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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 30/126
291
- Lee, Sang-Yun
- Journal of astronomy and space sciences
- 32, n.1
- pp.45-50
- 2015
- 원문 바로보기
We have developed a 2.5-dimensional electromagnetic particle simulation code using the particle-in-cell (PIC) method to investigate electromagnetic phenomena that occur in space plasmas. Our code is based on the leap-frog method and the centered difference method for integration and differentiation of the governing equations. We adopted the relativistic Buneman-Boris method to solve the Lorentz force equation and the Esirkepov method to calculate the current density while maintaining charge conservation. Using the developed code, we performed test simulations for electron two-stream instability and electron temperature anisotropy induced instability with the same initial parameters as used in previously reported studies. The test simulation results are almost identical with those of the previous papers.
292
- Hwang, Kyoung-Joo
- Journal of astronomy and space sciences
- 32, n.1
- pp.1-11
- 2015
- 원문 바로보기
Earth's magnetopause separating the fast and often turbulent magnetosheath and the relatively stagnant magnetosphere provides various forms of free energy that generate low-frequency surface waves. The source mechanism of this energy includes current-driven kinetic physical processes such as magnetic reconnection on the dayside magnetopause and flux transfer events drifting along the magnetopause, and velocity shear-driven (Kelvin-Helmholtz instability) or density/pressure gradient-driven (Rayleigh-Taylor instability) magnetohydro-dynamics (MHD) instabilities. The solar wind external perturbations (impulsive transient pressure pulses or quasi-periodic dynamic pressure variations) act as seed fluctuations for the magnetopause waves and trigger ULF pulsations inside the magnetosphere via global modes or mode conversion at the magnetopause. The magnetopause waves thus play an important role in the solar wind-magnetosphere coupling, which is the key to space weather. This paper presents recent findings regarding the generation of surface waves (e.g., Kelvin-Helmholtz waves) at the Earth's magnetopause and analytic and observational studies accountable for the linking of the magnetopause waves and inner magnetospheric ULF pulsations, and the impacts of magnetopause waves on the dynamics of the magnetopause and on the inner magnetosphere.
293
- Song, Young-Joo
- Journal of astronomy and space sciences
- 32, n.3
- pp.257-268
- 2015
- 원문 바로보기
Characteristics of delta-V requirements for deploying an impactor from a mother-ship at different orbital altitudes are analyzed in order to prepare for a future lunar CubeSat impactor mission. A mother-ship is assumed to be orbiting the moon with a circular orbit at a 90 deg inclination and having 50, 100, 150, 200 km altitudes. Critical design parameters that are directly related to the success of the impactor mission are also analyzed including deploy directions, CubeSat flight time, impact velocity, and associated impact angles. Based on derived delta-V requirements, required thruster burn time and fuel mass are analyzed by adapting four different miniaturized commercial onboard thrusters currently developed for CubeSat applications. As a result, CubeSat impact trajectories as well as thruster burn characteristics deployed at different orbital altitudes are found to satisfy the mission objectives. It is concluded that thrust burn time should considered as the more critical design parameter than the required fuel mass when deducing the onboard propulsion system requirements. Results provided through this work will be helpful in further detailed system definition and design activities for future lunar missions with a CubeSat-based payload.
294
- Lee, Kwangwon
- Journal of astronomy and space sciences
- 32, n.4
- pp.387-393
- 2015
- 원문 바로보기
This study presents a precise relative navigation algorithm using both laser and Global Positioning System (GPS) measurements in real time. The measurement model of the navigation algorithm between two spacecraft is comprised of relative distances measured by laser instruments and single differences of GPS pseudo-range measurements in spherical coordinates. Based on the measurement model, the Extended Kalman Filter (EKF) is applied to smooth the pseudo-range measurements and to obtain the relative navigation solution. While the navigation algorithm using only laser measurements might become inaccurate because of the limited accuracy of spacecraft attitude estimation when the distance between spacecraft is rather large, the proposed approach is able to provide an accurate solution even in such cases by employing the smoothed GPS pseudo-range measurements. Numerical simulations demonstrate that the errors of the proposed algorithm are reduced by more than about 12% compared to those of an algorithm using only laser measurements, as the accuracy of angular measurements is greater than <TEX>$0.001^{\circ}$</TEX> at relative distances greater than 30 km.
295
- Choi, Kyu-Cheol
- Journal of astronomy and space sciences
- 32, n.4
- pp.427-434
- 2015
- 원문 바로보기
Coronal Mass Ejections (CME), which originate from active regions of the Sun's surface, e.g., sunspots, result in geomagnetic storms on Earth. The variation of the Earth's geomagnetic field during such storms induces surface currents that could cause breakdowns in electricity power grids. Hence, it is essential to both monitor Geomagnetically Induced Currents (GICs) in real time and analyze previous GIC data. In 2012, in order to monitor the variation of GICs, the Korean Space Weather Center (KSWC) installed an induced current measurement system at SINGAPYEONG Substation, which is equipped with 765 kV extra-high-voltage transformers. Furthermore, in 2014, two induced current measurement systems were installed on the 345 kV high-voltage transformers at the MIGEUM and SINPOCHEON substations. This paper reports the installation process of the induced current measurement systems at these three substations. Furthermore, it presents the results of both an analysis performed using GIC data measured at the SINGAPYEONG Substation during periods of geomagnetic storms from July 2013 through April 2015 and the comparison between the obtained GIC data and magnetic field variation (dH/dt) data measured at the Icheon geomagnetic observatory.
