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Design of All-SiC Lightweight Secondary and Tertiary Mirrors for Use in Spaceborne Telescopes
배종인,이행복,김정원,김명훈 한국광학회 2022 Current Optics and Photonics Vol.6 No.1
We report on the design of the secondary and the tertiary mirrors used in lightweight assemblies made entirely of silicon carbide (SiC). The essential design points are weight reduction within the acceptable deformation of the mirror surface by gravity release, temperature change, and vibration during or after space launch. To find a design that achieves the target requirements, we established finite element models for various candidate designs and subjected each one to wave front error analyses along gravity directions and in operation temperatures. We also calculated the natural frequencies of the candidate assemblies. Our study suggested that a triangular cell with bipod flexure support can satisfy the target weight within the requirements.
배종인,이행복,김정원,이경묵,김명훈 한국광학회 2022 한국광학회지 Vol.33 No.2
The entire process, from the raw material to the final system qualification test, has been developed to fabricate a large-diameter, lightweightreflective-telescope system for a satellite observation. The telescope with 3 anastigmatic mirrors has an aperture of 700 mm and a total mass of66 kg. We baked a silicon carbide substrate body from a carbon preform using a reaction sintering method, and tested the structural and chemical properties, surface conditions, and crystal structure of the body. We developed the polishing and coating methods considering the mechanical andchemical properties of the silicon carbide (SiC) body, and we utilized a chemical-vapor-deposition method to deposit a dense SiC thin film more than 170 μm thick on the mirror’s surface, to preserve a highly reflective surface with excellent optical performance. After we made the SiC mirrors, we measured the wave-front error for various optical fields by assembling and aligning three mirrors and support structures. We conducted major spaceenvironment tests for the components and final assembly by temperature-cycling tests and vibration-shock tests, in accordance with the qualifications for the space and launch environment. We confirmed that the final telescope achieves all of the target performance criteria.
항공기 외장형 정찰 장비용 냉각 시스템의 성능 특성에 관한 실험적 연구
정대윤,이행복,Jung, Daeyoon,Lee, Hang Bok 한국군사과학기술학회 2013 한국군사과학기술학회지 Vol.16 No.1
In this paper, we have proposed a vapor cycle refrigeration system as a cooling system to provide cooling air to the aircraft external reconnaissance stores. In the proposed vapor cycle system, receiver which prevents refrigerant from subcooling was eliminated and thermal expansion valve was replaced with electronic expansion valve. The vapor cycle refrigeration system is aimed to provide cooling air to the reconnaissance stores which is added to the aircraft in the form of external store. The wide temperature range of ambient air from the flight conditions can decrease the cooling performance and can make the refrigeration system unstable in low ambient temperature. Performance characteristics of the vapor cycle refrigeration system has been experimented under air conditions which is derived from the flight envelope. From the experiments, the vapor cycle refrigeration system has been proved to provide enough cooling air to the reconnaissance equipment and to be stable under all the flight conditions.
액상 실리콘 침투법으로 제작된 대구경 위성 망원경용 SiC 반사경의 결함 검사와 물성 계수 측정
배종인,김정원,이행복,김명훈 한국광학회 2022 한국광학회지 Vol.33 No.5
We have investigated reliable inspection methods for finding the defects generated during the manufacturing process of lightweight, large-aperturesatellite telescope mirrors using silicon carbide, and we have measured the basic physical properties of the mirrors. We applied the advanced ceramic material (ACM) method, a combined method using liquid-silicon penetration sintering and chemical vapor deposition for the carbon molded body,to manufacture four SiC mirrors of different sizes and shapes. We have provided the defect standards for the reflectors systematically by classifying the defects according to the size and shape of the mirrors, and have suggested effective nondestructive methods for mirror surface inspection and internal defect detection. In addition, we have analyzed the measurements of 14 physical parameters (including density, modulus of elasticity, specific heat, and heat-transfer coefficient) that are required to design the mirrors and to predict the mechanical and thermal stability of the final products. In particular, we have studied the detailed measurement methods and results for the elastic modulus, thermal expansion coefficient, and flexural strengthto improve the reliability of mechanical property tests.
송대범,윤용은,이행복,Song, Dae-Buem,Yoon, Yong-Eun,Lee, Hang-Bok 한국군사과학기술학회 2013 한국군사과학기술학회지 Vol.16 No.2
Alignment tolerance for EO/IR airborne camera using common optic is an important factor in stabilization accuracy and geo-pointing accuracy. Before airborne camera is mounted on the aircraft, defining alignment tolerance and verification of it is essential in production as well as research and development. In this paper we establish basic concept on the definition and elements of alignment tolerance for airborne camera and propose how to measure each of those elements. Components and the measurement sequence of alignment tolerance are as follows: 1) tolerance of alignment between EO and IR LOS. 2) tolerance of sensor alignment. 3) tolerance of position reporting accuracy. 4) tolerance of mount alignment