Abstract:
A system which features an actuator mechanism for controlling orientations of reflecting surfaces of an optical reflector or antenna is disclosed. As integrated into the system, the actuator may control both pan and tilt characteristics of reflective surfaces to create an adaptive system for focusing or otherwise directing light or other radiation. The invention is suited to large aperture, low density, and high surface accuracy segmented optical or other electromagnetic wave receivers needed for terrestrial and space-deployed applications in fields such as astronomy, communications, earth imaging, and directed energy.

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to adaptive optics and, more particularly, to a segmented reflecting system and an actuator for providing position adjustment of individual optical elements of a segmented reflecting system. 
     Launch costs and payload volume restrictions currently prohibit sending extremely large reflecting mirror or antenna systems into space. Space-based systems also have stringent weight requirements because of the cost of sending a payload into space. There are several motivations, however, to develop these systems for defense and commercial telescopes and directed energy applications. For example, design of large and low-weight structures for optics and antennas is a primary technology to be developed for the U.S. Air Force (USAF), as identified by the USAF Scientific Advisory Board. In addition, the Jet Propulsion Laboratory (JPL) is studying proposals for a terrestrial planet finder space telescope, which is an example of a project that needs a lightweight mirror system that can provide massive light-gathering capacity, while allowing compact stowage in a spacecraft payload compartment. Even the relatively small Hubble space telescope mirror is very heavy at 200 kilograms (Kg). At a typical rate of $30 thousand per kilogram for launch costs, ground glass mirrors such as the Hubble mirror represent an inefficient solution for reflecting systems in space. 
     Thus, new methods to provide extremely large and accurate optical and antenna systems that accommodate launch constraints are needed. Some of the proposed methods include using low-weight materials. Design of single-piece structures with accurate geometry, however, is difficult with any material. Attaching reflectors to large foldable structures involves challenges in packing the foldable structures within payload compartments. Another problem with foldable structures is that there must be components within the design that function just to allow the foldable structure to be collapsed for launch and deployed in space. The components enabling this add cost and weight without providing functional value. 
     Free-flying mirrors have also been proposed that can be adaptively controlled for positioning in space. These segmented systems with their large reflecting surfaces, however, entail design challenges similar to those of any large system so that the practical assembly of these huge reflecting systems would still require launching large structures. An additional proposal includes making adaptive membrane mirrors. An obstacle to this approach is that it is difficult to correct local aberrations in the membrane surface without affecting the form of the surrounding reflecting area. 
     Typical space-based telescope or antenna systems include radiation sensitive components attached to a supporting structure. The radiation sensitive components can be optical devices—such as mirrors—for a telescope or reflectors for a radio wave antenna. These systems also typically include an alignment apparatus for directing the radiation sensitive component at a desired target. The alignment apparatus may also be used to make fine adjustments to the position of the radiation sensitive component to improve the image of the desired target. In general, an alignment apparatus may include the ability to accurately control the position of one part of a system relative to a second part, either to effect a relative displacement between the parts or to maintain a desired spatial relationship between the parts. One type of device used in the art for position control is the actuator mechanism. Actuator mechanisms, however, tend to be mechanical in nature and, consequently, can be heavy and unreliable. 
     One such actuator mechanism is an “inch worm” type linear actuator in which high resolution is achieved by directly moving an actuator armature in small steps using thermal, piezoelectric, electromagnetic, or magnetostrictive armature translators. For example, ceramics exhibiting the piezoelectric effect have been used as actuators for accurate positioning purposes, but the range of movement is small—about 5 micrometers (μm)—and relatively large voltages are required for their operation. Such armature translators can easily move the armature in nanometer range increments and can exert very large forces, since they rely on the stiffness of an expanding or contracting material. Sequential operation of paired, electromagnetic clamp assemblies and the armature translator provides a step-wise linear motion. When power is removed, the mechanism prevents further motion of the armature. Due to their weight and power requirements, however, these actuator mechanisms generally are not suitable for large, space-based telescope and antenna systems. Because of the weight constraints described above, it is desired to reduce the weight of the various components and to provide lightweight and reliable components for use in space-based telescope and antenna systems. 
     Terrestrial optical and antenna systems, used where gravity is significant, may also benefit from the use of lightweight reflecting systems. Any terrestrial mirror system will deform when its orientation to gravity is changed, for example, by aiming the system. The use of heavy monolithic mirrors addresses the problem by designing the mirror structure with high stiffness. However, regardless of stiffness, weight is always a factor due to deformation of the mirror structure from gravity. An approach is needed that allows the system to adapt to changing gravity loads and other factors that cause deformations. 
