribs <NUM>, and combinations thereof. The support structure supports the reflector <NUM>. The reflector and/or support structure may be coupled to an object, such as the collector or other reflector, by struts <NUM>.

In an exemplary embodiment, the support structure comprises an outer frame <NUM>. The support structure may include any enclosed shapes such as elliptical, circular, polygon, clam shell, etc. The support structure may comprise a curved structure or discrete linear sections angled with respect to adjacent linear sections to approximate a curved surface. Exemplary embodiments include a torus outer frame.

In an exemplary embodiment, the support structure comprises ribs <NUM>. Any number of ribs may traverse the enclosed space within the perimeter of the outer frame. Ribs <NUM> provide support for the reflective surface of reflector <NUM>. Ribs <NUM> may be used to define the shape of the reflective surface of reflector <NUM>. Ribs may define a symmetric or asymmetric configuration. As shown in <FIG>, ribs may attach at one terminal end to the outer frame and extend toward each other to directly or indirectly attach to each other at an opposite terminal end. The ribs may approach a central axis of the outer frame <NUM> to define a symmetric support structure. The ribs may be curved to define a desired reflective surface of the antenna. As seen in <FIG>, the ribs may extend out of the plane of the outer frame <NUM>.

The ribs that define the reflector shape, such as an approximate parabolic shape, may be made with a cross section that increases its area moment of inertia for added stiffness such as an I-beam or a T-beam. The stiffness may also or alternatively be increased by the inclusion of cross-ribs coupled between adjacent ribs. <FIG> illustrates an exemplary embodiment having cross-ribs for the offset geometry. However, such configuration may also be used for any known or disclosed embodiment.

In an exemplary embodiment, struts <NUM> may be used to couple component parts. For example, struts may extend between reflectors, between reflectors and collectors, or between any combination thereof or other component. Struts may couple directly or indirectly to the support structure.

In an exemplary embodiment, the support structure, including outer frame <NUM> and/or ribs <NUM>, and/or struts <NUM> comprises a shape memory composite material. The shape memory composite material permits the antenna to collapse under imposition of an outside force in a non-structured fashion. The collapsed configuration may therefore be dynamically determined based on the storage compartment or the outside force applied. For example, the shape memory composite may be flexible or deformable along a length when a force is applied. The shape memory composite, however, returns to a remembered configuration, once the force is removed. Therefore, exemplary embodiments may include a stored configuration in which the support structure is retained in the stored configuration having a reduced storage volume through application of an outside force; and a deployed configuration in which the support structure is fully deployed having a larger storage volume when the outside force is removed. In other words, the remembered or biased configuration may be a deployed configuration in which the support structure is configured for use as an RF reflector. In an exemplary embodiment, the shape memory composite may flex in any direction under application of an outside force. In an exemplary embodiment, the shape memory composite may flex at multiple locations along a length of the member or along an entire length of the member. In an exemplary embodiment, the shape memory composite may return to a remembered configuration, such as linear, circular, ovoid, curved, parabolic, or other predefined shape when the outside force is removed.

An exemplary shape memory composite material includes a base material of one or more of carbon fabric or tows, Vectran, or Kevlar. The base material comprises strands. The strands may be generally aligned along a length of the structure, may include one or more aligned arrangements, may be wound or helically positioned, may be woven, or any combination thereof. The shape memory composite material includes a matrix around and/or between the base material. The matrix may be silicone, urethane, or epoxy. Exemplary shape memory composite materials are described in co-owned patent application <CIT>, titled "Composite Material".

