Patent Publication Number: US-11398681-B2

Title: Shape memory deployable antenna system

Description:
FIELD OF INVENTION 
     This invention relates to deployable antennae in general and to shape memory deployable antenna in particular. 
     BACKGROUND OF INVENTION 
     Parabolic reflector antennae are desirable for many types of space communications as they offer the highest so-called antenna ‘gain’ (concentration and beam width of the signal energy) and through it, extend a satellite&#39;s effective communications range. For a given electromagnetic wavelength, the larger the diameter of an antenna, the higher its ‘gain’. 
     Other types of antennae, for example, a patch-type, have only moderate gain figures, as their underlying technologies preclude their attaining the high gains of parabolic reflector antennae. 
     Rigid permanent dish antennae due to their size and geometry are largely not feasible for mini-, micro- and nano-satellites. Present deployable dish antennae have been largely unfeasible as well, due to their size, shape, weight and deployment mechanism complexity. 
     At present, deployable paraboloid reflector antennae used in satellites generally fall into two groups. One group comprises dish antenna assemblies with several petal-shaped rigid elements forming a paraboloid reflector when unfolded. Because these elements are rigid, they are often stowed as a stack, to be opened and deployed rotationally. 
     The other group includes antenna reflectors which comprise a set of supports to which a flexible reflective membrane is attached. The supporting structures, such as radial ribs, are relatively rigid and are customarily stowed as an elongated bundle folded along its longitudinal axis. When deployed some membrane supporting structures take a form of complex three-dimensional lattices which unfurl/unfold in space and support the attached reflective membrane in the required paraboloid shape. 
     A wide variety of the paraboloid reflector antenna deployment mechanisms exist or have been proposed. They include mechanical gearing assemblies, cables and tensioners and some limited shape memory actuators. Majority of them are mechanically quite complex and sometimes fail to deploy the antennae. 
     The present deployable paraboloid reflector assemblies are awkward to store since they have to be located and oriented in very limited and specific ways to conform to the available envelopes aboard the launch vehicles while still be a part of a satellite. 
     Also, because of the necessity to conform to the launch vehicle&#39;s configuration and the overall satellite physical envelope, the location selection of the antenna on a satellite itself is complicated, subject to numerous constraints and trade-offs. 
     Additionally, the sometimes off-axis placement of the antenna deployment mechanism adversely affects the center of gravity and rotational moments of a satellite and introduces complications for in-flight positioning and maneuvering of a satellite. 
     The addition of the deployment mechanisms and their rigid mechanical interfaces with the antennae themselves add to the assemblies&#39; bulk, weight and complexity, the latter leading to their reduced overall reliability. 
     Objectives of the Invention 
     Thus, it is the objective of instant invention to provide a compact deployable paraboloid reflector antenna assembly which would prior to deployment be stowable in a variety of locations and at various attitudes on the satellite. 
     Another objective is to provide antennae whose deployment would be reliable. 
     Another objective is to provide antennae with high volumetric packing efficiency. 
     Yet another objective is to provide antennae which would not require separate mechanical deployment mechanism. 
     Another objective is to provide antennae which would be lightweight. 
     Yet another objective is to provide antennae which would be compatible with deep space environment. 
     Another objective is to provide antennae whose deployment would be energy efficient. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, shape memory based deployable antennae are described. Several embodiments are illustrated, some with shape memory radially extending ribs which support a reflective membrane and some where a solid reflective paraboloid is formed from a tightly folded shape memory preform sheet. 
     The shape memory antenna elements such as supporting ribs or the paraboloid reflector itself during manufacturing are formed into their desired deployed shape. 
     Subsequently, for packaging they are mechanically restrained in the packaged geometry while being heated at—or above the phase—or glass transition temperature of the shape memory material. 
     Afterwards, they are allowed to cool off and the mechanical constraints are removed. The packaged antennae elements can be highly folded/corrugated or coiled to provide for efficient storage. 
     The shape memory antennae elements remain in their packaged configuration until they are heated for deployment to—or above the phase—or glass transition temperature of the shape memory material, and return to their original as-manufactured shape. 
     In addition to the supporting ribs and the reflector paraboloid reflector itself, several shape memory antenna feeds are also described, some with telescopic waveguide elements extended by several types of shape memory actuators and some having an extendable shape memory waveguides formed from corrugated shape memory preforms. These feeds can be used interchangeably with the shape memory antenna paraboloid reflectors. 
     Some antennae, in addition include deployable sub-reflectors positioned above the main reflector and facing the feeds, and some use small patch antennas instead of feeds and sub-reflectors. 
     Prior Art 
     The prior art for deployable antennae is extensive, since these antennae have been a key piece of communications equipment for satellites from the dawn of space exploration. 
     For example, U.S. Pat. No. 7,710,348 to Taylor et al. teaches a deployable antenna reflector which utilizes a shape memory element to open conventional rigid ribs supporting a flexible reflector. 
