COMPACTLY STOWABLE, THIN CONTINUOUS SURFACE-BASED ANTENNA HAVING RADIAL AND PERIMETER STIFFNESS THAT DELPOY AND MAINTAIN ANTENNA SURFACE IN PRESCRIBED SURFACE GEOMETRY

Abstract: A space deployable antenna reflector surface is formed as a continuous laminate that is shaped to conform with a predetermined energy-focusing surface geometry. The laminate is formed of thin layers of flexible material, such as thin sheets of graphite epoxy, containing collapsible radial and perimeter stiffening regions. Due to its thinness, the reflector laminate is collapseible into a folder shape, that facilitates stowage in a restricted volume, usch as aboard the space shuttle. The stiffening elements of the mlaminate antenna structure facilitate depolying and maintaining the reflector in its intended geometric shape.

Description: COMPACTLY STOWABLE, THIN CONTINUOUS SURFACE-BASED ANTENNA HAVING RADIAL AND PERIMETER STIFFENERS THAT DEPLOY AND MAINTAIN ANTENNA SURFACE IN PRESCRIBED SURFACE GEOMETRY The present invention relates to energy-focusing surfaces, such as radio wave antennas, solar concentrators, and the like, and is particularly directed to a compactly stowable antenna reflector that is formed of a thin continuous laminate material containing radial and perimeter stiffening regions or stiff eners. The thinness of the laminate and that of the stiff eners readily allow the reflector to be collapsed into a compact shape that facilitates stowage in a confined volume on board a spacecraft launch vehicle, such as the space shuttle, while also causing the reflector to deploy into and conform with a prescribed energy-focusing surface geometry. The field of deployable platforms, such as space-deployed energy-directing structures, including radio frequency (RF) antennas, solar concentrators, and the like, has matured substantially in the past decade. What was once a difficult art to master has developed into a number of practical appHcations by commercial enterprises. A significant aspect of this s development has been the reliable deployment of a variety of spacecraft-supported antenna systems, similar to that employed by the NASA tracking data and relay satellite (TDRS) . Indeed, commercial spacecraft production has now exceeded military/ civil applications, so that there is currently a demand for structural systems with proven reliability and performance, and the ever present requirement for "reduced cost." The mission objective for a typical deployable o space antenna is to provide reliable RF energy reflection to an energy collector (feed) located at the focus of a prescribed geometry (e.g. parabolic) energy collecting surface. The current state of parabolic space antenna design is essentially based upon what may be termed a segmented construction approach which, as diagrammatically illustrated in Figures 1-4, is configured much like an umbrella. In this type of antenna, a plurality of arcuate segments 5 1 are connected to a central hub 3, that supports an antenna feed 5. A mechanically advantaged linear actuator (not shown) is used to drive the segments 1 from their stowed or unfurled condition, shown in the side and end views of Figures 1 and 2, into a locked, over-driven, position, so as to deploy an Rf reflector surface 7, as shown in the side and end views of Figures 3 and 4. o Principal shortcomings of this type of antenna system include the hardware complexity of the antenna reflector, its attendant deployment mechanism, and the considerable stowage volume associated with that structure. As a consequence, new approaches to deployable antenna structures have been sought. The industry desire for these new approaches is based upon the premise that the stowed packaging density for deployable antennas can be 5 significantly increased, while rna tadning a deployed reHability that the space community has enjoyed in the past. If the stowed volume can be reduced (and therefore an increase in packaging density for a given weight), launch services can be applied more efficiently. The present invention includes an apparatus comprising a flexible, energy-directing medium having a substantially continuous surface and shaped to conform with a 0 predetermined geometry, a distribution of plural of layers of flexible material attached with respective portions of the surface of said medium and forming a plurality of collapsible stiffening elements which, in a deployed configuration of said medium, cause said medium to conform with said predetenxuned geometry and, in a non-deployed configuration of said medium, cause said medium to conform with a stowage configuration. The invention also includes a deployable radio wave antenna that deploys to a 5 predetermined surface of revolution, comprising a flexible, energy-directing material having a substantially continuous surface containing a plurality of radially adjoining arcuate segments, and being shaped to conform with a predeterrnined energy-directing geometry, a plurality of collapsible radial stiffening elements attached to said flexible, energy-directing material along radial lines between said radially adjoining arcuate segments, a respective radial stiffening l o element being formed of a generally radial strip of flexible material having a transverse surface dimension greater than a distance between attachment locations thereof to said flexible, ener y- directing material, so as to form a substantially tubular-configured radial stiff ener along a radial line of said flexible, energy-directing material in said deployed configuration thereof, and a substantially trough-shaped element in a stowage configuration thereof. is Advantageously, these objectives are successfully achieved by configuring the reflector as a continuous laminate of very thin layers of flexible material, having a relatively low coefficient of thermal expansion (CTE), such as thin sheets of graphite epoxy and the like. The flexible laminate is shaped to conform with a prescribed energy-focusing surface geometry (e.g., paraboloid). Because of its thinness, the reflector laminate is has reduced weight and is readily 20 collapsible into a folded shape, that facilitates stowage in a restricted volume. In addition, the laminate structure of the invention includes a plurality of radial and perimeter stiffening regions, that not only function to deploy and maintain the reflector in its intended geometric shape, but are configured to facilitate collapsing the reflector laminate into a compact (serpentine) stowed configuration. 