This article aiming at the high performance requirements of the space camera mirror assembly, and in order to ensure that the space camera main mirror has good surface shape accuracy and high first-order natural frequency, the mirror and flexible support structure are studied and designed. First, according to the selection principle of the mirror material, SiC is selected as the mirror blank material of the mirror. According to the empirical formula, the three-point support scheme on the back of the mirror and the structural size parameters of the mirror body are determined. And a flexible support structure with multi-axis flexible hinge and dual-axis flexible hinge in series is designed for the mirror. Finally, the parameter optimization method is used to optimize the position radius of the mirror back support hole and the key dimensions of the flexible structure. The static analysis and modal analysis of the mirror assembly were carried out using the finite element method. The results show that the surface shape accuracy of the mirror is 0.015λ nm, the first-order natural frequency of the mirror is 145.57Hz, the weight is 135.35Kg, and the lightweight rate is 87.57%.
A space mission called “Earth 2.0 (ET)” is being developed in China to address a few of fundamental questions in the exoplanet field: How frequently habitable Earth-like planets orbit solar type stars (Earth 2.0s)? How do terrestrial planets form and evolve? Where did floating planets come from? ET consists of six 30 cm diameter transit telescope systems with each field of view of 500 square degrees and one 35 cm diameter microlensing telescope with a field of view of 4 square degrees. The ET transit mode will monitor ~1.2M FGKM dwarfs in the original Kepler field and its neighboring fields continuously for four years while the microlensing mode monitors over 30M I< 20.6 stars in the Galactic bulge direction. ET will merge its photometry data with that from Kepler to increase the time baseline to 8 years. This enhances the transit signal-to-noise ratio, reduce false positives, and greatly increases the chance to discover Earth 2.0s. Simulations show that ET transit telescopes will be able to identify ~17 Earth 2.0s, about 4,900 Earth-sized terrestrial planets and about 29,000 new planets. In addition, ET will detect about 2,000 transit-timingvariation (TTV) planets and 700 of them will have mass and eccentricity measurements. The ET microlensing telescope will be able to identify over 1,000 microlensing planets. With simultaneous observations with the ground-based KMTNet telescopes, ET will be able to measure masses of over 300 microlensing planets and determine the mass distribution functions of free-floating planets and cold planets. ET will be operated at the Earth-Sun L2 orbit with a designed lifetime longer than 4 years.
The Earth 2.0 (ET) mission is a Chinese space mission to detect thousands of Earth-sized terrestrial planets, including habitable Earth-like planets orbiting solar type stars (Earth 2.0s), cold low-mass planets, and free-floating planets. The six 30 cm diameter transit telescopes will be equipped with a CMOS camera which consists of 4(2×2)9K×9K CMOS sensors. A prototype camera with a 8900×9120 pixel GSENSE 1081 BSI type CMOS sensor and temperature control is designed and developed for high precision photometry measurements. In this paper, details of this camera design and performance test results are reported.
Optical design of a small reflecting telescope for use in a 1U CubeSat mission is reported in this study. A Ritchey-Chretien with field correction lens type telescope for earth observation techniques is adopted in this design. The primary mirror and secondary mirror are circular apertures with 70-mm and 21-mm in diameter. The effective focal length is 390-mm operated at 600-km altitude. A commercial 2560 × 2160 CCD image sensor CIS2521 with a pixel size of 6.5 μm is applied, which capture a 25km swath area. The ground resolution is better than 10m for CubeSat application. The MTF is expected to be about 0.3 at Nyquist frequency at 77lp/mm. The tolerance analysis is performed for further understanding on fabrication and assembly errors. In order to reduce the telescope size, the optical system uses a reflective optical system, and the circuit board is arranged behind the system and above. The telescope envelope size(all contained) is less than 96mm × 90mm × 90mm and the weight is approximately 600g. At present, the aspherical primary mirror has completed the processing and assembly.
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