DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] To better understand the present invention, brief reference will be made to a conventional thermal louver, shown in FIG. 1 . The thermal louver to be described adjusts the amount of heat radiation to the outside in accordance with temperature, as stated earlier. As shown, the thermal louver includes a bimetal or actuator 10 and blades 12 The bimetal 10 drives the blade 12 in order to increases or decreases the effective area and therefore the temperature of heat radiation surfaces. There are also shown in FIG. 1 a frame 14 , a bimetal housing 16 , shafts 18 , and bearings 20 .

[0015] A heat control device in accordance with the present invention is characterized in that it uses a heat radiation characteristic particular to a substance itself in place of a mechanical principle. As for a spacecraft expected to navigate a vacuum environment, heat radiation from outside surfaces is the only heat radiating means available. The amount of heat radiation dictates the temperature inside the spacecraft.

[0016] The heat control device of the present invention is implemented by a variable-phase substance (La 1-X Sr X MnO 3 ) arranged on the heat radiation surfaces of a spacecraft. The variable-phase substance belongs to a family of oxides of perovskite Mn and undergoes phase transition around room temperature. The characteristic of this kind of substance is similar to the characteristic of metal in a low temperature phase, but similar to the characteristic of an insulator in a high temperature phase. Also, the heat radiation ratio of the substance is low when conductivity is high, but high when conductivity is low. The substance therefore has an automatic temperature adjusting ability, i.e., automatically increases its heat radiation ratio at high temperatures and decreases it at low temperatures. FIG. 1 shows the dependency of the resistivity and infrared reflectivity of La 1-X Sr X MnO 3 on temperature, reported in the past. As FIG. 2 indicates, the reflectivity noticeably changes with changes in temperature around photon energy of about 0.12 eV (10 μm) which is the peak of heat radiation around room temperature. The phase transition temperature is variable between 250 K and 350 K in accordance with the composition ratio x of La and Sr.

[0017] FIG. 3 shows data representative of the hemispherical reflectivity of La 0.825 Sr 0.175 MnO 3 and measured in the range of from 170 K to 380 K. As shown, the reflectivity sharply changes in the range of from 300 K to 280 K, i.e., at the phase transition temperatures. As a result, the above substance exhibits the characteristic of metal at the low temperature side, but exhibits the characteristic of an insulator at the high temperature side.

[0018] FIG. 4 shows data representative of the result of measurement of resistivity. As shown, the resistivity changes by about four times as in FIG. 2 .

[0019] In the heat control device of the present invention, the variable-phase substance should only be arranged on heat radiation surfaces in the farm of a film and is therefore space-saving and light weight. Moreover, the device is highly reliable because it needs no movable portions. When the device is mounted in a position getting the sunlight, a silicon plate transparent for thermal infrared rays, but opaque for the sunlight, may be positioned in front of the variable-phase substance in order to minimize the sunlight absorption of the device.

[0020] For the variable-phase substance, use may be made of an oxide of Mn-containing perovskite represented by A 1-X B X MnO 3 where A denotes at least one of La, Pr, Nd and Sm rare earth ions, and B denotes at least one of Ca, Sr and Ba alkaline rare earth ions. Further, such a substance may be implemented by an oxide of Cr-containing corundum vanadium, preferably (V 1-X Cr X ) 2 O 3 .

[0021] Referring to FIG. 5, a first embodiment of the heat control device in accordance with the present invention will be described. As shown, the device is implemented by a variable-phase substance 1 for controlling the temperature of a desired object 2 . The substance 1 exhibits the characteristic of metal in a high temperature phase, but exhibits the characteristic of an insulator in a low temperature phase. Also, the substance 1 radiates a great amount of heat in the high temperature phase, but radiates a small amount of heat in a low temperature phase. The substance 1 is affixed to the object 2 by powder coating, evaporation, crystalline adhesion or similar affixing means. In the Illustrative embodiment, the substance 1 is implemented by La I-X Sr X MnO 3 belonging to a family of oxides of perovskite Mn.

[0022] Specifically, the object 2 is representative of the heat radiation wall of a spacecraft. The substance 1 is arranged on the surface 3 of the wall 2 in the form of a several hundred micron thick film. The substance 1 is thermally coupled to the surface 3 and substantially the same in temperature as the wall 2 .

[0023] In operation, when the temperature of the surface 3 rises and heats the substance above the phase transition temperature, then the heat radiation ratio of the substance increases. As a result, the amount of heat radiation to the outside environment increases and lowers the temperature of the surface 3 . Conversely, when the temperature of the surface 3 drops and cools off the substance below the phase transition temperature, the heat radiation ratio of the substance 1 and therefore the amount of heat radiation decreases, raising the temperature of the surface 3 . With this mechanism, the substance 1 automatically controls the temperature of the surface 3 to a range around its phase transition temperature.

[0024] The substance 1 has a cubic crystal structure and has an optical property not dependent on the orientation of the crystallographic axis. It follows that the substance 1 can be arranged on the surface 3 by any one of conventional schemes including powder coating, evaporation, crystal line adhesion and other affixing means and the adhesion of a film implemented by a powdery phase-variable substance containing, e.g., a binder.

[0025] The illustrative embodiment is practicable only if the variable-phase substance is implemented by, e.g., an oxide of Mn-containing perovskite represented by A 1-X B X MnO 3 where A denotes at least one of La, Pr, Nd and Sm rare earth ions, and B denotes at least one of Ca, Sr and Ba alkaline rare earth ions. Further, such a substance may be implemented by an oxide of Cr-containing corundum vanadium, preferably (V 1-X Cr X ) 2 O 2 .

[0026] A second embodiment of the heat control device in accordance with the present invention will be described with reference to FIG. 6 . As shown, the device is also implemented by the variable-phase substance 1 for controlling the temperature of the object 2 . The substance 1 exhibits the characteristic of metal in a high temperature phase, but exhibits the characteristic of an insulator in a low temperature phase, as stated earlier. In addition, the substance 1 radiates a great amount of heat in the high temperature phase, but radiates a small amount of heat in a low temperature phase, as also stated previously. In the illustrative embodiment, a silicon plate 4 transparent for infrared rays, but opaque for visible rays, is positioned an the substance 1 .

[0027] As shown in FIG. 2 , La 1-X Sr X MnO 3 constituting the substance 1 has reflectively as low as about 0.2 in the sunlight wavelength range (0.3 μm to 2.5 μm), i.e., it shows high absorbance to the sunlight in such a range. Therefore, when the substance is positioned in an area directly getting the sunlight, its absorbance is increased to obstruct heat radiation. In such a case, as shown in FIG. 6 , the silicon plate 4 transparent for infrared rays, but opaque for visible rays, is mounted on the front of the substance 1 . This embodiment is therefore identical in principle with the first embodiment except that the silicon plate 4 reflects the sunlight.

[0028] If desired, the silicon plate 4 may be replaced with any other member, e.g., a plate or a film containing germanium so long as it can transmit infrared rays.

[0029] In summary, it will be seen that the present invention provides a small size, light weight heat control device using an optical property particular to a substance itself in place of a mechanical principle applied to a conventional thermal louver. In addition, the device of the present invention is highly reliable and long life because it needs no movable portions which would bring about wear, fatigue and other problems.

[0030] Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof.