Abstract:
Disclosed is a thermal control apparatus which comprises a base plate associated with a target object in a heat-exchangeable manner therebetween, at least one heat-exchange paddle attached to the base plate in such a manner as to be selectively deployed and retracted, paddle drive means provided at an end of the base plate and adapted to drive a deployment movement and a retraction movement of the heat-exchange paddle so as to change an angle of the heat-exchange paddle, and a heat transport element provided to connect the base plate and the heat-exchange paddle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present patent application claims priority from Japanese Patent Application No. 2007-111144, filed on Apr. 20, 2007. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a thermal control apparatus suitable for use in cosmic environments or ground environments with large temperature changes, to thermally control a device, such as an on-board device for spacecrafts. 
         [0004]    2. Description of the Related Art 
         [0005]    In spacecrafts to be exposed to both low-temperature and high-temperature environments, it is necessary to keep an on-board device within an allowable temperature range. Typically, a thermal design for the on-board device is performed in conformity to high temperature environments, and a temperature-keeping control based on heating with a heater is combined therewith in low-temperature environments. However, in spacecrafts to be exposed to large environmental changes, such as moon/planetary probe vehicles, a power consumption of the heater will be unacceptably increased to cause difficulty in realizing thermal design. 
         [0006]    A “thermal louver” and a “deployable radiator” have been known as conventional thermal control techniques for spacecrafts. The thermal louver is capable of passively coping with changes in thermal environment, whereas it involves problems, such as incapability of increasing an amount of heat dissipation, structural complexity and heavy weight. The deployable radiator intended to promote heat dissipation is deployable only in a unidirectional manner, and therefore incapable of coping with thermal control in low-temperature environments by itself. Moreover, the deployable radiator is typically used in combination with a heat pipe or a fluid loop serving as a heat transport element for efficiently transporting heat to a paddle, which leads to a heavy and complicated mechanism, and is therefore applicable only to large spacecrafts. 
       SUMMARY OF THE INVENTION 
       [0007]    In view of the above conventional problems, it is an object of the present invention to provide a novel thermal control apparatus capable of facilitating weight reduction and structural/mechanistic simplification, and desirably usable in spacecraft environments or ground environments with large temperature differences. 
         [0008]    In order to achieve this object, the present invention provides a thermal control apparatus which comprises a base plate associated with a target object in a heat-exchangeable manner therebetween, at least one heat-exchange paddle attached to the base plate in such a manner as to be selectively deployed and retracted, paddle drive means provided at an end of the base plate and adapted to drive a deployment movement and a retraction movement of the heat-exchange paddle so as to change an angle of the heat-exchange paddle, and a heat transport element provided to connect the base plate and the heat-exchange paddle. In this thermal control apparatus, the base plate has a first surface on an opposite side relative to the target object, and the heat-exchange paddle has a second surface which is a front surface thereof, and a third surface which is a rear surface thereof. The first, second and third surfaces are ones selected from the group consisting of a heat-dissipating surface, a heat-absorbing surface, a heat-insulating surface and a variable heat-emissivity surface. Further, the paddle drive means is adapted to variably set a deployed angle of the heat-exchange paddle. 
         [0009]    Preferably, the paddle drive means is one selected from the group consisting of: a reversible shape memory alloy; a bimetal; a unidirectional or bidirectional paraffin actuator; drive means using a combination of a unidirectional shape memory alloy and a biasing spring; an electrically-driven motor; a spring drive mechanism; and a manual drive mechanism. In this case, the shape memory alloy may be a heat pipe-type shape memory alloy having a heat pipe structure incorporated therein. 
         [0010]    Preferably, the heat transport element is a graphite sheet or a carbon fiber fabric. 
         [0011]    The heat transport element may comprise a heat pipe or a fluid loop. 
         [0012]    The heat-dissipating surface may have one selected from the group consisting of a silver-deposited polyetherimide film, an aluminum-deposited teflon film, an optical solar reflector (OSR), a white-colored paint film, a black-colored paint film and a multilayer thin film. 