     U.S. Pat. Nos. 8,259,033 and 9,281,569, both to Taylor et al. teach a deployable antenna reflector with longitudinal and circumferential shape memory stiffeners supporting a reflective elastic material. 
     U.S. Pat. No. 10,170,843 to Thomson et al. teaches mechanically actuated foldable support conventional ribs for antenna reflector and a pleated foldable reflector itself. 
     None of the prior art above suggests or teaches shape memory support ribs which extend radially, as per instant invention. 
     None teaches a deployable shape memory solid reflector created from a folded/corrugated preform. 
     None teaches deployable shape memory antenna feeds or sub-reflector supports, or using patch antennas in conjunction with parabolic reflectors. 
     Objects and Advantages 
     In contrast to the prior art mentioned hereinabove, the instant invention describes shape memory paraboloid reflector antennae which offer the following advantages. 
     High Volumetric Storage Efficiency 
     The supporting reflector elements of the instant antennae systems extend radially outwards and as a result are advantageously stored very compactly prior to deployment. Since they do not require direct mechanical actuation, but merely application of heat, the elements can be tightly folded or coiled, thus offering a very dense package. The required heaters can be very compact. 
     In addition, the very shapes of the deployable elements, thanks to their being made from shape memory materials, can be optimized for storage (such as coiling), to revert to operational shape (also optimized) upon deployment. Thus, greater design latitudes exist to optimize packaging, interface with the satellite, and deployment of the antennae. 
     Light Weight 
     Due to the absence of the relatively heavy mechanical deployment drives, the weight of instant antenna systems is greatly reduced. The required heaters can be very thin and lightweight and in some applications the actuating heat can be generated by passing electric current directly through the support elements themselves. A completely passive heating and antenna deployment can be achieved by exposing antenna elements to sunlight by appropriately maneuvering the satellite. In the vacuum of space, solar heating can be considerable. 
     No Complicated Pleating/Folding of the Flexible Reflector or Support Structures 
     The precisely timed deployment of the antennae support elements and the way they deploy, e.g. their 3-dimensional deployment movement, can be accurately controlled by localized and timed application of heat to the elements. In contrast, it is difficult to achieve a complex movement with mechanical deployment actuators without incurring considerable design complexity and lowered reliability. In contrast, the deployment of the flexible reflector of instant invention is well controlled and so it can be stowed in a very compact folded package prior to deployment. 
     Simplified Construction 
     The deployment heaters of instant invention are much smaller and less complicated than mechanical actuators of the present deployable antennas. There are basically no separate ‘actuators’ per se, other than heaters, with the support elements deploying themselves upon application of heat, having stored elastic energy at the time of packaging. 
     Improved Reliability 
     With thermal actuation of instant invention replacing present electro-mechanical actuators the instant antennae systems are much more reliable, since the only moving parts are the very support elements themselves being deployed. With timed heater activation specific deployment sequences are possible to minimize the risk of malfunction. 
     Easier Redundancy Implementation 
     Since it is much easier to provide redundancy to an electrically heated deployment system than to a mechanical actuator(s)-based one, the shape memory based antennae systems can have more redundancy of their deployment apparatuses. 
     Heating and Deployment by Sunlight 
     As mentioned above, since heating of satellite components by solar radiation in space can be considerable, the support elements can be exposed to sunlight instead of heaters for deployment. This also can be used as a backup procedure in case of a heater failure. To facilitate sunlight heating the support elements can have radiation-absorptive coating(s). 
     High Stored Energy 
     The shape memory materials used for the support elements store considerable elastic energy and can generate considerable forces during deployment to overcome potential adhesions, friction and snags. 
     Relaxed Requirements for Orientation/Location on Satellite or Launch Vehicle. 
     Due to the compact size of the antennae assemblies their locations on a satellite are not as restrictive as for the present deployable antennae systems. This can simplify the design of the satellite itself and/or its operations, since the antenna or satellite itself may not have to be re-targeted/re-pointed after deployment to support antenna operations. In addition, an antenna assembly can be more easily placed to minimize its effect on the location of the satellite&#39;s center of gravity, which will simplify satellite operations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the antenna assembly embodiment 2 in stowed configuration. 
         FIG. 1A  is a perspective view of the bottom of the antenna assembly embodiment 2 in stowed configuration (heaters not shown). 
         FIG. 2  is an exploded view of the antenna assembly embodiment 2 in stowed configuration. 
         FIG. 3  is a perspective view of the feed assembly  40  in stowed configuration. 
         FIG. 4  is a perspective view of the feed assembly  40  in deployed configuration  40   a.    
         FIG. 5  is a perspective view of the antenna rib elements  10   a  in deployed configuration and feed assembly  40  in deployed configuration  40   a.    
         FIG. 6  is a perspective view of the antenna embodiment 2 in deployed configuration  2   a.    
         FIG. 7  is a perspective view of the antenna assembly embodiment 4 in stowed configuration. 
         FIG. 8  is a perspective view of the feed assembly  42  in stowed configuration. 
