LIGHTWEIGHT COLLAPSIBLE DISH STRUCTURE AND PARABOLIC REFLECTOR EMBODYING SAME
United States Patent 3599218
A collapsible lightweight, dish-shaped structure is provided for use as a parabolic reflector and other uses. The structure has a dish constructed of a lightweight, thin film membrane, such as an aluminized polymeric plastic film selected from the class including Mylar and Kapton. Lightweight elastic ribs or beams, which are preferably slender tubes constructed of the same thin film material as the dish, are bonded to the rear surface of the dish and are preformed to cause the dish to normally assume a predetermined geometric configuration, such as a parabolic shape. The structure may be folded for stowage in a container, or the like, in such a way that the structure, when released from the container, is deployed to its predetermined configuration by the elastic strain energy stored in the folded beams of the structure. Deployment of the dish structure from its folded configuration may be aided by auxiliary deployment means, such as leaf springs secured to the inner ends of the beams, an inflatable ring secured about the rim of the dish, guy wires extending between the rim and a telescopic actuator at the center of the dish, and/or a separable thin film cover defining with the dish an inflatable chamber.
US Patent References:
Collapsible antenna
Fitzgerald et al. - September 1956 - 2763002
Inflatable antenna
Justice - March 1961 - 2977596
Antenna with wire mesh reflector collapsing in a pinwheel manner
Miller - November 1965 - 3217328
Collapsible reflector
Webb - December 1967 - 3360798
Collapsible dish reflector
Carman et al. - August 1968 - 3397399
Collapsible antenna
Fitzgerald et al. - September 1956 - 2763002
Inflatable antenna
Justice - March 1961 - 2977596
Antenna with wire mesh reflector collapsing in a pinwheel manner
Miller - November 1965 - 3217328
Collapsible reflector
Webb - December 1967 - 3360798
Collapsible dish reflector
Carman et al. - August 1968 - 3397399
Inventors:
Williamson, Clyde E. (Los Angeles, CA)
Bochory, Michael E. (Los Angeles, CA)
Bochory, Michael E. (Los Angeles, CA)
Application Number:
04/759136
Publication Date:
08/10/1971
Filing Date:
09/11/1968
View Patent Images:
Export Citation:
Assignee:
TRW Inc. (Redondo Beach, CA)
Primary Class:
Other Classes:
343/872, 343/915
International Classes:
H01Q15/16; H01Q15/14; H01Q19/12; H01Q15/20
Field of Search:
343/840,912,915,872
US Patent References:
| 3406404 | Furlable and unfurlable member | October 1968 | Maier |
Primary Examiner:
Lieberman, Eli
Claims:
What we claim as new in support of Letters Patent is
1. A lightweight collapsible dish structure adapted to be folded for storage and deployed for use, comprising:
2. A lightweight collapsible dish structure adapted to be folded for storage and deployed for use, comprising:
3. A dish structure according to claim 2 wherein:
4. A lightweight collapsible dish structure adapted to be folded for storage and deployed for use, comprising:
5. A dish structure according to claim 4 including:
6. A dish structure according to claim 5 wherein:
7. A lightweight collapsible dish structure adapted to be folded for storage and deployed for use, comprising:
8. A lightweight collapsible parabolic reflector for a radiofrequency antenna adapted to be folded for stowage and deployed for use comprising:
9. A parabolic reflector according to claim 8 including:
10. A lightweight collapsible parabolic reflector adapted to be folded for stowage and deployed for use comprising:
11. A lightweight collapsible parabolic reflector adapted to be folded for stowage and deployed for use, comprising:
12. A lightweight collapsible parabolic reflector adapted to be folded for stowage and deployed for use, comprising:
13. A lightweight collapsible parabolic reflector adapted to be folded for stowage and deployed for use, comprising:
1. A lightweight collapsible dish structure adapted to be folded for storage and deployed for use, comprising:
2. A lightweight collapsible dish structure adapted to be folded for storage and deployed for use, comprising:
3. A dish structure according to claim 2 wherein:
4. A lightweight collapsible dish structure adapted to be folded for storage and deployed for use, comprising:
5. A dish structure according to claim 4 including:
6. A dish structure according to claim 5 wherein:
7. A lightweight collapsible dish structure adapted to be folded for storage and deployed for use, comprising:
8. A lightweight collapsible parabolic reflector for a radiofrequency antenna adapted to be folded for stowage and deployed for use comprising:
9. A parabolic reflector according to claim 8 including:
10. A lightweight collapsible parabolic reflector adapted to be folded for stowage and deployed for use comprising:
11. A lightweight collapsible parabolic reflector adapted to be folded for stowage and deployed for use, comprising:
12. A lightweight collapsible parabolic reflector adapted to be folded for stowage and deployed for use, comprising:
13. A lightweight collapsible parabolic reflector adapted to be folded for stowage and deployed for use, comprising:
Description:
REFERENCE TO RELATED APPLICATIONS
Reference is made herein to copending application Ser. No. 757,267 filed Sept. 4, 1968 under Docket -4060, and entitled "Light-Weight Elastically Deformable Plastic Article of Manufacture and Method of Forming Same."
