Abstract:
The invention is a satellite assembly suitable for use with small payloads. In detail, the invention includes a foldable flexible sheet. A housing for containing the payload of the satellite is mounted at the center of the sheet. A plurality of inflatable tubular members is coupled at a first end to the housing and along it&#39;s length to the sheet having a second end terminating at the periphery of the sheet, the tubular elements movable from a collapsed condition to an inflated condition. A plurality of flat solar panels is attached to the sheet in a manner allowing the sheet to be folded.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of Provisional Patent Application Ser. No. 60/145,168 “Inflatable Nano-Satellite”, filed Jul. 22, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to the field of satellites and, in particular, to inflatable satellites. 
     2. Description of Related Art 
     Inflatable satellites are old in the art. For example, the ECHO satellite launched in the early dates of space flight was a large balloon with a reflective coating. Of course, later designs such as disclosed in U.S. Pat. No. 5,386,953 “Spacecraft Designs For Satellite Communication System” by J. R. Stuart were far more sophisticated communications satellite including an inflatable torus shaped structure incorporating an array of antennas and solar cells. However, this design does not store in a very small volume, nor is it light in weight. In addition, continued pressurization is required to insure that its shape is maintained. Thus a large supply of pressurized gas is required in order to maintain internal pressurization over a long time period. Therefore there is a need for a low cost and small size satellite that can be used for missions requiring small payloads. 
     Thus, it is a primary object of the invention to provide an inflatable satellite design. 
     It is another primary object of the invention to provide an inflatable satellite design that stores in a very small volume when un-inflated. 
     It is a further object of the invention to provide an inflatable satellite design that once inflated remains rigidized upon elimination of internal pressurization. 
     SUMMARY OF THE INVENTION 
     The invention is a satellite assembly suitable for use with small payloads. In detail, the invention includes a foldable flexible sheet. A housing for containing the payload of the satellite is mounted at the center of the sheet. A plurality of inflatable tubular members is coupled at a first end to the housing and along it&#39;s length to the sheet having a second end terminating at the periphery of the sheet, the tubular elements movable from a collapsed condition to an inflated condition. A plurality of flat solar panels is attached to the sheet in a manner allowing the sheet to be folded. 
     A system is included for internally pressurizing the tubular members such that they become rigid. In addition, it is preferable to include a system for rigidizing the tubular members after inflation such that should internal pressure be lost, the tubular members remain rigid. Typically, this is accomplished by coating the interior of the tubular members with an ultra-violet curing resin, such that when the satellite is placed in orbit, exposure to ultra-violet radiation from the sun cures the resin coating, thereby rigidizing the tubular members. 
     Preferably the solar arrays are mounted about a portion of the foldable flexible sheet connected to the housing. Another approach is to have the solar arrays comprise a series of rectangular shaped panels mounted in a space relationship such that the foldable flexible sheet is foldable along the spaces between the rectangular shaped panels. 
     The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description in connection with the accompanying drawings in which the presently preferred embodiments of the invention are illustrated by way of example. It is to be expressly understood, however, that the drawings are for purposes of illustration and description only and are not intended as a definition of the limits of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of a first embodiment of the satellite. 
     FIG. 2 is a side view of the first embodiment of the satellite shown in FIG. 1 taken along the arrow  2 . 
     FIG. 3 is a is a cross-sectional view of FIG. 1 taken along the line  3 — 3 . 
     FIG. 4 is a cross-sectional view of FIG. 1 taken along the line  4 — 4 . 
     FIG. 5 is view of the satellite shown in FIG. 1 illustrating the satellite in the stored position and in the intermediate steps to the deployed position. 
     FIG. 6 is a schematic of a pressurization system for inflating the satellite from the stored position to the deployed position. 
     FIG. 7 is a top view of a second embodiment of the satellite. 
     FIG. 8 is a view of satellite shown in FIG. 7 in the stored condition and in the intermediate steps to the deployed position. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1-3, the satellite, generally indicated by numeral  10  includes a central circular housing  12  having a top surface  14 , bottom surface  15  and peripheral side surface  16  and contains the satellite payload  17 . The housing  12  includes four tubular mounting members  22  that extend from the peripheral side surface  16  equally spaced at 90 degrees to each other. Mounted to each of the four members  22  are flexible tubes  24 A,  24 B,  24 C and  24 D, each having first and second ends  25 A and  25 B, respectively, having side surfaces  26 A and  26 B and top and bottom surfaces  27 A and  27 B. Preferably the tubes  24 A-D are made of an outer layer  28  of a material such as polyimide, for example Kapton® manufactured by E. I. DuPont de Nemours &amp; Company, Williamsburg, Del. Such materials can serve as a pressure barrier. The inner layer  30  is made of a fiber-reinforced layer impregnated with an ultraviolet radiation curable resin. The inner layer  30  can be made of such materials as a liquid crystal thermotropic (melt spun) polyester polyrarylate fiber, for example VECTRAN® manufactured by Hoechat Celanese, Charlotte, N.C. or SPECTRA® manufactured by Allied Signal, Petersberg, Va. to carry the axial loads. Another high strength material is lyotropic (solvent spun) aromatic polyaramide fiber, such as KEVLAR®, which is manufactured by E. I. DuPont de Nemours &amp; Company. 