In an exemplary embodiment, the reflector may include a flexible membrane having a highly reflective surface. The surface may be created by coating, laminating, depositing, or otherwise attaching a material to the membrane surface or from the membrane surface itself. In an exemplary embodiment, the membrane comprises mylar, kapton, polyurethane-coated nylon (PCN), tedlar, Teflon, other polyimide or plastic materials, and combinations thereof. The reflective coating may include a layer of high conductivity metal, such as aluminum, silver, silver-inconel, and combinations thereof. The membrane may also be made of a conductive material such as foils of aluminum or stainless steel as well as carbon fabric or a conductive mesh. The membrane may also consist of a laminate of a combination of some or all of the above materials. The surface may be coated with a layer of high conductivity metal such as aluminum or silver or silver-inconel. The thickness of the metallization can be between <NUM> to <NUM>,<NUM> Angstroms.

In an exemplary embodiment, the reflector may include a monolithic surface made of a shape memory composite material laminated with a layer or layers of metallized membrane such as mylar, kapton, polyurethane-coated nylon (PCN), tedlar, Teflon or other polyimide or plastic material. The shape memory composite may be coated with a layer of high conductivity metal such as aluminum or silver or silver-inconel, as described herein. The reflective coating may be directly on the shape memory composite material or on a membrane overlaying the shape memory composite material. In an exemplary embodiment, the monolithic surface of shape memory composite material may replace the struts and/or outer frame of the support structure. Essentially, the monolithic shape memory composite material becomes a self-supporting structure.

In an exemplary embodiment, the reflector element is a packageable membrane coated with a layer of high conductivity metal. The membrane may be mylar, kapton, polyurethane-coated nylon (PCN), tedlar, teflon, or other polyimide or plastic material. The double curvature of the membrane is obtained via the joining of accurately-cut flat gores of the membrane joined by adhesive or material melting at the seams or with the use of direct casting or thermo-forming. The support structures are the toroidal ring, radial, ribs and struts. These are made of composite material consisting of one or a combination of carbon fabric or tows, Vectran, or Kevlar. The matrix of the composite may be silicone, urethane, or epoxy. The support structures are designed and fabricated such that they are collapsible for folding-packaging and stowing. They may also be fabricated using shape memory composites. The composite ribs are fabricated to have the curvature necessary to achieve high antenna gain and efficiency. As an example, for a parabolic surface reflector, all the ribs lie on the surface of the paraboloid. For packaging, the toroidal ring, ribs, and struts are folded, similar to a folding umbrella and the reflector membrane stowed between or over the ribs, struts, and toroidal ring. Deployment is effected by allowing the packaged antenna to deploy to its final antenna configuration by releasing the stored strain energy in its packaged (or stowed) configuration. By the very nature of the material of the support structures, their springiness is tailorable up and down the stiffness scale at the time of fabrication.

However, the preferred embodiment of the CoSMeRA reflector design consists of gores of a low-coefficient of thermal expansion polyimide membrane coated with <NUM>,<NUM> angstroms of Silver-Inconel with the support structures made of a foldable shape memory carbon composite material.

In some cases, it may be preferable to have the support structures made of hollow tubes, instead of foldable rods. Their deployment may be initiated by the use of an onboard pump and an inflatant gas such as nitrogen, carbon dioxide, or other inert substances like helium or argon. Other gases may also be used, depending on the mission concept.

In an exemplary embodiment, the shape memory material may be used for all or only portions of the support structure. For example, the reflector outer frame may comprise shape memory material, while the ribs comprise conventional rigid segmented materials. Other combinations of shape memory structures with conventional structures are also contemplated hereby. Therefore, any combination of shape memory composite materials, inflatable materials, rigidizable materials, or rigid materials across any combination of components are contemplated hereby.

<FIG> illustrates an exemplary compactable deployable antenna configuration. As shown a support structure may be created by an outer frame <NUM> and a plurality of struts <NUM>. The struts extend from the outer frame to the spacecraft or collector (referred to generally as the hub). The outer frame <NUM> and plurality of struts <NUM> define the support structure for the reflector <NUM>. The support structure may comprise the shape memory composite as described above or other known material, such as an inflatable, rigidizable, or static foldable structure. As shown, the support structure includes a toroidal outer frame and three struts. However, any number of struts, preferably two to six may be used. The support structure defines an outer envelope or surface for which the reflective surface is fully contained. The support structure is the deployable structure to define the shape of the deployed antenna.