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to lightweight collapsible structures and more particularly to a novel lightweight, thin film dish-shaped structure which may be folded to a compact stowage configuration in such a way that the structure, when released, is deployed to its normal dish shape by the elastic strain energy stored within folded reinforcing beams of the structure. The invention relates also to a parabolic reflector embodying the dish structure.
2. Prior Art
Lightweight collapsible dish structures of the kind to which this invention pertains may be used for various purposes. The dish structure which constitutes the subject matter of the present invention is intended primarily for use as a reflector for a parabolic antenna and will be described in connection with such use. However, the present dish structure may be utilized for other applications so that the disclosed antenna application will be understood to be purely illustrative and not limiting in nature.
Parabolic antennas are well known in the art and are characterized by the advantage of directional transmitting and receiving capability. A typical parabolic antenna is equipped with a parabolic dish or reflector constructed of a material having a high degree of reflectivity to the radiofrequency energy to be transmitted and/or received, and an antenna feed mechanism situated on the antenna axis adjacent the focal point of the reflector. Because of their directional transmitting and receiving capability, parabolic antennas are commonly employed on space vehicles for receiving radio signals from control stations on the earth and/or transmitting radio signals back to monitoring stations on the earth. However, the design of parabolic antennas for space vehicles poses a problem for the reason that the antenna reflector is often so large as to require the reflector to be collapsible for stowage within the spacecraft body during the launch phase. When final orbit is achieved, the reflector is deployed to its normal parabolic configuration.
A variety of collapsible parabolic reflectors have been devised for this purpose. These existing parabolic reflectors are generally characterized, respectively, by rigid petals, inflatable rigidizable shells, spin stabilized membranes, and rib-stiffened membranes. While the existing reflectors are satisfactory to some degree, they have several inherent disadvantages which detract from their usefulness, particularly for space applications. Among the foremost of these disadvantages are excessive weight, excessive stowage volume requirements, excessive cost and complexity, the necessity of using mechanical latching means for retaining the reflectors in their collapsed condition and active or powered deployment mechanisms for deploying the reflectors, and a tendency to malfunction.
SUMMARY OF THE INVENTION
According to one of its narrower aspects, the present invention provides an improved parabolic reflector which avoids the above noted and other disadvantages of the existing reflectors of this type. In general terms, the present parabolic reflector is characterized by a lightweight parabolic reflector dish constructed of a thin radiofrequency reflective film reinforced with slender elastic ribs or beams. These beams are prestressed or preformed to cause the reflector dish to assume a normally generally parabolic dish shape. While various thin film materials may be used for the reflector dish, the latter preferably comprises an aluminized polymeric film selected from the class including Mylar and Kapton. The reflector beams are preferably tubular in cross section and constructed of the same thin film material as the reflector dish. If desired the reflector dish and beams may have a laminated construction including two outer thin film layers bonded to opposite sides of an intervening reinforcing layer, such as metallic screen. Mounted on the axis of the parabolic reflector, adjacent at its focal point, is an antenna feed mechanism.
The thin film construction of the present parabolic reflector provides the latter with several unique and highly important advantages. By way of example, two primary advantages of the reflector from the standpoint of space use reside in the fact that the reflector is extremely light in weight and may be folded to a very compact configuration for stowage within a minimum stowage volume, as within a spacecraft body during launch. In this regard, it will become evident from the ensuing description that the reflector may be folded in various ways but is preferably folded in generally serpentine fashion, in a manner similar to a parachute, for packaging within a bag or other stowage container which may be opened on command to release the reflector for deployment to its normal parabolic configuration. Folding of the reflector for stowage creates strain energy within the elastic beams of the reflector which is utilized to unfold or deploy the reflector when the container is opened. To this end, the reflector dish and beams are prestressed or preformed to assume a normally generally parabolic curvature when deployed. Additional advantages of the present invention, therefore, reside in the fact in that complex mechanical latching means to retain the parabolic reflector in its folded configuration and complex mechanical deployment mechanisms for deploying the reflector to its parabolic configuration are not required.
