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Kyu-hong Choi - One of the best experts on this subject based on the ideXlab platform.

  • Geostationary orbit determination for time synchronization using analytical dynamic models
    IEEE Transactions on Aerospace and Electronic Systems, 2004
    Co-Authors: Jae-cheol Yoon, Kyu-hong Choi, Young-keun Chang, Yong-sik Chun, Sung-woong Ra
    Abstract:

    A real time analytical orbit determination method has been developed for precision national time synchronization. The one-way time transfer technique via a geostationary TV satellite standard time and frequency signal (STFS) dissemination system was considered. The differential method was also applied for mitigating errors in geostationary satellite STFS dissemination system. Analytical dynamic orbit determination with extended Kalman filter (EKF) was implemented to improve differential mode STFS (DSTFS) service accuracy by acquiring better accuracy of a geostationary satellite position. The perturbation force models applied for satellite dynamics include the geopotential perturbation up to fifth degree and order harmonics, luni-solar perturbations, and solar radiation pressure. All of the perturbation effects were analyzed by secular, short, and long period variations for equinoctial orbit elements such as semimajor axis, Eccentricity Vector, inclination Vector, and mean right ascension of the geostationary satellite. The reference stations for orbit determination were composed of four calibrated stations. Simulations were performed to evaluate the performance of real time analytical orbit determination in Korea. The simulation results demonstrated that it is possible to determine real time position of geostationary satellite with the accuracy of 300 m rms. This performance implies that the time accuracy is better than 25 ns all over the Korean peninsula. The real time analytical orbit determination method developed in this research can provide a reliable, extremely high accurate time synchronization service through setting up domestic-only benchmarks.

  • Collocation of two GEO satellites and one inclined GSO satellite
    Aerospace Science and Technology, 2000
    Co-Authors: Byoung-sun Lee, Kyu-hong Choi
    Abstract:

    Abstract Three collocation strategies are planned and analyzed for the cluster of two geostationary orbit (GEO) satellites and one inclined geosynchronous orbit (GSO) satellite in the same longitude control band of 116°E±0.05° . The longitudinal control bands are allocated for the two GEO satellites and one inclined GSO satellite with seven-day East/West station-keeping maneuver cycle. The latitudinal control bands are allocated for the two GEO satellites with fourteen-day North/South station-keeping maneuver cycle. One inclined GSO satellite is allowed for natural inclination drift. The coordinated Eccentricity Vector and inclination Vector separation method is applied for the collocation, and the maneuver schedule is planned to minimize the operational load by avoiding simultaneous maneuvers. A total of six months of station-keeping maneuver simulations are performed for the three different strategies.

  • Analysis of a station-keeping maneuver strategy for collocation of three geostationary satellites
    Control Engineering Practice, 1999
    Co-Authors: Byoung-sun Lee, Jeong-sook Lee, Kyu-hong Choi
    Abstract:

    Abstract A collocation strategy has been planned and analyzed for three geostationary satellites in the same longitude control box. The orbit determination error analysis is performed when only one ground station is used for the angle tracking and ranging. Based on the orbit determination errors, the station-keeping bands are allocated for seven-day East/West and 14-day North/South station-keeping maneuver cycles. The Eccentricity control circle and inclination control box for individual satellites are allocated for the collocation. The Eccentricity Vector and inclination Vector separation method is applied for the collocation, and the maneuver schedule is planned to minimize the operational load by avoiding simultaneous maneuvers. A total of fourteen weeks of station-keeping maneuvers are performed for three KOREASAT satellites, collocated in 116°E±0.05° longitude band.

  • Analysis of a Station-Keeping Maneuver Strategy for Three Geostationary Satellites Collocation
    IFAC Proceedings Volumes, 1998
    Co-Authors: Byoung-sun Lee, Jeong-sook Lee, Kyu-hong Choi
    Abstract:

    Abstract A collocation strategy have been planned and analyzed for three geostationary satellites in the same longitude control box. The orbit determination error analysis is performed when only one ground station is used for the angle tracking and ranging. Based on the orbit determination errors, the station-keeping bands are allocated for 7-day East/West station-keeping maneuver cycle. The Eccentricity control circle and inclination control box for individual satellite are allocated for the collocation. The Eccentricity Vector and inclination Vector separation method is applied for the collocation, and the maneuver schedule is planned to minimize the operational load by avoiding simultaneous maneuvers. Total of eighty days of station-keeping maneuver simulations are performed for the three collocated satellites. The mutual distances between the satellites are monitored for avoiding collisions.

Byoung-sun Lee - One of the best experts on this subject based on the ideXlab platform.

