[P-CG18] Future missions and instrumentation for space and planetary science

[PCG18-P06] Metrology and Polish of 1.8m Off-Axis Parabola Mirror of PLANETS Telescope

*Masato Kagitani¹, Kazuya Nagata¹, Yasumasa Hirahara², Yusuke Hanamura², Mikio Kurita³, Takeshi Sakanoi¹, Yasumasa Kasaba¹ (1.Planetary Plasma and Atmospheric Research Center, Graduate School of Science, Tohoku University, 2.Graduate School of Environmental Studies, Nagoya University, 3.Graduate School of Science, Kyoto University)

Keywords:Profilometry, Off-axis Parabola

A low-scattered light telescope PLANETS (Polarized Light from Atmospheres of Nearby Extra-Terrestrial Systems) would be a 1.8m off-axis telescope on Mt. Haleakala, Hawaii. The primary mirror is an off-axis parabola made of CLEARCERAM with 1.85 m in diameter and 100 mm thick on edge. Grinding and pre-polish of the mirror blank were completed by ITT/Exelis. Then we have started the final phase work of polishing and figuring in collaboration with LogistLab Inc. in Japan. A unique profilometry technique “dragged three-probe method” (Kurita et al., 2016) was employed to test surface figure error. By dragging three laser probes across the test surface in several hundreds of scanning paths, we measure distribution of local curvature and derive distribution of surface figure error by integrating the curvature measurements. The measurement system is robust against environmental vibration and temperature variation. Combining with an industrial robotic arm system, we can quickly switch profilometry probes into a polishing tool enabling to shorten cycle of metrology and polish. We present latest result of metrology and polish of the PLANETS primary mirror.