• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.56.3-56.3
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• 2021

In a ΛCDM universe, most galaxies are believed to evolve by mergers and accretions. The debris resulting from such processes remains faint and/or diffuse structures, such as tidal streams and stellar halos. Although these structures are a good indicator of the recent mass assembly history of galaxies, they have the disadvantage of being difficult to observe due to their low surface brightness (LSB). To recover these LSB features by reducing the photometric uncertainties introduced by the optics system, we attempt to develop an optimized telescope, called a linear astigmatism free-three mirror system, that minimizes the loss and scattering of light within the telescope. With that prototype, we observe NGC 5907, known as a nearby galaxy with a fabulous loop structure(s), to inspect its performance. After a dedicated data reduction process, including flat-fielding with dark sky flat and sky subtraction, our observation reaches a 1σ surface brightness limit of μlim,r ≃ 28.3 mag arcsec-2 in 10×10 arcsec boxes. We finally identify a single tidal stream that is likely the remnant of a nearly disrupted galaxy. This finding emphasizes that the capability of LSB detection with our telescope is comparable to that of much larger telescopes.

• Bulletin of the Korean Space Science Society
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• 2011.04a
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• pp.20.3-20.3
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• 2011

감마선폭발 (Gamma Ray Burst) 사건에서 아직 관측이 안되고 있는 초기 방출 광자에 대한 연구를 위하여 Ultra Fast Flash Observatory (UFFO) 인공위성 프로젝트가 제안되었다. 이 탑재체의 주요 기기로써, 감마선 폭발의 위치를 측정하기 위하여 coded mask 기반의 X-ray 광시야각 망원경인 UFFO Burst Alert X-ray Trigger Telescope (UBAT)와 감마선 폭발의 자외선 및 가시광 초기 후광관측을 위한 Slewing Mirror Telescope(SMT)가 있다. UFFO 프로젝트는 한국이 주도하고 미국, 대만, 러시아, 덴마크, 스페인, 프랑스, 노르웨이, 폴란드가 참여하는 9개국 국제공동연구이며, 2011년 11월 UFFO pathfinder가 러시아 인공위성인 Lomonosov에 실려 발사될 예정이다. 차세대 UFFO-100는 2015년 발사 목표로 연구가 시작되고 있다. UFFO pathfinder의 현재 진행상황과 가능한 연구에 대하여 논의한다.

• Current Optics and Photonics
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• v.6 no.1
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• pp.60-68
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• 2022

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.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.66.3-66.3
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• 2020

We present the optical design of Linear Astigmatism Free - Three Mirror System (LAF-TMS) D200 for UVO-Multiband Polarizing Imager System (UVOMPIS). LAF-TMS D200 is the off-axis wide-field telescope with EPD = 200 mm, F/2, and Field of View (FoV) = 2° × 4°. Its optical mirrors are optimized to freeform surfaces for high-quality optical performance over a wide FoV. The proposed mirror holder consists of four aluminum optomechanical modules that have applied for LAF-TMS D150 which is a prototype of the LAF-TMS system. It can accurately mount mirrors and also can sustain from vibration environments. As a feasibility study, quasi-static, modal, harmonic, and random vibration analyses have been performed to LAF-TMS D150 optomechanical structure under the qualification level of the Soyuz-2/Fregat launch system. We evaluate the vibration analysis results in terms of von Mises stress and Margin of Safety.

• Korean Journal of Optics and Photonics
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• v.26 no.3
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• pp.155-161
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• 2015

We report the design and performance analysis of an off-axis three-mirror telescope as the fore optics for a new hyperspectral sensor aboard a small unmanned aerial vehicle (UAV), for low-altitude coastal remote sensing. The sensor needs to have at least 4 cm of spatial resolution at an operating altitude of 500 m, $4^{\circ}$ field of view (FOV), and a signal to noise ratio (SNR) of 100 at 660 nm. For these performance requirements, the sensor's optical design has an entrance pupil diameter of 70 mm and an F-ratio of 5.0. The fore optics is a three-mirror system, including aspheric primary and secondary mirrors. The optical performance is expected to reach $1/15{\lambda}$ in RMS wavefront error and 0.75 in MTF value at 660 nm. Considering the manufacturing and assembling phase, we determined the alignment compensation due to the tertiary mirror from the sensitivity, and derived the tilt-tolerance range to be 0.17 mrad. The off-axis three-mirror telescope, which has better performance than the fore optics of other hyperspectral sensors and is fitted for a small UAV, will contribute to ocean remote-sensing research.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.64.4-65
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• 2016

