High dynamic-range observation using a 1.8-m off-axis telescope PLANETS: feasibility study and telescope design
High dynamic-range observation using a 1.8-m off-axis telescope PLANETS: feasibility study and telescope design
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使用 1.8 米离轴望远镜进行高动态范围观测 PLANETS：可行性研究和望远镜设计
DOI：
10.1117/12.2556458
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发表时间：
2020
期刊：
影响因子：
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通讯作者：
Emilio Marcelo
中科院分区：
文献类型：
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作者：
Kagitani Masato;Sakanoi Takeshi;Kasaba Yasumasa;Hirahara Yasuhiro;Kurita Mikio;Kuhn Jeffrey R.;Berdyugina Svetlana V.;Emilio Marcelo
PLANETS将是一个1.8米的离轴望远镜，结合对比度增强技术，使我们能够观察明亮物体附近的微弱发射。这种“高动态范围”的能力在很大程度上取决于望远镜光学系统的精度以及大气的畸变。我们目前的可行性研究监测水羽木卫二，中性环土卫二附近，火星上的电离层使用PLANETS望远镜。为了检验在实际波前误差条件下进行高动态距离观测的可行性，考虑大气畸变和主镜形状误差引起的波前误差，基于夫琅和费计算对系统中的光传播进行了建模。然后计算了自适应光学下几种形状误差情况下的点扩散函数。仿真结果表明，中高精度主镜是实现高动态范围观测的必要条件。同时介绍了PLANETS的最新设计，特别是主镜的支撑结构。我们采用36点whiffletrees与33个翘曲吊带轴向支持，和24点Schwesinger支持横向支持。主动支撑系统预期将抛光前的RMS误差从1.51 μm减少到0.66 μm，对应于最终抛光的总体积减少70%。实验表明，支撑力RMS重复性<0.005kgf，驱动滞后< 0.7%的负载范围，满足控制或保持主镜面形的精度要求。
PLANETS will be a 1.8-m off-axis telescope combined with contrast enhancement techniques, enabling us to observe faint emissions in the vicinity of bright objects. This “high dynamic-range” capability is largely dependent upon precision of telescope optics as well as atmospheric distortion. We present feasibility study of monitoring water plumes on Europa, neutral torus close to Enceladus, and ionosphere on Mars using PLANETS telescope. To test feasibility of high dynamic-range observation under actual conditions of wavefront error, we modeled propagation of light though the system based on Fraunhofer calculation taking into account for wavefront error made by atmospheric distortion and by primary mirror figure error. Then point spread function is calculated for several cases of figure errors under use of adaptive optics. The modeling result predicts that the moderate or high-precision primary mirror is mandatory to accomplish the high dynamic-range observation. We also present the latest design of PLANETS, especially focus on the support structures of primary mirror. We employ 36-point whiffletrees with 33 warping harnesses for axial support, and 24-point Schwesinger support for lateral support. The active support system is expected to reduce pre-polished RMS error from 1.51 μm to 0.66 μm corresponding to 70% reduction in total volume of final polish. The laboratory experiment using one third part of prototype whiffletrees shows supporting force RMS repeatability < 0.005 kgf, and drive hysteresis < 0.7% of load range, which are precise enough to control or to keep the primary mirror figure.