• Journal of Astronomy and Space Sciences
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• v.16 no.2
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• pp.159-166
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• 1999

As the spatial resolution of remote sensing satellites becomes higher, very accurate determination of the position of a LEO (Low Earth Orbit) satellite is demanding more than ever. Non-symmetric Earth gravity is the major perturbation force to LEO satellites. Since the orbit propagation is performed in the celestial frame while Earth gravity is defined in the terrestrial frame, it is required to convert the coordinates of the satellite from one to the other accurately. Unless the coordinate conversion between the two frames is performed accurately the orbit propagation calculates incorrect Earth gravitational force at a specific time instant, and hence, causes errors in orbit prediction. The coordinate conversion between the two frames involves precession, nutation, Earth rotation and polar motion. Among these factors, unpredictability and uncertainty of Earth rotation, called UTI-UTC, is the largest error source. In this paper, the effect of UTI-UTC on the accuracy of the LEO propagation is introduced, tested and analzed. Considering the maximum unpredictability of UTI-UTC, 0.9 seconds, the meaningful order of non-spherical Earth harmonic functions is derived.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2002.04a
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• pp.82-83
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• 2002

궤도상에 올려진 위성들은 인형의 궤도 운행을 하게 된다. 그러나 지구가 완전한 구형이 아니고 태양과 달의 인력이 작용하여 위성에 섭동이 발생하게 된다. 그리고 무중력 상태의 우주이므로 태양풍이나 미세 운석 그리고 위성체 내부의 가스 누출이나 내부의 토크 변화에 의해 위성 자세에 조금의 변동을 야기한다. 통신 위성의 경우 지상의 한 지점을 계속 향하고 있어야 하므로 정기적인 자세제어가 필요하다. 위성의 섭동에 의해 EWSK(East-West station keeping)나 NSSK(North-South station keeping)를 하기 위해 추력 모델은 단일 $\Delta$$\upsilon$기동이나 회전 세차 운동(spin precession maneuver)을 지원해야 한다. 위성은 주어진 임무를 수행하는데 필요한 $\Delta$$\upsilon$기동을 위해 적절한 성능의 추력기와 임무기간 동안 사용할 적절한 양의 추진제를 탑재하고 있다. 지상에서 필요한 임무를 수행하기 위해 위성에 지령을 하였을 때, 추력기가 정상작동을 하였는지 그리고 잔류 추진제가 어느 정도 인지를 정확히 알 수 있어야 한다.

• Proceedings of the KIEE Conference
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• 1999.07b
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• pp.553-555
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• 1999

In this paper, we developed the new-type digital gyrocompass for ship. This is made of DTG(Dynamically Tuned Gyro) and two accelerometers. The simple structure of two-axis free gimbals and the digital precession by CPU unit are main differences from Sperry or Anschutz type gyrocompass. As experimental results, the developed gyrocompass seeks the true north within 1 hour and support maximum speed 100[knot], maximum latitude $75[^{\circ}]NS$. By the comparison with other company's Products, we show the uniqueness and the excellence of the proposed gyrocompass.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.47.4-48
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• 2017

In the middle of $19^{th}$ century, the Seong Gyeong 星鏡, which is a Korean historical astronomy book, was published by Nam Byeong-Gil(1820-1869). In this study, identification was conducted by considering the star catalogue recorded in the Yixiang Kaocheng Xubian 儀象考成續編. The Seong Gyeong 星鏡 recorded the information of 1,449 stars, and identified 1,413 stars among 1,449 stars, which is a rate of 97.5%. The positional error (angular distance) of the identified stars is $5.33{\pm}0.34$ arc-min. It was also confirmed that the magnitudes of the recorded stars have correlations with those of modern times. It was determined that the position error of the stars became larger as the magnitude of the stars became dimmer, or as the position of the stars came closer to the pole. Based on these analyses, the Seong Gyeong 星鏡 was confirmed that it is a result of correcting the precession of the selected stars from star catalogue of Yixiang Kaocheng Xubian 儀象考成續編.