According to a further feature of the invention, the present parabolic reflector may be equipped with auxiliary means to aid its deployment to the proper parabolic shape, and/or to adjust the parabolic curvature of the reflector. The disclosed embodiments of the invention, for example, are equipped with an inflatable ring about the rim of the reflector dish which acts to stretch the reflector radially and resist beam bending of the reflector. This ring cooperates with the reflector beams to eliminate wrinkles in the film of the reflector dish, thereby to assure a reflector with an accurate parabolic reflective surface. The ring also provides the reflector with sufficient structural rigidity in its deployed configuration to resist distortion due to thermal radiation, solar pressure, material degradation, drag and other factors. The reflector may be equipped with guy wires which extend radially between the rim and center of the reflector dish to aid the above function of the inflatable ring. Means may be provided for adjustably tensioning these wires and shifting the antenna feed mechanism along the reflector axis to adjust the parabolic curvature of the reflector and/or locate the feed mechanism in optimum transmitting and receiving relation to the reflector.
One illustrative embodiment of the invention is equipped with a second thin film which is situated in front of and parametrically sealed to the rim of the parabolic reflector. This front film and the reflector define therebetween a hermetic chamber which may be pressurized to aid deployment of the reflector to its proper parabolic shape. The front film may be transparent to the radiofrequency energy to be transmitted and received by the antenna so as to permit the film to remain in position in front of the antenna reflector during the operation of the antenna. Alternatively, the front film may be severed from the antenna reflector after deployment.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a perspective view of a parabolic antenna embodying a parabolic reflector according to the invention;
FIG. 2 is an enlarged fragmentary perspective view of the rear side of the reflector;
FIG. 3 is an enlarged fragmentary perspective view of one of the reflector beams;
FIG. 4 is an enlarged section taken on line 4-4 in FIG. 2;
FIG. 4a is an enlarged section of a reinforcing ring embodied in the antenna;
FIGS. 5--8 illustrate one method of folding the reflector for stowage;
FIG. 9 is a perspective view of a modified parabolic reflector; and
FIG. 10 is an enlarged perspective view of the reflector in FIG. 9 with a front cover film thereof severed from the reflector.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Turning now to FIGS. 1--8 of these drawings, there is illustrated a lightweight collapsible dish structure 10 according to the invention. In this instance, the dish structure forms the parabolic reflector of a parabolic antenna 12. The reflector has a parabolic dish 14, proper, and a number of preformed reinforcing ribs or beams 16 secured to the back side of the dish. In accordance with an important feature of the invention, dish 14 is fashioned from a lightweight sheet-thin film, and the ribs or beams 16 are provided with a slender, elastic construction, such that the parabolic reflector may be packaged for stowage within a minimum stowage volume by folding the reflector in the manner illustrated in the drawings. The folded parabolic reflector may then be contained within a storage container 18. This folding action creates elastic strain energy within the reflector beams 16. When the reflector is released from the container, the strain energy in the beams causes return of the latter and the parabolic dish 14 to their original parabolic configuration.
The parabolic dish 14 and its reinforcing beams 16 may be constructed of various materials. According to the preferred practice of the invention, however, these parts are fashioned from a polymeric plastic film material, selected from the class including Mylar and Kapton. In the particular embodiment of the invention which has been selected for illustration, for example, the parabolic reflector 10 is a radiofrequency reflector, wherein the reflector dish 14 is constructed of a metallic coated plastic film, such as aluminized Mylar or Kapton. The dish may have a single layer or a multiple layer laminated construction depending upon the required structural rigidity of the dish. The reflector beams 16 have a slender thin-walled tubular configuration and are fabricated from sheet-thin film material which is preferably the same plastic film material as that of the reflector dish 14. The beams extend radially of the reflector dish between its center and rim and are bonded or otherwise secured to the back side of the dish. The dish and beams are prestressed or preformed to normally assume a parabolic curvature.
It will be immediately evident to those versed in the art that the parabolic dish 14 and beams 16 may be fabricated in various ways. The illustrated dish, for example, is composed of a number of gore-shaped sections 20 which are individually preshaped to a parabolic curvature by stretch-forming or heat-forming the sections over a suitable parabolically curved mold. The several parabolic gore sections are then joined edge-to-edge by aluminized pressure sensitive Mylar tape or other suitable means. The reflector beams 16 are preferably heat formed in the manner disclosed in the aforementioned copending application, Ser. No. 757,267. Since the beam forming method is fully disclosed in the copending application, it is unnecessary to treat the method in detail in this disclosure. Suffice it to say that the beams are fabricated, either from strips of plastic film material which are ultrasonically welded or otherwise bonded along their longitudinal edges to form thin-walled sleeves or tubes, or from sleeves or tubes of plastic film material whose walls are squeezed flat and bonded face-to-face along diametrically opposite sides of the tubes. In either case, the completed plastic tubes have diametrically opposed, longitudinally extending flanges 22. These tubes are then heat-formed to normally assume a parabolic curvature by insertion of a parabolically curved rod or mandrel through each tube and exposure of the latter to a suitable forming temperature. The finished parabolically curved beams are then ultrasonically welded or otherwise bonded to the back side of the parabolic dish 14 in such a way that the beam flanges 22 parallel the dish as shown.
