• International Journal of Aerospace System Engineering
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• v.7 no.2
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• pp.6-12
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• 2020

The precise prediction of future position of satellite depends on the accurate determination of orbit, which is also helpful in performing orbit maneuvers and trajectory correction maneuvers. For estimating the orbit of satellite many methods are being used. Some of the conventional methods are based on (i) Differential Correction (DC) (ii) Extended Kalman Filter (EKF). In this paper, Differential Evolution (DE) is used to determine the orbit. Orbit Determination using DC and EKF requires some initial guess of the state vector to initiate the algorithm, whereas DE does not require an initial guess since a wide range of bounds for the design unknown variables (orbital elements) is sufficient. This technique is uniformly valid for all orbits viz. circular, elliptic or hyperbolic. Simulated observations have been used to demonstrate the performance of the method. The observations are generated by including random noise. The simulation model that generates the observations includes the perturbation due to non-spherical earth up to second zonal harmonic term.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.10
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• pp.40-50
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• 2003

The operational orbit evolution of the KOMPSAT-l over 3 years was analyzed. During LEOP, four orbit maneuvers were performed to obtain the optimized orbit and eight safe-hold modes happened. The effects of unpredictable occurrence of the safe-hold mode and the highest solar activity on the orbit evolution during the mission life were analyzed. The comparison of orbital elements between long-term predicted orbit and determined orbit from observed data was also performed. The operational orbit started from the optimized one was evolved within the boundary of the designed mission orbit except altitude and it was verified the sun-synchronous orbit was successfully maintained.

• Journal of The Korean Astronomical Society
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• v.51 no.1
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• pp.1-4
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• 2018

We study the pseudo-synchronous orbital motion of a binary system on the main sequence. The equations of the pseudo-synchronous orbit are derived up to $O(e^4)$ where e is the eccentricy of the orbit. We integrate the equations to present their solutions. The theoretical results are applied to the evolution of the orbit and spin of the binary star Y Cygni, which has a current eccentricity of $e_0\;=\;0.142$. We tabulate our numerical results for the evolution of the orbit and spin per century. The numerical results for the semi-major axes and rotational angular velocities in the evolutional time scales of three stages (synchronization, circularization, and collapse time scale) are also tabulated. Synchronization is achieved in about $5{\times}10^3\;years$ followed by circularization lasting about $1{\times}10^5\;years$ before decaying in $2{\times}10^5\;years$.

• Journal of Astronomy and Space Sciences
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• v.3 no.2
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• pp.93-102
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• 1986

For a geostationary satellite east-west station keeping maneuvers must control both the mean longitude and the orbit eccentricity simultaneously. The effect on the orbit eccentricity of maneuvers may be reprensented by a phse plane of $e_{c}$ verse $e_{s}$, since these eccentricity elements give the projection of the orbit center onto the equatorial plane in units of the semimajor axis. The evolution of the mean longitude and the orbit eccentricity are obtained.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.4
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• pp.377-386
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• 2015

DubaiSat-2 is the first satellite developed in Korea equipped with a hall-effect thruster. In this paper, the performance of the DubaiSat-2 hall-effect thruster is verified by analyzing the orbit information of DubaiSat-2. The preparation and performance of orbit operations during 8 months after launch (2013.11.21., UTC) is emphasized and the effects of solar activity on orbit evolution is analyzed. In particular, the hall-effect thruster's thrust is estimated by analyzing difference between observed orbit evolution and predicted orbit. As a result, the estimated thrust is similar to the ground experiment result of 11 mN. The summarized result in this paper would be important reference to improve the stability and effectiveness of satellite operation during the early operation and normal mission lifetime in case of low Earth orbit satellites.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.35.1-35.1
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• 2019

We present a statistical analysis on the spin-orbit alignment of dark matter halo pairs in cosmological simulations. The alignment is defined as the angular concurrence between the halo spin vector (${\vec{S}}$) and the orbital angular momentum vector (${\vec{L}}$) of the major companion. We identify interacting halo pairs with the mass ratios from 1:1 to 1:3, with the halo masses of 10.8 < $Log(M_{halo}/M_{sun}$) < 13.0, and with the separations smaller than a sum of their virial radii ($R_{12}<R_{1,vir}+R_{2,vir}$). Based on the total energy ($E_{12}$), the pairs are classified into flybys ($E_{12}$ > 0) and mergers ($E_{12}{\leq}0$). By measuring the angle (${\theta}_{SL}$) between ${\vec{S}}$ and ${\vec{L}}$, we confirm a strong spin-orbit alignment signal such that the halo spin is preferentially aligned with the orbital angular momentum of the major companion. We find that the signal of the spin-orbit alignment for the flyby is weaker than that for the merger. We also find an unexpected excess signal of the spin-orbit alignment at $cos{\theta}_{SL}{\sim}0.25$. Both the strength of the spin-orbit alignment and the degree of the excess depend only on the environment. We conclude that the halo spin is determined by the accretion in a preferred direction set by the ambient environment.