         FIG. 9  is a perspective view of the feed assembly  42  in deployed configuration  42   a.    
         FIG. 10  is a cross section of the antenna assembly embodiment 4 in stowed configuration taken along line  10 - 10  on  FIG. 9 . 
         FIG. 11  is a perspective view of the antenna assembly embodiment 4 in partially deployed configuration  4   a.    
         FIG. 12  is a perspective view of the rib assembly of the antenna embodiment 4 in partially deployed configuration. 
         FIG. 13  is a partial perspective view of the support rib assembly of the antenna embodiment 6 in stowed configuration. 
         FIG. 14  is an exploded view of the antenna assembly embodiment 6 in stowed configuration. 
         FIG. 15  is a perspective view of the corrugated feed assembly  120  in stowed configuration. 
         FIG. 16  is a cross section of the corrugated waveguide  123  taken along the line  16 - 16  on  FIG. 15 . 
         FIG. 17  is a perspective view of the corrugated feed assembly  150  in stowed configuration. 
         FIG. 18  is perspective view of the feed assembly  120  in deployed configuration  120   a.    
         FIG. 19  is perspective view of the feed assembly  150  in deployed configuration  150   a.    
         FIG. 20  is perspective view of the antenna assembly  8  in stowed configuration. 
         FIG. 21  is perspective view of the antenna assembly  8  in partially deployed configuration  8   a.    
         FIG. 22  is perspective view of the heater assembly  54 . 
         FIG. 23  is perspective view of the antenna assembly  8  in partially deployed configuration  8   b.    
         FIG. 24  is perspective view of the antenna assembly  8  in fully deployed configuration  8   c.    
         FIG. 25  is perspective view of the antenna rib assembly  17  in stowed configuration. 
         FIG. 26  is a plan view of the antenna rib assembly  17  in partially deployed configuration  17   a.    
         FIG. 27  is a fragmentary magnified plan view of the area  27  on  FIG. 26 . 
         FIG. 28  is a schematic of the direct electrical heating system for rib assemblies  17 . 
         FIG. 29  is a schematic of an alternative direct electrical heating system for rib assemblies  17 . 
         FIG. 30  is a schematic of a segmented electrical direct heating system of the rib assemblies  17 . 
         FIG. 31  is perspective view of the antenna coiled rib  18  in stowed configuration. 
         FIG. 32  is a plan view of the antenna rib  19  implemented in a heat pipe, connected to a heater, in stowed configuration. 
         FIG. 33  is a cross section of the antenna rib  19  taken along line  33 - 33  on  FIG. 32 . 
         FIG. 34  are cross sections of solid ribs  17  possible with shape memory materials upon heating. 
         FIG. 35  is a cross section of an expandable cylindrical hollow element possible with shape memory materials upon heating. 
         FIG. 36  is a cross section of an expandable rectangular hollow element possible with shape memory materials upon heating. 
         FIG. 37  is perspective view of the antenna assembly  9  in stowed configuration. 
         FIG. 38  is perspective view of the antenna assembly  9  in partially deployed configuration  9   a.    
         FIG. 39  is perspective view of the antenna assembly  9  in fully deployed configuration  9   b.    
         FIG. 40  is a partial perspective view of the antenna assembly  10  in stowed configuration. 
         FIG. 41  is a perspective view of the ribbon feed  180  in stowed configuration. 
         FIG. 42  is perspective view of the antenna assembly  10  in fully deployed configuration  10   a.    
         FIG. 43  is a cross section of feed  180  in deployed configuration  180   a  taken along line  43 - 43  on  FIG. 42 . 
         FIG. 44  is a diagram of the heaters activation sequence for antenna system embodiment 2. 
         FIG. 45  is a diagram of the heaters activation sequence for antenna system embodiment 4. 
         FIG. 46  is a diagram of the heaters activation sequence for antenna system embodiment 6. 
         FIG. 47  is a diagram of the heaters activation sequence for antenna system embodiment 8. 
         FIG. 48  is a diagram of the heaters activation sequence for antenna system embodiment 9. 
         FIG. 49  is a diagram of the heaters activation sequence for antenna system embodiment 10. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     In the foregoing description like components are labeled by the like numerals. 
     Deployable antenna assembly  2  is depicted on  FIGS. 1 through 6 . Referring to  FIG. 1 , antenna assembly  2  in stowed configuration comprises pliable primary reflector  20  folded into essentially a cylindrical shape. Feed assembly  40  coaxially extends through the middle of the packaged reflector  20  and is surrounded by coaxial upper heater  51  and lower heater  52 . Secondary reflector  60  is included on top of feed assembly  40  supported by elements  44  (not visible). Main reflector support rib elements  10  are not visible in this figure and neither are their respective bottom heaters  55   a ,  55   b  and  55   c.    