25 The present invention will now be described, by way of example, with reference to the accompanying drawings in which: Figures 1 and 2 are respective diagrammatic side and end views of the stowed condition of a conventional segmented radial rib-based space-deployable parabolic antenna; Figures 3 and 4 are respective diagrammatic side and end views of the deployed 3 o condition of the antenna of Figures 1 and 2; Figure 5 is a diagrammatic perspective view of applying the invention to a suitably parabolic RF antenna reflector surface; Figures 6 and 7 are respective diagrammatic perspective and end views of the antenna surface of Figure 5 collapsed into a 'serpentine' folded shape; 3 s Figure 8 is a diagrammatic plan view of the antenna of Figure 5 showing radial stiff eners along a plurality of lines extending radially from a central aperture to a ckcumferential perimeter; Figure 9 is an edge view of a portion of the antenna surface of Figure 5, showing radial stiffeners formed on a rear surface of the laminate; 40 Figure 10 is a diagrammatic enlarged sectional view taken along section lines 10-10 of Figure 8; Figure 11 diagrarnmatically illustrates trough-shaped nesting of a radial stiff ener of the antenna laminate surface of Figure 5 in its collapsed condition; Figure 12 shows arcuate segments of the antenna surface of Figure 5 collapsed into a set of 'serpentine' folds between successive radial stiffeners; and Figure 13 is a diagrammatic enlarged sectional view taken along lines 13-13 of Figure 8. The present invention will be described in connection with its application to an RF reflector antenna surface, having a predetermined geometry, such as a parabolic surface of revolution (or paraboloid), commonly employed in the comm.unicati.ons industry. The collapsible stiffening architecture disclosed may be incorporated into other energy-directing applications, such as but not limited to solar energy collection, including reflection and refraction systems, and acoustic energy applications. Figure 5 is a diagrammatic perspective view of applying the invention to a substantially parabolic RF antenna reflector surface 50. The material of the reflector surface 50 is preferably comprised of a continuous 1-αrιinate of thin layers of flexible material, that are shaped to conform with a prescribed energy-focusing surface geometry (e.g., a paraboloid in the present embodiment) . The layers themselves may be reflective to radio wave waves or the laminate may be coated with an RF reflective material such as a conductive paint. Preferably, the flexible radio wave surface material is made of a material having a relatively low coefficient of thermal expansion. As an example graphite epoxy may be employed. The reflector surface may be fabricated from thin sheets of graphite epoxy having a relatively small thickness on the order of only several mils, that are built up or layered into a multiply laminate structure having a prescribed compound curve shape and thickness on a precision mold that conforms with the intended geometry of the antenna reflector. Because of its substantial 'thinness', the reflector laminate 50 has substantial flexibility, so that it may be readily collapsed into a relatively compact folded shape, such as a substantially cylindrical shape shown at 60 in the diagrammatic perspective view of Figure 6 and the end view of Figure 7, which facilitates stowage within a confined volume on board a spacecraft launch vehicle, such as the space shuttle. In addition the thinness of the reflector laminate substantially reduces its payload weight and thereby cost of launch and deployment. In order to deploy and maintain the flexible material of the reflector surface 50 in its 0 intended geometric shape, the laminate structure of the invention includes a distribution of radial stiffeners 52 and perimeter or circumferential stiffeners 54. As shown in the plan view of Figure 8, the radial stiffeners 52 are located along a plurality of radial lines 81, that extend radially outwardly from a substantially central circular aperture 83 to a circumferential perimeter 85 of the antenna surface 50. The radial lines 81 effectively spatially define 5 therebetween a plurality of radially adjoining surface compound curve wedge-shaped segments 82. Although the illustrated example shows eight radial lines. The number and size may be tailored to accommodate the physical parameters of the particular antenna design. Similarly, the perimeter stiffeners 54 are located along the outer edge or chctrr f erential perimeter 87 of the antenna surface 50, adjoining termination points of the radial lines 81. o Figure 9 is an edge view of a portion of the antenna surface 50, showing radial stiffeners 52 formed on a rear surf ce 51 of the laminate 50, opposite to a front surface 53 upon which RF energy is incident. As further shown in the diagrammatic enlarged sectional view of Figure 10, which is taken along section lines 10-10 of Figure 8, an individual radial stiff ener is formed by attaching (for example, by means of a suitable epoxy graphite adhesive) a generally longitudinal strip of flexible material 100 along