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

• Korean Journal of Optics and Photonics
• /
• v.34 no.1
• /
• pp.22-30
• /
• 2023

The use of segmented mirrors is one of the ways to make the primary mirror of a spaceborne satellite larger, where several small mirrors are combined into a large monolithic mirror. To align multiple segmented mirrors as one large mirror, there must be no discontinuity in the x, y-axis (tilt) and axial alignment error (piston) between adjacent mirrors. When the tilt and piston are removed, we can collect the light in one direction and get an expected clear image. Therefore, we need a precise wavefront sensor that can measure the alignment error of the segmented mirrors in nm scale. The tilt error can be easily detected by the point spread image of the segmented mirrors, while the piston error is hard to detect because of the absence of apparent features, but makes a downgraded image. In this paper we used an optical testing interferometer such as a Fizeau interferometer, which has various advantages when aligning the segmented mirror on the ground, and focused on measuring the axial displacement error of a segmented mirror as the basic research of measuring the piston errors between adjacent mirrors. First, we calculated the relationship between the axial displacement error of the segmented mirror and the surface defocus error of the interferometer and verified the calculated formula through experiments. Using the experimental results, we analyzed the measurement uncertainty and obtained the limitation of the Fizeau interferometer in detecting axial displacement errors.

• 한국신재생에너지학회:학술대회논문집
• /
• 2010.11a
• /
• pp.59.2-59.2
• /
• 2010

Throughout history, daylight has been a primary source of lighting in buildings, supplemented originally with burned fuels and more recently with electrical energy. Before daylight was supplemented or replaced with electric light in the late 19th-century, consideration of good daylight strategies was essential. As we entered the mid-20th-century, electric light supplanted daylight in buildings in many cases. Fortunately, during the last quarter of the 20th-century and early years of this century, architects and designers have recognized the importance and value of introducing natural light into buildings. There are many simple strategies that can enhance daylighting and reduce the need for electric lights. Good quality daylight is always welcome, but remember that the electric lights must be dimmed or shut off in order for daylighting to save energy. We designed and built mirror systems and vertical daylighting devices to improve daylight condition of office buildings in bad condition because urban density is getting higher. This case study aims to analysis the principles and characteristics of mirror systems and vertical daylighting devices and selected the method that can improve constructability. The results of this study are going to use the back data to set-up the design standards. Hereafter we're going to progress the performance test and product the design manual to improve applicability of daylighting systems at design phase.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.18 no.2
• /
• pp.135-141
• /
• 2004

We developed a polarimetric fiber-optic current sensor system for protective relaying usage. A fiber sensing coil that consisted of a length of twisted fiber and a FRM (Faraday rotator mirror) was used in order to suppress the linear birefringence effect. From the experiments with various sensing coil configurations and environmental conditions, the proposed current sensor system showed feasibility of suppressing environmental noises, and the obtained measurement stability was less than $\pm$3％ at rated primary current.

• Journal of the Optical Society of Korea
• /
• v.9 no.2
• /
• pp.68-73
• /
• 2005

When aligning catoptric or catadioptric telescopes for space cameras, it is difficult to align precisely if the field of view is large or there are several reflective surfaces. The quantitative knowledge of mirror misalignments greatly helps align a misaligned telescope precisely, and also reduce the alignment time. This paper describes a generalized reverse-optimization alignment solution algorithm using Zernike sensitivity, and proposes the minimum number of fields to take interferograms. This method was successfully applied on a Cassegrain telescope design for Earth observation from space with arbitrary misalignments and a model including some primary mirror deformation.