     As can be seen, there is a need for a lightweight mirror system that can provide massive light-gathering capacity, while allowing compact stowage in a spacecraft payload compartment. There is also a need for a compact and low mass actuator mechanism for terrestrial and space-based reflecting systems. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention, an actuator mechanism for movement along a support membrane structure includes a ferromagnetic plug with a first coefficient of thermal expansion and a first coefficient of friction. The ferromagnetic plug is positioned on a surface of the support membrane structure and is magnetically coupled to the support membrane structure. The actuator mechanism also includes a center band with a third coefficient of friction, the center band being positioned on the surface of the support membrane structure and fixedly attached to the ferromagnetic plug, the center band encircles the ferromagnetic plug. The actuator mechanism includes an actuator material region with a second coefficient of thermal expansion. The actuator material region is positioned on the surface of the support membrane structure and adjacent to the center band. The actuator material region is separated from the ferromagnetic plug by the center band. Further, the actuator mechanism includes an outer band with a second coefficient of friction fixedly attached to the actuator material region. The outer band is positioned on the surface of the support membrane structure and adjacent to the actuator material region. The outer band is magnetically coupled to the support membrane structure. 
     In another aspect of the present invention, an actuator mechanism for movement along a diamagnetic support membrane structure includes a ferromagnetic plug with a first coefficient of thermal expansion and a first coefficient of friction. The ferromagnetic plug is positioned on a surface of the support membrane structure and the ferromagnetic plug is capable of expanding in a direction perpendicular to the surface of the support membrane structure. The actuator mechanism also includes a center band with a third coefficient of friction where the center band is positioned on the surface of the support membrane structure and is fixedly attached to the ferromagnetic plug. The center band encircles the ferromagnetic plug. The actuator mechanism further includes an actuator material region with a second coefficient of thermal expansion where the actuator material region is positioned on the surface of the support membrane structure and around the ferromagnetic plug. The actuator material region is capable of expanding in a direction parallel to the surface of the support membrane structure. Also, the actuator mechanism includes an outer band with a second coefficient of friction where the outer band is positioned on the side of the support membrane structure and encircling the actuator material region. The actuator mechanism includes a first magnetic region positioned on the opposed surface of the support membrane structure and adjacent to the ferromagnetic plug. Further, the actuator mechanism includes a second magnetic region positioned on the opposed surface of the support membrane structure and adjacent to the outer band. 
     In still another aspect of the present invention, an optical reflector or electromagnetic wave antenna system includes a diamagnetic support membrane structure with an actuator mechanism positioned on a surface of the support membrane structure. The actuator mechanism includes a ferromagnetic plug with a first coefficient of thermal expansion and a first coefficient of friction; the ferromagnetic plug is positioned on a surface of the support membrane structure where the ferromagnetic plug is capable of expanding in a direction perpendicular to the surface of the support membrane structure. The actuator mechanism includes a first band with a third coefficient of friction where the first band is positioned on the side of the support membrane structure and is fixedly attached to the ferromagnetic plug. The first band encircles the ferromagnetic plug. The actuator mechanism further includes an actuator material region with a second coefficient of thermal expansion where the actuator material region is positioned on the surface of the support membrane structure and around the first band. The actuator material region is capable of expanding in a direction parallel to the surface of the support membrane structure. The actuator mechanism also includes a second band with a second coefficient of friction where the second band is positioned on the surface of the support membrane structure and around the actuator material region. The second band is fixedly attached to the actuator material. Also, the actuator mechanism includes a first magnetic region positioned on an opposed surface of the diamagnetic support membrane structure and magnetically coupled to the ferromagnetic plug. Further, the actuator mechanism includes a second magnetic region positioned on the opposed surface of the diamagnetic support membrane structure and magnetically coupled to the second band. 
     The reflector or antenna system further includes an adjustment beam magnetically coupled to the first magnetic region and a frame structure connected to the adjustment beam. Also, the system includes a reflector segment fixedly attached to the adjustment beam and at least one heat source capable of heating the ferromagnetic plug and the actuator material region. 
     In yet another aspect of the present invention, a method of moving an actuator mechanism along a support membrane structure includes the steps of increasing a first temperature of a ferromagnetic plug wherein the ferromagnetic plug expands in a direction perpendicular to a surface of the support membrane structure lifting a center band off the surface of the support membrane structure; increasing a second temperature of an actuator material region at a first position wherein the actuator material region expands at the first position in a direction parallel to the surface of the support membrane structure moving the ferromagnetic plug and center band in a direction parallel to the surface of the support membrane structure; decreasing the first temperature so that the ferromagnetic plug contracts and the center band frictionally engages the surface of the support membrane structure; decreasing the second temperature; and increasing a third temperature of the actuator material at a second position wherein the actuator material region expands at the second position in a direction parallel to the surface of the support membrane structure. 
     In another aspect of the present invention, a method of adjusting and locking angular orientations of reflective elements of an optical reflector or antenna system relative to a support membrane structure includes the steps of directing a first beam of light onto a ferromagnetic plug magnetically coupled to a reflector segment, the first beam of light causing a first temperature in the ferromagnetic plug to increase wherein the ferromagnetic plug expands in a direction perpendicular to a surface of the support membrane structure, lifting a center band encircling the ferromagnetic plug off the surface of the support membrane structure; directing a second beam of light onto an actuator material region encircling the center band, the second beam of light causing a second temperature in the actuator material region to increase at a first position wherein the actuator material region expands in a direction parallel to the surface of the support membrane structure, moving the ferromagnetic plug, center band, and elements of the system that are attached to reflecting components in a direction parallel to the surface of the support membrane structure; turning off the first beam of light causing the second temperature to decrease so that the center band frictionally engages the surface of the support membrane structure; turning off the second beam of light causing the second temperature to decrease; and directing at least one of the first and second beams of light onto the actuator material region at a second position causing the outer band to move in a direction parallel to the surface of the support membrane structure to become centered about a center of the ferromagnetic plug. 
     These and other features, aspects, and advantages of the present invention will become better understood with reference to the following drawings, description, and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of an exemplary segmented reflector system in accordance with one embodiment of the present invention; 
         FIG. 2  is a side view of the exemplary segmented reflector system illustrated in  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of a spherical joint of the exemplary segmented reflector system illustrated in  FIG. 2 ; 
         FIG. 4A  is a side view of the exemplary segmented reflector system illustrated in  FIG. 1 , showing additional elements of the system in accordance with one embodiment of the present invention; 
         FIG. 4B  is a detail side view of the exemplary segmented reflector system illustrated in  FIG. 4A ; 
         FIG. 5  is a cross-sectional view of an actuator mechanism according to one embodiment of the present invention; 
         FIG. 6  is a plan view of an actuator mechanism illustrated in  FIG. 5 ; 
         FIG. 7  is a cross-sectional view of the actuator mechanism as illustrated in  FIG. 5 ; 
         FIG. 8  is a plan view of the actuator mechanism as illustrated in  FIG. 7 ; 
         FIG. 9  is a cross-sectional view of the actuator mechanism as illustrated in  FIG. 5 ; 
         FIG. 10  is a plan view of the actuator mechanism as illustrated in  FIG. 9 ; 
         FIG. 11  is a cross-sectional view of the actuator mechanism as illustrated in  FIG. 5 ; 
         FIG. 12  is a plan view of the actuator mechanism as illustrated in  FIG. 11 ; 
         FIG. 13  is a cross-sectional view of the actuator mechanism as illustrated in  FIG. 5 ; 
         FIG. 14  is a plan view of the actuator mechanism as illustrated in  FIG. 13 ; and 
         FIG. 15  is a cross-sectional view of an actuator mechanism in accordance with another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description is of the best currently contemplated mode of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
     Broadly, an embodiment of the present invention provides a lightweight, segmented, adaptive reflector system that may be used, for example, as an adaptive optical telescope reflector, a reflector for a radio wave antenna, or a reflector for directed-energy applications. When used as a spaceborne adaptive optical telescope reflector, for example, one embodiment can provide massive light-gathering capacity, while allowing compact stowage in a spacecraft payload compartment. When used as a reflector for a radio wave antenna, for example, one embodiment provides an antenna dish with an array of elements that are independently adjustable to fine-tune the focus of incident energy to a receiver or from a transmitter. For directed-energy applications, one embodiment may be used as a solar concentrator or to collect energy from a laser beam. For instance, an optical reflector system according to one embodiment could have a laser targeted at it from a great distance in space to receive energy for use at that location or to redirect it elsewhere. 
     A reflecting system, according to one embodiment, includes a compact and low mass actuator mechanism that may be useful for terrestrial as well as space-based adaptive reflecting systems. With this system, the form of the reflector surface can be continuously adapted using energy from a laser. Because the system can be erected in space from small subassemblies, loads during launch will not be problematic and the assemblies can be designed to use payload space efficiently. The segmented system, according to one embodiment, can be more accurate than prior art systems incorporating a large monolithic structure or adaptable membrane concept because each segment of the segmented system can be individually adjusted and adapted to changing conditions, preventing bending in portions of the reflector that do not require adjustment, in contrast, for example, to prior art adaptable membrane reflectors. 
     The present invention enables reflecting systems with huge reflecting surface areas and very high optical precision that, in addition, can be lightweight. For example, small reflecting segments can be designed to be very lightweight with high stiffness and high optical precision, yet with low mass because only small forces will act on them in space and because only low forces are needed to correct segment alignments. Extremely large reflecting systems can be assembled with small parts that can be mass produced. A reflecting system, according to an embodiment, may be arbitrarily large, at least in theory, because the individual components included in the system may include extremely low mass materials and any number of reflector segments can be coupled together. 
     A unique aspect of one embodiment of the present invention is that the orientation of numerous small reflecting segments of the system can be independently controlled throughout a wide angular range. This can occur with extreme precision due to the long adjustment beam and the fine adjustment from the thermal actuators. Energy has to be applied to the actuators only when it is necessary to adjust the position of a reflector because permanent magnets lock the position after the adjustments are made. 
     In one embodiment, individual adjustment of the reflecting segments is performed using a novel thermal actuator mechanism. According to one embodiment, the thermal actuator mechanism is magnetically attached to a membrane structure, for example, by the attraction of magnets to each other from opposite sides of a non-magnetic membrane structure. The thermal actuator mechanism may have three different contact surfaces with which to contact the membrane structure, respectively having a high, intermediate, and low coefficient of friction in relation to the membrane, and structurally arranged in a novel manner. When the actuator mechanism is energized, for example, by a laser beam from a remote source, the high friction contact surface can be lifted off the membrane structure through thermal expansion of a ferromagnetic plug, leaving the low friction contact surface on the membrane. At another part of the actuator, the intermediate friction contact surface remains in contact with the membrane structure. Thermal expansion of an actuator material region is used by the low friction contact surface to push against the intermediate friction contact surface, sliding the high (still lifted) and low friction contact surfaces together across the membrane structure. Cooling of the ferromagnetic plug returns the high friction contact surface into contact with the membrane structure. Thermal expansion of another part of the actuator material region is then used by the intermediate friction contact surface to push against the high friction contact surface, sliding the intermediate friction contact surface across the membrane structure to “catch up” again to the high and low friction contact surfaces. Thus, the actuator mechanism “walks” across the membrane structure. By coupling such an actuator to each reflector segment through a long adjustment beam, as in one embodiment, precise and accurate reflector segment adjustments can be made individually for each segment. The actuator mechanism may provide precision control in small increments and yet may allow gross movements, for example, by repetitive actuations. 
     A reflecting system with actuator mechanisms according to an embodiment of the present invention may exhibit several advantages over the prior art. For example, actuator reactions occur locally, minimizing bending of the support structure. Actuator movements depend on the energy level with which they are activated and the coefficient of thermal expansion (CTE) of the expanding material, allowing for extreme precision. Use of the long adjustment beam further increases precision. Actuators can be produced in miniature size, with low weight, and low cost with mass production processes. Mirror segments and actuators are held onto the supporting structure with magnetic force, making assembly simple. Since magnets are used, fasteners and installation tools are not needed. Some applications may use magnets for joining components of the main structure assembly. System repairs and replacement will be simple, since fasteners are not used for assembly. Segments can be controlled throughout a wide angular range. Depending on design factors, this may allow for simple supporting structures that are planar. Adjustments are self-locking and energy only has to be applied to the system as needed to make individual adjustments of the reflector segments. Lasers can be used to transmit energy for the actuators, which can be an important reduction of prior art wiring costs or similar costs incurred using other energy transmitting methods. In addition, transmission losses would be minimal in space for laser light, which can be an important design cost factor for space-based systems. In space, the light source apparatus may be free-flying and may be directed to target points on the actuator mechanism using algorithms and methods associated with established metrology technologies. 
     A system according to an embodiment of the present invention can be used for active control whether the actuators are energized by laser light, piezoelectric material, or other methods; however, it is most applicable as an intermittently adjusted system when lasers are used. A laser-controlled system that uses this reflector system can be active if aberrations from the main reflector are corrected in real-time with controls on the sensor optics. 
     A segmented reflecting system according to an embodiment of the present invention realizes cost and weight savings advantages over the prior art because segment actuators can be of miniature size, low mass, and low-cost. Automated fabrication techniques such as laser metal sintering, which require no specialized tooling, can be used for efficient component fabrication. Low cost design attributes will be important to production of any large-scale segmented precision mirror or antenna—especially when the system must have numerous segments. For instance, a circular reflecting system with a 10 meter (m) aperture and 10 centimeter (cm) diameter segments would require approximately 7,800 segments. Competing systems that use multiple conventional linear actuators for each segment would have to multiply weights and costs by the number of actuators per segment. If each conventional actuator must be connected into a structure on each end and there were three actuators per reflector segment, the number of connection features would be 46,800. By way of contrast, an embodiment of the present invention allows for just one actuator per segment that can be easily attached with magnetic attraction, avoiding fasteners or adhesives. In addition, these actuators allow wide travel with unlimited angular range and ultra-precision adjustment. While the actuators can accommodate extremely fine movements, the adjustment beam will compound the degree of adjustment precision based on the length of the beam. 
     A lightweight system, according to one embodiment, may be best suited for space applications where wind and gravity loads are not factors. With structures sized for wind and gravity loads, however, an embodiment of the present invention is applicable to land-based systems. One embodiment of the present invention, for example, allows the reflecting system to adapt to changing gravity loads and other factors that cause deformations. In addition, low weight terrestrial reflector systems may result in positive benefits for support structure designs, such as in reducing costs of beam elements and control devices. In one embodiment, a land-based telescope could be provided with significantly higher precision and light-collecting capacity than any existing land-based telescope. Since weight will be less important for land-based applications, the actuators could be wired rather than remotely energized so that it may be advantageous for terrestrial applications to change the actuator activation from thermal actuation to piezoelectric or some similar type of device. 
