• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.96.1-96.1
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• 2013

A Forbush decrease(FD) is a depression of cosmic ray intensity observed by ground-based neutron monitors(NMs). The cosmic ray intensity is thought to be modulated by the heliospheric magnetic structures including the interplanetary coronal mass ejection(ICME) surrounding the Earth. The different magnitude of the decreasing in intensity at each NM was explained only by the geomagnetic cutoff rigidity of NM station. However, sometimes NMs of the almost same rigidity in northern and southern hemispheres observe the asymmetric intensity depression magnitudes of FD events. Thus, in this study we intend to see the effects on cosmic ray intensity depression rate of FD event recorded at different NMs due to different ICME propagation direction as an additional parameter in the model explaining the cosmic ray modulation. Fortunately, since 2006 the coronagraphs of twin spacecraft of the STEREO mission allow us to infer the propagation direction of ICME associated with the FD event in 3-dimension with respect to the Earth. We confirm that the asymmetric cosmic ray decreasing modulations of FD events are determined by the propagation directions of the associated ICMEs.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.100.2-100.2
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• 2011

The dynamical evolution of the Earth's magnetosphere loaded with a transiently enhanced ring current is studied by numerical magnetohydrodynamic (MHD) simulation. Two cases with different values of the primitive ring current are considered. In one case, the initial ring current is strong enough to create a magnetic island in the magnetosphere. The magnetic island readily reconnects with the earth-connected ambient field and is destroyed as the system approaches a steady equilibrium. In the other case, the initial ring current is not so strong, and the initial magnetic field configuration bears no magnetic island, but a wake of bent field lines, which is smoothed out through the relaxing evolution of the magnetosphere. The relaxation time of the magnetosphere is found to be about five to six minutes, over which the ring current is reduced to about a quarter of its initial value. Before reaching a steady state, the magnetosphere is found to undergo an overshooting expansion and a subsequent contraction. Fast and slow magnetosonic waves are identified to play an important role in the relaxation toward equilibrium.

• The Bulletin of The Korean Astronomical Society
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• v.32 no.2
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• pp.70.1-70.1
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• 2007

• Proceedings of the KSRS Conference
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• v.1
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• pp.155-155
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• 2006

• The Bulletin of The Korean Astronomical Society
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• v.31 no.2
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• pp.65.1-65.1
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• 2006

• Electronics and Telecommunications Trends
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• v.38 no.2
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• pp.85-95
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• 2023

Space optical communication technology capable of large-capacity, high-speed, and low-latency communication can reduce the size, weight, and power consumption of radio frequency communications in existing satellite systems, thereby reducing launch costs, accommodating additional science instruments, and extending lifetime. Despite the high technical difficulty, various projects are being carried out in advanced countries regarding space technology for use in national security and defense, earth observation, and space communications. We review the advantages, key components, and development trends of space optical communication technology, which is attracting attention in applications such as satellite communications, intersatellite linking, and deep space communications.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.3
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• pp.483-488
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• 2019

The propagation prediction model of the earth-space communication link used as an international standard was used to calculate and analyze the total losses on the communication path. The standard definition and scope of ITU-R Rec. were analyzed for each parameter(rain, scintillation, atmospheric gas, clouds) used to calculate the total loss. The total losses were calculated using the standard model for each parameter and the statistical data provided by ITU-R, and the results were analyzed using the validation examples data. The rain losses were calculated using long-term local rainfall attenuation statistics data measured in the region, and compared with the calculation results using a rainfall map in the ITU-R Recommendation. The data of Cheollian satellites for the L-Band and Ka-Band were used to calculate the rainfall attenuation. In the range of 0.01% to 0.1%, it was found to have a greater attenuation slope when using local data than attenuation by the model of ITU-R.

• Journal of Astronomy and Space Sciences
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• v.27 no.1
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• pp.11-20
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• 2010

This paper designs a data link between a Lunar Orbiter (LO) and an Earth Station (ES), and analyzes the downlink performance of a space communications system for lunar exploration, conforming to the recommendations by the Consultative Committee for Space Data Systems (CCSDS). The results provided in the paper can be useful references for the design of reliable communication link for the Korean lunar exploration in the near future.

• Journal of Astronomy and Space Sciences
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• v.15 no.1
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• pp.75-82
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• 1998

A total of 842 observations (277 in B, 282 in V, and in R) for U Pegasi were made in October of 1996 at Mt. Sobaek Observatory. With our data we constructed the BVR light curves and determinded 5 times of minimum light. We also obtained physical parameters of the system by combined analysis of both light and radial velocity curves using the Wilson-Devinney code.

• The Korean Journal of Air & Space Law and Policy
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• v.9
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• pp.421-433
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• 1997

The orbit and frequency spectrum allocation for the communication and broadcasting satellite services are coordinated between the concerned parties according to the Radio Regulations of International Telecommunication Union (ITU). Currently, the geostationary orbit is filled with too many satellites for the commercial or military uses. In addition, a number of near earth satellite programs are being introduced. As each country claims for the space orbit and spectrum, the limited space resources are being exhausted. In this paper, the current situations in the worldwide satellite orbit demand are discussed, and some ideas on the peaceful, efficient and equitable use of space resources are proposed.