The compactable deployable antenna includes a net-mesh <NUM> enclosed and supported by the outer frame <NUM>. <FIG> illustrates an elevated view of the net-mesh, with <FIG> illustrating blown up views of notes of the net-mesh. The net-mesh may be any flexible material that provides a plurality of nodes <NUM> for attachment points as described herein. When the outer frame is deployed, the net-mesh is expanded. A plurality of nodes of the net-mesh are coupled to tension elements <NUM> that extend from the net-mesh to the hub. When the support structure is deployed, the tension elements are under tension and define the surface shape of the net-mesh. The net-mesh may define an out of plane, generally curved structure, from the outer frame, when in a deployed condition. The tension elements may retain the net-mesh toward the hub.

The tension elements may provide supporting structures for reflective membranes. A reflector <NUM> may therefore be defined within the volume defined by the net-mesh, outer frame, and struts. The reflector <NUM> may comprise a plurality of panels coupled to the tension elements. The position of the panels may define the reflector shape. The reflector surface may approximate a curved surface by step-wise placement of generally planar panels. The reflector <NUM> may comprise panels of mylar, kapton, polyurethane coated nylon (PCN) or tedlar coated with a layer of <NUM> to <NUM> Angstroms thick high-conductivity metal such as aluminum, silver, or silver-inconel. Other reflective surfaces as described herein or known by a person of skill in the art may also be used.

In an exemplary embodiment, a highly compactable deployable antenna includes a net-mesh with a perimeter toroidal ring support, three or more struts, a plurality of strings (tension ties), a conductive parabolic membrane surface, and combinations thereof (or combinations from other embodiments described herein). Lightweight high stiffness tension elements, strings, are attached to each of the nodes of the net-mesh structure. The other end of each of the strings is attached at its opposite end to the hub. When the strings are tensioned by deployment of the support structure, the net mesh deforms to the desired curved surface as illustrated to define, for example, an inverted net-mesh dome. The curved shape may be any surface of revolution including but not limited to a paraboloid, sphere or a hyperboloid. Exemplary embodiments describing curved surfaces include their approximation by piece-wise planar or linear segments.

Low-stowed volume antennas with aperture diameters on the order of tens of meters, up to <NUM> diameter can be fabricated using this design.

<FIG> illustrates the plan view of the net-mesh invert dome. The reflector surface may consist of triangular conductive facets of mylar, kapton, polyurethane coated nylon (PCN) or tedlar coated with a layer of <NUM> to <NUM> Angstroms thick high-conductivity metal such as aluminum, silver, or silver-inconel. The triangular metallized facets look very similar to that shown in <FIG>. Each of the vertices of the metalized triangular facet may be attached to the tensioned string at the appropriate locations to form a desired surface of revolution; e.g. a paraboloid. Because the conductive membrane facets do not have to be stretched to a high film stress, the loads on the support structures (toroidal ring and struts) may be small. This translates to lower mass for the overall system.

The reflector may also be made of accurately-cut flat gores of the metallized membrane joined by adhesive or material melting at the seams or with the use of direct casting or thermo-forming.

The support structure may include the toroidal ring and struts. The support structure may be made of composite material consisting of one or a combination of carbon fabric or toes, Vectran, or Kevlar. The matrix of the composite may be silicone, urethane, or epoxy. The support structures are designed and fabricated such that they are collapsible for folding-packaging and stowing. They may also be fabricated using shape memory composites. The net mesh of the reflector dome is fabricated to have the curvature necessary to achieve high antenna gain and efficiency. For packaging, the toroidal ring and struts are folded, similar and the reflector membrane stowed between or over the struts, and toroidal ring. Deployment may be effected by the use of either (a) a set of telescoping struts or (b) a set of struts and a toroidal ring, made from shape memory composite material, allowing the packaged antenna to deploy to its final antenna configuration by releasing the stored strain energy in its packaged (or stowed) configuration. By the very nature of the material of the support structures, their springiness may be tailorable up and down the stiffness scale at the time of fabrication.

