Abstract:
An embodiment of the present method may comprise: heating up at least one structural element beyond a change state temperature thereof; changing the configuration of the structural element from an extended configuration to a reduced size configuration; cooling the structural element to below the change state temperature thereof; covering the structural element with a thermal protection device; removing the thermal protection device to expose the structural element to heat radiation; and heating, via the heat radiation, at least a portion of the structural element to thereby cause the structural element to change from the reduced size configuration to the extended configuration. In one embodiment each of the structural elements is formed from a thin elastic memory composite material.

Description:
TECHNICAL FIELD 
     The invention relates generally to elastic memory composite structures and, more specifically, occulters that utilize elastic memory composite structures. 
     BACKGROUND 
     Currently, the direct detection of extrasolar planets (or exoplanets) is extremely difficult. This is primarily because exoplanets appear extremely close to their host stars when observed at astronomical distances. Also, exoplanets are incredibly dim compared to their host stars. Typically, the star will be approximately a billion times brighter than the orbiting planet. This makes it near-impossible to see planets against the star&#39;s glare. The difficulty of observing such a dim planet so close to a bright star is the obstacle that has prevented astronomers from directly photographing exoplanets. 
     It has been proposed to use an occulter to overcome the difficulty of distinguishing a planet in the glare of a bright star. The occulter would block all of the starlight from reaching the observing, while allowing the planet&#39;s light to pass undisturbed. This would allow the direct observation of orbiting planets. 
     The occulter may be a large sheet disc flown thousands of kilometers along the line of sight. The disc would likely be several tens of meters in diameter. One difficulty with this concept is that light incoming from the target star would diffract around the disc and constructively interfere along the central axis. Thus the starlight would still be easily visible, making planet detection impossible. Fortunately this effect can be negated be specifically shaping the occulter. By adding specially shaped petals to the outer edge of the disc, the starlight will disappear, allowing the suppression of the star&#39;s light. However, it is a drawback of the prior art that such structures are too large to be launched into space. 
     Thus, there is a need in the art for an improved structure that may be deployed after it launched into space. 
     SUMMARY 
     One embodiment of the present method and apparatus encompasses an apparatus. The apparatus may have: at least one heat radiation activated deployable structure; and a heat shield assembly that shields the deployable structure in a first position and that exposes the deployable structure to heat radiation in a second position. 
     Another embodiment of the present method and apparatus encompasses a method. The method may comprise: heating up at least one structural element beyond a change state temperature thereof; changing the configuration of the structural element from an extended configuration to a reduced size configuration; cooling the structural element to below the change state temperature thereof; covering the structural element with a thermal protection device; removing the thermal protection device to expose the structural element to heat radiation; and heating, via the heat radiation, at least a portion of the structural element to thereby cause the structural element to change from the reduced size configuration to the extended configuration. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The features of the embodiments of the present method and apparatus are set forth with particularity in the appended claims. These embodiments may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which: 
         FIG. 1  depicts a star shade according to the present method and apparatus. 
         FIG. 2  is a side view of a petal that has a tapered configuration. 
         FIG. 3  depicts a petal formed of the elastic memory composite material that has a curved shape across its width to provide a degree of structural stability. 
         FIG. 4  depicts a petal formed of the elastic memory composite material that has a flat shape across its width. 
         FIG. 5  depicts an embodiment in which a structural element is in a compact configuration and protected by a thermal protection device. 
         FIG. 6  depicts an embodiment in which a structural element is in a compact configuration, but is no longer protected by the thermal protection device. 
         FIGS. 7-10  depict a deployment of a structural element. 
     
    
    