       FIG. 1A  shows the bottom of the antenna assembly  2  in stowed configuration wherein supporting rib elements  10  are connected to the central tubular hub integral with lower heater  52 . Rib elements  10  in stowed configuration are advantageously folded into meandering trapezoidal shapes to efficiently utilize circular envelope volume under reflector  20  and thus increase packaging density of the assembly. Bottom heaters  55   a ,  55   b  and  55   c  are not shown for clarity. The lumen of feed assembly  40  is denoted by numeral  43 . 
       FIG. 2  shows an exploded view of antenna assembly  2  in stowed configuration. Feed assembly  40  comprises secondary reflector  60  supported by coiled shape memory extendable supports  44  positioned on support ring  46 . Telescoping waveguide assembly  67  rests on base  49  and is extended by the action of a coiled shape memory actuator  48 . 
     Bottom heaters  55   a ,  55   b  and  55   c  are positioned below rib elements  10  to controllably heat them for activation. 
       FIG. 3  depicts feed assembly  40  in stowed configuration comprising secondary reflector  60  supported by extendable supports  44  which rest on ring  46 . Waveguide assembly  67  comprises nesting tubular telescoping elements  62 ,  64 ,  66  and  68 . Coiled actuator  48  is positioned around waveguide assembly  67  and rests on ring  49 . Numeral  43  denotes the lumen of waveguide assembly  67 . 
       FIG. 4  depicts feed assembly  40  in its deployed configuration  40   a . Secondary reflector supports  44  extend to their deployed configuration  44   a  upon application of heat by heater  51  (not shown). Telescopic waveguide assembly  67  is extended into its deployed configuration  67   a  by extended actuator  48  which assumes deployed configuration  48   a  upon application of heat by heater  52  (not shown). 
       FIG. 5  shows deployed configuration of primary reflector  20  support rib elements  10  of antenna assembly  2  in their deployed configuration  10   a  and their corresponding heaters  55   a ,  55   b  and  55   c , along with feed assembly  40  in its deployed configuration  40   a.    
       FIG. 6  shows deployed configuration of antenna assembly  2   a . The primary reflector rib elements  10  when heated assume extended configuration  10   a  and support primary reflector  20  in its deployed stretched configuration  20   a . Deployed primary reflector  20   a  is of a paraboloid shape which directs electromagnetic waves to and from secondary reflector  60  which in turn conveys electromagnetic radiation into and out of waveguide lumen  43  of feed assembly  40   a.    
     An alternate antenna assembly  4  is shown on  FIGS. 7 through 12 . Antenna assembly  4  comprises several folded support rib assemblies  17  extending radially from the central hub/heater  52 , each comprising an essentially a C (mathematical symbol for a subset) shape, and each comprising, in addition three sections, namely,  10 ,  12  and  16  (shown in detail on  FIG. 25 ). Rib elements  10  and  12  in stowed configuration are advantageously folded into meandering trapezoidal shapes to better fit into a circular envelope above and underneath folded primary reflector  20 , respectively, to increase packaging density of the antenna assembly. Rib elements  10  and  12  expand radially upon heating, while elements  16  when heated unfold elements  12 . 
     Referring to  FIG. 10 , circular side heater  53  heats up rib sections  16 , upper heaters  56  unfold with—and heat up rib elements  12 . Lower heaters  55   a ,  55   b  and  55   c  heat up rib elements  10  at their distal, middle and proximal sections, respectively. Upper heater  51  heats up secondary reflector supports  44 , while lower heater  52  heats up waveguide extension actuators  41 . 
       FIG. 11  shows a partial deployment of antenna assembly  4   a  upon activation of heater  53  (not shown). Deploying rib elements  16   a  are in the process of positioning rib elements  12  for their subsequent extension by activation by the attached heaters  56 . Feed assembly  42  is still in its stowed configuration. The primary flexible reflector  20  is not shown for clarity. 
       FIG. 12  depicts partially deployed ribs  17  of antenna assembly  4  (the primary flexible reflector  20  is not shown for clarity), with rib elements  16   a  fully unfolded and elements  12  fully extended into their deployed configuration  12   a  by the action of heaters  53  and  56  respectively. Rib elements  10  are still in the stowed configuration, to be controllably extended by coordinated action of heaters  55   a ,  55   b  and  55   c.    
       FIG. 8  depicts feed assembly  42  which is a variant of feed  40 , comprising secondary reflector  60  supported by extendable supports  44  which rest on ring  46 . Telescopic waveguide assembly  67  comprising telescoping elements  62 ,  64 ,  66  and  68  rests on ring  49 . Coiled actuators  41  extend waveguide  67  into its deployed configuration  67   a  depicted on  FIG. 9 . On the same figure secondary reflector  60  supports assume their deployed configuration  44   a  and so do waveguide actuators in their respective deployed configuration  41   a.    
     Feed assembly  42  can be deployed independently of ribs  17  by actions of heaters  51  and  52 . 