  • Collocation of two GEO satellites and one inclined GSO satellite
    Aerospace Science and Technology, 2000
    Co-Authors: Byoung-sun Lee, Kyu-hong Choi
    Abstract:

    Abstract Three collocation strategies are planned and analyzed for the cluster of two geostationary orbit (GEO) satellites and one inclined geosynchronous orbit (GSO) satellite in the same longitude control band of 116°E±0.05° . The longitudinal control bands are allocated for the two GEO satellites and one inclined GSO satellite with seven-day East/West station-keeping maneuver cycle. The latitudinal control bands are allocated for the two GEO satellites with fourteen-day North/South station-keeping maneuver cycle. One inclined GSO satellite is allowed for natural inclination drift. The coordinated Eccentricity Vector and inclination Vector separation method is applied for the collocation, and the maneuver schedule is planned to minimize the operational load by avoiding simultaneous maneuvers. A total of six months of station-keeping maneuver simulations are performed for the three different strategies.

  • Analysis of a station-keeping maneuver strategy for collocation of three geostationary satellites
    Control Engineering Practice, 1999
    Co-Authors: Byoung-sun Lee, Jeong-sook Lee, Kyu-hong Choi
    Abstract:

    Abstract A collocation strategy has been planned and analyzed for three geostationary satellites in the same longitude control box. The orbit determination error analysis is performed when only one ground station is used for the angle tracking and ranging. Based on the orbit determination errors, the station-keeping bands are allocated for seven-day East/West and 14-day North/South station-keeping maneuver cycles. The Eccentricity control circle and inclination control box for individual satellites are allocated for the collocation. The Eccentricity Vector and inclination Vector separation method is applied for the collocation, and the maneuver schedule is planned to minimize the operational load by avoiding simultaneous maneuvers. A total of fourteen weeks of station-keeping maneuvers are performed for three KOREASAT satellites, collocated in 116°E±0.05° longitude band.

  • Analysis of a Station-Keeping Maneuver Strategy for Three Geostationary Satellites Collocation
    IFAC Proceedings Volumes, 1998
    Co-Authors: Byoung-sun Lee, Jeong-sook Lee, Kyu-hong Choi
    Abstract:

    Abstract A collocation strategy have been planned and analyzed for three geostationary satellites in the same longitude control box. The orbit determination error analysis is performed when only one ground station is used for the angle tracking and ranging. Based on the orbit determination errors, the station-keeping bands are allocated for 7-day East/West station-keeping maneuver cycle. The Eccentricity control circle and inclination control box for individual satellite are allocated for the collocation. The Eccentricity Vector and inclination Vector separation method is applied for the collocation, and the maneuver schedule is planned to minimize the operational load by avoiding simultaneous maneuvers. Total of eighty days of station-keeping maneuver simulations are performed for the three collocated satellites. The mutual distances between the satellites are monitored for avoiding collisions.

Stephen H. Lubow - One of the best experts on this subject based on the ideXlab platform.

  • Polar alignment of a protoplanetary disc around an eccentric binary – III. Effect of disc mass
    Monthly Notices of the Royal Astronomical Society, 2019
    Co-Authors: Rebecca G. Martin, Stephen H. Lubow
    Abstract:

    Martin & Lubow (2017) found that an initially sufficiently misaligned low mass protoplanetary disc around an eccentric binary undergoes damped nodal oscillations of tilt angle and longitude of ascending node. Dissipation causes evolution towards a stationary state of polar alignment in which the disc lies perpendicular to the binary orbital plane with angular momentum aligned to the Eccentricity Vector of the binary. We use hydrodynamic simulations and analytic methods to investigate how the mass of the disc affects this process. The simulations suggest that a disc with nonzero mass settles into a stationary state in the frame of the binary, the generalised polar state, at somewhat lower levels of misalignment with respect to the binary orbital plane, in agreement with the analytic model. Provided that discs settle into this generalised polar state, the observational determination of the misalignment angle and binary properties can be used to determine the mass of a circumbinary disc. We apply this constraint to the circumbinary disc in HD 98800. We obtain analytic criteria for polar alignment of a circumbinary ring with mass that approximately agree with the simulation results. Very broad misaligned discs undergo breaking, but the inner regions at least may still evolve to a polar state. The long term evolution of the disc depends on the evolution of the binary Eccentricity that we find tends to decrease. Although the range of parameters required for polar alignment decreases somewhat with increasing disc mass, such alignment appears possible for a broad set of initial conditions expected in protostellar circumbinary discs.

  • Polar alignment of a protoplanetary disc around an eccentric binary – II. Effect of binary and disc parameters
    Monthly Notices of the Royal Astronomical Society, 2018
    Co-Authors: Rebecca G. Martin, Stephen H. Lubow
    Abstract:

    In a recent paper Martin & Lubow showed that a circumbinary disc around an eccentric binary can undergo damped nodal oscillations that lead to the polar (perpendicular) alignment of the disc relative to the binary orbit. The disc angular momentum Vector aligns to the Eccentricity Vector of the binary. We explore the robustness of this mechanism for a low mass disc (0.001 of the binary mass) and its dependence on system parameters by means of hydrodynamic disc simulations. We describe how the evolution depends upon the disc viscosity, temperature, size, binary mass ratio, orbital Eccentricity and inclination. We compare results with predictions of linear theory. We show that polar alignment of a low mass disc may occur over a wide range of binary-disc parameters. We discuss the application of our results to the formation of planetary systems around eccentric binary stars.

