环境对大口径SiC轻量化主镜视宁度的影响

由于地基大口径望远镜主镜视宁度与望远镜系统成像质量相关,本文研究了环境对主镜视宁度的影响。理论分析了影响主镜视宁度大小的因素,得出主镜视宁度会随主镜表面和环境之间温差的增大而增大的结论。利用有限元法分析了自然对流和吹风条件下主镜的温度变化和温度分布;最后通过相应工况条件下2mSiC轻量化主镜的温度测试实验对仿真分析结果进行了验证。实验结果显示:在初始温差为6℃的无风自然对流情况下,主镜与环境达到温度平衡约需4h;而在初始温差为8℃的吹风情况下,主镜与环境达到热平衡仅需1.5h。分析和实验结果表明:采用强迫对流热控措施可快速而有效地将主镜视宁度控制在合理的范围内,可获得更多的望远镜观测时间,同时保证大口径望远镜系统的成像质量。

Affect of environment on mirror seeing of large-aperture SiC lightweight primary mirror

As the primary mirror seeing of a ground based large aperture telescope is directly related to its image quality, this paper researches the effect of environments on the primary mirror seeing. Through theoretical analysis, it points out that the size of the primary mirror seeing will increase with the temperature change between the primary mirror surface and the environments. Then using thermal analysis software Radtherm, the temperature changes and temperature distributions of a 2 m SiC lightweight primary mirror were analyzed under two different conditions of natural convection and natural flowing. Finally, the some temperature experiments on the 2 m SiC lightweight primary mirror under the working conditions mentioned above were performed to verify simulation results. The experiment results indicate that it takes about 4 hours to reach temperature equilibrium with the environment for the primary mirror in case of natural convection with initial 6 ℃ temperature difference; however, it takes only about 1.5 hours in case of natural flowing with initial 8 ℃ temperature difference. It shows the greater temperature difference but much less consumed time. These means that when the thermal control system and control method are forced to the large-aperture telescope system to perform the convective heat control, the mirror seeing will be controlled in a reasonable range more quickly and more effectively, and more telescope observation time can be obtained meanwhile maintaining much better image quality.