     An alternative antenna system embodiment 6 is illustrated on  FIGS. 13 and 14 .  FIG. 14  shows an exploded view of antenna system  6  which incorporates feed assembly  42  supporting secondary reflector  60 . Instead of the flatly stowed ribs  17  of embodiments 2 and 4, deployable ribs  18  are coiled instead. Coiling of the ribs for storage provides a smaller footprint for the assembly, at the cost of an extended height. Coiled ribs  18  in addition are advantageously made to have a generally conical shape, to fully utilize the available circular envelope on top of heaters  55   a ,  55   b  and  55   c .  FIG. 13  shows partial view of assembly  6  depicting coiled ribs  18 , with main reflector  20  not shown for clarity. 
     An alternative, single-piece feed assembly  120  with waveguide  123  made from a shape memory material is shown on  FIG. 15 . Waveguide  123  is shown in cross section on  FIG. 16 . It comprises pleats  122  and lumen  124 . 
     Referring to  FIG. 18  extendable supports  44 , which rest on ring  46  and support secondary reflector  60 , expand to their deployed configuration  44   a  upon being heated by upper heater  51  (not shown). Waveguide  123  expands and assumes its deployed configuration  123   a  comprising lumen  124   a  upon being heated by upper heater  52  (not shown). 
     An alternative, single-piece feed assembly  150  is shown on  FIG. 17 . Referring to  FIG. 19  upon application of heat by heaters  51  and  52  (not shown) feed assembly  150  assumes its deployed configuration  150   a . Waveguide  123 , reflector supports  156  and slots  152  transform into their respective deployed configurations  123   a ,  156   a  and  152   a . Slots  152   a  permit electromagnetic energy to reach secondary reflector  60  upon being reflected off deployed primary reflector  20   a  (not shown), or for the electromagnetic energy to reach reflector  20   a  upon exiting waveguide lumen  124   a  and being reflected off secondary reflector  60 . 
     A yet another alternative antenna system embodiment 8 is shown on  FIGS. 20 through 24 . Antenna system  8  is close in construction to embodiment 4, with the difference being the supports for secondary reflector  60 . 
     Referring to  FIGS. 21 and 23 , in contrast to the previous 2, 4 and 6 antenna embodiments, in embodiment 8 instead of the waveguides, secondary reflector  60  supports  160  are connected to distal ends of ribs elements  12  of ribs  17 . Supports  160  extend from their stowed configuration to their intermediate extended configuration  160   a  upon being heated by heater assembly  54 , for the partial deployment configuration of antenna system  8   a  depicted on  FIG. 21 . 
     On  FIG. 23 , upon deployment of supports  160  to their intermediate configuration  160   a  rib elements  16  of ribs  17  unfold upon being heated by heater  53  and place antenna assembly into its intermediate configuration  8   b . In this configuration supports  160   a  resiliently bend to accommodate the movement of rib elements  12 . 
     On  FIG. 24 , when rib elements  12  (not shown) are fully extended by being heated by heaters  56  (not shown), rib elements  10  extend to their deployed configuration  10   a  by being heated by heaters  55   a ,  55   b  and  55   c  (not shown), and feed assembly  45  is extended to its deployed configuration  45   a  by being heated by heater  52  (not shown), deployed supports  160   a  assume their fully deployed configuration  160   b  and position secondary reflector  60  to face the deployed paraboloid primary reflector  20   a  and feed  45   a , thus transforming antenna system  8  into its fully deployed configuration  8   c.    
     Referring to  FIG. 20 , supports  160  are of the coiled type, are connected to their respective rib  12  distal endpoints, and are heated by heater assembly  54  shown on  FIG. 22 . Heater assembly  54  is frusto-conical in shape with aperture  57   a  at its apex to accommodate secondary reflector  60  and fits on top of stowed coiled supports  160  when installed in the assembly and is shown in broken line on  FIG. 20 . 
     Referring again to  FIG. 22 , heater assembly  54  further comprises heating elements  54   a ,  54   b ,  54   c  and  54   d  which are partially separated from each other by slots  57 . When activated, supports  160  extend through slots  57  to deploy reflector  60 . The connections between individual heating elements  54   a ,  54   b ,  54   c  and  54   d  are made to fracture when primary reflector support ribs  17  deploy, so as not to impede their unfolding. 
     Feed  45  is identical to feed  40  with the exception of absence of supports  44 . 
     Referring to  FIGS. 26 and 27 , coupling rings  11  are connected to flexible reflector  20  and are allowed to slide along ribs  17  during deployment of antenna system. Proximal ends of rib elements  10  are permanently connected to heater assembly  52  while rib elements  12  are allowed to extend radially and outwardly while connected on their distal ends to capture devices  13  fixed to reflector  20 . When ribs  17  expand radially upon application of heat they stretch reflector  20  and impart a paraboloid shape to it. 
     Coupling rings  11  are also utilized with coiled ribs  18  as shown on  FIG. 31 . 
     Referring to  FIG. 28 , each rib  17  has on it has dedicated heater elements  200  and  202  connected by an electrical contact  15 . Electric current generated by external voltage source  210  heats up heaters  200  and  202  and through them rib  17  facilitating its deployment. 