• Journal of Astronomy and Space Sciences
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• v.33 no.4
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• pp.257-264
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• 2016

A planet revolving around binary star system is a familiar system. Studies of these systems are important because they provide precise knowledge of planet formation and orbit evolution. In this study, a method to determine the evolution of an exoplanet revolving around a binary star system using different rates of stellar mass loss will be introduced. Using a hierarchical triple body system, in which the outer body can be moved with the center of mass of the inner binary star as a two-body problem, the long period evolution of the exoplanet orbit is determined depending on a Hamiltonian formulation. The model is simulated by numerical integrations of the Hamiltonian equations for the system over a long time. As a conclusion, the behavior of the planet orbital elements is quite affected by the rate of the mass loss from the accompanying binary star.

• Journal of Astronomy and Space Sciences
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• v.38 no.1
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• pp.65-82
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• 2021

For the vast majority of geostationary satellites currently in orbit, station keeping activities including orbit determination and maneuver planning and execution are ground-directed and dependent on the availability of ground-based satellite control personnel and facilities. However, a requirement linked to satellite autonomy and survivability in cases of interrupted ground support is often one of the stipulated provisions on the satellite platform design. It is especially important for a geostationary military-purposed satellite to remain within its designated orbital window, in order to provide reliable uninterrupted telecommunications services, in the absence of ground-based resources due to warfare or other disasters. In this paper we investigate factors affecting the robustness of a geostationary satellite's orbit in terms of the maximum duration the satellite's station keeping window can be maintained without ground intervention. By comparing simulations of orbit evolution, given different initial conditions and operations strategies, a variation of parameters study has been performed and we have analyzed which factors the duration is most sensitive to. This also provides valuable insights into which factors may be worth controlling by a military or civilian geostationary satellite operator. Our simulations show that the most beneficial factor for maximizing the time a satellite will remain in the station keeping window is the operational practice of pre-emptively loading East-West station keeping maneuvers for automatic execution on board the satellite should ground control capability be lost. The second most beneficial factor is using short station keeping maneuver cycle durations.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.40.1-40.1
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• 2012

In the hierarchical universe, galaxy merger is predicted to be frequent, and thus it is an important element for understanding galaxy evolution. In particular, star formation is greatly enhanced during the merger. The aim of this study is to understand the position and rate change of star formation caused by equal-mass edge-on mergers. We use the GADGET2- N-body/SPH code, and fully consider gas cooling, star formation, and supernova feedback. We show the star formation rate (SFR), and the magnitude and color evolution of the merger remnants for 18 different configurations varying orbit elements and inclinations of host galaxies against orbit planes. Then we construct the mock images of the remnants and investigate on how equal-mass galaxy merger affects the SFR and color/magnitude evolution while considering dust reddening. We conclude that over 90% mass of SF in equal-mass merger is in the central region. SF in tidal feature involves a small fraction of new stars and thus is difficult to detect unless deep imaging is performed. Around 55 ${\pm}$ 5 percent of gas turns into stars until the final coalescence which typically corresponds to 0.8, 1.2, and 2.5 Gyr for direct, parabolic, and elliptical orbit, respectively. This result is roughly consistent with Cox et al. 2000. We plan to implement this result into semi-analytic model of galaxy formation. Caveats and future work on merging conditions are discussed.

• Journal of Astronomy and Space Sciences
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• v.31 no.3
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• pp.199-204
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• 2014

This paper intends to highlight the effect of the third-body in an inclined orbit on a spacecraft orbiting the primary mass. To achieve this goal, a new origin of coordinate is introduced in the primary and the X-axis toward the node of the spacecraft. The disturbing function is expanded up to the second order using Legendre polynomials. A double-averaged analytical model is exploited to produce the evolutions of mean orbital elements as smooth curves.