At the center of the parabolic dish 14 is an antenna mounting hub 24. This hub has a generally cylindrical housing 26 which projects rearwardly from the dish on its central axis. Integrally formed on the front end of the housing 26 is a flange 28. Flange 28 is parametrically secured to the parabolic dish 14 about a central opening 30 in the dish.
Coaxially mounted on and extending forwardly from the hub 24 is a telescoping antenna feed mechanism or horn 32. This feed mechanism includes a telescoping fluid pressure actuator 34 having a cylinder 36 centered on the axis of the reflector dish 14 and rigidly secured at its rear end to the hub 24. Guy wires 38 may be secured between the hub flange 28 and the actuator cylinder 36 to brace the cylinder in the lateral direction. Movable in the cylinder is a telescoping plunger 40 which mounts the receiving and/or radiating element 42 of the antenna. When the antenna is in its normal operating configuration, this element is located at the focal point of the parabolic dish 14. Accordingly, radiofrequency waves incident on the front reflective surface of the dish are reflected to the element 42, and radiofrequency waves emanating from the element are reflected forwardly from the dish parallel to its axis, depending upon whether the antenna is operating in a receiving or transmitting mode.
As noted earlier, the parabolic dish structure or reflector 10 is adapted to be folded for stowage in the manner illustrated in the drawings and to be later released for deployment by the elastic strain energy stored within the folded reflector beams 16. The particular embodiment of the invention under discussion includes three additional deployment means 46, 48, and 50 for aiding proper deployment of the reflector. The deployment means 46 comprises leaf springs 52 which are fixed at one end to the antenna hub flange 28. The opposite, free ends of these leaf springs extend into the adjacent inner ends of the reflector beams 16 and mount resilient pads 54 for engaging the inner walls of the beams. When the parabolic reflector 10 is folded for stowage, the leaf springs 52 are bent or bowed in the manner illustrated so that elastic strain energy is stored in the springs. When the reflector is released for deployment, this elastic strain energy returns the springs to their original or normal unstressed conditions. It will be understood, therefore, that the springs aid deployment of the parabolic reflector 10 from its collapsed or stowed configuration to its deployed parabolic configuration.
The deployment means 48 comprises an inflatable torus or ring 56 which is secured to the parabolic dish 14 about its rim. When the parabolic reflector 10 is folded for stowage, the ring is deflated. During deployment of the reflector, the ring is inflated in any convenient way. In the drawings, for example, the ring is inflated through a tube 58 which extends from the ring, radially inward along the back side of the parabolic dish 14, to a pressurized fluid source (not shown). When inflated, the ring tends to stretch the parabolic reflector 10 radially in such a way as to cause the reflector to assume its normal parabolic shape. The inflated ring also reinforces the reflector against beam bending. The torus ring 56 may be a simple plastic tube or a laminate. In the latter case, there is interposed between two plastic layers 56a (FIG. 4a) a screen metal mesh 56b. Upon inflation of the torus ring 56, the metal mesh is prestressed to assume a torus shape. In the event the inflatable ring 56, deflates itself, or the plastic material starts degrading in the space environment, the metal mesh would have enough structural rigidity to restrain the deflection of the beams due to solar pressure. Upon degradation of the plastic surface of the ring, the guy wires will remain attached to the metal mesh, as will the ends of the beams to which the ring is attached.
The remaining deployment means 50 comprises a number of slender guy wires 60 of fiberglass or other suitable material which extend between the rim of the parabolic dish 14 and the front end of the actuator plunger 40. These wires are arranged in a uniformly spaced array, as shown, and aid in deploying the parabolic reflector to and retaining the reflector in its parabolic configuration. The parabolic curvature of the reflector may be adjusted within limits by extending and retracting the plunger 40.
The additional deployment means 46, 48, 50 may not be required in all applications of the invention. Accordingly, it should be understood that any one or more of these deployment means may be omitted.
It will be observed in FIGS. 5--8 that the parabolic reflector 10 may be stowed by first gathering the reflector inwardly toward its axis in a manner similar to that involved in closing an umbrella. The gathered reflector is then folded laterally of its beams 16 in serpentine fashion, preferably with the aid of packaging rolls 62 placed between the adjacent folds, to a final stowage configuration within the stowage container 18. In this instance, the container is a pleated bag secured about the edge of the antenna hub flange 28. After the reflector is properly folded, the bag is gathered about the reflector and the mouth of the bag is closed by a suitable release mechanism 64. In the case of the parabolic antenna for a space vehicle, this release mechanism may be designed for release on command by radio signals from a ground station. When released, the bag opens to release, in turn, the folded parabolic reflector 10 which then deploys to its normal parabolic configuration under the action of the elastic strain energy in the beams 16. It should be understood that the illustrated manner of folding the reflector for stowage is purely illustrative and that the reflector may be stowed by folding it in other ways.