Observations of the early photons from evolution of optical afterglows or internal shock provides the crucial clues on the nature of the bursts and environments. Hundreds of GRBs afterglow observations in multi-wavelength region have been made mainly thanks to the fast (~ 60 seconds after the trigger) localisation GRB by Swift and its fast alert to the ground telescope. It helps to improve our understandings tremendously, however many enigmas still remain, such as burst mechanism, transition prompt emission to the afterglow, early optical flash, rise phase of the early optical light curve and some missing afterglows. They could be addressed by fast slewing and multi colour and IR follow-up by future telescopes. The primary aim of UFFO/Lomonosov is to follow up optical fast ever, within a couple of seconds after trigger by onboard X-ray telescope. Its optical FOV is $30{\times}30degrees$. As a key instrument, the Slewing Mirror to redirect the optical beam from GRBs rapidly to the Ritchey-Chretien telescope. The status and launch schedule of the UFFO/Lomonosov and its test performance will be reported and prospects for the next missions will be discussed.

• Journal of Astronomy and Space Sciences
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• v.35 no.4
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• pp.253-261
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• 2018

Korea Astronomy and Space Science Institute (KASI) has been developing the space optical and laser tracking (SOLT) system for space geodesy, space situational awareness, and Korean space missions. The SOLT system comprises satellite laser ranging (SLR), adaptive optics (AO), and debris laser tracking (DLT) systems, which share numerous subsystems, such as an optical telescope and tracking mount. It is designed to be capable of laser ranging up to geosynchronous Earth orbit satellites with a laser retro-reflector array, space objects imaging brighter than magnitude 10, and laser tracking low Earth orbit space debris of uncooperative targets. For the realization of multiple functions in a novel configuration, the SOLT system employs a switching mirror that is installed inside the telescope pedestal and feeds the beam path to each system. The SLR and AO systems have already been established at the Geochang station, whereas the DLT system is currently under development and the AO system is being prepared for testing. In this study, the design and development of the SOLT system are addressed and the SLR data quality is evaluated compared to the International Laser Ranging Service (ILRS) tracking stations in terms of single-shot ranging precision. The analysis results indicate that the SLR system has a good ranging performance, to a few millimeters precision. Therefore, it is expected that the SLR system will not only play an important role as a member of the ILRS tracking network, but also contribute to future Korean space missions.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.49.4-49.4
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• 2018

We present measurement results of the fabricated ultra wideband corrugated horn for the planned ASTE band7+8 receiver. Return loss and vector beam pattern measurements were carried out over 275-500 GHz frequency range. Hardware set-ups for these measurements are described as well as beam measurement data are compared with such design criteria as beam width, phase curvature and cross-polarization. We discuss the impact of these beam measurement results to the aperture efficiency of the proposed 2-mirror receiver optics for the ASTE telescope.

• Journal of The Korean Astronomical Society
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• v.56 no.2
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• pp.169-185
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• 2023

The GMT-Consortium Large Earth Finder (G-CLEF) is the first instrument for the Giant Magellan Telescope (GMT). G-CLEF is a fiber feed, optical band echelle spectrograph that is capable of extremely precise radial velocity measurement. G-CLEF Flexure Control Camera (FCC) is included as a part in G-CLEF Front End Assembly (GCFEA), which monitors the field images focused on a fiber mirror to control the flexure and the focus errors within GCFEA. FCC consists of an optical bench on which five optical components are installed. The order of the optical train is: a collimator, neutral density filters, a focus analyzer, a reimager and a detector (Andor iKon-L 936 CCD camera). The collimator consists of a triplet lens and receives the beam reflected by a fiber mirror. The neutral density filters make it possible a broad range star brightness as a target or a guide. The focus analyzer is used to measure a focus offset. The reimager focuses the beam from the collimator onto the CCD detector focal plane. The detector module includes a linear translator and a field de-rotator. We performed thermoelastic stress analysis for lenses and their mounts to confirm the physical safety of the lens materials. We also conducted the global structure analysis for various gravitational orientations to verify the image stability requirement during the operation of the telescope and the instrument. In this article, we present the opto-mechanical detailed design of G-CLEF FCC and describe the consequence of the numerical finite element analyses for the design.

• Publications of The Korean Astronomical Society
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• v.18 no.1
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• pp.87-95
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• 2003

FIMS (Far-ultraviolet IMaging Spectrograph) is the main payload of STSAT-1 satellite which was successfully launched on September 27, 2003. The optical system of FIMS consists of two sets of parabolic cylinder mirror, slit, ellipsoidal reflection grating, and baffle system. We designed two types of baffle system for the FIMS: FOV baffle and order baffle. FOV baffle in the mirror house controls the field of view, and the order baffle in the vacuum box blocks the rays reflected rays by different orders.