• 충청수학회지
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• 제24권4호
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• pp.863-868
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• 2011

The purpose of this paper is to study the orbit behaviours near almost periodic points. We introduce notions of uniformly recurrent and u-recurrent points and investigate some relationships between these properties.

• Journal of Astronomy and Space Sciences
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• 제31권1호
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• pp.41-50
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• 2014

The Earth is not perfectly spherical and its rotational axis is not fixed in space, and these geophysical and kinematic irregularities work as dominant perturbations in satellite orbit propagation. The International Earth Rotation Service (IERS) provides the Conventions as guidelines for using the Earth's model and the reference time and coordinate systems defined by the International Astronomical Union (IAU). These guidelines are directly applied to model orbital dynamics of Earth satellites. In the present work, the effects of the latest conventions released in 2010 on orbit propagation are investigated by comparison with cases of applying the previous guidelines, IERS Conventions (2003). All seven major updates are tested, i.e., for the models of the precession/nutation, the geopotential, the ocean tides, the ocean pole tides, the free core nutation, the polar motion, and the solar system ephemeris. The resultant position differences for one week of orbit propagation range from tens of meters for the geopotential model change from EGM96 to EGM2008 to a few mm for the precession/nutation model change from IAU2000 to IAU2006. The along-track differences vary secularly while the cross-track components show periodic variation. However, the radial-track position differences are very small compared with the other components in all cases. These phenomena reflect the variation of the ascending node and the argument of latitude. The reason is that the changed models tested in the current study can be regarded as small fluctuations of the geopotential model from the point of view of orbital dynamics. The ascending node and the argument of latitude are more sensitive to the geopotential than the other elements. This study contributes to understanding of the relation between the Earth's geophysical properties and orbital motion of satellites as well as satellite-based observations.

• 한국항공우주학회지
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• 제47권4호
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• pp.283-288
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• 2019

본 논문은 천리안위성 2A호가 2018년도 12월 5일에 발사되고 태양전지판구동기의 초기운영을 수행하면서 획득된 텔레메트리를 통해 지상에서 개발하고 시험한 결과에 대한 우주검증 결과를 정리하였다. 특히, 전이궤도 이후 정지궤도에 진입하면서 태양전지판구동기의 위치 설정 로직과 open-loop 제어에 의한 누적오차 보상 로직에 대한 결과를 검증하고 정상 운영이 되고 있음을 확인할 수 있었다. 또한, 설계 단계에서 확인되지 못했던 정지궤도 대비 태양의 위치가 시간에 따라 주기적인 오프셋이 있음을 발견하고 그에 적합한 보정 threshold 값을 설정하게 된 결과도 정리하였다.

• Journal of Astronomy and Space Sciences
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• 제5권1호
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• pp.19-30
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• 1988

지구-달계의 질량비인 $\mu$-0.9878449 와 Jacobi 상수 2.9~3.4인 범위의 조건일 때 j종족 충돌궤도가 존재하는가를 조사하였다. 수치적인 방법으로는 Birckhoff의 정칙화 평면에서 Fehlberg(1968)의 5차 Runge-Kutta가변구간 수치적분방법을 사용하여 궤도의 주기성을 검증하였다. 그 결과 4개의 j종족 충돌궤도와 5개의 특이형궤도를 얻었고, 또한, 이 j 종족 충돌궤도가 Pinotsis와 Zikides(1984)가 제시한 주기와 궤도형태의 상관관계를 보였다.

• 천문학회지
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• 제29권spc1호
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• pp.351-354
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• 1996

In this paper it is explained how most of asteroids can avoid very close approach to Jupiter, to the earth for earth orbit crossing asteroids, and to Neptune for Kuiper-belt asteroids by mechanisms which work also for Neptune-Pluto system. In fact the mutual distance of the planets cannot become very small as the critical argument librates around $180^{\circ}$ because of 2:3 mean motion resonance and the argument of perihelion of Pluto librates around $90^{\circ}$. And it is found that among nearly 40 Kuiper-belt asteroids discovered in recent years $40\%$ have orbits similar to Pluto. For main-belt asteroids the distribution with respect to the semi-major axes has peculiar characteristics and the author tries to explain how their peaks and gaps are created. It is also found that $30\%$ of 80 earth orbit crossing asteroids which have minimum perihelion distances less than 1.04AU have no chance to collide with the earth. Still $30\%$ of them have a few probability to collide with the earth as they have dynamical characteristics of short-periodic comets.