In an exemplary embodiment, the support structures or portions of the support structures are made of hollow tubes. Deployment of the tubular support structures may be effected by the use of inflatant gas such as nitrogen, carbon dioxide, or other inert substance like helium or argon. Other gases may also be used.

To prevent tangling of the tension elements, each string may be packaged within two enclosures <NUM>, one at the net-mesh end <NUM>, and the other attached at the opposite end <NUM>, proximate the hub, as shown in <FIG>. As the struts are deployed, the strings are pulled out of their enclosure. The enclosure may be any circumferential enclosure, such as a tube. The enclosure may be flexible and deformable, such that it does not have to retain a given shape, but simply separates one string from another.

It should be emphasized that many variations and modifications may be made to the herein-described embodiments, the elements of which are to be understood as being among other acceptable examples. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims. Moreover, any of the steps described herein can be performed simultaneously or in an order different from the steps as ordered herein. Moreover, as should be apparent, the features and attributes of the specific embodiments disclosed herein may be combined in different ways to form additional embodiments, all of which fall within the scope of the present disclosure.

Certain terminology may be used in the following description for the purpose of reference only, and thus are not intended to be limiting. For example, terms such as "above" and "below" refer to directions in the drawings to which reference is made. Terms such as "front," "back," "left," "right," "rear," and "side" describe the orientation and/or location of portions of the components or elements within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the components or elements under discussion. Moreover, terms such as "first," "second," "third," and so on may be used to describe separate components. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import.

Conditional language used herein, such as, among others, "can," "could," "might," "may," "e.g.," and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include certain features, elements and/or states. However, such language also includes embodiments in which the feature, element or state is not present as well. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments or that one or more embodiments necessarily exclude components not described by another embodiment.

Moreover, the following terminology may have been used herein. Thus, for example, reference to an item includes reference to one or more items. The term "ones" refers to one, two, or more, and generally applies to the selection of some or all of a quantity. The term "plurality" refers to two or more of an item. The term "about" or "approximately" means that quantities, dimensions, sizes, formulations, parameters, shapes and other characteristics need not be exact, but may be approximated and/or larger or smaller, as desired, reflecting acceptable tolerances, conversion factors, rounding off, measurement error and the like and other factors known to those of skill in the art. The term "substantially" means that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide. For example, the terms "approximately", "about", and "substantially" may refer to an amount that is within less than <NUM>% of, within less than <NUM>% of, within less than <NUM>% of, within less than <NUM>% of, and within less than <NUM>% of the stated amount or characteristic. Numbers preceded by a term such as "about" or "approximately" also include the recited numbers. For example, "about <NUM>" includes "<NUM>. For example, the disclosure expressly contemplates being able a value or range proceeded by a term such as "about" or "approximately" in this disclosure with or without such term.

Claim 1:
A deployable antenna, comprising:
a collector (<NUM>);
a support structure (<NUM>, <NUM>, <NUM>), comprising a shape memory composite having a remembered configuration, which is configured to deform along a length when a force is applied and is configured to return to the remembered configuration when the force is removed; and
a reflector (<NUM>) configured to direct radio frequency waves received at the reflector (<NUM>) to the collector (<NUM>),
wherein the deployable antenna comprises a stowed configuration in which the support structure (<NUM>, <NUM>, <NUM>) is configured to be deformed in a non-structured fashion under the imposition of an outside force and a deployed configuration in which the support structure (<NUM>, <NUM>, <NUM>) is configured to be in the remembered configuration, wherein the deployable antenna is retained in the stowed configuration having a reduced storage volume through application of an outside force.