         [0013]    The heat-absorbing surface may have one selected from the group consisting of a graphite sheet, a selective heat-absorptive coating, a black-colored coating and a multilayer thin film. 
         [0014]    The variable heat-emissivity surface may have a perovskite-structured manganese oxide film or a vanadium oxide film. In the case where, the variable heat-emissivity surface has the perovskite-structured manganese oxide film, it may further include a multilayer thin film. 
         [0015]    The heat-insulating surface may have one selected from the group consisting of a metal-deposited film, a multilayer heat-insulating material and a foamed heat-insulating material. 
         [0016]    The thermal control apparatus can accelerate heat-dissipation, maintain temperature and absorb heat in a selective manner by a single apparatus, to facilitate reduction in weight and energy consumption of a spacecraft. In addition, when the spacecraft lands on the Moon, the thermal control apparatus can dissipate and absorb heat during daylight and maintain temperature at night by a single apparatus. Further, the thermal control apparatus can protect an on-board device from contamination due to flying regoliths on the lunar surface. The deployed angle of the paddle can be changed to adjust a heat-dissipation characteristic and a heat-absorption characteristic. The adjustment of the paddle deployed angle makes it possible to autonomously compensate degradation in the heat-dissipation characteristic. 
         [0017]    The thermal control apparatus of the present invention can be used as a lightweight deployable radiator for a small satellite. This makes it possible to provide a simplified deployable radiator while achieving enhanced reliability. Further, a high-temperature-heat transport graphite sheet may be used as the heat transport element to eliminate a need for using liquid so as to avoid the problem about freezing of the liquid at low temperatures. 
         [0018]    Based on the above advantages, the thermal control apparatus makes it possible to thermally control an on-board device with enhanced efficiency not only in cosmic environments but also ground environments, such as desert regions and vicinities of the Polar Regions. 
         [0019]    These and other objects, features and advantages of the invention will become more apparent upon reading the following detailed description along with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a sectional view showing a thermal control apparatus  10  according to a first embodiment of the present invention. 
           [0021]      FIG. 2  is a schematic diagram showing a thermal control apparatus for a medium or large spacecraft, according to a second embodiment of the present invention, wherein a fluid loop is employed. 
           [0022]      FIG. 3  is a schematic diagram showing the thermal control apparatus according to the second embodiment. 
           [0023]      FIG. 4  is a schematic diagram showing a thermal control apparatus for a medium or large spacecraft, according to a third embodiment of the present invention, wherein a combination of a fluid loop and a high-temperature-heat transport element is employed. 
           [0024]      FIG. 5  is a schematic diagram showing the thermal control apparatus according to the third embodiment. 
           [0025]      FIG. 6  is a schematic diagram showing a thermal control apparatus according to a fourth embodiment of the present invention, which is suitable for use in celestial objects, such as the Moon and Mars, and polar environments of the Earth. 
           [0026]      FIG. 7  is a schematic diagram showing the thermal control apparatus according to the fourth embodiment. 
           [0027]      FIG. 8  is a conceptual diagram showing a radiator for a small satellite, according to a fifth embodiment of the present invention. 
           [0028]      FIG. 9  is a conceptual diagram showing the radiator according to the fifth embodiment. 
           [0029]      FIG. 10  is a conceptual diagram showing an energy storage system according to a sixth embodiment of the present invention. 
           [0030]      FIG. 11  is a conceptual diagram showing the energy storage system according to the sixth embodiment. 
           [0031]      FIGS. 12(   a ) to  12 ( f ) are explanatory diagrams showing various layouts of a high-temperature-heat transport element in a thermal control apparatus according to a seven embodiment of the present invention. 
           [0032]      FIG. 13  is a table showing a summary of structural elements/configurations applicable to a thermal control apparatus of the present invention. 
           [0033]      FIG. 14  is a table showing a summary of materials/mechanisms applicable to components/elements of a thermal control apparatus of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0034]    With reference to the drawings, various embodiments of the present invention will now be described. 