• Journal of Korean Medical classics
• /
• v.28 no.1
• /
• pp.71-95
• /
• 2015

Objectives : I'd like to introduce a Korean medical scientist, Lee Gyoojoon (李圭晙, 1855-1923)'s achievements about Huangdi's Internal Classic (黃帝內經, HIC) to examine the Section of Viscera and Bowels to inspect the Medical Classics (稽經藏府篇, SVBIM) of the Double grinded Medical Mirror (醫鑑重磨, DMM), which is a medical book published in 1922, his last studies. And I'd like to describe its meaning of medical history. Methods : For this, I compared the DMM with two primary texts, the representative medical books of Joseon dynasty, Treasured Mirror of Eastern Medicine (東醫寶鑑, TMEM) and Lee's former research result of HIC, Major Essentials of Huangdi's Internal Classic Plain Question (黃帝內經素問大要, MEHIC), in the aspects of the original text, annotation, editing, attached theses, and so on. Results : Lee Gyoojoon criticized the TMEM in two aspects. First, it was unfocused and miscellaneous, second, it intended to help Yin Qi (陰氣) and reduce Yang Qi (陽氣) so that it regards a prime mover, Yang Qi, as an enemy. In order to solve these problems he deleted miscellaneous articles and sort out the points to accord with the HIC. As a result, he had written the Section of SVBIM of the DMM in the form of revising the subtitles or refuting the contents of TMEM and quoted the partial texts of MEHIC to be written by the view of Supporting Yang Qi (扶陽). Conclusions : Lee Gyoojoon proposed the Supporting Yang Qi medicine to preserve the Heart fire (心火) based on his lifelong Neo-Confucianism (性理學) study. The Section of SVBIM of the DMM showed how to apply his medical theory, which is achieved by the study of the medical classic HIC to real clinical medicine through a medium of the TMEM. In addition, it could explain concretely how the Confucianists studied the medicine and how Confucianism can impact to the development of medical theory.

• Journal of The Korean Astronomical Society
• /
• v.55 no.1
• /
• pp.11-22
• /
• 2022

We introduce the Transformable Reflective Telescope (TRT) kit that applies an aluminum profile as a base plate for precise, stable, and lightweight optical system. It has been utilized for optical surface measurements, developing alignment and baffle systems, observing celestial objects, and various educational purposes through Research & Education projects. We upgraded the TRT kit using the aluminum profile and truss and isogrid structures for a high-end optical test device that can be used for prototyping of precision telescopes or satellite optical systems. Thanks to the substantial aluminum profile and lightweight design, mechanical deformation by self-weight is reduced to maximum 67.5 ㎛, which is an acceptable misalignment error compared to its tolerance limits. From the analysis results of non-linear vibration simulations, we have verified that the kit survives in harsh vibration environments. The primary mirror and secondary mirror modules are precisely aligned within 50 ㎛ positioning error using the high accuracy surface finished aluminum profile and optomechanical parts. The cross laser module helps to align the secondary mirror to fine-tune the optical system. The TRT kit with the precision aluminum mirror guarantees high quality optical performance of 5.53 ㎛ Full Width at Half Maximum (FWHM) at the field center.

• Korean Journal of Optics and Photonics
• /
• v.26 no.3
• /
• pp.155-161
• /
• 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
• /
• v.38 no.2
• /
• pp.81.1-81.1
• /
• 2013

The GMT project is moving ahead smoothly and is approaching the construction phase expected to begin around mid 2014. In this contribution, we will introduce the status of activities being made for the preparation of construction phase, including the Preliminary Design Review of sub-systems, the casting of primary mirror segments, and the GMT retreat.

• Journal of The Korean Astronomical Society
• /
• v.29 no.spc1
• /
• pp.399-400
• /
• 1996

LAMOST is a special reflecting Schmidt telescope. Both the refleting Schmidt plate $M_A$ and the spherical primary mitrror $M_B$ are segmened mirrors. These two cofocus but not co-phase. The diffraction of the optical system is decided by the shape overlapping of $M_A$ and $M_B$. This paper describes the diffraction caculating results with different declination and different field angle. The diffraction influence to the image quality is acceptable in the error buget of optical system. It also proves that the size seletion of the sub-mirror is reasonable.