• Proceedings of the Korean Magnestics Society Conference
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• 2010.06a
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• pp.202-203
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• 2010

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.34.2-34.2
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• 2010

The 3C84 (NGC 1275), one of Seyfert 2 galaxy, is an interesting object with its peculiar sub-mas structure. We found that the inner jet (r < 2.5mas) of 3C84 seemed to even changed its position angle and flux over one and a half years based on the result of global 86GHz VLBI survey (Lee et al. 2008). In order to confirm the 'precession' of jet, we observed the object in 4 epochs May07, Oct.07, May08 and Oct.08 with the GMVA (Global mm-VLBI Array) at 3mm (86.25GHz) and the each observation time is about 14 hours. Here we present observation and preliminary result of Oct.07 and May08 epochs.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.130-130
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• 2012

Axial bindings of diatomic molecules to metalloporphyrins involve in the dynamic processes of biological functions such as respiration, neurotransmission, and photosynthesis. The binding reactions are also useful in sensor applications and in control of molecular spins in metalloporphyrins for spintronic applications. Here, we present the binding structures of diatomic molecules to surface- supported Co-porphyrins studied using scanning tunneling microscopy. Upon gasexposure, three-lobed structures of Co-porphyrins transformed to bright ring shapes on Au(111), whereas H2-porphyrins of dark rings remained intact. The bright rings are explained by the structures of reaction complexes where a diatomic ligand, tilted away from the axis normal to the porphyrin plane, is under precession. Our results are consistent with previous bulk experiments using X-ray diffraction and nuclear magnetic resonance spectroscopy.

• Proceedings of the Korean Society for Emotion and Sensibility Conference
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• 1999.03a
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• pp.147-152
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• 1999

We have measured viscoelastic properties of fabrics in thickness direction. We assume that Maxwell model is very useful in stress relaxation of viscoelastic theories and appropriate formulas for fabric are calculated. Measurement system constitute of high precession load cell, translator and laser displacement sensor for viscoelastic properties was designed and elastic coefficients and damping coefficients were measured for 10 fabric samples. Elastic coefficients measured were 19~25 kN/㎡ and Damping coefficients measured were 4.8~8.7 MN$.$s/㎡. We concluded that these coefficients are good related with FUKURAMI collected from KESF system

• International Journal of Aeronautical and Space Sciences
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• v.14 no.4
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• pp.379-386
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• 2013

The hemispherical resonator gyroscope is a type of vibratory gyroscope, which can measure angle or angular rate, based on its operating mode. This paper deals with the case when the hemispherical resonator gyroscope is operated in angle measurement mode. In angle measurement mode, the resonator pattern angle precesses, with respect to the external rotation input, by the principle of the Coriolis effect, so that the external rotation can be estimated, by measuring the amount of precession angle. However, this pattern angle drifts, due to the manufacturing error of the resonator. Since the drift effect causes degradation of the angle estimation performance of the resonator, the corresponding drift compensation control should be performed, to enhance the estimation performance. In this paper, a mathematical model of the hemispherical resonator gyro is first introduced. By using the mathematical model, a nonlinear observer for imperfection parameter estimation, and the corresponding compensation controller are designed to operate hemispherical resonator gyros, as angle measurement sensors.

• Applied Microscopy
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• v.41 no.1
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• pp.75-79
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• 2011

For quantitative analysis of nano-crystal structure, we reported the accuracy improvement method of lattice parameters measured from electron diffraction. For calculation of Au lattice parameters used as a standard crystal structure, it was considered two different acquisition methods (detector and enegy-filter) and three different calculation methods (conventional, least-square and regression fit). As a result, the measurement reliability could be enhanced by using CCD camera which gives higher performance, while energy-filtering did not affect the improvement the camera constant accuracy. Also, the accuracy of lattice parameters could be improved up to $10^{-4}$ order by regression fitting with correction formula. Finally, it is expected that the combination of regression fitting and intensity extraction from energy-filtered precession electron diffraction gives a solution of quantitative structure analysis for unknown nano-crystals.