     Embodiments of the present invention include low areal density adaptive reflecting systems for terrestrial and space-based applications. While a practical and lightweight solution is disclosed for reflecting systems, which allows precise and adaptive angular control of reflecting elements, some applications may require focusing with wavelength phase control. Methods to adaptively control the distance of the reflective elements to the focal point of the system may be integrated into the adaptive reflector system that is disclosed here, with the angular control of the reflector segments accomplished as enabled by the present invention. For instance, actuators can be conceived that function in a manner similar to the mechanism disclosed in the present invention which would individually adjust distances of the reflector segments to the focal point of the system. As an alternative to incorporating additional control in the reflector system for focusing, adaptive sensor optics can be used to accommodate aberrations due to wavelength phasing for applications where this is necessary. 
     Referring now to the figures, in which like items are referenced with the same numeral,  FIG. 1  shows a plan view of an adaptive, segmented, reflecting system  100  in accordance with one embodiment. System  100 , for example, may be an optical reflector system for a space telescope or an antenna system array. It will be understood that system  100  may include any mechanical system which may be moved or adjusted with an actuator mechanism and the illustration of an optical reflector or antenna system is for simplicity and ease of discussion. Further, it will be understood that system  100  may be used to transmit or receive electromagnetic radiation in a wavelength region of interest. For example, it is well known in the art that it may be desirable to collect light in the visible or infrared wavelength regions. Further, it will be understood that the chosen wavelength region of interest does not restrict the scope of the invention in any way. 
     System  100  may comprise an array, as shown in  FIG. 1 , of independent reflector segments  106  arranged on a space frame structure  102  to form a system of any practical size and shape desired. Reflector segments  106  may be connected to frame structure  102  at nodes  104 . Generally, reflector segments  106  may be circular or hexagonal in shape, although it may be understood that reflector segments may have any shape for a desired reflective characteristic, such as rectangular, triangular, or the like. Further, reflective surfaces of reflector segments  106  may be curved or flat. 
       FIG. 2  shows a side view of system  100 , in which it is more clearly seen that each reflector segment  106  may be rigidly attached to an adjustment beam  110 .  FIG. 2  also shows that each adjustment beam  110  may be connected to frame structure  102  at nodes  104 , so that reflector segments  106  may be connected to frame structure  102  at nodes  104 , as described above. 
     As more clearly shown in  FIG. 3 , adjustment beam  110  may be connected to frame structure  102  at node  104  with a spherical joint  108 . Spherical joint  108  is shown in cross section in  FIG. 3 . Spherical joint  108  may allow movement of adjustment beam  110  at node  104  on frame structure  102 . For example, spherical joint  108  may allow angular movement of adjustment beam  110  relative to frame structure  102  so that reflector segment  106  may be adjusted to provide focusing of adaptive, segmented, reflecting system  100 . Reflector segments  106 , space frame structure  102 , and adjustment beam  110  may be fabricated, for example, from aluminum, titanium, or other appropriately strong and lightweight materials. 
       FIG. 4A  shows the full length of adjustment beam  110  along with a side view, similar to  FIGS. 2 and 3 , of a reflector segment  106  and a portion of space frame structure  102 .  FIG. 4B  shows a detail view of the indicated portion of  FIG. 4A . As shown in  FIGS. 4A and 4B , system  100  may include a diamagnetic support membrane structure  112 , which may be comprised of a nonferrous material—such as aluminum—or a lightweight composite material—such as graphite with resin—and thin membrane structural elements. 
     Membrane structure  112  may support a plurality of actuators, such as actuator  114 . Actuator  114  may be magnetically coupled to support membrane structure  112 , for example, through magnetic attraction of ferromagnetic plug  132  to magnetic region  128  through diamagnetic support membrane structure  112  or by magnetic attraction of outer ring-like band  134  to magnetic region  126  through diamagnetic support membrane structure  112 , as seen more clearly in  FIG. 5 . Actuator  114  may be magnetically coupled, or attached, to an adjustment beam  110  at the end of adjustment beam  110 . Thus, the end of adjustment beam  110  may be attached to support membrane structure  112  via actuator  114 . Furthermore, support membrane structure  112  may be attached to frame structure  102  with truss elements or the like. 
       FIG. 4A  also shows adjustment beam  110  and reflector segment  106  at a first position A. A second position B of adjustment beam  110  (marked  110 ′) and corresponding second position B of reflector segment  106  (marked  106 ′), achieved by movement of actuator  114  from a first position A to a second position B, is shown in phantom. As shown in  FIG. 4A , movement of actuator  114  from first position A to second position B may cause adjustment beam  110  to pivot about spherical joint  108  at node  104 , producing an angular deflection of reflector segment  106  about spherical joint  108 . It should be noted that the angular deflection of reflector segment  106  is shown exaggerated in  FIG. 4A  for greater clarity of illustration and is not shown to scale with the angular deflection of adjustment beam  110 . The long lever arm provided by adjustment beam  110  between actuator  114  and spherical joint  108  compared to the short lever arm provided by adjustment beam  110  between spherical joint  108  and reflector segment  106  provides a large mechanical advantage to actuator  114 . Thus, the force required of actuator  114  can be small, as described above. Also the longer adjustment beam  110  is made, the greater is the mechanical advantage, and the finer is the adjustment of reflector segment  106  for a given movement of actuator  114 . Thus, the precision of adjustments to reflector segments  106  can be increased as desired by increasing the length of adjustment beam  110 . 
