• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.49.1-49.1
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• 2018

The MATS (Mesosphere Airglow/Aerosol Tomography Spectroscopy) satellite is the next Swedish science microsatellite. We report optical performance test results of the limb telescope, which is the major payload. This telescope is designed with "linear astigmatism-free" (LAF) off-axis optical system in order to have high optical performance across the wide field of view. We measured Modulation Transfer Function (MTF) and Encircled Energy Diameter (EED) of the limb telescope. Full field imaging tests show expected results without linear astigmatism across the full field of view ($5.67^{\circ}{\times}0.91^{\circ}$). Since the amount of stray light is from the earth and the sun, we also simulated and measured the stray light in the field image.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.41.2-41.2
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• 2021

I will start with presenting new results on the stellar populations of galaxies at a redshift of z=9-11, when the universe was only a few hundred million years old. By combining Hubble Space Telescope observations with Spitzer imaging data, I will show how challenging it is currently to measure basic physical properties of these objects such as star-formation rates, stellar masses and stellar ages. In particular, the current measurements greatly depend on the assumptions (priors) for the spectral energy distribution modeling. Finally, I will discuss how the James Webb Space Telescope (JWST) will revolutionize this field next year and allow us to probe and characterize the first generation of galaxies in much greater detail. Specifically, I will present an overview of the JWST Advanced Deep Extragalactic Survey (JADES), a joint program of the JWST/NIRCam and NIRSpec Guaranteed Time Observations (GTO) teams involving 950 hours of observation.

• Journal of Astronomy and Space Sciences
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• v.32 no.3
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• pp.269-279
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• 2015

Future space missions will have larger telescopes in order to look deeper into space while improvising on spatial resolution. The primary mirrors for these telescopes will be so large that using a monolithic mirror will be nearly impossible because of the difficulties associated with its fabrication, transportation, and installation on a launch vehicle. The feasibility of launching these huge mirrors is limited because of their small launch fairing diameter. The aerodynamic shape of the fairing requires a small diameter, but the height of the launch vehicle, which is available for designers to utilize, is larger than the fairing diameter. This paper presents the development of an axial deployment mechanism based on the screw jack principle. The mechanism was designed and developed, and a prototype was constructed in order to demonstrate a lab model.

• Journal of Astronomy and Space Sciences
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• v.20 no.4
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• pp.393-402
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• 2003

The Multi-Spectral Camera (MSC) is the payload of KOMPSAT-2 which is designed for earth imaging in optical and near-infrared region on a sun-synchronous orbit. The telescope in the MSC is a Ritchey-Chretien type with large aperture. The telescope structure should be well stabilized and the optical alignment should be kept steady so that best images can be achieved. However, the MSC is exposed to adverse thermal environment on the orbit which can give impacts on optical performance. Solar incidence can bring non-uniform temperature rise on the telescope tube which entails unfavorable thermal distortion. Three ways of preventing the solar radiation were proposed, which were installing external mechanical shield, internal shield, and maneuvering the spacecraft. After trade-off study, internal sun shield was selected as a practical and optimal solution to minimize the effect of the solar radiation. In addition, detailed designs of the structure and sunshield were produced and analyses have been performed. The results were assessed to verify their impacts to the image quality. It was confirmed that the internal sunshield complies with the requirements and would improve image quality.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.66.4-67
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• 2020

Gyeonggi science high school for the gifted (GSHS) installed 60cm telescope, which is waiting for student observers. It is essential to understand the characteristics of the photometric system, consisting of telescope, filter, and CCD, to get reliable data. CCD images of SA98 Landolt standard field and M67 were obtained on 19th March 2020. The images of each field were combined by filters, i.e., we ignored the monochromatic atmospheric extinction since the photometric objects themselves are standard stars. 24 standard stars in SA98 field and 12 standard stars in M67 were used to derive the tentative transformation equation between our bv photometric system and Johnson BV photometric system. In this poster, we present the preliminary standardization result for Johnson BV photometric system in GSHS 60cm telescope. The reproductivity is discussed by comparing color coefficients of two fields. We plan to extend this process to Johnsons-Cousins BVRI photometric system and narrow-band filters for flux calibration.