     DETAILED DESCRIPTION 
     In order to prevent the incredibly bright star from overwhelming a planet&#39;s much dimmer light, the starlight may be blocked with an occulter. An occulter is simply an object that prevents light from another object from reaching the observer. For example, during a solar eclipse, the moon occults the sun. By making a large enough disc and launching it into space any star&#39;s light may be blocked out, allowing the planets around the star to be viewed. 
     The basic concept for this design is reasonably simple. However there are details that must be considered with this idea. The most challenging obstacle is caused by diffraction. Diffraction is the bending of waves around a corner. Thus the starlight hitting the edge of the occulting disc will diffract around the edge and still be visible, defeating the purpose of the occulter. 
     When two waves of light meet, they interfere with each other. If the two waves are “in phase” (i.e. their crests and troughs line up) then the waves interfere constructively. This means that the two waves add together to create a bright spot. If the two waves are out of phase (the crests of one wave line up with the troughs of another), then they combine destructively. This means that the two waves effectively cancel each other out, leaving a dark spot. 
     If one were to use the disc shaped occulter and stand behind it, one would see a bright ring around the edge. Because the light traveling around the disc all travels the same length to reach one&#39;s eyeball, they are all in phase with each other, thus they constructively interfere. 
     Fortunately, by specially designing the occulting disc, the constructive diffraction may be eliminated. By adding petals onto the disc&#39;s edge, the path length of each ray of light is offset just enough so that the combined effect is destructive interference. As the light waves diffract around the petals, each ray of light will destructively interfere with another ray, therefore no light will be seen if one stands behind the starshade. The shadow created behind the occulter will be large enough to fly a space telescope within. By flying in the starshade&#39;s shadow, the telescope will be able to look for the faint planet-light without being blinded by the star&#39;s light. However, an actual shade would be too large to launch into space as is (a few tens of meters). Therefore it would have to be launch folded up inside a rocket and be unfolded in space. 
     In general, embodiments according to the present method and apparatus may be used for a variety of purposes, such as deployable star shades, long antennas, or other structures that must be stored in a compact configuration and them extended to a predetermined configuration. In order for the structure to change shape a thin elastic memory composite (EMC) material may be used. 
     EMC materials are similar to traditional fiber-reinforced composites except for the use of an elastic memory thermoset resin-matrix. The elastic memory matrix is a fully cured polymer, which can be combined with a wide variety of fiber and particulate reinforcements and fillers. The unique properties of the matrix enable EMC materials to achieve high packaging strains without damage. Strains are induced by elevating the temperature of the EMC material and then applying a mechanical force. The shape memory characteristics enable the high packaging strains to be “frozen” into the EMC by cooling. Deployment (i.e., shape recovery) is effected by elevating the temperature. The temperature at which these operations occur is adjustable. 
     At lower temperatures, the performance of EMC materials follows classical composite laminate theory. At higher temperatures, EMCs exhibit dramatically reduced stiffnesses due to significant matrix softening of the resin. Adequately addressing the mechanics of the “soft-resin” will enable the EMC materials to provide repeatable stowage and deployment performance without damage and or performance changes. Products fabricated from these materials can be deformed and reformed repeatedly. Products utilizing EMC materials can be fabricated with conventional composite fabrication processes and tooling. 
       FIG. 1  depicts a star shade according to the present method and apparatus. The star shade embodiment may, for example, have a plurality of petals  101  or, in general, structural elements that are operatively coupled to a base structure  102 . It is to be understood that the star shade may have more or less than the number of petals  101  depicted in  FIG. 1 . 
       FIG. 2  is a side view of a petal  201  that has a tapered configuration. In this embodiment the structural elements  201  or membranes may be approximately 25 meters long and may taper to a point. The structural element  201  may, for example, be formed from a thin (approximately 0.15 inches thick) elastic memory composite material. 
       FIG. 3  depicts a petal  301  formed of the elastic memory composite material that has a curved shape across its width to provide a degree of structural stability. 
       FIG. 4  depicts a petal  401  formed of the elastic memory composite material that has a flat shape across its width. Other cross sectional shapes and structural shapes in general are within the embodiments of the present method and apparatus. 
       FIG. 5  depicts an embodiment in which a structural element is in a compact configuration and protected by a thermal protection device. For storage the structural element  501  may be heated up beyond its change state temperature and then rolled onto a mandrel  502 , The structural element  501  may be covered by a thermal protection device  503  during, for example, a launch phase when a device, such as a star shade, is to be utilized in space. 
     A first end  504  of the thermal protection device  503  may be permanently attached to a base  505 . A second end  506  of the thermal protection device  503  may be releaseably attached to the base  505  by a latch  507 . The thermal protection device  503  may be made of a variety of materials, such as spring steel. 
       FIG. 6  depicts an embodiment in which a structural element is in a compact configuration, but is no longer protected by the thermal protection device. When in position for deployment, the thermal protection device  603  may be removed or withdrawn by releasing the latch  607 . In the depicted embodiment the second end  606  of the thermal protection device  603  has been released and the first end  604  is still attached to the body  605 . With the thermal protection device  603  in an open position, the sun would warm an outside area  608  of the roll of the structural element  601  causing the structural element  601  to return to its original shape. As the structural element  601  straightens out more of the roll of the structural element  601  is revealed causing further deployment until the entire structural element  601  is deployed. 
       FIGS. 7-10  depict a deployment of a structural element.  FIG. 7  shows a structural element  701  that has been rolled onto a mandrel  702 . A first end  703  of the structural element  701  is attached to a body  704 . Heat radiation  705 , such as from the sun, is absorbed in an area  706  of the structural element  701  causing the structural element  701  to return to its original shape. 
       FIGS. 8 ,  9  and  10  show the structural element  701  in various stages as the structural element  701  unrolls. Finally, in  FIG. 10  the structural element  701  is completely unrolled. 
     It is to be understood that embodiments of the present method and apparatus may have a variety of different shapes and configurations, and may be formed from a variety of different materials. Depending upon the application, there may be one or a plurality of structural elements. Also, the plurality of structural elements may be arranged indifferent configurations relative to one another depending upon the application. 
     The present method and apparatus are not limited to the particular details of the depicted embodiments and other modifications and applications are contemplated. Certain other changes may be made in the above-described embodiments without departing from the true spirit and scope of the present method and apparatus herein involved. It is intended, therefore, that the subject matter in the above depiction shall be interpreted as illustrative and not in a limiting sense.