       First Embodiment 
       [0035]      FIG. 1  is a sectional view showing a thermal control apparatus  10  according to a first embodiment of the present invention, wherein a left half thereof shows a state after a paddle of the thermal control apparatus is closed (i.e., retracted), and a right half thereof shows a state after the paddle is opened (i.e., deployed). The thermal control apparatus  10  according to the first embodiment is intended to be installed in a spacecraft, particularly in a small satellite. In  FIG. 1 , the reference numeral  1  indicates one of various on-board devices of a spacecraft, which are to be subjected to thermal control (hereinafter referred to as “target object”). The thermal control apparatus  10  comprises a base plate  15 . In the first embodiment, the base plate  15  is formed as a part of a satellite structure. 
         [0036]    As shown in  FIG. 1 , the thermal control apparatus  10  according to the first embodiment includes a pair of right and left deployable/retractable heat-exchange paddles  12   b ,  12   a  (hereinafter referred to as “deployable/retractable heat-exchange paddle  12 ” or “paddle  12 ” when they are collectively described). The paddle  12  serves as a means for heat-exchange with an external environment (in this embodiment, cosmic space). The paddle  12  has a front surface  16  which faces outwardly (i.e., faces the external environment) when deployed, and faces inwardly (i.e., faces the spacecraft or the on-board device), and a rear surface  17  on an opposite side of the front surface  16 . 
         [0037]    The rear surface  17  of the paddle  12  may be one selected from the group consisting of a heat-dissipating surface, a heat-absorbing surface, a heat-insulating surface and a variable heat-emissivity surface. As used in this specification, the term “heat-dissipating surface” means one of the front and rear surfaces  16 ,  17  which has a heat-emissivity greater than the other surface (wherein the one surface may have a solar absorptance less than that of the other surface or may have a solar absorptance equal to or greater than that of the other surface). The term “heat-absorbing surface” means one of the front and rear surfaces  16 ,  17  which has a solar absorptance greater than the other surface (wherein the one surface may have a heat-emissivity less than that of the other surface or may have a heat-emissivity equal to or greater than that of the other surface). The term “heat-insulating surface” means a surface having a low heat-emissivity (heat conductivity) so as to prevent solar energy from being transferred (conducted) inside the paddle to suppress heat-exchange with the external environment. The term “variable heat-emissivity surface” means a surface which suppresses heat-dissipation at low temperatures and accelerates heat-dissipation at high temperatures, i.e., which exhibits a relatively low heat-emissivity at low temperatures and exhibits a relatively high emissivity at high temperatures. 
         [0038]    The thermal control apparatus  10  includes a heat transport element  13  serving as a means to transport heat. In the first embodiment, a high-temperature-heat transport graphite sheet is used as a material of the heat transport element  13 . The graphite sheet is desirable as a material of the heat transport element  13  because it has both high heat conductivity and flexibility. Alternatively, a high-temperature heat-conducting fluid may be used as the heat transport element  13 . In this case, the heat transport element  13  may be designed such that this fluid flows through a loop-shaped flexible hose pipe. 
         [0039]    The thermal control apparatus  10  includes a deploying/retracting mechanism  14  serving as a means to selectively deploy and retract the paddle  12 . The deploying/retracting mechanism  14  may be selected from a passive type or an active type. As the active type, one of a shape-memory alloy, a bimetal, a paraffin actuator, and a shape memory alloy having a heat pipe structure incorporated therein may be used to utilize a temperature-dependent change in spring force thereof (this mechanism may also be used in each of after-mentioned embodiments). As the active type, an electrically-heatable shape-memory alloy or an electrically-driven motor may be used. The target object  11  is connected to the deploying/retracting mechanism  14  directly or indirectly. That is, the deploying/retracting mechanism  14  is designed such that a temperature thereof is changed in conjunction with a change in temperature of the target object. 
