• Journal of Korea Fishing Vessel Association
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• v.71
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• pp.10-17
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• 1998

• The Science & Technology
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• no.8 s.447
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• pp.62-65
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• 2006

• Journal of Korea Fishing Vessel Association
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• v.68
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• pp.13-21
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• 1996

• Bulletin of the Korean Space Science Society
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• 1999.04a
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• pp.37-37
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• 1999

• Satellite Communications and Space Industry
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• v.15 no.1
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• pp.81-87
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• 2008

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.8
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• pp.141-147
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• 2002

Estimation of thrusters efficiency is a very important process at the end of lifetime of a satellite. This paper introduces a technique to estimate the efficiency change of thrusters considering bubble effect for Koreasat I. During APEMAC(Automatic Pitch Error/ Momentum Adjust Control), the change in thruster efficiency is estimated to compare the attitude telemetry data of the Koreasat I with the results of the control logic using Simulink. The outcome of this study is expected to contribute to improving the operational load at the end of generic communication satellite mission.

• Journal of Astronomy and Space Sciences
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• v.18 no.2
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• pp.137-144
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• 2001

This paper presents the REA thrusters performance estimation results for the KOREASAT F1&F2 launched in 1995 The satellite tracking data obtained from the ground system from end of 1999 to beginning of the 2000 are used to estimate the thruster performance. The estimation algorithm is derived from the least square estimation theory and designed to estimate the velocity change induced by the on-boarded thruster firing as well as the orbit parameter. The estimation results show that the Koreasat F1 thruster are in bad thruster condition of 64% performance for REA when it fires in on-pulse mode. Here, the performance is defined by the ratio of the resulted velocity change to that of planned. But, in the case o( the Koreasat F2, it is found that the performance approximately reaches up to 100%, even after the 5 years of the mission.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.8
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• pp.787-795
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• 2003

Three types of array antennas are developed for broadcasting band of Koreasat III. First, the specification of the array antenna is decided. Second, characteristics and advantages of three types of antennas using the radial waveguide characteristics is investigated and discussed. Third, design method fur those antenna is studied to meet antenna specifications, and then antennas are designed and tested. Finally, it is concluded that these types of antennas can be efficiently design compared to both parabola antennas and microstrip array within the limited size.

• Satellite Communications and Space Industry
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• v.4 no.3
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• pp.73-84
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• 1996

• Journal of Korean Society of Forest Science
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• v.90 no.4
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• pp.445-449
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• 2001

The objective of this study was to develop a new technique to control crown form of Hiscus syriacus to be used for an upright street tree with a single stem. Fertilization and raising the clear-bole length were the main treatments to compare the diameter and height growth of this species. The trees maintained with clear-bole length of 100, 150, and 200cm showed diameter growth of 15.7. 13.8, and 10.8mm, respectively, indicating the reduced diameter growth of trees with increasing clear-bole length, which is known as a typical characteristics in tending trees in silviculture. The effects of fertilization was not shown in this study. At the end of the two-year study from 1999 to 2,000, optimum diameter growth was obtained with the treatments of clear-bole length of 80-120cm, or 121-150cm. It is concluded that height and clear-bole length should be considered first in raising Hibiscus syriacus for street trees. Further study may be needed to obtain the effects of fertilization and raising the clear-bole length on uprightness of this species.