     On  FIG. 29  ribs  17  are directly heated by passing through them electric current generated by external voltage source  210 . Contacts  15   f  provide electrical connection from source  210  to rib  17 . Shape memory materials utilized for ribs  17 , such as metallic Ni-based alloys are advantageously suited for this, as they possess high electrical resistivity. 
       FIG. 30  shows rib  17  in partial deployment configuration  17   a  after rib element  16  has been directly heated by electric current supplied by voltage source  210   a  to assume its deployed configuration  16   a . Source  210   a  is connected to rib  17  by contacts  15   a  and  15   b . This rib configuration generally corresponds to antenna embodiment configuration  4   a  on  FIG. 11 . 
     Also on  FIG. 30  external voltage sources  210   b  and  210   c  connect to rib  17 &#39;s elements  12  and  10  by contacts  15   b - 15   c , and  15   a - 15   d , respectively. 
     When ribs  17  are to be directly electrically heated, in antenna embodiments 2, 4, 6, 8 and 9, heaters  53 ,  56 ,  55   a ,  55   b  and  55   c  are not required. In embodiment 9, in addition, heater  54  is not required either. 
     Likewise, direct electrical heating can be used for feed deployment, obviating feed deployment heaters  51  and  52  or, again,  54  (used for feed  180  of embodiment 10). 
     Referring to  FIGS. 34 through 36 , ribs  17 , supports  44  and  160 , and feed actuators  41  can have cross sections optimized both for storage and for deployment. Mark ‘-FT’ denotes application of heat for transformation. 
     For example, per  FIG. 34 , a rib can have round cross section  25  optimized for storage and coiling, while it would transform upon deployment into a ‘T-beam’, ‘I-beam’ or a tri-lobe configurations,  25   a ,  25   b  and  25   c , respectively which would offer increased stiffness in certain directions vs. the rib of the original cross-section. 
     Referring to  FIGS. 35 and 36 , ribs  27  and  29 , respectively, having hollow oblong cross sections can be made pliable in the direction perpendicular to their thickness, which would facilitate their folding or winding for efficient storage. Upon deployment, however, their cross sections can be transformed into stiffer, more symmetric forms, such as  27   a  and  29   a , respectively, which would be optimized for deployment and would open up their lumens  27   b  and  29   b  to  27   c  and  29   c  respectively. 
       FIGS. 37, 38 and 39  illustrate antenna system  9  which is based on flexible primary reflector  20  supported by ribs  17  but instead of a feed and a secondary reflector has a patch antenna  61  which can be used for both transmitting and receiving. Supports  160  are made of shape memory material and activated by heater  54  (shown in broken line). Also not shown on these figures are annular heaters  55   a ,  55   b , and  55   c  for rib sections  10  and a radio-frequency cable which would normally connect patch antenna  61  to a transceiver on a satellite. Such cable would be routed from a transceiver to patch  61  along one of supports  160   b.    
     An alternative antenna system embodiment 10 is shown on  FIGS. 40 through 43 . A ribbon feed  180  is spirally wound in its stowed configuration and positioned in the middle of the antenna assembly inside heater  52 . It is actuated by heater  52  and extends to its deployed configuration  180   a  shown on  FIG. 42 . Feed  180   a  assumes a hook-like shape so its distal end is positioned at the focal point of deployed primary reflector  20   a  and faces reflector  20   a . This configuration obviates the need for a secondary reflector for the antenna system. During actuation feed  180  not only unfurls, but its compressed lumen  186  assumes its deployed round shape  186   a  shown on  FIG. 43 , which is conducive to transmission of electromagnetic radiation. Primary reflector  20  is transformed into its deployed configuration  20   a  by radial extension of ribs  18  into their deployed configuration  18   a  upon being heated by heaters  55   a ,  55   b , and  55   c  shown on  FIG. 40 . 
     The shape memory materials used in the instant antenna system construction may include shape memory alloys (‘SMAs’) or shape memory polymers (‘SMPs’). 
     Shape memory alloys comprise numerous alloys such as AgCd, AuCd, cobalt-, copper-, iron-, nickel- and titanium-based, with most well-known and used being Cu—Al—Ni and Ni—Ti alloys (the latter known as ‘nitinols’). 
     Shape memory polymers comprise linear block polymers such as polyurethanes, polyurethanes with ionic or mesogenic components made by prepolymer method, block copolymer of polyethylene terephthalate (PET) and polyethyleneoxide (PEO), block copolymers containing polystyrene and poly(1,4-butadiene), and an ABA triblock copolymer made from poly(2-methyl-2-oxazoline) and polytetrahydrofuran. 
     Also, cross-linked PEO-PET block copolymers and PEEK can be used as shape memory elements of instant invention. 
     Some of these SMPs can be made to contain carbon which makes them electrically conductive. This conductivity can be advantageous for their direct heating with electrical current and the reflectance of the antenna dish made from them. 
