Patent Application
20080257525
The present patent application claims priority from Japanese Patent Application No. 2007-111144, filed on Apr. 20, 2007.
1. Field of the Invention
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.
2. Description of the Related Art
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.
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.
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.
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.
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.
Preferably, the heat transport element is a graphite sheet or a carbon fiber fabric.
The heat transport element may comprise a heat pipe or a fluid loop.
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.
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.
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.
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.
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.
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.
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.
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.
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.
With reference to the drawings, various embodiments of the present invention will now be described.
As shown in
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.
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.
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.
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).
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.
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.
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.
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.
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
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.
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
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.
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.
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
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.
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
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
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
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.
As shown in
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.
During a launch of the satellite 80, the heat-dissipating paddle 82 is closed, i.e., retracted, as shown in
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.
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.
During daytime with solar light, the heat-exchange paddle 92 is deployed as shown in
At night with a relatively low temperature due to there being no solar light, the heat-exchange paddle 92 is retracted as shown in
With reference to
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
As an example, structural elements/configurations and materials/mechanisms applicable to a thermal control apparatus of the present invention will be described below.
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.
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)
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP 2007-111144 | Apr 2007 | JP | national |