Jeong-sook Lee - One of the best experts on this subject based on the ideXlab platform.

  • Analysis of a station-keeping maneuver strategy for collocation of three geostationary satellites
    Control Engineering Practice, 1999
    Co-Authors: Byoung-sun Lee, Jeong-sook Lee, Kyu-hong Choi
    Abstract:

    Abstract A collocation strategy has been planned and analyzed for three geostationary satellites in the same longitude control box. The orbit determination error analysis is performed when only one ground station is used for the angle tracking and ranging. Based on the orbit determination errors, the station-keeping bands are allocated for seven-day East/West and 14-day North/South station-keeping maneuver cycles. The Eccentricity control circle and inclination control box for individual satellites are allocated for the collocation. The Eccentricity Vector and inclination Vector separation method is applied for the collocation, and the maneuver schedule is planned to minimize the operational load by avoiding simultaneous maneuvers. A total of fourteen weeks of station-keeping maneuvers are performed for three KOREASAT satellites, collocated in 116°E±0.05° longitude band.

  • Analysis of a Station-Keeping Maneuver Strategy for Three Geostationary Satellites Collocation
    IFAC Proceedings Volumes, 1998
    Co-Authors: Byoung-sun Lee, Jeong-sook Lee, Kyu-hong Choi
    Abstract:

    Abstract A collocation strategy have been planned and analyzed for three geostationary satellites in the same longitude control box. The orbit determination error analysis is performed when only one ground station is used for the angle tracking and ranging. Based on the orbit determination errors, the station-keeping bands are allocated for 7-day East/West station-keeping maneuver cycle. The Eccentricity control circle and inclination control box for individual satellite are allocated for the collocation. The Eccentricity Vector and inclination Vector separation method is applied for the collocation, and the maneuver schedule is planned to minimize the operational load by avoiding simultaneous maneuvers. Total of eighty days of station-keeping maneuver simulations are performed for the three collocated satellites. The mutual distances between the satellites are monitored for avoiding collisions.

D. Lucchesi - One of the best experts on this subject based on the ideXlab platform.

  • LAGEOS II perigee rate and Eccentricity Vector excitations residuals and the Yarkovsky-Schach effect
    Planetary and Space Science, 2004
    Co-Authors: D. Lucchesi, Ignazio Ciufolini, José I. Andrés, Erricos C. Pavlis, Roberto Peron, R. Noomen, Douglas G. Currie
    Abstract:

    Abstract We have analysed LAGEOS II perigee rate and Eccentricity Vector excitation residuals over a period of about 7.8 years, adjusting and computing the satellite orbit with the full set of dynamical models included in the GEODYN II software code. The long-term behaviour of these orbital residuals appears to be characterised by several distinct frequencies which are a clear signature of the Yarkovsky–Schach perturbing effect. This non-gravitational perturbation is not included in the GEODYN II models for the orbit determination and analysis. Through an independent numerical analysis, and using the new LOSSAM model to represent the spin-axis behaviour of the satellite, we propagated the Yarkovsky–Schach effect on LAGEOS II perigee rate and compared the results obtained with the orbital residuals. We have thus been able to satisfactorily fit the amplitude of the Yarkovsky–Schach effect to the observed residuals. Our approach here has proven very successful with very positive results. We have been able to obtain a fractional reduction of about 40% of the post-fit rms with respect to the pre-fit value. When analysing the Eccentricity Vector residuals, we have been able to obtain a better result in the case of the real component, with a fractional reduction of the post-fit rms of about 49% of the initial value. The analysis of the effect's imaginary component in the Eccentricity Vector rate is more complicated and deserves additional scrutiny. In this case we need a deeper study which includes the analysis of other unmodelled and mismodelled effects acting on the imaginary component. The study performed in this paper will be of significant relevance not only for the geophysical applications involving LAGEOS II orbit analysis, but also for a refined re-analysis of the general relativistic precession produced by the Earth angular momentum, i.e., the Lense-Thirring effect.

  • The asymmetric reflectivity effect on the LAGEOS satellites and the germanium retroreflectors
    Geophysical Research Letters, 2003
    Co-Authors: D. Lucchesi
    Abstract:

    [1] We propose a new mechanism to explain the physical cause of the empirical asymmetric reflectivity effect observed for the LAGEOS satellites. To reach this result we have modelled the reflection of the Sun's visible light from the four Germanium Cube Corner Retroreflectors of these laser-ranged satellites. The position of the cubes play a crucial role in defining the characteristics of the effect and its impact in the satellites orbit. We analyzed the long-term effects of the perturbation in the satellites Eccentricity Vector excitations and in their perigee rate. With the new model we have been able to reproduce the time evolution of LAGEOS Eccentricity Vector excitations and perigee rate as due to the empirical effect. In the case of LAGEOS II, the asymmetric reflectivity effect needs to be modelled with an analytical expression different from that for LAGEOS.