     Operational Details 
     The deployment sequences of several embodiments of instant antenna systems are shown on  FIGS. 44 through 49 . 
     The controlled deployment sequences of antenna system elements ensure reliable deployment of the antenna and its achieving its reflector desired paraboloid shape  20   a , and proper deployment and positioning of the feed, secondary reflector  60  or patch antenna  61 . 
     Referring to  FIG. 44 , in sequence  200  which pertains to antenna system  2 , supports  44  and feed  40  are extended by activating heaters  51  and  52  (steps  210  and  220 ) respectively. The rib elements  10  are extended by a timed action of heaters  55   a ,  55   b  and  55   c : first the distal tips of rib elements  10  are activated by heater  55   a  (step  230 ), then their middle sections activated by heater  55   b  (step  240 ), and finally their proximal ends activated by heater  55   c  (step  250 ). This sequence ensures reliable deployment of the flexible primary reflector  20  from the stored configuration outwards, to form a paraboloid reflector  20   a.    
     Referring to  FIG. 45 , in sequence  400  which pertains to antenna system  4 , supports  44  and feed  42  are extended by activating heaters  51  and  52  (steps  410  and  420 ) respectively. Rib elements  16  are activated by heater  53  and unfold elements  12  and their heaters  56  (step  430 ). Rib elements  12  radially extend as heaters  56  are turned on (step  440 ). The rib elements  10  are then controllably extended radially by a timed action of heaters  55   a ,  55   b  and  55   c : first the distal tips of rib elements  10  are activated by heater  55   a  (step  450 ), then their middle sections activated by heater  55   b  (step  460 ), and finally their proximal ends activated by heater  55   c  (step  470 ). Just like in the previous embodiment, this sequence ensures reliable deployment of the flexible primary reflector  20  from its stowed configuration outwards, to form a paraboloid reflector  20   a.    
     Referring to  FIG. 46 , in sequence  600  which pertains to antenna system  6 , supports  44  and feed  42  are extended by activating heaters  51  and  52  (steps  610  and  620 ) respectively. Rib elements  18  are controllably extended radially by a timed action of heaters  55   a ,  55   b  and  55   c : first the distal tips of rib elements  18  are activated by heater  55   a  (step  630 ), then their middle sections activated by heater  55   b  (step  640 ), and finally their proximal ends activated by heater  55   c  (step  650 ). This sequence ensures reliable deployment of the flexible primary reflector  20  from the stored configuration outwards, to form a paraboloid reflector  20   a.    
     Referring to  FIG. 47 , in sequence  800  which pertains to antenna system  8 , supports  160  are extended by activating heater assembly  54  (step  810 ). Rib elements  16  are activated by heater  53  and unfold elements  12  and their heaters  56  (step  820 ). Rib elements  12  then radially extend as heaters  56  are turned on (step  830 ). Rib elements  10  are then controllably extended radially by a timed action of heaters  55   a ,  55   b  and  55   c : first the distal tips of rib elements  10  are activated by heater  55   a  (step  840 ), then their middle sections activated by heater  55   b  (step  850 ), and finally their proximal ends activated by heater  55   c  (step  860 ). Telescopic feed  45  is then activated by the action of heater  52  (step  870 ). This sequence ensures reliable deployment of the flexible primary reflector  20  from its stored configuration outwards, to form a paraboloid reflector  20   a.    
     Referring to  FIG. 48 , in sequence  900  which pertains to antenna system  9 , supports  160  are extended first by activating heater assembly  54  (step  910 ). Rib elements  16  are then activated by heater  53  and unfold elements  12  and their heaters  56  (step  920 ). Rib elements  12  then radially extend as heaters  56  are turned on (step  930 ). Rib elements  10  are then controllably extended radially by a timed action of heaters  55   a ,  55   b  and  55   c : first the distal tips of rib elements  10  are activated by heater  55   a  (step  940 ), then their middle sections activated by heater  55   b  (step  950 ), and finally their proximal ends activated by heater  55   c  (step  960 ). As ribs  17  assume their final deployed configuration, supports  160   a  assume their final deployed configuration  160   b  while positioning patch antenna  61  at the focus of reflector  20   a.    
     Referring to  FIG. 49 , in sequence  1000  which pertains to antenna system embodiment 10. Ribbon feed  180  is deployed by being heated by heater assembly  54  (step  1010 ). Rib elements  16  of ribs  17  are activated by heater  53  and unfold elements  12  and their heaters  56  (step  1020 ). Rib elements  12  then radially extend as heaters  56  are turned on (step  1030 ). Rib elements  10  are then controllably extended radially by a timed action of heaters  55   a ,  55   b  and  55   c : first the distal tips of rib elements  10  are activated by heater  55   a  (step  1040 ), then their middle sections activated by heater  55   b  (step  1050 ), and finally their proximal ends activated by heater  55   c  (step  1060 ). 
