• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2015.07a
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• pp.60-62
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• 2015

Dynamic Positioning System(DPS)은 동력, DP control 장치, DP 컴퓨터, 위치참조시스템(PRS), 센서, thruster 시스템 및 DP 운용자(DPO) 7가지로 구성되어 있다. DP 선박은 이들 구성요소들에 문제가 발생하면 그 기능을 상실할 수 있다. 본 연구에서는 2001~2010년까지 10년 동안 IMCA 보고된 DP 선박 관련사고 612건에 대한 분석을 바탕으로 DPS의 7가지 구성요소와 관련된 사고 원인을 파악하고 이들 중 가장 높은 비율을 차지하는 원인을 정성적, 정량적으로 상세 분석하여 요소별 관계와 주요 작용 요소를 확인하고자 한다. 이를 통해 DP 선박의 LOP사과 관련 분석에 있어 베이지안 네트워크의 활용성을 확인해 보았다. 10년 평균 가장 높은 비율을 차지한 DPS 사고원인 요인은 PRS이었으며 이를 전문가 브레인스토밍을 통해 작성된 flowchart를 바탕으로 베이지안 네트워크를 통해 상세 분석해 본 결과 PRS의 각 요소별 조건부 확률 확인할 수 있었다. DP 선박의 drive off를 발생시키는데 주요한 영향을 미치는 것은 DGPS, microwave radar 및 HPR 이었고 DGPS에 주요한 영향을 미치는 에러 요인은 signal blocked, electric components failure, relative mode error 및 signal weak or fail 이었다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.1
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• pp.86-92
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• 2012

The well-used actuators for the attitude control of spacecrafts are thruster, reaction wheel, control moment gyroscope, and magnetic torquer. Among them, the control moment gyroscope(CMG) which generates the torque based on the gyroscopic principle in physics, has an advantage of the high torque output compared to the low power consumption. This paper introduces an outline of CMG hardware technology, its application history in spacecrafts, and their associated hardware characteristics. Moreover, its spin-off cases to the other industrial fields such as ship, robotics, and MEMS including their research trend are provided.

• 제어로봇시스템학회:학술대회논문집
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• 1990.10b
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• pp.1361-1364
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• 1990

In order to tackle global environmental problems such as destruction of the ozone layer or climatic changes due to atmospheric temperature increase, the acquisition of plentiful and precise data is necessary. Therefore, a means of conducting long-lasting high-resolution measurements over broad areas is required. A feasibility study has been made on a high altitude (20km), super-pressured helium-filled PLTA (Powered Ligher-than-Air) vehicle as an ideal platform for environmental observation. It has a long service life and carries a larger payload than an artificial satellite. This PLTA platform uses an electric propulsion system to maintain position in space against wind currents. The thruster is driven by solar power acquired from solar cells. For night use, solar energy is stored in regenerative fuel cells. This study focuses on energy balance and structural analysis of the hull and platform. The platform is capable of conducting high resolution remote sensing as well as having the capability to serve as a telecommunications relay. The platform could replace a number of ground-based telecommunications relay facilities, guaranteeing sufficient radio frequency intensity to secure good quality telecommunication transmittal. The altitude at which the platform resides has the lowest wind flow in the lower stratosphere, and permits viewing from the ground within a 1,000km range. Because this altitude is much lower than that required of an artificial satellite, the measuring resolution is a couple of thousand times higher than with artificial satellites. The platform can also be used to chase typhoons and observe them from their sources in tropical regions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.1
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• pp.62-71
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• 2015

Geostationary satellites use the thruster in order to control the location change and mount the suitable amount of liquid propellant depending on the operating lifetime. Therefore the lifetime of the geostationary satellite depends on the residual propellant amount and the precise residual propellant gauging is very important for the mitigation of economic losses arised from premature removal of satellite from its orbit, satellites replacement planning, slot management and so on. The propellant gauging methods of geostationary satellite are mostly used PVT method, thermal mass method and bookkeeping method. In this paper, we analysis the modeling of COMS(Communication, Ocean & Meteorological Satellite) bipropellant system for bookkeeping method and COMS GTO(Geostationary Transfer Orbit) injection propellant estimation using Monte-Carlo method.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.4
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• pp.84-90
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• 2004