296
- Kim, Sang Hyuk
- Journal of astronomy and space sciences
- 32, n.4
- pp.395-401
- 2015
- 원문 바로보기
We investigated the six remaining Yang-cheon-cheoks (量天尺), which were first described in the Veritable Record of King Sukjong (肅宗實錄). These woodblock sundials from Korea are structurally very similar to a Gyupyo (圭表, gnomon) or an altitude sundial and are light, compact, and portable. The front side of a Yang-cheon-cheok has two holes for styluses and several hour-lines. We compared the intervals of the hour-lines from the originating point of the stylus placement on all Yang-cheon-cheoks and found that two of the relics had the same hour-lines using the standard of the unit of 1 chon (寸). These two were actually the same sundial although the physical size was different. In spite of the lack of time accuracy, we hypothesize that various-sized Yang-cheon-cheoks were made and widely distributed throughout the public in the late Joseon Dynasty.
297
- Korsunova, Lidiya P.
- Journal of astronomy and space sciences
- 32, n.2
- pp.137-140
- 2015
- 원문 바로보기
The results of the study of ionospheric variations in the summer months of 1998-2002 at an ionospheric station of vertical sounding 'Petropavlovsk-Kamchatsky' are presented. Anomalous variations of virtual sporadic-E height (h'Es), Es blanketing frequency (fbEs), and the critical frequency of the ionospheric F2 layer (foF2) (which can be attributed to the possible earthquake precursors) are selected. The high efficiency of the selection of ionospheric earthquake precursors based on the several parameters of Es and F2 layers is shown. The empirical dependence, which reflects the connection between the lead-time of the earthquake moment, the distance to the epicenter from the observation point, and the magnitude of the earthquake are obtained. This empirical dependence is consistent with the results of the detection of earthquake precursors by measuring the physical parameters of the Earth's crust in the same region.
298
- Kim, Youn-Kyu
- Journal of astronomy and space sciences
- 32, n.4
- pp.419-425
- 2015
- 원문 바로보기
In this study, a new idea for developing a space scale for measuring mass in a microgravity environment was proposed by using the inertial force properties of an object to measure its mass. The space scale detected the momentum change of the specimen and reference masses by using a load-cell sensor as the force transducer based on Newton's laws of motion. In addition, the space scale calculated the specimen mass by comparing the inertial forces of the specimen and reference masses in the same acceleration field. By using this concept, a space scale with a capacity of 3 kg based on the law of momentum conservation was implemented and demonstrated under microgravity conditions onboard International Space Station (ISS) with an accuracy of <TEX>${\pm}1g$</TEX>. By the performance analysis on the space scale, it was verified that an instrument with a compact size could be implemented and be quickly measured with a reasonable accuracy under microgravity conditions.
299
- Choi, Yong-Dae
- Journal of astronomy and space sciences
- 32, n.2
- pp.151-159
- 2015
- 원문 바로보기
The fundamental conception in physics of the propagation of the electromagnetic wave polarization in matter is newly understood as the cardinal keyword in free-space quantum communication technology and cosmology in astrophysics. Interactive visualization of the propagation mechanism of polarized electromagnetism in a medium with its helicity has accordingly received attention from scientists exploiting the protocol of quantum key distribution (QKD) to guarantee unconditional security in cryptography communication. We have provided a dynamic polarization platform for presenting the polarization modes of a transverse electromagnetic wave, converting the state of polarization through the arrangement of optical elements, using Jones vectors calculations in Methematica. The platform graphically simulates the mechanism of production and propagation of the polarized waves in a medium while satisfying Maxwell's equations.
300
- Yi, Eung Seok
- Journal of astronomy and space sciences
- 32, n.2
- pp.161-166
- 2015
- 원문 바로보기
Analysis of lunar samples returned by the US Apollo missions revealed that the lunar highlands consist of anorthosite, plagioclase, pyroxene, and olivine; also, the lunar maria are composed of materials such as basalt and ilmenite. More recently, the remote sensing approach has enabled reduction of the time required to investigate the entire lunar surface, compared to the approach of returning samples. Moreover, remote sensing has also made it possible to determine the existence of specific minerals and to examine wide areas. In this paper, an investigation was performed on the reflectance distribution and its trend. The results were applied to the example of the double ray stretched in parallel lines from the Tycho crater to the third-quadrant of Mare Nubium. Basic research and background information for the investigation of lunar surface characteristics is also presented. For this research, resources aboard the SELenological and ENgineering Explorer (SELENE), a Japanese lunar probe, were used. These included the Multiband Imager (MI) in the Lunar Imager/Spectrometer (LISM). The data of these instruments were edited through the toolkit, an image editing and analysis tool, Exelis Visual Information Solution (ENVI).