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1984년 ~ 2026년까지 1,258 건의 한국우주과학회지를 계간으로 확인하실 수 있습니다.
- The Korean Space Science Society (The Korean Astronomical Society)
- 계간 (Quarterly)
- ISSN : 1225-052x (ISSN : 1225-052x)
1225-052x
- DB구축현황 : 1,258건 (DB Construction : 1,258 Articles)
총 게시글 1,258건
페이지 46/126
451
- Kim, Sang-Hyuk
- Journal of astronomy and space sciences
- 28, n.1
- pp.79-91
- 2011
- 원문 바로보기
Ongnu (Jade Clepsydra; also called Heumgyeonggaknu) is a water clock was made by Jang Yeong-sil in 1438. It is not only an automatic water clock that makes the sound at every hour on the hour by striking bell, drum and gong, but also an astronomical clock that shows the sun's movement over time. Ongnu's power mechanism used is a water-hammering method applied to automatic time-signal device. The appearance of Ongnu is modeled by Gasan (pasted-paper imitation mountain) and Binpungdo (landscape of farming work scene) is drawn at the foot of the mountain. The structure of Ongnu is divided into the top of the mountain, the foot of the mountain and the flatland. There located are sun-movement device, Ongnyeo (jade female immortal; I) and Four gods (shaped of animal-like immortals) at the top of the mountain, Sasin (jack hour) and Musa (warrior) at the foot of the mountain, and Twelve gods, Ongnyeo (II) and Gwanin on the flatland. In this study, we clearly and systematically understood the time-announcing mechanism of each puppet. Also, we showed the working mechanism of the sun-movement device. Finally, we completely established the 3D model of Ongnu based on this study.
452
- Kim, Jae-Hyuk
- Journal of astronomy and space sciences
- 28, n.3
- pp.183-192
- 2011
- 원문 바로보기
The current study analyzes the effects of the scaling parameters of the batch unscented transformation on precision satellite orbit determination. Satellite laser ranging (SLR) data are used in the orbit determination algorithm, which consists of dynamics model, observation model and filtering algorithm composed of the batch unscented transformation. TOPEX/Poseidon SLR data are used by utilizing the normal point (NP) data observed from ground station. The filtering algorithm includes a repeated series of processes to determine the appropriate scaling parameters for the batch unscented transformation. To determine appropriate scaling parameters, general ranges of the scaling parameters of <TEX>${\alpha}$</TEX>, <TEX>${\beta}$</TEX>, k, <TEX>$\lambda$</TEX> are established. Depending on the range settings, each parameter was assigned to the filtering algorithm at regular intervals. Appropriate scaling parameters are determined for observation data obtained from several observatories, by analyzing the relationship between tuning properties of the scaling parameters and estimated orbit precision. The orbit determination of satellite using the batch unscented transformation can achieve levels of accuracy within several tens of cm with the appropriate scaling parameters. The analyses in the present study give insights into the roles of scaling parameters in the batch unscented transformation method.
453
- Kim, Bang-Yeop
- Journal of astronomy and space sciences
- 28, n.2
- pp.103-108
- 2011
- 원문 바로보기
The latitudinal variation of sunspots appearing during the period from 1874 to 2009 has been studied in terms of centerof-latitude (COL). The butterfly diagram has been used to study the evolution of the magnetic field and the dynamics at the bottom of the solar convection zone. Short-term periodicities have been of particular interest, in that they are somehow related to the structure and dynamics of the solar interior. We thus have focused our investigation on shortterm periodicities. We first calculated COL by averaging the latitude of sunspots with the weight function in area. Then, we analyzed the time series of COL using the wavelet transform technique. We found that a periodicity of ~5 years is the most dominant feature in the time series of COL, with the exception of the ~11 year solar cycle itself. This periodicity can be easily understood by considering small humps between the minima in the area-weighted butterfly diagram. However, we find that periodicities of ~1.3 (0.064), ~1.5 (0.056), or ~1.8 (0.046) years (<TEX>$\frac{1}{month}$</TEX>), month ), which have been previously suggested as evidence of links between the changing structure of the sunspot zone and the tachocline rotation rate oscillations, are insignificant and inconsistent. We therefore conclude that the only existing short-term periodicity is of ~5 years, and that periodicities of ~1.3, ~1.5, or ~1.8 years are likely to be artifacts due to random noise of small sunspots.
