• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.7
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• pp.684-692
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• 2010

Based on the planar restricted three body problem formulation, optimized trajectories for the Earth-Moon transfer are obtained. Mixed impulsive and continuous thrust are assumed to be used, respectively, during the Earth departure and Earth-Moon transfer/Moon capture phases. The continuous, dynamic trajectory optimization problem is reformulated in the form of discrete optimization problem by using the method of direct transcription and collocation, and then is solved using the nonlinear programming software. Representative results show that the shape of optimized trajectory near the Earth departure and the Moon capture phases is dependent upon the relative weight between the impulsive and the continuous thrust.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.11
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• pp.1021-1032
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• 2011

This paper presents the results of a parametric study for the design of optimal Earth-Moon transfer trajectory using mixed impulsive and continuous thrust. Various types of the optimal Earth-Moon transfer trajectories were designed by adjusting the relative weight between the impulsive and the continuous thrust, and flight time. Two very different transfer trajectories can be obtained by different combination of design parameters. Furthermore, it was found that all thus designed trajectories permit the ballistic capture by the Moon gravity. Finally, the required thrust profiles are presented and analyzed in detail.

• Journal of Astronomy and Space Sciences
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• v.22 no.3
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• pp.249-262
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• 2005

Optimization problems are formulated to calculate optimal impulses for deflecting Earth-Crossing Objects using a Nonlinear Programming. This formulation allows us to analyze the velocity changes in normal direction to the celestial body's orbital plane, which is neglected in many previous studies. The constrained optimization in the three-dimensional space is based on a patched conic method including the Earth's gravitational effects, and yields impulsive ${\Delta}V$ to deflect the target's orbit. The optimal solution is dependent on relative positions and velocities between the Earth and the Earth-crossing objects, and can be represented by optimal magnitude and angle of ${\Delta}V $ as a functions of a impulse time. The perpendicular component of ${\Delta}V $ to the orbit plane can sometimes play un-negligible role as the impulse time approaches the impact time. The optimal ${\Delta}V $ is increased when the original orbit of Earth-crossing object is more similar to the Earth's orbit, and is also exponentially increased as the impulse time reaches to the impact time. The analyses performed in present paper can be used to the deflection missions in the future.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.10
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• pp.998-1011
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• 2010

For preparing Korean lunar missions, an Earth-Moon transfer trajectory is designed and analyzed using finite thrust. To be a more realistic scenario, kick motor's performance which is used for TLI (Trans Lunar Injection) maneuver is assumed to have a certain maximum capability. Under this assumption, optimal Earth-Moon transfer trajectory analysis is made from the beginning of Earth departure to the final lunar closest approach. As a results, optimal Earth-Moon transfer trajectory solutions with finite thrust are compared to those of designed with impulsive thrust in previous study. It is confirmed that if the trajectory solutions derived with impulsive burn is directly applied to estimate the finite burn trajectory solutions, careful consideration for finite burn losses must be paid as for TLI maneuver. Presented algorithm and various results will give numerous insights into the future Korea's Lunar missions using finite thrust engines.

• Bulletin of the Korean Space Science Society
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• 2000.04a
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• pp.35-35
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• 2000

• Bulletin of the Korean Space Science Society
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• 2000.04a
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• pp.36-36
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• 2000

• Bulletin of the Korean Space Science Society
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• 2007.10a
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• pp.53-53
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• 2007

• Aerospace Engineering and Technology
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• v.1 no.2
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• pp.51-56
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• 2002

Satellite propulsion system is employed for orbit transfer, orbit correction, and attitude control. The monopropellant feeding system in the low-earth-orbit satellite blowdowns fuel to the thrust chamber. The thrust produced by the thruster depends on fuel amount flowed into the combustion chamber. If the thruster valve be given on-off signal from on-board commander in the satellite, valve will be opened or closed. When the thrusters fire fuel flows through opened thruster valve, instantaneous stoppage of flow in according to valve actuation produces transient pressure due to pressure wave. This paper describes transient pressure predictions of the KOMPSAT-2 propulsion system resulting from latching valve and thrust control valve operations. The time-dependent set of the fluid mass and momentum equations are calculated by MOC.

• 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.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.375-378
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• 2011

A valve's high response for controlling thruster is essential for rapid turning during initial short moment after launching. The actuator for controlling the valve is simultaneously used in controlling canard of a guided missile. This paper explain development process for the electromechanical actuator interlocked with canard by arranging in following order, design, analysis, manufacture, test and evaluation.