A performance evaluation is made in terms of thrust, impulse bit. and specific impulses for a set of mono-propellant hydrazine thrusters producing 0.95 lbf of nominal thrust at an inlet pressure of 350 psia. With a brief description on the hot-firing test configuration and procedures. a typical data obtained from steady-state firing mode is given directly showing the variational behavior of propellant supply pressure, mass flow rate, vacuum condition, and thrust. The performance features are successfully compared to the reference criteria of 1-lbf standard mono-propellant rocket engine. Additionally. a statistical inter-thruster treatment is concisely depicted for the justification of selected thrusters as a grouped member of flight model for spacecraft propulsion system.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.271-277
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• 2004

As one of the concepts of the laser/electric hybrid propulsion system, a feasibility study on possibilities of electrostatic acceleration of a laser ablation plasma induced from a solid target was conducted. Energy distributions of accelerated ions were measured by a Faraday cup. A time-of-flight measurement was also conducted for ion velocity measurement. It was found that an average speed of ions from a pure laser ablation in this case was about 20 km/sec for pulse energy of 40 $\mu$J/pulse with pulse width of 250 psec. On the other hand, through an electrostatic field with a + I ,000 V electrode, the speed could be accelerated up to 40 km/sec. It was shown that the electrode with positive potential was more effective than that with negative potential for positive-ion acceleration in laser induced plasma, or pulsed plasma, in which ions were induced with the Coulomb explosion following electrons. In addition, the ion-acceleration or deceleration strongly depended on conditions of pairs of inner diameter and electrodes gap.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.364-367
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• 2017

The basic design concept of the DACS(Divert and Attitude Control System) propellant is presented and the geometry optimization of the DACS propellant with limited outer diameter and maximum burning rate of the propellant is performed. Two-side burning surface conditions burned at the core and the one side of the propellant are applied to the propellant. And the optimized values for the radius of core, length of propellant, angle of end-side surface are obtained by the PSO algorithm. The direction for DACS propellant design is suggested by analyzing optimized design points for various burning rate.

• Journal of Ocean Engineering and Technology
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• v.27 no.6
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• pp.56-64
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• 2013

Crabbing motion is the pure sway motion of a ship without surge velocity. Thus, it can be applied to a berthing operation. Crabbing motion is induced by a peculiar operation method called the push-pull mode. The push-pull mode is induced by using a combination of the main propeller and side thruster. Two propellers generating the same amounts of thrust and rotating in opposite directions produce some yawing moment on a vessel but do not induce longitudinal motion. With the additional operation of side thrusters, the push-pull mode is used to induce a large amount of lateral force. In this paper, three-degree-of-freedom equations of motion such as for the surge, sway, and yaw are constructed for the crabbing motion. Based on these equations of motion, a feedback linearization control method is applied to auto-berthing control for a twin-screw ship with side thrusters. The controller can deal with the nonlinearity of a system, which is present in the berthing maneuver of a twin screw ship. A simulation of the auto-berthing of a ship is performed to validate the performance of the designed controller.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.175-178
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• 2011

A performance characteristics and application status of liquid-monopropellants used for 3-axis control thrusters are surveyed, in this paper. Hydrogen peroxide was widely used as monopropellant until mid-1960s, but it is rapidly replaced with hydrazine which has better performance of specific impulse, storability, and so on. Hydrazine is mostly employed as a liquid-monopropellant of satellite, interplanetary spacecraft, and space launch vehicle owing to its moderate performance features.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.179-182
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• 2011

A practical application of flight-axes/attitude control thrusters to the space launch vehicle and their design development localization are investigated and analyzed. Hydrazine thrusters are mostly used in a final stage of space launch vehicles on account of its higher specific impulse and reliability necessary for the precise attitude control attaining the orbit insertion with higher accuracy.