454
- Lim, Hyung-Chul
- Journal of astronomy and space sciences
- 28, n.2
- pp.155-162
- 2011
- 원문 바로보기
Korea Astronomy and Space Science Institute has been developing one mobile and one stationary satellite laser ranging system for the space geodesy research and precise orbit determination since 2008, which are called as ARGO-M and ARGO-F, respectively. They will be capable of daytime laser ranging as well as nighttime and provide the accurate range measurements with millimeter level precision. Laser ranging accuracy is mostly dependent on the optics and optoelectronic system which consists of event timer, optoelectronic controller and photon detectors in the case of ARGO-M. In this study, the optoelectronic system of ARGO-M is addressed and its critical design is also presented. Additionally, the experiment of the integrated optoelectronic system was performed in the laboratory to validate the functional operation of each component and its results are analyzed to investigate ARGO-M performance in advance.
455
- Jeong, Jang-Hae
- Journal of astronomy and space sciences
- 28, n.3
- pp.163-172
- 2011
- 원문 바로보기
An intensive analysis of 185 timings of WZ Cep, including our new three timings, was made to understand the dynamical picture of this active W UMa-type binary. It was found that the orbital period of the system has complexly varied in two cyclical components superposed on a secularly downward parabola over about 80y. The downward parabola, corresponding to a secular period decrease of <TEX>$-9.{^d}97{\times}10^{-8}y^{-1}$</TEX>, is most probably produced by the action of both angular momentum loss (AML) due to magnetic braking and mass-transfer from the massive primary component to the secondary. The period decrease rate of <TEX>$-6.^{d}72{\times}10^{-8}y^{-1}$</TEX> due to AML contributes about 67% to the observed period decrease. The mass flow of about <TEX>$5.16{\times}10^{-8}M_{\odot}y^{-1}$</TEX> from the primary to the secondary results the remaining 33% period decrease. Two cyclical components have an <TEX>$11.^{y}8$</TEX> period with amplitude of <TEX>$0.^{d}0054$</TEX> and a <TEX>$41.^{y}3$</TEX> period with amplitude of <TEX>$0.^{d}0178$</TEX>. It is very interesting that there seems to be exactly in a commensurable 7:2 relation between their mean motions. As the possible causes, two rival interpretations (i.e., light-time effects (LTE) by additional bodies and the Applegate model) were considered. In the LTE interpretation, the minimum masses of <TEX>$0.30M_{\odot}$</TEX> for the shorter period and <TEX>$0.49M_{\odot}$</TEX> for the longer one were calculated. Their contributions to the total light were at most within 2%, if they were assumed to be main-sequence stars. If the LTE explanation is true for the WZ Cep system, the 7:2 relation found between their mean motions would be interpreted as a stable 7:2 orbit resonance produced by a long-term gravitational interaction between two tertiary bodies. In the Applegate model interpretation, the deduced model parameters indicate that the mechanism could work only in the primary star for both of the two period modulations, but could not in the secondary. However, we couldn't find any meaningful relation between the light variation and the period variability from the historical light curve data. At present, we prefer the interpretation of the mechanical perturbation from the third and fourth stars as the possible cause of two cycling period changes.
456
- Kim, Jae-Hyuk
- Journal of astronomy and space sciences
- 28, n.4
- pp.319-332
- 2011
- 원문 바로보기
The objectives of this study are to analyze the satellite visibility at the randomly established ground sites, to determine the five optimal ground sites to perform the optical surveillance and tracking of domestic satellites, and to verify the acquisition of the optical observation time sufficient to maintain the precise ephemeris at optimal ground sites that have been already determined. In order to accomplish these objectives, we analyzed the visibility for sun-synchronous orbit satellites, low earth orbit satellites, middle earth orbit satellites and domestic satellites as well as the continuous visibility along with the fictitious satellite ground track, and calculate the effective visibility. For the analysis, we carried out a series of repetitive process using the satellite tool kit simulation software developed by Analytical Graphics Incorporated. The lighting states of the penumbra and direct sun were set as the key constraints of the optical observation. The minimum of the observation satellite elevation angle was set to be 20 degree, whereas the maximum of the sun elevation angle was set to be -10 degree which is within the range of the nautical twilight. To select the candidates for the optimal optical observation, the entire globe was divided into 84 sectors in a constant interval, the visibility characteristics of the individual sectors were analyzed, and 17 ground sites were arbitrarily selected and analyzed further. Finally, five optimal ground sites (Khurel Togoot Observatory, Assy-Turgen Observatory, Tubitak National Observatory, Bisdee Tier Optical Astronomy Observatory, and South Africa Astronomical Observatory) were determined. The total observation period was decided as one year. To examine the seasonal variation, the simulation was performed for the period of three days or less with respect to spring, summer, fall and winter. In conclusion, we decided the optimal ground sites to perform the optical surveillance and tracking of domestic satellites and verified that optical observation time sufficient to maintain the precise ephemeris could be acquired at the determined observatories.