     There are any number of usable ultra-violet radiation curable resins, for example U.S. Pat. No. 4,999,136, entitled “Ultra Violet Curable Conductive Resin” by W. A. Su, et al discloses a suitable resin. The first end  25 A of the tubes  24 A-D are bonded to the member  22  and are additionally secured by clamps  32 , while the second end  25 B is bonded to an end cap  34  and additionally secured with a clamp  36 . Bonding can be accomplished by exposing the ends  25 A and  25 B only to ultra-violet radiation. This is easily accomplished by masking off all of the tubes  24 A-D excepting the ends. Other types of tube rigidizing methods can be used, including mechanical reinforcements. 
     A web  40 , made up of four sections  40 A,  40 B,  40 C and  40 D made of a flexible cloth such as polyimide, is joined to the tubes  24 A-D. For example section  40 A is joined to side surfaces  26 A and  26 B, respectively of tubes  24 A and  24 B, section  40 B is joined to side surfaces  26 A and  26 B, respectively of tubes  24 B and  24 C, section  40 C is joined to side surfaces  26 A and  26 B, respectively, of tubes  24 C and  24 D, and section  40 D is joined to sides  26 A and  26 B, respectively, of tubes  24 D and  24 A, forming a square, and is bonded to the tubes at its sides  26 A and  26 B by forming simple lap joints  41  using a pressure sensitive adhesive. A suitable polyimide web  32  material is again Kapton®. Bonded to the web  32  are solar array panels  42 A,  42 B,  42 C and  42 D partially covering the web. 
     Additionally, triangular shaped webs  43 A,  43 B,  43 C, and  43 D are bonded to the top surfaces  27 A and to an inflatable hemispherical shaped cover  44  mounted on the top surface  14  of the housing  12 . Triangular shape webs  46 A,  46 B,  46 C and  46 D are bonded to the bottom surfaces  27 B of the tubes  24 A-D and to a second hemispherical shaped cover  48  mounted on the bottom surface  15  of the housing  12 . The hemispherical shaped covers  44  and  48  also comprise an outer polyimide layer  50  and an inner ultra-violet resin impregnated fiber-reinforced layer  51 . The webbing  43 A-D and  46 A-D are also bonded to the covers  44  and  48 , respectively, by simple lap joints  52  (best seen in FIG.  3 ). Bonding is accomplished in a manner similar to the sections  40 A-D of the web  40 . 
     The referring to FIGS. 1-4 and additionally to FIGS. 5 and 6, the stored satellite  10 ′ is opened therefrom through an intermediate position  10 ″ and to the open position  10  by a stored gas system  53  comprising a pressurized gas source  54  coupled to a control valve  55  and regulator  56  via line  57 . Line  57  connects to the port  58  and to the interior of the covers  44  and  48  (best seen in FIG.  3 ). An electronic controller  59  controls the system  53 . Thus upon opening of the valve  55 , the tubes  24 A-D and hemispherical shaped covers  44  and  48  are pressurized and expand and become rigid. Once in space, the resin impregnating the inner layer  30  of tube  24  becomes cured by exposure to the ultra-violet radiation from the sun and the inner layer also rigidizes the tube. Thus if gas pressure is lost over time, the tubes  24 A-D will still remain rigid. It should be noted that solid-state gas generation systems can also be used. In addition, mechanical rigidizing systems are usable. 
     The cap  34  at the end of the tubes  24 A-D can be used to mount global positioning antennas  62 , and the like as well as attitude control system  63  having nozzles  64 . These can be connected to the housing  12  by means of control system line assemblies  67  and  66 , respectively. The attitude control system  63  could use gas from the stored gas system  53 , for once the inner layer  30  is rigid, the gas is no longer required for rigidization. The covers  44  and  48 , which have also been inflated, also become permanently rigid, causing the triangular shaped webs  43 A-D and  46 A-D to become taut. These triangular shaped webs  43 A-D and  46 A-D help in reacting the thrust loads caused by the attitude control system  63 . 
     A second embodiment of the satellite is illustrated in FIGS. 7 and 8, generally indicated by numeral  70 , and is essentially similar to the first embodiment shown in FIGS. 1-5, except for the placement of the solar panels and method of storing and deployment. Thus all similar items remain as previously identified. The satellite  70  includes the same central circular housing  12  and tubular members  24 A-D. However, the difference here is the four segments  40 A-D of the web  40  include rigid solar panels  75 A,  75 B,  75 C, and  75 D in a grid pattern having spaces  74  therebetween. Referring particular to FIG. 8 the satellite is stored in the stored position, indicated by reference numeral  70 ′ wherein the web  40  is folded along spaces  74  so that the solar panels  75 A-D are not bent during launch and release into orbit. Upon reaching orbit, the satellite  70 ′ is initially opened to an intermediate position  70 ″ and finally to the fully open position  70 . In all other attributes, the satellite  70  is similar to the satellite  10 . 
     While the invention has been described with reference to particular embodiments, it should be understood that the embodiments are merely illustrative as there are numerous variations and modifications, which may be made by those skilled in the art. Thus, the invention is to be construed as being limited only by the spirit and scope of the appended claims. 
     INDUSTRIAL APPLICABILITY 
     The invention has applicability to the satellite manufacturing industry.