As described earlier, the antenna feed mechanism 32 comprises a telescoping actuator 34. This actuator is retracted to its contracted condition when the parabolic reflector 10 is folded for stowage. The actuator is extended to its operating position after deployment of the reflector to its normal parabolic configuration. The ring 56 on the parabolic dish 14 is inflated during deployment as explained earlier, to aid proper deployment of the reflector to its parabolic shape and reinforce the reflector against beam bending.
Reference is now made to the drawing FIGS. 9 and 10 which illustrate a modified parabolic antenna 100 according to the invention. The modified antenna is identical to the antenna just described except that a cover film 102 is disposed in front of and sealed about its edge to the rim of the parabolic reflector 10. This front film may be preformed to normally assume a parabolic curvature and is folded with the reflector for stowage in the manner explained earlier. In this case, means 104 are provided for pressurizing or inflating, during deployment, the hermetic chamber 106 defined between the parabolic reflector 10 and the front film 102. Inflation of the chamber 106 aids deployment of the reflector to its proper parabolic configuration. The front film 102 may be constructed of a material, such as uncoated Mylar or Kapton, which is transparent to radiofrequency waves, in which case the front film may remain in position on the reflector 10 during operation of the antenna 100. Alternatively, the front film may be separated from the reflector after deployment of the latter to its parabolic configuration. In the particular embodiment of the invention illustrated, for example, a hot wire 108 is bonded to the front cover film 102 about its edge and immediately adjacent to the rim of the reflector. After deployment, this wire is electrically heated with sufficient current to sever the film from the reflector. The modified parabolic antenna 100 is otherwise identical to and is folded, deployed, and operated in the same manner as the first described parabolic antenna of the invention.
At this point, it will be evident to those versed in the art that while the invention is disclosed in connection with a parabolic antenna, the parabolic dish structure of the invention may be used for other purposes. For example, the dish structure could conceivably be employed as an optical reflector, a cover or shelter, or other lightweight collapsible structure.
Accordingly, while the invention has been disclosed in connection with certain physical embodiments thereof, various modifications of the invention are possible within the spirit and scope of the following claims.
Reference is made herein to copending application Ser. No. 757,267 filed Sept. 4, 1968 under Docket -4060, and entitled "Light-Weight Elastically Deformable Plastic Article of Manufacture and Method of Forming Same."
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to lightweight collapsible structures and more particularly to a novel lightweight, thin film dish-shaped structure which may be folded to a compact stowage configuration in such a way that the structure, when released, is deployed to its normal dish shape by the elastic strain energy stored within folded reinforcing beams of the structure. The invention relates also to a parabolic reflector embodying the dish structure.
2. Prior Art
Lightweight collapsible dish structures of the kind to which this invention pertains may be used for various purposes. The dish structure which constitutes the subject matter of the present invention is intended primarily for use as a reflector for a parabolic antenna and will be described in connection with such use. However, the present dish structure may be utilized for other applications so that the disclosed antenna application will be understood to be purely illustrative and not limiting in nature.
Parabolic antennas are well known in the art and are characterized by the advantage of directional transmitting and receiving capability. A typical parabolic antenna is equipped with a parabolic dish or reflector constructed of a material having a high degree of reflectivity to the radiofrequency energy to be transmitted and/or received, and an antenna feed mechanism situated on the antenna axis adjacent the focal point of the reflector. Because of their directional transmitting and receiving capability, parabolic antennas are commonly employed on space vehicles for receiving radio signals from control stations on the earth and/or transmitting radio signals back to monitoring stations on the earth. However, the design of parabolic antennas for space vehicles poses a problem for the reason that the antenna reflector is often so large as to require the reflector to be collapsible for stowage within the spacecraft body during the launch phase. When final orbit is achieved, the reflector is deployed to its normal parabolic configuration.
A variety of collapsible parabolic reflectors have been devised for this purpose. These existing parabolic reflectors are generally characterized, respectively, by rigid petals, inflatable rigidizable shells, spin stabilized membranes, and rib-stiffened membranes. While the existing reflectors are satisfactory to some degree, they have several inherent disadvantages which detract from their usefulness, particularly for space applications. Among the foremost of these disadvantages are excessive weight, excessive stowage volume requirements, excessive cost and complexity, the necessity of using mechanical latching means for retaining the reflectors in their collapsed condition and active or powered deployment mechanisms for deploying the reflectors, and a tendency to malfunction.