• Journal of Astronomy and Space Sciences
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• 제5권2호
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• pp.129-141
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• 1988

제한 3체 문제의 수치해를 이용하여 태양-목성계와 지구-달계의 $L_5$점 근처에서 각각 490여개, 1,600여개의 주기 궤도를 구하였다. 태양-목성계의 경우에서는 주기의 증가에 따라 에너지와 주기 궤도 크기가 단조롭게 커졌다. 그러나 지구-달계에서의 주기 궤도 모양은 복잡하고 변곡점이 나타나며 서로 겹치는 경우도 있다. 또한, 지구-달계에서 단일주기에 3개의 에너지가 동시 대응하는 영역이 존재하며 이 영역에소는 주기와 에너지가 반비례하는 구역이 있다. 태양-목성계의 $L_5$ 점 근처에서 목성의 중력 섭동 외의 기타의 작은 섭동에 의해 불안정한 주기 궤도가 될 수 있는 영역이 존재 가능하다. 이 영역 중 $L_5$점(5.2AU)에 가장 가까운 지역들이 a~5.12AU와 a~5.29AU 근처인데, 이 곳에는 이심률과 궤도 경사각이 작은 Trojan 소행성들이 존재하기 어렵다고 할 수 있다.

• Coupled systems mechanics
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• 제7권5호
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• pp.611-626
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• 2018

We theoretically consider a possible influence of periodic oceanic tides on non-periodic changes in the dynamics of the Earth and Moon over a long time scale. A particular emphasis will be placed on the contribution from rotating tidal waves, which rotate along the inner edge of an oceanic basin surrounded by topographic boundary. We formulate the angular momentum and the mechanical energy of the rotating tidal wave in terms of celestial parameters with regard to the Earth and Moon. The obtained formula are used to discuss how the energy dissipation in the rotating tidal wave should be relevant to the secular variation in the Earth's spin rotation and the Earth-Moon distance. We also discuss the applicability of the formula to general oceanic binary planets subject to tidal coupling.

• Journal of applied mathematics & informatics
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• 제42권1호
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• pp.139-148
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• 2024

The purpose of this research is to investigate sufficient conditions for the existence of limit cycles of the fifth-order differential equation x⁽⁵⁾ + (p² + q²)$_{x}^{...}$ + p²q²$_{x}^{.}$ = εF(t, x, $_{x}^{.}$, $_{x}^{..}$, $_{x}^{...}$, $_{x}^{....}$), where p, q are rational numbers different from 0, p ≠ ±q, ε is a small real parameter, and F is a 2kπ-periodic function in the variable t. Also, we provide some applications.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 추계학술대회 논문집
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• pp.487-490
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• 1995

This paper discisses the effects geometric errors on the measurement of error motions of rotor with the cylindrical capacitive displacement sensor. Analytic model of the measuring process with this sensor is derived and this model shows that the effect of geometric errors of sensor is larger than that of rator on the measurement of error motions of rotor. The computer simulation shows effect of periodic errors in this sensor on the measuring orbit.

• 대한수학회보
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• 제33권3호
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• pp.385-392
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• 1996

Smale [16] posed the following question; is having an attracting periodic orbit a generic property for diffeomorphisms of two-sphere $S^2\ulcorner$(A generic property of $f \in Diff(M)$ is one that is true for a Baire set in Diff(M)). Mane[5] and Plykin[13] had an positive answer for Axiom A diffeomorphisms of $S^2$. To explain our theorem, we begin by briefly recalling stability conjecture posed by palis and smale.