     Referring now to  FIGS. 5 and 6 ,  FIG. 5  shows a more detailed cross-sectional view from the same direction as the side view of  FIG. 4B , and shows actuator mechanism  114 , a portion of support membrane structure  112 , and the end of adjustment beam  110  of adaptive, segmented, reflecting system  100  in accordance with one embodiment. Actuator mechanism  114  may include a ferromagnetic plug  132 , which may be shaped, for example, in the form of a flat, circular disk, as viewed from the side in  FIG. 5  and as viewed from the top in  FIG. 6 . Ferromagnetic plug  132  may include a ferromagnetic material such as iron, cobalt, or nickel, for example. Ferromagnetic plug  132  may be positioned on, and in contact with, a surface  133  of support membrane structure  112 . A center ring-like band  130  may be attached to ferromagnetic plug  132  near the top, or portion, of ferromagnetic plug  132  that is furthest away from surface  133 , as shown in cross section in  FIG. 5 . Center band  130  may be a flat, annular disk and may be formed so that center band  130  may encircle the disk portion of ferromagnetic plug  132 . Thus, a portion of center band  130  is shown on either side of ferromagnetic plug  132  in the cross section view of  FIG. 5 , and the inside boundary of center band  130  is indicated by a dashed circle in the top view of  FIG. 6 , with a second dashed circle indicating an outside boundary of ferromagnetic plug  132 . A gap  131  may be left between center band  130  and ferromagnetic plug  132 , where center band  130  encircles ferromagnetic plug  132 . Gap  131  may provide thermal insulation between center band  130  and ferromagnetic plug  132 . Center band  130  may be positioned on, and in contact with, surface  133  of support membrane structure  112 . 
     Although circular shapes have been chosen to illustrate one embodiment of actuator  114 , it is conceivable that other geometric shapes could be used for any of ferromagnetic plug  132 , center band  130 , and outer band  134 . Referring to the shape of any of these as the shape of actuator  114 , then, it may be said that while the actuator  114  is shown circular, it could function as any shape. For example, actuator  114  could be square, hexagonal, triangular, an oval with the 2 foci separated only by a small distance, an ovoid, a 20-sided regular polygon, or the like. The actuator  114  does not need to be circular, but it is an obvious design choice to control any angular movement of the reflector segments due to the circle&#39;s symmetry to itself in all directions. The circular shape also lends itself to ease of manufacture. Nevertheless, it is conceivable that some other shape may be chosen to meet some particular design consideration for a special application. 
     Ferromagnetic plug  132  may include ferrous material, for example, and may have a relatively low coefficient of friction relative to surface  133  of support membrane structure  112 . Center band  130  may be made of practically any material to include aluminum, titanium, or a variety of plastics. Center band  130  may have a relatively high coefficient of friction relative to surface  133  of support membrane structure  112 . The coefficient of thermal expansion of ferromagnetic plug  132  may be sufficiently large so that when ferromagnetic plug  132  is heated, for example, by a laser beam, ferromagnetic plug  132  may be capable of expanding in a direction perpendicular to surface  133  of support membrane structure  112  far enough to lift center band  130  away from and out of contact with surface  133 . Thus, the assembly comprising ferromagnetic plug  132  and center band  130  may be “switched” between having a high coefficient of friction and a low coefficient of friction on surface  133  depending on whether ferromagnetic plug  132  is, respectively, either cooled or heated. Gap  131  may improve the lifting action by helping to confine heating and expanding action to ferromagnetic plug  132 , so that heating and expanding of center band  130  may be minimized. A reflective target  140 , shown in  FIG. 6 , may be positioned on a center  141  of ferromagnetic plug  132 . Target  140  may guide an energy beam, for example, a laser beam, to ferromagnetic plug  132 , and may, thus, improve the efficacy of energizing, i.e., heating, ferromagnetic plug  132 . 