SUMMARY OF THE INVENTION
According to one of its narrower aspects, the present invention provides an improved parabolic reflector which avoids the above noted and other disadvantages of the existing reflectors of this type. In general terms, the present parabolic reflector is characterized by a lightweight parabolic reflector dish constructed of a thin radiofrequency reflective film reinforced with slender elastic ribs or beams. These beams are prestressed or preformed to cause the reflector dish to assume a normally generally parabolic dish shape. While various thin film materials may be used for the reflector dish, the latter preferably comprises an aluminized polymeric film selected from the class including Mylar and Kapton. The reflector beams are preferably tubular in cross section and constructed of the same thin film material as the reflector dish. If desired the reflector dish and beams may have a laminated construction including two outer thin film layers bonded to opposite sides of an intervening reinforcing layer, such as metallic screen. Mounted on the axis of the parabolic reflector, adjacent at its focal point, is an antenna feed mechanism.
The thin film construction of the present parabolic reflector provides the latter with several unique and highly important advantages. By way of example, two primary advantages of the reflector from the standpoint of space use reside in the fact that the reflector is extremely light in weight and may be folded to a very compact configuration for stowage within a minimum stowage volume, as within a spacecraft body during launch. In this regard, it will become evident from the ensuing description that the reflector may be folded in various ways but is preferably folded in generally serpentine fashion, in a manner similar to a parachute, for packaging within a bag or other stowage container which may be opened on command to release the reflector for deployment to its normal parabolic configuration. Folding of the reflector for stowage creates strain energy within the elastic beams of the reflector which is utilized to unfold or deploy the reflector when the container is opened. To this end, the reflector dish and beams are prestressed or preformed to assume a normally generally parabolic curvature when deployed. Additional advantages of the present invention, therefore, reside in the fact in that complex mechanical latching means to retain the parabolic reflector in its folded configuration and complex mechanical deployment mechanisms for deploying the reflector to its parabolic configuration are not required.
According to a further feature of the invention, the present parabolic reflector may be equipped with auxiliary means to aid its deployment to the proper parabolic shape, and/or to adjust the parabolic curvature of the reflector. The disclosed embodiments of the invention, for example, are equipped with an inflatable ring about the rim of the reflector dish which acts to stretch the reflector radially and resist beam bending of the reflector. This ring cooperates with the reflector beams to eliminate wrinkles in the film of the reflector dish, thereby to assure a reflector with an accurate parabolic reflective surface. The ring also provides the reflector with sufficient structural rigidity in its deployed configuration to resist distortion due to thermal radiation, solar pressure, material degradation, drag and other factors. The reflector may be equipped with guy wires which extend radially between the rim and center of the reflector dish to aid the above function of the inflatable ring. Means may be provided for adjustably tensioning these wires and shifting the antenna feed mechanism along the reflector axis to adjust the parabolic curvature of the reflector and/or locate the feed mechanism in optimum transmitting and receiving relation to the reflector.
One illustrative embodiment of the invention is equipped with a second thin film which is situated in front of and parametrically sealed to the rim of the parabolic reflector. This front film and the reflector define therebetween a hermetic chamber which may be pressurized to aid deployment of the reflector to its proper parabolic shape. The front film may be transparent to the radiofrequency energy to be transmitted and received by the antenna so as to permit the film to remain in position in front of the antenna reflector during the operation of the antenna. Alternatively, the front film may be severed from the antenna reflector after deployment.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a perspective view of a parabolic antenna embodying a parabolic reflector according to the invention;
FIG. 2 is an enlarged fragmentary perspective view of the rear side of the reflector;
FIG. 3 is an enlarged fragmentary perspective view of one of the reflector beams;
FIG. 4 is an enlarged section taken on line 4-4 in FIG. 2;
FIG. 4a is an enlarged section of a reinforcing ring embodied in the antenna;
FIGS. 5--8 illustrate one method of folding the reflector for stowage;
FIG. 9 is a perspective view of a modified parabolic reflector; and
FIG. 10 is an enlarged perspective view of the reflector in FIG. 9 with a front cover film thereof severed from the reflector.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Turning now to FIGS. 1--8 of these drawings, there is illustrated a lightweight collapsible dish structure 10 according to the invention. In this instance, the dish structure forms the parabolic reflector of a parabolic antenna 12. The reflector has a parabolic dish 14, proper, and a number of preformed reinforcing ribs or beams 16 secured to the back side of the dish. In accordance with an important feature of the invention, dish 14 is fashioned from a lightweight sheet-thin film, and the ribs or beams 16 are provided with a slender, elastic construction, such that the parabolic reflector may be packaged for stowage within a minimum stowage volume by folding the reflector in the manner illustrated in the drawings. The folded parabolic reflector may then be contained within a storage container 18. This folding action creates elastic strain energy within the reflector beams 16. When the reflector is released from the container, the strain energy in the beams causes return of the latter and the parabolic dish 14 to their original parabolic configuration.
