• Korean Journal of Optics and Photonics
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• v.13 no.5
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• pp.442-448
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• 2002

In the earth telescope for space observation, the adaptive optical (AO) system that immediately compensates atmospheric turbulence is helpful to get high-resolution images. An adaptive optics for earth telescopes is very attractive, since the Earth telescopes can be made at lower costs and have larger optical apertures than space telescopes. Generally. in order to remove the wavefront error produced by atmospheric turbulence, a deformable mirror, whose surface shape changes in a controllable way in response to a drive signal, is used. The characteristics and patterns of actuators are very important for the effective control of a deformable mirror. The mirror surface shape deformed by one actuator is defined as an influence function and the deformable mirror can be effectively modeled and designed using this influence function. In this paper. by simplifying the actual influence function obtained by FEM analyses into the Gaussian function and introducing the coupling coefficient between actuators, the influence function is constructed. The proper coupling coefficient of the target system can be obtained by performance analyses of a deformable mirror for various coupling coefficients. Using the constructed influence function, the deformable mirror with equally spaced triangular and square actuator patterns is analyzed for various spacings and an effective actuator pattern is proposed.

• 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.

• Journal of Korea Society of Industrial Information Systems
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• v.15 no.5
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• pp.37-51
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• 2010

In this paper, we discuss the program implementation and system optimization for the effective transfer of huge amount of data. In VLBI which is observing the celestial bodies by using radio telescope hundreds thousands km apart, it is necessary for each VLBI observatory to transfer up to terabytes of observed data. For this reason, e-VLBI research based on advanced network is being actively carried out for the transfer of data efficiently. Following this trend, in this paper, we discuss design & implementation of system for the high speed Gbps data transfer rates. As a data transfer protocol, we use UDP for designing data transmission program with much higher speeds than currently available via VTP(VLBI Transport Protocol). Tsunami-UDP algorithms is applied to implementing data transfer program so that transmission performance could be maximize, also we make it possible to transfer observed data more fast and reliable through optimization of computer systems in each VLBI statopm.

• Journal of Astronomy and Space Sciences
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• v.16 no.2
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• pp.227-240
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• 1999

We performed CCD photometric observations of W UMa type contact binary BV Dra during eight nights from May 1996 to June 1999 using 61cm telescope at Sobaeksan Optical Astronomy Observatory, and completed BV R light curves of the system. From our observations, we derived nine new times of minimum lights (five timings for primary eclipse, four for secondary) and determined new light elements with the times of minima observed since 1999. Our BV R light curves and Batten & Lu(1986)'s radial-velocity ones were simultaneously analyzed with contact mode (Mode 3) of Wilson-Devinney's binary model, and the photometric and spectroscopic solutions for BV Dra were solved. In the analysis, we derived the solutions of 1999 light curves with and without spots, respectively. As the results, asymmetry of light curves may be interpreted as produced by the existence of two spots; hot spot on the secondary and cool on the primary. Combining solutions of light curves and radial-velocity ones, absolute dimensions of BV Dra are $M_1=0.40M_{odot}$, $M_2=1.01M_{odot}$, $R_1=0.72R_{odot}$, $R_2=0.40R_{odot}$. In mass-radius diagram, the less massive and hotter primary component of BV Dra is near TAMS and the secondary is near ZAMS, which is very similar to the other W-type W UMa binaries.

• Journal of Astronomy and Space Sciences
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• v.33 no.2
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• pp.127-135
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• 2016

Inactive space objects are usually rotating and tumbling as a result of internal or external forces. KOREASAT 1 has been inactive since 2005, and its drift trajectory has been monitored with the optical wide-field patrol network (OWL-Net). However, a quantitative analysis of KOREASAT 1 in regard to the attitude evolution has never been performed. Here, two optical tracking systems were used to acquire raw measurements to analyze the rotation period of two inactive satellites. During the optical campaign in 2013, KOREASAT 1 was observed by a 0.6 m class optical telescope operated by the Korea Astronomy and Space Science Institute (KASI). The rotation period of KOREASAT 1 was analyzed with the light curves from the photometry results. The rotation periods of the low Earth orbit (LEO) satellite ASTRO-H after break-up were detected by OWL-Net on April 7, 2016. We analyzed the magnitude variation of each satellite by differential photometry and made comparisons with the star catalog. The illumination effect caused by the phase angle between the Sun and the target satellite was corrected with the system tool kit (STK) and two line element (TLE) technique. Finally, we determined the rotation period of two inactive satellites on LEO and geostationary Earth orbit (GEO) with light curves from the photometry. The main rotation periods were determined to be 5.2 sec for ASTRO-H and 74 sec for KOREASAT 1.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.40.1-40.1
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• 2010

The Main payload of the STSAT-3 (Korea Science & Technology Satellite-3), MIRIS (Multipurpose Infra-Red Imaging System) has been developed for last 3 years by KASI, and its Flight Model (FM) is now being developed as the final stage. All optical lenses and the opto-mechanical components of the FM have been completely fabricated with slight modifications that have been made to some components based on the Engineering Qualification Model (EQM) performances. The components of the telescope have been assembled and the test results show its optical performances are acceptable for required specifications in visual wavelength (@633 nm) at room temperature. The ensuing focal plane integration and focus test will be made soon using the vacuum chamber. The MIRIS mechanical structure of the EQM has been modified to develop FM according to the performance and environment test results. The filter-wheel module in the cryostat was newly designed with Finite Element Analysis (FEM) in order to compensate for the vibration stress in the launching conditions. Surface finishing of all components were also modified to implement the thermal model for the passive cooling technique. The FM electronics design has been completed for final fabrication process. Some minor modifications of the electronics boards were made based on EQM test performances. The ground calibration tests of MIRIS FM will be made with the science grade Teledyne PICNIC IR-array.