         [0040]    The front and rear surfaces  16 ,  17  of the paddle  12  can be formed of ones selected from the aforementioned surfaces to perform a specific thermal control depending on an intended purpose. For example, if one of the surfaces which is to be exposed to the external environment when the paddle  12  is closed (i.e., retracted) (in the first embodiment, the rear surface  17 ) is formed as the heat-dissipating surface, the surface will function to accelerate heat-dissipation when the paddle  12  is retracted, so that the temperature of the target object  11  can be lowered. If the surface to be exposed to the external environment when the paddle  12  is retracted is formed as the heat-absorbing surface, it will function to suppress heat-dissipation and absorb solar light when the paddle  12  is retracted, so that the temperature of the target object  11  can be increased. If the surface to be exposed to the external environment when the paddle  12  is retracted is formed as the heat-insulating surface, it will function to suppress heat-exchange with the external environment when the paddle  12  is retracted, so that the temperature of the target object  11  can be maintained at a value when the paddle  12  is closed. If the surface to be exposed to the external environment when the paddle  12  is retracted is formed as the variable heat-emissivity surface, it will function to suppress heat-dissipation when the paddle  12  is retracted (at low temperatures), and to accelerate heat-dissipation when the paddle  12  is deployed (at high temperatures). 
         [0041]    In the first embodiment, the deploying/retracting mechanism  14  is designed to move the paddle  12  between a fully deployed position (full open position) and a fully retracted position (full closed position). In addition, the deploying/retracting mechanism  14  is designed to variably set the fully deployed position at any angle. Based on this function of changing the angle of the fully deployed position of the paddle  12 , an amount of heat-exchange can be adjusted to further adequately control the temperature of the target object  11 . 
         [0042]    The thermal control apparatus  10  according to the first embodiment can be installed in a spacecraft, such as a satellite, to obtain the following advantages. As one advantage, the thermal control apparatus  10  can accelerate heat-dissipation, maintain temperature and absorb heat by a single apparatus, to facilitate reduction in weight and energy consumption of the spacecraft. As another advantage, when the spacecraft lands on the Moon or Mars, the thermal control apparatus can dissipate and absorb heat during daylight and maintain temperature at night by a single apparatus. As yet another advantage, the thermal control apparatus can protect the heat-dissipating surface and the on-board device from contamination due to flying regoliths on the lunar surface. As still another advantage, the deployed angle of the paddle can be changed to adjust a heat-dissipation characteristic and a heat-absorption characteristic so as to autonomously compensate degradation in the heat-dissipation characteristic according to the adjustment of the deployed angle of the paddle. 
         [0043]    The thermal control apparatus  10  according to the first embodiment can be used as a lightweight deployable radiator for a small satellite. This makes it possible to provide a simplified deployable radiator while achieving enhanced reliability. Further, a high-temperature-heat transport graphite sheet may be used as the heat transport element  13  to eliminate a need for using liquid so as to avoid a problem about freezing of the liquid at low temperatures. 
         [0044]    Based on the above advantages, the thermal control apparatus  10  makes it possible to thermally control an on-board device with enhanced efficiency not only in cosmic environments but also ground environments, such as desert regions and vicinities of the Polar Regions. 
       Second Embodiment 
       [0045]    As a second embodiment of the present invention, a thermal control apparatus  21  for a medium or large spacecraft, which employs a fluid loop, will be described with reference to  FIGS. 2 and 3 .  FIGS. 2 and 3  show a medium or large spacecraft  20  equipped with the thermal control apparatus  21  according to the second embodiment, wherein a heat-exchange paddle  23  of the thermal control apparatus  21  illustrated in  FIG. 2  is set in its opened (i.e., deployed) position, and the heat-exchange paddle  23  illustrated in  FIG. 3  is set in its closed (i.e., retracted) position. 
         [0046]    The thermal control apparatus  21  comprises a heat-receiving member  22  which encloses or covers an on-board device generating heat, the heat-exchange paddle  23 , a base plate  24 , a deploying/retracting mechanism  25  and a fluid loop  26 . The heat-exchange paddle  23  and the base plate  24  have a pipe  27  attached onto respective surfaces thereof to extend all over the surfaces while allowing fluid to flow therethrough. The fluid loop  26  connects a pipe attached on a top wall of the heat-receiving member  22  and the pipe on the heat-exchange paddle  23  and the base plate  24 , in a closed-loop manner. The thermal control apparatus  21  further includes a mechanical pump  28  for driving circulation of the fluid, and two evaporating elements  29 ,  30  are provided on the top wall of the heat-receiving member  22  and a rear surface of the heat-exchange paddle  23  to generate a capillary force within the fluid loop  26 . A heat-dissipating material  35  is attached onto each of a front surface of the heat-exchange paddle  23  and a front surface of the base plate  24 , and a heat-absorbing material  36  is attached onto the rear surface of the heat-exchange paddle  23 . 