spaced apart edges 101 and 102 thereof to the back surface 51 of the laminate 50. Each strip of flexible material 100 has an .overall transverse surface 5 dimension between attachment locations 101 and 102 that is greater than the distance along the surface 55 of the laminate material 50 between the attachment locations 101 and 102. This urges the flexible strip 100 into a substantially bowed or concave shape, causing the stiffening strip to store tensile forces that tend to spread or deploy the surface 50 in a circumf erential direction (as shown by arrows 61 and 62) into its intended compound curve o shape. The convexly bowed strip also forms a substantially tubular-shaped radial spine or stiffener that imparts a predetermined degree of rigidity to the adjacent surface portion 55 of the antenna laminate surface 50. As a consequence a distribution of such radial stiffeners 100 serves to impart radial stiffness to the antenna surface 50 and so maintain the intended compound curve configuration of the antenna surface in its deployed state. 15 The degree of radial stiffness imparted by a radial strip 100 will depend upon the properties of the material of the antenna surface 50 and those of the flexible strip 100, such as but not limited to thickness, width of the strip 100, tensile coefficient, etc. As a non-li-rr ting example, stiffening strip 100 may be made of the same material (e.g., graphite epoxy) and contain multiple, built-up plies of the laminate 50, to realize a predetermined stiffness, while 2 o still being sufficiently flexible to allow a trough-shaped nesting of the adjacent surface portion 55 of the antenna laminate surface 50 in its collapsed condition for stowage, as shown in Figure 11. The number and size of radial stiffeners may be tailored to accommodate the physical parameters of the particular antenna design. The number of folds to which the antenna surface 25 50 collapses will depend, in part, on the spatial separation of the radial stiffeners on the rear side 53 of the antenna laminate surface. In the partial end view of the generally cylindrical stowed configuration of the antenna surface of the invention, Figure 12 shows an example of the manner in which arcuate segments of the antenna surface 50 may be collapsed to nest as a set of meandering, ct rilinear or 'serpentine' folds 121, 122 and 123 between successive radial 30 stiffeners 100. Figure 13 is a diagrammatic enlarged sectional view taken along lines 13-13 of Figure 8, showing a respective one of a plurality of perimeter or circurnf erential stiffening elements 54 that are sequentially distributed along the perimeter 85 of the antenna surface 50. As shown therein, a perimeter stiffening element 54 is comprised of a pair of generally annular shaped 35 strips 130 and 140 of flexible material that are attached together (e.g., by means of a graphite epoxy adhesive) at respective radial interior and exterior side edges 131/141 and 132/142 thereof. One of the strips (for example, annular strip 130) may comprise the actual material of an annular perimeter region of the antenna surface 50 proper, while the other strip (for example, 40 annular strip 140) may comprise a separate annular section of material. Each flexible annular perimeter strip 130/140 has an overall transverse surface dimension between attachment its locations 131/141 and 132/142 that is greater than the radial separation 56 therebetween along the surface of the laminate material 50, so that each strip 130/140 is bowed into a concave shape that stores tensile forces that tend to deploy and maintain the perimeter 85 of the antenna surf ce 50 deployed in its intended circular shape. Like the radial stiffeners 100, the circumferential stiffness imparted by a respective perimeter stiffener 54 will depend upon the properties of the material of the antenna surface 50 and those of the pair of adjoining armular strips 130/140. Each of perimeter strips 130/140 may be made of the same material (e.g., graphite epoxy) and contain multiple, built-up plies of the laminate 50, to realize a prescribed stiffness, while being sufficiently flexible to comply with the above-described serpentine-fold nesting of the antenna laminate surface 50 in its collapsed condition, shown in Figures 6 and 7. An object is of significantly increasing the stowed packaging density of a deployable antenna, while at the same time reliably rnamtaining its intended deployed geometry reliability may be successfully achieved by configuring the antenna reflector surface as a continuous laminate of very thin layers of low CTE flexible material, such as very thin sheets of graphite epoxy, that are shaped to conform with a prescribed energy-focusing surface geometry (e.g., paraboloid) . Because of its thinness, the reflector laminate is collapsible into a folded shape, that facilitates stowage in a restricted volume. In addition, the laminate structure of the invention includes a plurality of radial and perimeter stiffening regions, that not only function to deploy and maintain the reflector in its intended geometric shape, but are configured to facilitate collapsing the reflector laminate into a compact (serpentine) stowed configuration. A space deployable antenna reflector surface is formed as a continuous laminate that is shaped to conform with a predetermined energy-focusing surface geometry. The lamimate is formed of thin layers of flexible material, such as thin sheets of graphite epoxy, containing collapsible radial and perimeter stiffening regions. Due to its thinness, the reflector laminate is collapsible into a folded shape, that facilitates stowage in a restricted volume, such as aboard the space shuttle. The stiffening elements of the laminate antenna structure facilitate deploying and mamtain ng the reflector in its intended geometric shape.