• Journal of The Korean Astronomical Society
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• v.43 no.5
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• pp.169-181
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• 2010

We develop a proto-model of an off-axis reflective telescope for infrared wide-field observations based on the design of Schwarzschild-Chang type telescope. With only two mirrors, this design achieves an entrance pupil diameter of 50 mm and an effective focal length of 100 mm. We can apply this design to a mid-infrared telescope with a field of view of $8^{\circ}{\times}8^{\circ}$. In spite of the substantial advantages of off-axis telescopes in the infrared compared to refractive or on-axis reflective telescopes, it is known to be difficult to align the mirrors in off-axis systems because of their asymmetric structures. Off-axis mirrors of our telescope are manufactured at the Korea Basic Science Institute (KBSI). We analyze the fabricated mirror surfaces by fitting polynomial functions to the measured data. We accomplish alignment of this two-mirror off-axis system using a ray tracing method. A simple imaging test is performed to compare a pinhole image with a simulated prediction.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.57.3-58
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• 2016

We analyze an optical system of a telescope based on Fresnel type objective lens as suggested by Hyde (1999). The Fresnel objective lens can be thin, light-weight and foldable, and therefore it is possible to develop a space telescope with an aperture larger than that of traditional telescopes. Moreover a lens, whatever it is either Fresnel type or conventional, allows much larger fabrication tolerances. We design a medium-sized telescope adopting Fresnel lens as an objective lens for use in space and possibly on the ground. The well-known chromatic aberration of the Fresnel primary lens is corrected by a field lens and another Fresnel lens using Schupmann method. An additional lens is used for forming images. We analyze the chromatic and off-axis aberrations of the proposed system analytically and suggest methods for the minimization of off-axis aberrations and for the operation in wider spectral range. We also conduct ray tracing and optimize the whole optical system with commercial software. Finally we present the design parameters of a telescope with an aperture of 0.5 to 1 meters, enabling diffraction limited operation for a moderate field of view about 10 arc-minutes.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.69.3-69.3
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• 2020

우주개발과 활용이 주요 화두가 된 현대에 보다 빠르고 정확한 우주환경 예보는 전략적으로 매우 중요하다. 이에 우리는 광대역태양영상분광망원경(Wide-Field Solar Spectro-Imaging Telescope, Post SOlar Flare Telescope: PSOFT)을 활용한 태양전면 영상분광감시체계를 구성하고자 한다. 전세계 세 곳에 PSOFT를 배치하여 우주환경에 중대한 영향을 주는 요소인 태양의 플레어와 홍염 분출과 같은 현상과 표면의 다양한 활동들을 실시간으로 관측 분석하고자 한다. PSOFT는 30cm 구경의 광학계에 고속영상분광기를 결합하여 태양 전면의 분광영상을 약 1초각의 영상해상도와 5분의 시간해상도로 획득한다. 태양 전면을 슬릿으로 스캔하는 방식으로 H alpha와 Ca II 854.2nm선의 분광정보를 획득하는데 팁틸트 미러를 이용하여 1차적인 시상보정과 함께 스캔모션을 함께 구현함으로써 1)광학계 구조를 단순화하고, 2) 빠른 스캔이 가능하다. PSOFT로 얻은 태양전면 채층분광영상 데이터는 정밀한 우주환경 예보에 필요한 플레어나 홍염분출의 발생초기 정보를 제공할 뿐 아니라 태양 저층대기에서 발생하는 자기재연결, 파동 등에 대한 통계적 연구자료를 제공할 것으로 기대한다.

• Journal of Space Technology and Applications
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• v.1 no.3
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• pp.283-301
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• 2021

In order to satisfy the intellectual curiosity of mankind to explore the unknown, National Aeronautics and Space Administration (NASA) in the United States and European Space Agency (ESA) in Europe are embarking on various R&D under the motto of the grand dream of pioneering space into a safe and sustainable environment. In the 2020s and 30s, it is expected that advanced giant observation equipment will be in operation, such as the development of a 10-meter-class telescope in space. In Korea, following the development of the 0.15 m Near-Infrared Imaging Spectrometer (NISS), Korea Astronomy and Space Science Institute (KASI) is also participating a 0.2 m Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx) as an international cooperation partner in small exploration telescope. However, domestic experience in the development and operation of the space telescopes is still insufficient, and there is no plan with long-term prospects for constructing telescopes. In order to answer questions about the unknown world that mankind has not experienced using our own equipment, planning and preparation for the construction of a space telescope through close cooperation among industry-university-institute-government is urgently needed. In this paper, the necessity, background, development goals, and expected effects of the development of the Korean Space Telescope are summarized conceptually, and a working group (WG) is also proposed. In the WG activities, Korea shall take the lead in establishing the Korean-style space telescope development plan, and will start a valuable step to establish the national direction in the field of space astronomy and related technologies. We hope that the WG will be another milestone in Korea's space development.

• Bulletin of the Korean Space Science Society
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• 1997.04a
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• pp.17.1-17
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• 1997

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