         [0047]    In the second embodiment, when the heat-receiving member  22  (i.e., on-board device) in the spacecraft has a relatively high temperature, the deploying/retracting mechanism  25  is operable to deploy the heat-exchange paddle  23  so as to swingably move the heat-exchange paddle  23  to the opened (i.e., deployed) position as illustrated in  FIG. 2 . Thus, heat is dissipated from the front and rear surfaces of the heat-exchange paddle  23  and the front surface of the base plate  24 . When the temperature of the heat-receiving member  22  in the spacecraft is less than a predetermined value, the deploying/retracting mechanism  25  is operable to retract the heat-exchange paddle  23  so as to swingably move the heat-exchange paddle  23  to the closed (i.e., retracted) position as illustrated in  FIG. 3 . 
         [0048]    Thus, the base plate  24  is fully covered by the front surface of the heat-exchange paddle  23 , and only the rear surface of the heat-exchange paddle  23  is exposed to cosmic space so as to suppress heat-dissipation at a minimum level. 
         [0049]    When a temperature of the rear surface of the heat-exchange paddle  23  becomes greater than that of the inside of the spacecraft due to solar light, the mechanical pump  28  or the evaporating elements  29  incorporated in the heat-exchange paddle  23  and the heat-receiving member  22  are activated to transport solar heat energy to the heat-receiving member  22  so as to increase the temperature of the on-board device. 
       Third Embodiment 
       [0050]    As a third embodiment of the present invention, a thermal control apparatus  41  for a medium or large spacecraft, which employs a combination of a fluid loop and a high-temperature-heat transport element, will be described with reference to  FIGS. 4 and 5 .  FIGS. 4 and 5  show a medium or large spacecraft  40  equipped with the thermal control apparatus  41  according to the third embodiment, wherein a heat-exchange paddle  43  of the thermal control apparatus  41  illustrated in  FIG. 4  is set in its opened (i.e., deployed) position, and the heat-exchange paddle  43  illustrated in  FIG. 5  is set in its closed (i.e., retracted) position. 
         [0051]    The thermal control apparatus  41  comprises a heat-receiving member  42  which encloses or covers an on-board device generating heat, the heat-exchange paddle  43 , a base plate  44 , a deploying/retracting mechanism  45  and a fluid loop  46 . The base plate  44  has a pipe  47  attached onto a surface thereof to extend all over the surface while allowing fluid to flow therethrough. The fluid loop  46  connects a pipe attached on a top wall of the heat-receiving member  42  and the pipe on the base plate  44 , in a closed-loop manner. The thermal control apparatus  41  further includes a mechanical pump  48  for driving circulation of the fluid, and two parallel heating elements  50  are provided on the top wall of the heat-receiving member  42  to generate a capillary force within the fluid loop  46 . A heat-dissipating material  55  is attached onto each of a front surface of the heat-exchange paddle  43  and a front surface of the base plate  44 , and any one of a heat-absorbing material, a temperature-keeping material and a heat-insulating material  36  is attached onto a rear surface of the heat-exchange paddle  23 . 
         [0052]    In the third embodiment, when the heat-receiving member  42  in the spacecraft has a relatively high temperature, the deploying/retracting mechanism  45  is operable to deploy the heat-exchange paddle  43  so as to swingably move the heat-exchange paddle  43  to the opened (i.e., deployed) position as illustrated in  FIG. 4 . Thus, heat is dissipated from the front and rear surfaces of the heat-exchange paddle  43  and the front surface of the base plate  44 . 