     An outer band  134  with a relatively medium coefficient of friction—intermediate between that of ferromagnetic plug  132  and that of center band  130 —may be positioned on, and in contact with, surface  133  of support membrane structure  112 . Outer band  134  may encircle ferromagnetic plug  132  and center band  130  as shown in  FIG. 6 . Outer band  134  may be adjacent to, and also encircle, an actuator material region  124 . Further, outer band  134  may be fixedly attached to actuator material region  124 . Actuator material region  124  may be positioned on or above surface  133  of support membrane structure  112  and adjacent to outer band  134 . Actuator material region  124  may encircle center band  130  and may be separated from center band  130  by a gap  142  as shown in  FIGS. 5 and 6 . The material of actuator material region  124  may be chosen to have a coefficient of thermal expansion so that portions of actuator material region  124  may be capable of expanding in a direction parallel to surface  133  of support membrane structure  112  by an amount, for example, that is twice the width of gap  142 . Thus, by heating and expanding a portion of actuator material region  124 , closing gap  142 , actuator material region  124  can be used to transmit forces between center band  130  and outer band  134  in a direction parallel to surface  133 . 
     As illustrated in  FIG. 6 , actuator material region  124  may include a plurality of slots  138  extending radially outward from gap  142  around ferromagnetic plug  132 , diverging from center  141  of ferromagnetic plug  132 , forming a plurality of finger-like segments  125  in actuator material region  124 . Slots  138  may inhibit heat conduction between adjacent segments  125  of actuator material region  124  so that selective heating of a desired portion, for example, a single segment  125 , of actuator material region  124  may be achieved. Furthermore, each segment  125  in the plurality of segments  125  may be capable of independently expanding, as it is heated, towards center  141  of ferromagnetic plug  132  and transmitting a force between outer band  134  and center band  130  in a direction parallel to surface  133  of support membrane structure  112 . 
     For example, when the assembly comprising ferromagnetic plug  132  and center band  130  is “switched” to a low coefficient of friction (heated state), force transmitted between the low friction assembly and medium friction outer band  134  may result in movement of the assembly relative to surface  133  while outer band  134  stays still. Conversely, when the assembly comprising ferromagnetic plug  132  and center band  130  is “switched” to a high coefficient of friction (cooled state), force transmitted between the high friction assembly and medium friction outer band  134  may result in movement of outer band  134  relative to surface  133  while the assembly stays still. Thus, by energizing and causing thermal expansion of portions of actuator material region  124  in coordination with “switching” of the assembly comprising ferromagnetic plug  132  and center band  130 , actuator  114  can be walked across surface  133 , as described in more detail below. 
     The coefficient of thermal expansion of actuator material region  124  may be chosen to tailor the speed and precision of actuator  114 . For example, a lower coefficient of thermal expansion may cause the energized portion of actuator material region  124  to expand less for a given amount of energy input so that actuator  114  moves a smaller distance for the given amount of energy input, decreasing the speed of actuator  114  and concomitantly increasing the precision of adjustments, for example, to reflector segment  106 , made by actuator  114 . Conversely, a higher coefficient of thermal expansion of actuator material region  124  may increase the speed and concomitantly decrease the precision of adjustments made, for example, to reflector segment  106  by actuator  114 . 
     Actuator mechanism  114  may include a magnetic region  128  positioned on a surface  135  of support membrane structure  112 . Magnetic region  128  may include a ferromagnetic material—such as iron, cobalt, or nickel—and may be a ferrous permanent magnet, for example. Magnetic region  128  may be magnetically coupled to ferromagnetic plug  132 . The magnetic coupling between magnetic region  128  and ferromagnetic plug  132  may hold magnetic region  128  and ferromagnetic plug  132  on support membrane structure  112  while allowing magnetic region  128  and ferromagnetic plug  132  to slide along surfaces  135  and  133 , respectively. Furthermore, a magnetic region  126  may be positioned on surface  135  of support membrane structure  112  and may be magnetically coupled to outer band  134 . Magnetic region  126  may include a ferromagnetic material—such as iron, cobalt, or nickel—and also may be, for example, a ferrous permanent magnet. The magnetic coupling between magnetic region  126  and outer band  134  may hold magnetic region  126  and outer band  134  on support membrane structure  112  while allowing magnetic region  126  and outer band  134  to slide along surfaces  135  and  133 , respectively. Further, it may be understood that magnetic region  126  may include a band structure or a plurality of individual elements. 
     Adjustment beam  110  may be magnetically coupled to magnetic region  128  with an end cap  122  fixedly attached to adjustment beam  110 . It may be understood that end cap  122  may include a magnetic material which magnetically couples end cap  122  with magnetic region  128 . Furthermore, it may be understood that adjustment beam  110  may be attached to magnetic region  128  in an alternative embodiment to the one illustrated in  FIGS. 5 and 6 . 
     In operation, actuator  114  may be energized to move from a position A to a second position B as shown in  FIGS. 4A and 5 . As shown in more detail in  FIG. 5 , center  141  may move a distance d 1    144  from a point A to a point B by selectively heating and cooling select segments  125  of actuator mechanism  114  in a sequence of events illustrated in  FIGS. 7 through 14 . 
