DEVELOPMENT OF MIDIUM-SIZE COOLED LIGHT-WIGHT SILICON CARBIDE MIRRORS FOR INFRARED ASTRONOMICAL SATELLITES

通过对160mm厚的测试镜在低温下的测量，确定了碳化硅（SiC）多孔芯和SiC CVD涂层镜坯的制备工艺。我们已经发现，CVD涂层必须施加在反射镜的整个表面上，以防止抛光液渗透到坯件中。我们已经证实，用这种方法制成的反射镜即使在冷却到液氦温度时也不会出现任何明显的变形。我们还检查了胶水的效果，发现如果金属部件预先进行良好的热处理，它不会产生重大问题。在此基础上研制了700mm的SiC反射镜，并在液氦温度下对其进行了测试。我们已经发现，非弹性变形的发生是由于在低温下的支撑部件（金属）和反射镜之间的热膨胀系数的差异。这对于红外波长的使用来说仍然不会造成重大问题，我们得出结论，本研究的主要目的已经实现。然而，变形过程的细节，特别是其可重复性，以及其在室温下的调节过程中的效果，必须在下一步中详细研究。

We have established the process to make a mirror blank of silicon carbide(SiC)porous core and SiC CVD coat based on the measurement of 160mm test mirrors at cryogenic temperatures. We have found that the CVD coat has to be applied on the entire surface of the mirror to prevent the polishing liquid from permeating into the blank. We have confirmed that the mirror made in this way does not show any appreciable deformation even when it is cooled down to liquid helium temperature. We have also examined the effects of the glue and found that it would not make significant problems if the metal part is well treated thermally in advance. We have fabricated a 700mm SiC mirror based on these processes and tested it at liquid helium temperature together with the supporting parts attached. We have found that the non-elastic deformation occurred due to the difference in the coefficients of thermal expansion between the supporting parts(metal)and the mirror at cryogenic temperatures. This will still not make a significant problem for use in infrared wavelengths and we have concluded that the main purpose of the present research has been achieved. However, details of the deformation process, particularly its repeatability, and its effects at room temperature in the adjustment process have to be investigated in detail in next step.