         [0053]    When the temperature of the heat-receiving member  42  in the spacecraft is less than a predetermined value, the deploying/retracting mechanism  45  is operable to retract the heat-exchange paddle  43  so as to swingably move the heat-exchange paddle  43  to the closed (i.e., retracted) position as illustrated in  FIG. 5 . Thus, the base plate  44  is fully covered by the front surface of the heat-exchange paddle  43 , and only the rear surface of the heat-exchange paddle  43  is exposed to cosmic space. This makes it possible to suppress heat-dissipation at a minimum level while preventing freezing of the fluid (liquid phase). In the case where the heat-absorbing material is attached onto the rear surface of the heat-exchange paddle  43 , it will absorb heat of solar light incident thereon to warm the base plate  44  based on heat conduction and radiation. 
       Fourth Embodiment 
       [0054]    As a fourth embodiment of the present invention, a thermal control apparatus  60  suitable for use in celestial objects, such as the Moon and Mars, and polar environments of the Earth, will be described with reference to  FIGS. 6 and 7 .  FIGS. 6 and 7  show the thermal control apparatus  60  according to the fourth embodiment, wherein a paddle unit of the thermal control apparatus  60  illustrated in  FIG. 6  is set in its closed (i.e., retracted) position, and the paddle unit illustrated in  FIG. 7  is set in its opened (i.e., deployed) position. 
         [0055]    The thermal control apparatus  60  according to the fourth embodiment is designed to thermally control the on-board device  61  in celestial objects, such as the Moon and Mars, and polar environments of the Earth. The thermal control apparatus  60  comprises a heat storage material  64  having a heat storing (i.e., accumulating) function, a rotatable paddle  63 , an actuator  64  for controlling a rotational movement of the rotatable paddle  63 , two deployable/retractable paddles  65 ,  66  swingably connected to respective opposite ends of the rotatable paddle  63 , and two actuators  67 ,  68  for controlling respective swing movements of the deployable/retractable paddles  65 ,  66  between their deployed positions and retracted positions. Each of the rotatable paddle  63  and the deployable/retractable paddles  65 ,  66  has a front surface  70  having a low heat-emissivity material or a heat-insulating material attached thereon, and a rear surface  71  having a heat-reflecting material (i.e., material with a function of reflecting heat) attached thereon. The thermal control apparatus  60  further includes a heat-insulating member  72  disposed between the on-board device  61  and the heat storage material  62 . 
         [0056]    As shown in  FIG. 6 , the actuator  64  is operable, during daytime, i.e., when the on-board device has a relatively high temperature, to rotatably move the rotatable paddle  63  to an approximately vertical position, and simultaneously the actuators  67 ,  68  are operable to swingably move the respective deployable/retractable paddles  65 ,  66  to their retracted positions. The rotatable paddle  63  has a heat-insulating function. Thus, the heat-insulating member  72  and the rotatable paddle  63  preclude heat-exchange between the on-board device  61  and the heat storage material  62 , so that heat of the on-board device  62  can be dissipated while allowing the heat storage material to absorb solar heat. 
         [0057]    At night i.e., when the on-board device has a relatively low temperature, the actuator  64  is operable to rotatably move the rotatable paddle  63  to an approximately horizontal position, and simultaneously the actuators  67 ,  68  are operable to swingably move the respective deployable/retractable paddles  65 ,  66  to their approximately horizontal deployed positions, so as to close a shade  69  to block heat-exchange with an external environment, as shown in FIG.  7 . Further, the heat-insulating member  72  between the on-board device  61  and the heat storage material  62  is removed to supply radiation heat from the heat storage material  62  to the on-board device  61  which will otherwise be cooled to an excessively low temperature, so as to keep the on-board device  61  at an adequate temperature. 
       Fifth Embodiment 
       [0058]      FIGS. 8 and 9  are conceptual diagrams showing a radiator for a small satellite, according to a fifth embodiment of the present invention. In  FIGS. 8 and 9 , the reference numeral  80  indicates a small spacecraft to be subjected to thermal control. A heat-dissipating paddle  82  is attached to a structure of the small spacecraft  80  in a deployable manner. A high emissivity material is attached onto each of a surface  81  of the spacecraft structure and front and rear surfaces of the heat-dissipating paddle  82 . The heat-dissipating paddle  82  is composed of a high-temperature-heat transport element. 