       FIGS. 7 through 14  illustrate several views of a sequence of events as actuator mechanism  114  moves along support membrane structure  112  from point A to point B. Referring specifically to  FIGS. 7 and 8 , an energy source (not shown) may direct a beam of energy onto ferromagnetic plug  132  so that plug  132  expands. In the embodiment illustrated in  FIGS. 7 through 14 , the energy source may include a source of electromagnetic radiation—such as light, infrared, or microwave—with a wavelength λ 1    152  where the electromagnetic radiation source may be a laser, for example. Furthermore, it may be understood that reflective target  140  may be used for laser alignment, i.e. to guide the electromagnetic radiation to plug  132 . As plug  132  expands, center band  130  may be lifted off of surface  133  to form a gap  136  between band  130  and surface  133 . Thus, center band  130  may be frictionally disengaged from surface  133 . Furthermore, outer band  134  may be centered about center  141 , as shown in  FIG. 8 . Outer band  134  may be centered about center  141  when a width of actuator material region  124  is equal to d 2    146  for all angles around center  141 . 
     Referring now to  FIGS. 9 and 10 , the energy source may apply heat to actuator material region  124  at a Position  1  so that region  124  expands at Position  1  and distance d 2    146  at Position  1  increases to a distance d 3    148 , as shown in  FIG. 10 . Consequently, center  141  moves by a small increment from Point A to Point B as desired. In general, the expansion of actuator material region  124  may be no more than twice gap  142 , although it is shown larger for simplicity and illustrative purposes. Furthermore, it should be understood that the small movement may not be sufficient to compress actuator material region  124  at Position  2  as is depicted in the illustration. Thus, the illustrations in  FIGS. 9 and 10  are not drawn to scale. 
     In the embodiment illustrated in  FIGS. 7 through 14 , the energy source may include an electromagnetic radiation source with a wavelength λ 1    152  where the electromagnetic radiation source may be a laser, for example. The distance between center band  130  and outer band  134  at a Position  2  may decrease to a distance d 4    150  as center band  130  is moved within gap  142  between actuator material region  124  and center band  130 . Actuator material region  124  at Position  1  may expand towards center  141  as illustrated while outer band  134  is frictionally held in place because the coefficient of friction of band  134  is greater than the coefficient of friction of plug  132 . Thus, outer band  134  is no longer centered about center  141 . 
     Referring now to  FIGS. 11 and 12 , the energy source may be removed from ferromagnetic plug  132  so that ferromagnetic plug  132  decreases in temperature and contracts so that center band  130  frictionally engages surface  133 . Outer band  134  may be no longer centered about center  141  as illustrated in  FIG. 12 . 
     Referring now to  FIGS. 13 and 14 , the energy input may be removed from actuator material region  124  at Position  1  and ferromagnetic plug  132  may be held in place by the coefficient of friction of center band  130 . Furthermore, a heat source may be applied to actuator material region  124  at Position  2 , as shown in  FIG. 12 , to realign outer band  134  around center  141  as illustrated in  FIG. 14 , where the previous position of outer band  134  is shown in phantom as outer band  134 ′. Actuator material  124  at Position  2  will expand in a direction away from center  141  because the coefficient of friction of center band  130  is greater than the coefficient of friction of outer band  134 . Thus, outer band  134  will become centered about center  141  as distance d 4    150  increases to d 2    146 . 
     It may be understood that one or more lasers may be used to heat ferromagnetic plug  132  and actuator material region  124 . Furthermore, it may be understood that the lasers may have the same wavelength or may have different wavelengths where the wavelength λ 1    152  or λ 2    154  may be chosen for the material included in ferromagnetic plug  132  and actuator material region  124 . 
     A method of moving actuator mechanism  114  along a support membrane structure  112 , in accordance with the present invention may begin with a step of heating a ferromagnetic plug  132  until center band  130  lifts off of surface  133 . Actuator material region  124  may be heated at a Position  1  until actuator material region  124  at Position  1  expands and moves center  141  from Point A to Point B. Ferromagnetic plug  132  may be cooled by removing the heat to plug  132  so that plug  132  contracts and center band  130  frictionally engages surface  133 . Actuator material region  124  at a Position  2  may be heated so that region  124  at Position  2  expands in a direction away from center  141  so that outer band  134  becomes centered about center  141 . Once outer band  134  may be centered, the input of heat may be removed from actuator material region  124  at Position  2 . The process may be repeated to again move center  141  until actuator mechanism  114  may be moved to the desired position. 
       FIG. 15  illustrates an actuator mechanism  180 , in accordance with another embodiment of the present invention, in which the heat source includes a current source. Actuator mechanism  180  may include a conductive terminal  182  electrically connected to ferromagnetic plug  132  and conductive terminals  184  and  186  electrically connected to actuator material region  124  at Positions  1  and  2 , respectively. Hence, conductive terminals  182 ,  184 , and  186  may be used to provide an electric current to actuator material region  124  or plug  132  and heat actuator material region  124  and plug  132  as discussed above in  FIGS. 7 through 14 . 
     It should be understood, of course, that the foregoing relates to preferred embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.