• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.55.4-55.4
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• 2021

한국천문연구원에서는 낮은 표면밝기(Low Surface Brightness; LSB)의 천체를 효율적으로 관측할 수 있는 소형(〉30cm) 광시야(〉1°×1°) 광학망원경 및 관측기술 개발을 통한 은하형성 규명 연구를 수행 중에 있다. 이번에 개발한 K-DRIFT pathfinder는 비축 자유곡면 3반사 망원경 시스템(Linear Astigmatism Free-Three Mirror System; LAF-TMS)으로 넓은 시야에서 고품질의 이미지를 효율적으로 얻을 수 있는 광학 설계를 적용하고, 배경 값 변동 요인을 분석하여 가까운 우주의 LSB 천체 관측에 최적화될 수 있도록 하였다. 이번 특별세션에서는 '왜 LSB 우주 탐사를 하고, K-DRIFT를 개발하는지?'에 대해서 소개하고, K-DRIFT pathfinder의 개발 과정, 보현산 천문대에서의 시험관측 결과 소개와 함께, LSB 천체 연구를 위한 맞춤형 시뮬레이션 개발 및 수행 내용을 소개한다.

• Journal of The Korean Astronomical Society
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• v.51 no.6
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• pp.207-214
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• 2018

A coelostat is often used for solar observations, because it corrects the image rotation automatically by guiding sunlight into a fixed telescope with two plane mirrors. For the purposes of education and spectroscopic observation, the solar group at Seoul National University (SNU) plans to develop the SNU coelostat (SNUC) and install it in the SNU Astronomical Observatory (SAO). Requirements of the SNUC are < 1" positioning accuracy with 30 cm beam size on the entrance pupil in the compact dome. To allow for installation in the small dome, we design a compact slope type coelostat with a 45 cm primary plane mirror and a 39 cm secondary plane mirror. The motion of the SNUC is minimized by fixing the position of the slope frame. Numerical simulations of the available observational time of the designed coelostat shows that the sun can be observed ay all times from June to early August and at least three hours in other months. Since the high accuracy driving motors installed in the SNUC can be affected by external environment factors such as humidity and temperature variations, we design a prototype to test the significance of these effects. The prototype consists of a 20 cm primary plane mirror, a 1 m slope rail, a direct drive motor, a ballscrew, a linear motion guide, an AC servo motor, a reduction gear and a linear encoder. We plan to control and test the accuracy of the prototype with varying atmospheric conditions in early 2019. After testing the prototype, the SNUC will be manufactured and installed in SAO by 2020.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.11
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• pp.953-960
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• 2021

Korea Astronomy and Space Science Institute has been verifying the multipurpose laser tracking system with three functions of satellite laser tracking, adaptive optics and space debris laser tracking for not only scientific research but also national space missions. The system employs an optical telescope consisting of a 100 cm primary mirror and an altazimuth mount for fast and precise tracking. The precise pointing and tracking capability in a tracking mount is considered as one of important performance metrics in the fields of automatic tracking and precise application research. So it is required to analyze a mount model for investigating pointing error factors and compensating pointing error. In this study, we investigated various factors causing static pointing errors of tracking mount and analyzed the pointing accuracy of the tracking mount at Geochang observatory by estimating mount parameters based on the least square method.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.52.3-53
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• 2015

The GMT-Consortium Large Earth Finder (G-CLEF) is a fiber-fed, optical band high dispersion echelle spectrograph that selected as the first light instrument for the Giant Magellan Telescope (GMT). This G-CLEF has been designed to be a general- purpose echelle spectrograph with the precisional radial velocity (PRV) capability of 10 cm/sec as a goal. The preliminary design review (PDR) was held on April 8 to 10, 2015 and the scientific observations will be started in 2022 with four mirrors installed on GMT. We have been participating in this preliminary design study in flexure control camera (slit monitoring system), calibration lamp sources, dichroic assembly and the fabrication of the proto-Mangin Mirror. We present the design concept on the parts KASI undertaken, introducing the specifications and capabilities of G-CLEF.

• Korean Journal of Optics and Photonics
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• v.19 no.4
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• pp.287-293
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• 2008

The collimator which makes a collimated beam, is an essential instrument for assembly and evaluation of telescopes. Recently, the Cassegrain type collimator has been widely used for its compact size as the focal length of high resolution cameras becomes longer. However, this kind of collimator has a disadvantage in that the secondary mirror is a heat source which can degrade the evaluation accuracy for an IR camera system. In this paper, we present the fabrication and measurement process for an off-axis parabolic mirror with the physical diameter pf 1 m, effective diameter 930 mm, and the focal length 6 m. After four months of works we obtained the final surface wave-front error of 30.4 nm rms ($\lambda$/138, ${\lambda}=4.2\;{\mu}m$), which is capable of evaluation of an IR camera as well as a visible camera.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.10
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• pp.851-868
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• 2015