         [0059]    During a launch of the satellite  80 , the heat-dissipating paddle  82  is closed, i.e., retracted, as shown in  FIG. 8 . Then, at a certain timing after the satellite  80  is placed in an orbit, the heat-dissipating paddle  82  is unidirectionally deployed, as shown in  FIG. 9 . 
         [0060]    The term “unidirectionally” means that, if the heat-dissipating paddle  82  is deployed once, it is permanently kept in its deployed position without being retracted. This can eliminate the need for providing a mechanism for retracting the heat-dissipating paddle  82 , so as to allow the thermal control device to be structurally simplified while reducing the risk of malfunction. 
         [0061]    In response to deploying the heat-dissipating paddle  82 , internal heat of the small satellite is transported to the hear-dissipating paddle  82  through the high-temperature-heat transport element to accelerate heat-dissipation. This makes it possible to provide an efficient deployable radiator with a simplified structure. 
       Sixth Embodiment 
       [0062]      FIGS. 10 and 11  are conceptual diagrams showing an energy storage system according to a sixth embodiment of the present invention. The energy storage system  90  according to the sixth embodiment comprised a wall  91  which has a front surface formed as a heat-absorbing surface and a rear surface formed as a heat-insulating surface, a deployable/storable heat-exchange paddle  92  which has a front surface formed as a heat-absorbing surface and a rear surface formed as a heat-insulating surface, a high-temperature-heat transport element  93  for transporting heat, and an energy storage unit  94  for storing heat transported by the high-temperature-heat transport element  93 . Each of the heat-absorbing surfaces of the wall  91  and the heat-exchange paddle  92  are connected to the high-temperature-heat transport element  93 . 
         [0063]    During daytime with solar light, the heat-exchange paddle  92  is deployed as shown in  FIG. 10 . In this deployed position, the respective front heat-absorbing surfaces of the wall  91  and the heat-exchange paddle  92  are irradiated with solar light to absorb heat of the solar light. This heat is transported to the inside of the system through the high-temperature-heat transport element  93  connected to these heat-absorbing surfaces, and stored in the energy storage unit  94 . During this process, the rear heat-insulating surfaces of the wall  91  and the heat-exchange paddle  92  make it possible to efficiently store energy while preventing dissipation of the heat stored in the energy storage unit  94 . 
         [0064]    At night with a relatively low temperature due to there being no solar light, the heat-exchange paddle  92  is retracted as shown in  FIG. 11 , and the heat-absorbing surfaces of the wall  91  and the heat-exchange paddle  92  come into contact with each other in opposed relation. Thus, the wall  91  and the heat-exchange paddle  92  are disposed as if they are a single plate which has opposite sides each formed of a heat-insulating surface, to suppress dissipation of the heat stored in the energy storage unit  94  at a minimum level. 
       Seventh Embodiment 
       [0065]    With reference to  FIGS. 12(   a ) to  12 ( f ), various layouts of a high-temperature-heat transport element in a thermal control apparatus according to a seven embodiment of the present invention will be described below. In  FIGS. 12(   a ) to  12 ( f ), a first high-temperature-heat transport element  100  indicated by a thick block line is actually connected between the paddle and the component located closer to the spacecraft, in each of the deployable/retractable thermal control apparatuses according to the first embodiment ( FIG. 1) , the second embodiment ( FIGS. 2 and 3 ), the third embodiment ( FIGS. 4 and 5 ), and the fifth embodiment ( FIGS. 8 and 9 ). In  FIGS. 12(   a ) to  12 ( f ), the reference numeral  101  indicates a base plate as the component located closer to the spacecraft, and the reference numeral  102  indicates one of various on-board devices to be subjected to thermal control (i.e., target object). The reference numeral  103  indicates a second high-temperature-heat transport element incorporated in the base plate. 
         [0066]      FIG. 12(   a ) shows one example where the first high-temperature-heat transport element  100  is attached onto a top surface of the base plate  101 , and  FIG. 12(   b ) shows another example where the first high-temperature-heat transport element  100  is attached onto a bottom surface of the base plate  101 .  FIG. 12(   c ) shows yet another example where the first high-temperature-heat transport element  100  is directly attached onto the target object  102 , and  FIG. 12(   d ) shows still another example where the first high-temperature-heat transport element  100  is attached onto only an end region of the top surface of the base plate  101  incorporating the second high-temperature-heat transport element, such as a heat pipe or a fluid loop.  FIGS. 12(   e ) and  12 ( f ) show other examples where a third high-temperature-heat transport element, such as a heat pipe or a fluid loop, is directly attached onto the target object  102 , wherein the third high-temperature-heat transport element in  FIG. 12(   e ) is composed of the first high-temperature-heat transport element  100  and the second high-temperature-heat transport element attached to the target object  102 , and the third high-temperature-heat transport element in  FIG. 12(   f ) consists only of the second high-temperature-heat transport element, such as a fluid loop. In  FIG. 12(   e ), heat is transported in the following order: the on-board device→the second heat transport element, such as a fluid loop→the heat transport element, such as a high conductivity material→cosmic space. In  FIG. 12(   f ), heat is transported in the following order: the on-board device→the second heat transport element, such as a fluid loop→cosmic space. 
         [0067]    As an example, structural elements/configurations and materials/mechanisms applicable to a thermal control apparatus of the present invention will be described below. 
         [0068]      FIG. 13  is a table showing a summary of the applicable structural elements/configurations. In  FIG. 13 , the section “A. Attachment of High-Temperature-Heat Transport Element” shows options about an attachment position of a high-temperature-heat transport element for transporting heat to a paddle, which includes: attaching it onto a top surface of a base plate; attaching it onto a bottom surface of the base plate, and directly attaching it to an on-board device. The section “B. Structure of Paddle” shows options which included one type where a single paddle is attached to one end of the base plate; and another type where two paddles are attached to respective opposite ends of the base plate. The section “C. Heat-Exchange Surface with Cosmic Space” shows options about the number of surfaces for use in heat-exchange with cosmic space. In this section, the “paddle front surface” means a surface of the paddle to be located on the same side as that of the base plate in its deployed position (i.e., a surface of the paddle to be located in opposed relation to that of the base plate in its retracted position). In the type having two paddles (double hinged type), the number of heat-exchange surfaces may be set in the range of two to five. 
         [0069]    The section “D. Properties of Front/Rear Surfaces” shows options about how to select each property of front and rear surfaces of the paddle from a heat-dissipating surface, a heat-absorbing surface, a heat-insulating surface and a variable heat-emissivity surface. As mentioned above, the term “heat-dissipating surface” means one of the front and rear surfaces which has a heat-emissivity greater than the other surface (regardless of a solar absorptance of one surface relative to that of the other surface), and the term “heat-absorbing surface” means one of the front and rear surfaces which has a solar absorptance greater than the other surface (regardless of a heat-emissivity of the one surface relative to that of the other surface). Further, the term “heat-insulating surface” means a surface having a low heat-emissivity (low heat conductivity) and a low solar heat absorptance, and the term “variable heat-emissivity surface” means a surface which exhibits a relatively low heat-emissivity at low temperatures and exhibits a relatively high emissivity at high temperatures. 
         [0070]    The section “E. Direction of Deployment” shows options which includes one type where the paddle is bidirectionally deployable (can be reversibly deployed and retracted), and another type where the paddle is unidirectionally deployable (can be only deployed) 
         [0071]      FIG. 14  is a table showing a summary of materials/mechanisms applicable to components/elements of the thermal control apparatus. These materials/mechanisms are particularly preferable although materials/mechanisms for the components/elements are not limited to those in the table of  FIG. 14 . 
         [0072]    Advantageous embodiments of the invention have been shown and described. It is obvious to those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope thereof as set forth in appended claims.