The parabolic dish 14 and its reinforcing beams 16 may be constructed of various materials. According to the preferred practice of the invention, however, these parts are fashioned from a polymeric plastic film material, selected from the class including Mylar and Kapton. In the particular embodiment of the invention which has been selected for illustration, for example, the parabolic reflector 10 is a radiofrequency reflector, wherein the reflector dish 14 is constructed of a metallic coated plastic film, such as aluminized Mylar or Kapton. The dish may have a single layer or a multiple layer laminated construction depending upon the required structural rigidity of the dish. The reflector beams 16 have a slender thin-walled tubular configuration and are fabricated from sheet-thin film material which is preferably the same plastic film material as that of the reflector dish 14. The beams extend radially of the reflector dish between its center and rim and are bonded or otherwise secured to the back side of the dish. The dish and beams are prestressed or preformed to normally assume a parabolic curvature.
It will be immediately evident to those versed in the art that the parabolic dish 14 and beams 16 may be fabricated in various ways. The illustrated dish, for example, is composed of a number of gore-shaped sections 20 which are individually preshaped to a parabolic curvature by stretch-forming or heat-forming the sections over a suitable parabolically curved mold. The several parabolic gore sections are then joined edge-to-edge by aluminized pressure sensitive Mylar tape or other suitable means. The reflector beams 16 are preferably heat formed in the manner disclosed in the aforementioned copending application, Ser. No. 757,267. Since the beam forming method is fully disclosed in the copending application, it is unnecessary to treat the method in detail in this disclosure. Suffice it to say that the beams are fabricated, either from strips of plastic film material which are ultrasonically welded or otherwise bonded along their longitudinal edges to form thin-walled sleeves or tubes, or from sleeves or tubes of plastic film material whose walls are squeezed flat and bonded face-to-face along diametrically opposite sides of the tubes. In either case, the completed plastic tubes have diametrically opposed, longitudinally extending flanges 22. These tubes are then heat-formed to normally assume a parabolic curvature by insertion of a parabolically curved rod or mandrel through each tube and exposure of the latter to a suitable forming temperature. The finished parabolically curved beams are then ultrasonically welded or otherwise bonded to the back side of the parabolic dish 14 in such a way that the beam flanges 22 parallel the dish as shown.
At the center of the parabolic dish 14 is an antenna mounting hub 24. This hub has a generally cylindrical housing 26 which projects rearwardly from the dish on its central axis. Integrally formed on the front end of the housing 26 is a flange 28. Flange 28 is parametrically secured to the parabolic dish 14 about a central opening 30 in the dish.
Coaxially mounted on and extending forwardly from the hub 24 is a telescoping antenna feed mechanism or horn 32. This feed mechanism includes a telescoping fluid pressure actuator 34 having a cylinder 36 centered on the axis of the reflector dish 14 and rigidly secured at its rear end to the hub 24. Guy wires 38 may be secured between the hub flange 28 and the actuator cylinder 36 to brace the cylinder in the lateral direction. Movable in the cylinder is a telescoping plunger 40 which mounts the receiving and/or radiating element 42 of the antenna. When the antenna is in its normal operating configuration, this element is located at the focal point of the parabolic dish 14. Accordingly, radiofrequency waves incident on the front reflective surface of the dish are reflected to the element 42, and radiofrequency waves emanating from the element are reflected forwardly from the dish parallel to its axis, depending upon whether the antenna is operating in a receiving or transmitting mode.
As noted earlier, the parabolic dish structure or reflector 10 is adapted to be folded for stowage in the manner illustrated in the drawings and to be later released for deployment by the elastic strain energy stored within the folded reflector beams 16. The particular embodiment of the invention under discussion includes three additional deployment means 46, 48, and 50 for aiding proper deployment of the reflector. The deployment means 46 comprises leaf springs 52 which are fixed at one end to the antenna hub flange 28. The opposite, free ends of these leaf springs extend into the adjacent inner ends of the reflector beams 16 and mount resilient pads 54 for engaging the inner walls of the beams. When the parabolic reflector 10 is folded for stowage, the leaf springs 52 are bent or bowed in the manner illustrated so that elastic strain energy is stored in the springs. When the reflector is released for deployment, this elastic strain energy returns the springs to their original or normal unstressed conditions. It will be understood, therefore, that the springs aid deployment of the parabolic reflector 10 from its collapsed or stowed configuration to its deployed parabolic configuration.