457
- Jang, Sung-Soo
- Journal of astronomy and space sciences
- 28, n.2
- pp.133-141
- 2011
- 원문 바로보기
A satellite power system should generate and supply sufficient electric power to perform the satellite mission successfully during the satellite mission period, and it should be developed to be strong to the failure caused by the severe space environment. A satellite power system must have a high reliability with respect to failure. Since it cannot be repaired after launching, different from a ground system, the failures that may happen in space as well as the effect of the failures on the system should be considered in advance. However, it is difficult to use all the hardware to test the performance of the satellite power system to be developed in order to consider the failure mechanism of the electrical power system. Therefore, it is necessary to develop an accurate model for the main components of a power system and, based on that, to develop an accurate model for the entire power system. Through the power system modeling, the overall effect of failure on the main components of the power system can be considered and the protective design can be devised against the failure. In this study, to analyze the failure mode of the power system and the effects of the failure on the power system, we carried out modeling of the main power system components including the solar array regulator, and constituted the entire power system based on the modeling. Additionally, we investigated the effects of representative failures in the solar array regulator on the power system using the power system model.
458
- Sohn, Bong-Won
- Journal of astronomy and space sciences
- 28, n.4
- pp.267-271
- 2011
- 원문 바로보기
I developed an enhanced correction method for Ricean bias which occurs in linear polarization measurement. Two known methods for Ricean bias correction are reviewed. In low signal-to-noise area, the method based on the mode of the equation gives better representation of the fractional polarization. But a caution should be given that the accurate estimation of noise level, i.e. <TEX>${\sigma}$</TEX> of the polarized flux, is important. The maximum likelihood method is better choice for high signal-to-noise area. I suggest a hybrid method which uses the mode of the equation at the low signal-to-noise area and takes the maximum likelihood method at the high signal-to-noise area. A modified correction coefficient for the mode solution is proposed. The impact on the depolarization measure analysis is discussed.
459
- Jo, Jung-Hyun
- Journal of astronomy and space sciences
- 28, n.1
- pp.93-102
- 2011
- 원문 바로보기
Korea Astronomy and Space Science Institute (KASI) launched the development project of two satellite laser ranging (SLR) systems in early 2008 after the government fund approval of the SLR systems in 2007. One mobile SLR system and one permanent SLR station will be developed with the completion of the project. The main objectives of these systems will be focused on the Space Geodetic researches. A system requirement review was held in the second half of the same year. Through the following system design review meeting and other design reviews, many unsolved technical and engineering issues would be discussed and resolved. However, the design of the mobile SLR system is a corner stone of whole project. The noticeable characteristics of Korea's first SLR system are 1) use of light weight main mirror, 2) design of compact optical assembly, 3) use of KHz laser pulse, 4) use of commercial laser generator, 5) remote operation capability, 6) automatic tracking, 7) state of art operation system, etc. In this paper, the major user requirement and pre-defined specification are presented and discussed.
460
- Cho, Il-Hyun
- Journal of astronomy and space sciences
- 28, n.1
- pp.1-7
- 2011
- 원문 바로보기
Characteristics of latitude variations of sunspots in the northern and southern hemispheres are investigated using the daily sunspot area and its latitude during the period from 1874 to 2009. Solar magnetic activity is portrayed in the form of sunspot, regions of concentrated fresh magnetic fields observed on the surface of the Sun. By defining center-of-latitude (COL) as an area-weighted latitude, we find that COL is not monotonically decreasing as commonly assumed. In fact, small humps (or short plateaus) between solar minima can be seen around every solar maxima. We also find that when the northern (southern) hemisphere is magnetically dominant, COL is positive (negative), except the solar cycle 23, which may give a hint that these two phenomena are consistently regulated by one single mechanism. As a result of periodicity analysis, we find that several significant periodicities, such as, of ~5.5, ~11, ~49, and ~167 years.