     Other Embodiments 
       FIGS. 32 and 33  depict rib  19  implementation using heat pipe technology. A number of heat pipe technologies are well known in their respective art, and are widely used for heat transfer applications in satellites. 
     Hollow rib  19  is made of shape memory material, is hermetically sealed at both ends and filled with a phase-change heat transfer working compound. Rib  19  is then folded into the stowed configuration similar to rib element  10  of other embodiments and depicted on  FIG. 32  as an example. As shown on  FIG. 33  hollow rib  19  is lined inside with a wick layer  19   a  with lumen  19   b  occupied by a vapor phase of the heat transfer material. Heat to rib  19  can be applied by heater  55   c  which would be common to all ribs  19  of the antenna assembly replacing ribs  17  (not shown for clarity). 
     Heat pipes advantageously transfer heat from one of their ends to another. As a result, a heat pipe is uniquely suitable for heating the distal end of the heat pipe-based rib  19  first, so it extends before the rest of the rib  19 &#39;s sections do. 
     As the distal end of rib  19  heats up and assumes its deployed shape, the heat is diffused along the rib and gradually raises the temperature of the middle—and then the proximal sections of rib  19 . 
     As a result, ribs  19  in the antenna assembly radially extend to their full deployed length and shape and all of them working in cooperation stretch the coupled flexible reflector  20  to its deployed paraboloid configuration  20   a.    
     Heat pipe technology can also be used for a version of coiled rib  18  and folded rib  17 . For the heat pipe version of rib  18  the heat source required is  55   c.    
     The heat sources required for the heat pipe version of rib  17  actuation are heater  53  used for unfolding operation and heater  55   c  for extension of sections  12  and  10  heat pipe versions. 
     By using heat pipe technology, heating of the shape memory elements can be simplified, since heat can be applied from proximal ends only (with the exception of a variant of folded rib  17 ). 
     Heaters  55   a ,  55   b  and  56  are no longer required for the assembly, since heat pipe technology will inherently heat up distal sections  12  slightly ahead of proximal sections  10  for reliable deployment and in steady state will ensure a fairly uniform temperature along entire ribs  17 . 
     Additionally, feed actuators  41  and  48 , supports  44  and  160 , and ribbon feed  180  itself can all be realized with heat pipe technology. 
     By using heat pipe technology, heating of the shape memory elements can be greatly simplified, since heat can be applied from their proximal ends only and the resulting temperature distribution is fairly uniform from one end of a heat pipe to another. 
     The heat pipes working compound can be water, ammonia or other, the first two being especially chemically compatible with nickel-titanium shape memory alloys which can be utilized for the antenna system. 
     Other deployable antenna configurations, although not illustrated, are feasible. 
     For example, paraboloid reflectors made with thin flexible metallic membranes or foils stretched into the deployed shape by deployable ribs are possible. 
     Thin metallized polyimide films, e.g. MYLAR® and KAPTON® manufactured by DuPont, Inc. can be used for the flexible reflector  20 . 
     Flexible metallic wire meshes stretched by the deployed ribs are also well known in the art. 
     Patch antenna  61  can have a receiver pre-amplifier and/or a transmit power amplifier integrated in a combined package held by supports  160   b.    
     Skeleton rib antenna structures utilizing only supporting ribs  17  without reflector  20  can be used at lower operating frequencies. 
     Heaters  56  can be divided into several individually controlled sub-heaters to provide a more controlled heating of distal segments  12  of ribs  17 . 
     Various heat sources can be used to activate the shape memory elements and deploy the antenna, such as sunlight, chemical heat generators, electric infrared sources, and nuclear sources. 
     Shape memory components can have thermally absorbing coatings to facilitate their heating and deployment by sunlight. 
     Electrical contacts used for direct heating of shape memory components by electric current can be made to disengage from the heated components upon deployment. 
     The electrical contacts can also be made frangible, to also disengage from the components upon deployment. 
     The power leads to the heaters on the shape memory components or the components themselves can be made retractable or coiled to retreat after the components&#39; deployment. 
     Shape memory antenna components can have conductive or resistive film coating or coatings deposited on their surfaces on top of electrically insulating layer or layers in various patterns to facilitate their controlled heating by electric current applied to these coatings. 
     Heaters  55   a ,  55   b  and  55   c  can be combined in a single assembly. 
     The described feeds are interchangeable among the embodiments, except for embodiments 8 (its feed doesn&#39;t comprise reflector supports),  9  (does not require a feed) and  10  (has a unique feed configuration). 
     The feeds do not have to be centered with respect to the primary reflector, and the reflector itself does not have to be circularly symmetric. Rather, off-axis operation is possible, and, indeed, is practiced in the art. 
     Although shown as circular, feed lumens  43 ,  124   a  and  186   a  can be oval or rectangular, with different proportions. The resulting waveguides of these lumen geometries and their performance are well known in the art. 
     Although descriptions provided above contain many specific details, they should not be construed as limiting the scope of the present invention. 
     Thus, the scope of this invention should be determined from the appended claims and their legal equivalents.