A radio telescope which has been dominantly used for millimeter and submillimeter wave radio astronomy is a cassegrain antenna. A various receivers with specified observing bandwidths are installed on cassegrain antenna so as to carry out to investigate a diverse radio astronomy. A beam guiding system should be required so that a various receiver can be conducted their own observational frequency bands. The beam guiding system based on Gaussian beam transmission theory consists of quasi-optical circuit used such ellipsoidal mirror, dielectric lens and feed horn. In this paper, not only Gaussian beam transformations based on Gaussian beam theory are presented, but also design techniques for quasi-optical circuit are given. By using proposed design techniques, both Gaussian beam quasi-optical circuits to be used for cassegrain antenna and design results are also described. Properties of key focusing elements such ellipsoidal mirror and dielectric lens and feed horn are also discussed. It is expected that beam guiding system to be applied cassegrain antenna could be easily designed by using proposed design techniques.

• Journal of The Korean Astronomical Society
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• v.44 no.4
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• pp.115-123
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• 2011

To perform imaging observations of optically red objects such as high redshift quasars and brown dwarfs, the Center for the Exploration of the Origin of the Universe (CEOU) recently developed an optical CCD camera, Camera for QUasars in EArly uNiverse (CQUEAN), which is sensitive at 0.7-1.1 ${\mu}m$. To enable observations with long exposures, we develop an auto-guiding system for CQUEAN. This system consists of an off-axis mirror, a baffle, a CCD camera, a motor and a differential decelerator. To increase the number of available guiding stars, we design a rotating mechanism for the off-axis guiding camera. The guiding field can be scanned along the 10 arcmin ring offset from the optical axis of the telescope. Combined with the auto-guiding software of the McDonald Observatory, we confirm that a stable image can be obtained with an exposure time as long as 1200 seconds.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.87.1-87.1
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• 2011

Since early 90's, the solar X-ray telescopes such as Yohkoh SXT and Hinode XRT have observed coronal magnetic structures on the Sun's surface in the range of about $40'{\times}40'$ field-of-view (FOV) covering the full solar disk. Thus it has been stressed by the scientists that the optical structure of solar telescopes should be designed with care for improving the uniformity over a wide FOV. There would be, however, no unique solution in designing the optical system of a telescope for overcoming perfectly the problem of off-axis response variation. As a consequence, the correction of optical imperfectness of telescopes has become an important calibration step that should be performed beforehand when the observed images are to be used for photometric purposes. In particular, a special care should be taken when performing the temperature analysis with thin and thick filters for flaring activities observed at the periphery of the full FOV. From the analyses of both pre-launch calibration and in-flight observation data, the optical characteristics for describing the performance of solar X-ray telescopes, especially in view of their energy dependence, will be introduced and discussed in our presentation.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.68.2-68.2
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• 2020

UVO-Multiband Polarizing Imager System (UVOMPIS) is an ultraviolet to visible light multi-wavelength polarization/imaging system for Compact Advanced Satellite. We developed Linear Astigmatism Free-Three Mirror System (LAF-TMS) D200F2 as an optical system of UVOMPIS which has an entrance pupil diameter of 200 mm, a focal ratio of 2, a field of view of 2° × 4°. LAF-TMS is a confocal off-axis reflecting telescope system that removes linear astigmatism, and its all mirrors (M1, M2, M3) are optimized with the freeform surface to reduce high-order aberrations. Through the sensitivity analysis and Monte-Carlo simulation as the tolerance analysis, we can confirm the feasibility of the system, relatively sensitive parameters (tilt, decenter, despace, surface RMS error), and considerations for optomechanical design. From the sensitivity analysis, we can discover the relatively sensitive optical alignment parameters to a single perturbation. Further more, in the monte-carlo simulation, we investigate the minimum tolerance budget satisfying the required optical performance and whether the tolerance range is satisfied within manufacturing error.

• Journal of Aerospace System Engineering
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• v.12 no.4
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• pp.75-80
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• 2018

The working principle of a satellite camera involves a focusing mechanism for controlling the focus of the optical system, which is essential for proper functioning. However, research on focusing mechanisms of satellite optical systems in Korea is in the beginning stage and developed technology is limited to a thermal control type. Therefore, in this paper, we propose a motor-driven focusing mechanism applicable to small satellite optical systems. The proposed mechanism is designed to generate z-axis displacement in the secondary mirror by a motor. In addition, three flexure hinges have been installed on the supporter for application of preload on the mechanism resulting in minimization of the alignment error arising due to manufacturing tolerance and assembly tolerance within the mechanism. After fabrication of the mechanism, the alignment errors (de-space, de-center, and tilt) were measured with LVDT sensors and laser displacement meters. Conclusively, the proposed focusing mechanism could achieve proper alignment degree, which can be applicable to small satellite optical system.