Claims: CLAIMS: 1. An apparatus comprising a flexible, energy-directing medium having a substantially continuous surface and shaped to conform with a predetermined geometry, a distribution of plural of layers of flexible material attached with respective portions of the surface of said medium and forming a plurality of collapsible stiffening elements which, in a deployed configuration of said medium, cause said medium ' to conform with said predetermined geometry and, in a non-deployed configuration of said medium, cause said medium to conform with a stowage configuration. 2. An apparatus according to dai 1, wherein said geometry comprises a surface of revolution, and said plural layers of flexible material include layers of flexible material distributed along radial portions of said surf ce of revolution, so as to incorporate a plurality of collapsible radial stiffening elements with said flexible, energy-directing medium., in which said plural layers of flexible material include layers of flexible material extending along a perimeter portion of said medium, so as to incorporate a plurality of collapsible circumf erential stiffening elements with said perimeter portion of said medium. 3. An apparatus as claim in claim 2, wherein a respective circumferential stiffening element comprises a perimeter region of said medium and a generally longitudinally extending strip of flexible material attached thereto, each of said perimeter region of said medium and said generally longitudinally extending strip of flexible material having a transverse dimension greater than a width of said circumferential stiffening element, so as to deploy to mutually adjacent convex shapes and stow to a generally trough shape. 4. An apparatus as claimed in claim 1, wherein a respective layer of flexible material and an adjacent portion of said medium form a generally tubular-configured stiffener in said deployed configuration of said medium, and a generally trough-shaped element in said stowage 5 configuration of said medium, in which said respective layer of flexible material is comprised of the same flexible material as said medium. 5. An apparatus as claimed in claim 2, wherein a respective layer of flexible material comprises a substantially longitudinal strip of flexible material attached to a radial surface portion of said medium in a manner that forms a generally tubular-configured radial stiffener o along said radial surface portion of said medium in said deployed configuration thereof, and a trough-shaped element in said stowage configuration thereof. 6. An apparatus as claimed in claim 2, wherein a respective stiffening element comprises a substantially longitudinal region of said medium and a substantially longitudinally extending strip of flexible material attached thereto, said longitudinally extending strip of 5 flexible material having a transverse dimension greater than a width of said stiffening element, so as to deploy to a convex shaped stiffening element and stow to a substantially trough shape., and preferably each of said medium and said flexible material comprises a generally continuous web material. 7. A deployable radio wave antenna that deploys to a predetermined surface of o revolution, comprising a flexible, energy-directing material having a substantially continuous surface containing a plurahty of radially adjoining arcuate segments, and being shaped to conform with a predetermined energy-directing geometry, a plurality of collapsible radial stiffening elements attached to said flexible, energy-directing material along radial lines between said radially adjoining arcuate segments, a respective radial stiffening element being formed of a generally radial strip of flexible material having a transverse surface dimension greater than a distance between attachment locations thereof to said flexible, energy-directing material, so as to form a substantially tubular-configured radial stiffener along a radial line of said flexible, energy-directing material in said deployed configuration thereof, and a substantially trough-shaped element in a stowage configuration thereof. 8. A deployable radio wave antenna as claimed in clai 7, wherein said respective radial stiffening element is made of said flexible, energy-directing material, including a plurality o of circumf erential stiffening elements located along perimeter portions of said plurahty of radially adjoining arcuate segments, a respective circumferential stiffening element comprising a perimeter region of said flexible, energy-directing material, and a generally longitudinally extending strip of flexible material attached thereto, each of said perimeter region of said flexible, energy-d ectmg material and said generally longitudinally extending strip of flexible s material having a transverse dimension greater than a width of said circumferential stiffening element, so as to deploy to mutually adjacent convex shapes forming a generally tubular circumf erential stiffening element, and stow to a generally trough shape. 9. A deployable radio wave antenna as claimed in claim 7, wherein said flexible, energy-directing material comprises a flexible laminate of layers of substantially continuous o web material, said respective circumferential stiffening element is made of said flexible, ener y- directing material.

Inventors: ALLEN BIBB, HARLESS RICHARD, SORRELL RODNEY, VALENTIN RODOLFO, WILLER CHARLES, ALLEN, BIBB, HARLESS, RICHARD, SORRELL, RODNEY, VALENTIN, RODOLFO, WILLER, CHARLES
Applicants: HARRIS CORP, HARRIS CORPORATION
Application year: 2001
Main classification: H01Q15
IPC codes: H01Q1, H01Q15