The deployment means 48 comprises an inflatable torus or ring 56 which is secured to the parabolic dish 14 about its rim. When the parabolic reflector 10 is folded for stowage, the ring is deflated. During deployment of the reflector, the ring is inflated in any convenient way. In the drawings, for example, the ring is inflated through a tube 58 which extends from the ring, radially inward along the back side of the parabolic dish 14, to a pressurized fluid source (not shown). When inflated, the ring tends to stretch the parabolic reflector 10 radially in such a way as to cause the reflector to assume its normal parabolic shape. The inflated ring also reinforces the reflector against beam bending. The torus ring 56 may be a simple plastic tube or a laminate. In the latter case, there is interposed between two plastic layers 56a (FIG. 4a) a screen metal mesh 56b. Upon inflation of the torus ring 56, the metal mesh is prestressed to assume a torus shape. In the event the inflatable ring 56, deflates itself, or the plastic material starts degrading in the space environment, the metal mesh would have enough structural rigidity to restrain the deflection of the beams due to solar pressure. Upon degradation of the plastic surface of the ring, the guy wires will remain attached to the metal mesh, as will the ends of the beams to which the ring is attached.
The remaining deployment means 50 comprises a number of slender guy wires 60 of fiberglass or other suitable material which extend between the rim of the parabolic dish 14 and the front end of the actuator plunger 40. These wires are arranged in a uniformly spaced array, as shown, and aid in deploying the parabolic reflector to and retaining the reflector in its parabolic configuration. The parabolic curvature of the reflector may be adjusted within limits by extending and retracting the plunger 40.
The additional deployment means 46, 48, 50 may not be required in all applications of the invention. Accordingly, it should be understood that any one or more of these deployment means may be omitted.
It will be observed in FIGS. 5--8 that the parabolic reflector 10 may be stowed by first gathering the reflector inwardly toward its axis in a manner similar to that involved in closing an umbrella. The gathered reflector is then folded laterally of its beams 16 in serpentine fashion, preferably with the aid of packaging rolls 62 placed between the adjacent folds, to a final stowage configuration within the stowage container 18. In this instance, the container is a pleated bag secured about the edge of the antenna hub flange 28. After the reflector is properly folded, the bag is gathered about the reflector and the mouth of the bag is closed by a suitable release mechanism 64. In the case of the parabolic antenna for a space vehicle, this release mechanism may be designed for release on command by radio signals from a ground station. When released, the bag opens to release, in turn, the folded parabolic reflector 10 which then deploys to its normal parabolic configuration under the action of the elastic strain energy in the beams 16. It should be understood that the illustrated manner of folding the reflector for stowage is purely illustrative and that the reflector may be stowed by folding it in other ways.
As described earlier, the antenna feed mechanism 32 comprises a telescoping actuator 34. This actuator is retracted to its contracted condition when the parabolic reflector 10 is folded for stowage. The actuator is extended to its operating position after deployment of the reflector to its normal parabolic configuration. The ring 56 on the parabolic dish 14 is inflated during deployment as explained earlier, to aid proper deployment of the reflector to its parabolic shape and reinforce the reflector against beam bending.
Reference is now made to the drawing FIGS. 9 and 10 which illustrate a modified parabolic antenna 100 according to the invention. The modified antenna is identical to the antenna just described except that a cover film 102 is disposed in front of and sealed about its edge to the rim of the parabolic reflector 10. This front film may be preformed to normally assume a parabolic curvature and is folded with the reflector for stowage in the manner explained earlier. In this case, means 104 are provided for pressurizing or inflating, during deployment, the hermetic chamber 106 defined between the parabolic reflector 10 and the front film 102. Inflation of the chamber 106 aids deployment of the reflector to its proper parabolic configuration. The front film 102 may be constructed of a material, such as uncoated Mylar or Kapton, which is transparent to radiofrequency waves, in which case the front film may remain in position on the reflector 10 during operation of the antenna 100. Alternatively, the front film may be separated from the reflector after deployment of the latter to its parabolic configuration. In the particular embodiment of the invention illustrated, for example, a hot wire 108 is bonded to the front cover film 102 about its edge and immediately adjacent to the rim of the reflector. After deployment, this wire is electrically heated with sufficient current to sever the film from the reflector. The modified parabolic antenna 100 is otherwise identical to and is folded, deployed, and operated in the same manner as the first described parabolic antenna of the invention.
At this point, it will be evident to those versed in the art that while the invention is disclosed in connection with a parabolic antenna, the parabolic dish structure of the invention may be used for other purposes. For example, the dish structure could conceivably be employed as an optical reflector, a cover or shelter, or other lightweight collapsible structure.
Accordingly, while the invention has been disclosed in connection with certain physical embodiments thereof, various modifications of the invention are possible within the spirit and scope of the following claims.