• Journal of the Institute of Convergence Signal Processing
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• v.15 no.4
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• pp.183-191
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• 2014

This paper describes the development of the observational data transmission algorithm for high-speed network in radio astronomy. For the preprocessing of VLBI data observed by radio telescope, data transmission algorithm uses the VDIF specification, VDIFCP, and UDP protocol by transferring VLBI data stored in a massive storage server with one-to-one correspondence between the server and the RVDB of Daejeon correlator. A transmission method is proposed, which reads the recorded data in Mark5B VSI format and trnasmits 2048 Mbps VLBI data by software through UDP packet transmission, while RVDB system is waiting for the transmitting data from the server. In order to check the effectiveness of the proposed method, the data transmission between the massive storage server and RVDB is conducted and the transmitted data is correlated by Daejeon correlator for the accurate comparison concerning the data before and after. The transmitted data is shown to be completely the same as the original data without any data transmission loss. Henceforth, the developed data transmission algorithm in this research is expected to be applied effectively as e-VLBI for KaVA network.

• Journal of the Institute of Convergence Signal Processing
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• v.15 no.4
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• pp.176-182
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• 2014

This paper introduces the development of global fringe search (GFS) software for preprocessing of Daejeon Correlator. In case of the VLBI observation, a observer conducts the observation for the reference sources with strong and point-like radio stars on schedule in order to confirm the well-observedness of the radio source by the radio telescope. The correlator performs the correlation for the reference sources to detect the fringe completely. We developed the GFS software by calculating the precise delay time between each observatory based on specific observatory. Then, this software calculates the precise delay time by using the delay model (correlator model) of reference source and information of time offset between the Hydrogen Maser frequency standard and GPS (Global Positioning System) clock located in each observatory through the correlation preprocessing. In order to confirm the performance of the developed software, experiments were carried out for the reference sources and target sources observed by the KaVA (KVN and VERA Array). Experimental results show that the GFS software has effectively good performance by finding the precise delay time offset according to the comparison between the compensated delay time offset and one without compensation.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.52.2-52.2
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• 2014

The Immersion Grating Infrared Spectrometer (IGRINS) is an unprecedentedly minimized infrared cross-dispersed echelle spectrograph with a high-resolution and high-sensitivity optical performance. A silicon immersion grating features the instrument for the first time in this field. IGRINS will cover the entire portion of the wavelength range between 1.45 and $2.45{\mu}m$ accessible from the ground in a single exposure with spectral resolution of 40,000. Individual volume phase holographic (VPH) gratings serve as cross-dispersing elements for separate spectrograph arms covering the H and K bands. On the 2.7m Harlan J. Smith telescope at the McDonald Observatory, the slit size is $1^{\prime\prime}{\times}15^{\prime\prime}$. IGRINS has a $0.27^{\prime\prime}$ pixel-1 plate scale on a $2048{\times}2048$ pixel Teledyne Scientific & Imaging HAWAII-2RG detector with SIDECAR ASIC cryogenic controller. The instrument includes four subsystems; a calibration unit, an input relay optics module, a slit-viewing camera, and nearly identical H and K spectrograph modules. The use of a silicon immersion grating and a compact white pupil design allows the spectrograph collimated beam size to be 25mm, which permits the entire cryogenic system to be contained in a moderately sized rectangular vacuum chamber. The fabrication and assembly of the optical and mechanical hardware components were completed in 2013. In this presentation, we describe the major design characteristics of the instrument and the early performance estimated from the first light commissioning at the McDonald Observatory.

• Journal of the Korea Institute of Construction Safety
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• v.1 no.1
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• pp.47-56
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• 2018

In this paper, we analyze various cases of accidents caused by vehicle-mounted MEWPs(mobile elevated work platforms) which are most widely used for the high position level works, review the safety improvement measures for each of them, and propose basic data for the revision of related laws. The accidents by MEWPs were caused by the high level of works, which lead to fatal personnel accidents, so the measures for safety must be thoroughly carried out and the obligatory regulations by the related laws must be strictly observed. In this paper, we classify the cases of accidents at the workshop as 4 representative types and propose measures and remedies for them. According to the current regulations, it is possible to prepare for the accidents such as the wire rope breakage by switching to the all-chain drive method which does not have a daily use time limit instead of the wire rope drive method which is widely used at present. Also, it is suggested to add the daily use timetable to the nameplate attachment duty item according to the driving class.