• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.2
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• pp.107-119
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• 2013

We study three axis attitude control method including two axis high agile maneuver using four reaction wheels and two control moment gyros. We investigate singularity conditions due to two control moment gyros and propose singularity escape method. Based on this, we propose actuator control algorithm for high agile maneuver. Also, we propose actuator momentum management method which preserves momentum of reaction wheels and control moment gyroscopes before and after satellite attitude control. Through numerical simulation, we show that our method achieves three axis attitude control including two axis high agile maneuver and preserves actuators' momentum.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.1099-1102
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• 1996

In this paper, roll/yaw attitude control of spacecraft using a double gimbaled wheel is discussed with two feedback controllers designed. One is a PD controller with no phase difference between roll and yaw control input. The other is a PD controller with a phase lag compensator about the yaw control input. The phase lag compensator is designed as a first order system and a lag parameter is designed for the yaw angle control. There are two case simulations for each controller ; constant disturbance torques and initial errors of nutation at motion. We obtain the results through simulations that steady-state error and rising time of yaw angle are determined by the compensator. Simulation parameters used in this study are the values of KOREASAT F1.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.4
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• pp.409-416
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• 2007

A momentum type actuator produces force and torque disturbances as well as its designed control torque. These disturbances are ones of the largest disturbance sources inside the spacecraft, which deteriorate the pointing stability of the high precision spacecraft. The measurement and analysis of actuator disturbances are therefore imperative for such a spacecraft, and thus a three dimensional torque measurement table has been developed for that purpose. The data acquired from the measurement table are processed in the frequency domain and displayed in the power spectral density(PSD). Through this process, disturbance model parameters are obtained and used for the attitude stability simulation. The process has been adopted for the disturbance measurement of the reaction wheel, and the validity of measurements and parameter identification procedure is verified.

• Aerospace Engineering and Technology
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• v.7 no.2
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• pp.88-94
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• 2008

In this study, triaxial velocity is analyzed for COMS(Communication, Ocean and Meteorological Satellite) configuration, which is generated when thrusters are used to dump wheel momentum. Since COMS is designed to periodically change the thruster set in order to uniformly decrease the performance of thrusters, triaxial velocity would be different during the change of thruster set. So, the triaxial velocity generated due to the change of thruster set is optimized.

• Proceedings of the Korean Magnestics Society Conference
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• 2002.12a
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• pp.134-135
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• 2002

모든 인공 위성이 궤도 올라가서 정확한 업무를 수행하기 위해서는 정확한 위치 정보와 안정된 자세제어 시스템을 필요로 한다. 궤도에 올라간 후 안정된 자세를 잡기 위해서는 위성체의 덤블링 방지해야되므로 초기 자세제어가 매우 중요하다. 그리고, 안정된 제도에 도달하여 자세를 잡기 의해서는 정확한 자세 정보와 자세를 조절하는 장치가 필요하며, 이를 얻기 위해서 thruster, momentum wheel, 마그네틱 토커, 마그네토미터 등과 같은 장치들이 사용되어진다. (중략)

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.4
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• pp.40-46
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• 2006

It is required to develop a highly reliable attitude & orbit control system of satellite that is less expensive as the technology of satellite design & integration is recently matured dramatically. To accomodate this kind of needs, the two axis attitude control method for wheel-based momentum-biased satellite system whose momentum bias vector points to a certain direction(sun direction), is developed using simple but reliable sensors and actuator: three axis magnetometer and coarse sun sensor are used as sensors, and magnetic torque bars are used as actuator. Classical PD type controller design methodologies are applied on a satellite system for the two axis control with the proper assumptions. Nonlinear simulation results are included to demonstrate the long term stability and the performance of closed-loop system design results.

• Korean Journal of Pharmacognosy
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• v.19 no.2
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• pp.141-151
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• 1988

The sedative, antipyretic, analgesic and anticonvulsive action, action on the isolated ileum in mice, retricting action on edema, action on blood pressure and respiration of Sipmidojuksan were evaluated. The results were as follows; sedative effects were recognized by the unbalanced effects of spontaneous momentum by wheel cage method, muscle relaxing action by rotor rod method and prolongation of sleeping hours. In mice, a significant antipyretic effect to endotoxin was recognized. Significant anagesic effects by acetic acid and Randall-Sellito method were recognized. Significant anticonvulsive effects to strychnine and picrotoxin were recognized. Spontaneous momentum of isolated ileum in mice was restricted, and relaxing effects on smooth muscle of digestive organ were noted by anti-acetylcholine, anti-barium chloride and anti-histamine effects. Significant antiedemic effects to carrageenin and histamine were recognized. Dilatation of blood vessels and decrease of blood pressure were noted.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.3
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• pp.505-514
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• 1994

Koreasat spacecraft requires accurate and reliable attitude control to provide beam pointing for tenyear long communication and direction broadcasting services. This paper describes the detailed design and performance of an on-orbit normal mode attitude control subsystem for the spacecraft. Koreasat used a momentum wheel which has nominal momentum 475in-1b sec(547.6cm-kg sec) aligned with the pitch axis to control pitch attitude and provide gyroscopic stiffness in roll/yaw plane and used a 300 atm magnetic torquer to control the roll and yaw attitudes. An Earth Sensor Assembly (ESA) is used to provide pitch and roll information for the on-board micropocessor. The roll/yaw control used bang-off-bang control and while pitch axis control used proportional and integral control law. Control system errors during the operational normal mode are 0.03 deg, 0.1 deg and 0.01 deg in roll, yaw and pitch axes, respectively. Current attitude control system provides adequate control performances to capture initial attitude errors and spacecraft nutation.

• Journal of Astronomy and Space Sciences
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• v.36 no.3
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• pp.181-186
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• 2019

The attitude information of spacecraft can be obtained by the sensors attached to it using a star tracker, three-axis magnetometer, three-axis gyroscope, and a global positioning signal receiver. By using these sensors, the spacecraft can be maneuvered by actuators that generate torques. In particular, electromagnetic-torque bars can be used for attitude control and as a momentum-canceling instrument. The spacecraft momentum can be created by the current through the electrical circuits and coils. Thus, the current around the electromagnetic-torque bars is a critical factor for precisely controlling the spacecraft. In connection with these concerns, a solar-cell array can be considered to prevent generation of a magnetic dipole moment because the solar-cell array can introduce a large amount of current through the electrical wires. The maximum value of a magnetic dipole moment that cannot affect precise control is $0.25A{\cdot}m^2$, which takes into account the current that flows through the reaction-wheel assembly and the magnetic-torque current. In this study, we designed a 300-W solar cell array and presented an optimal wire-routing method to minimize the magnetic dipole moment for space applications. We verified our proposed method by simulation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.7
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• pp.651-657
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• 2008

A new approach for maximizing torque capability of low efficient reaction wheel assembly is addressed in this paper. At first, to find out a solution in constrainted field, weighted pseudo-inverse and momentum minimized allocation are suggested instead of a general control allocation called pseudo-inverse. The second method is a structural manner to enlarge torque capability of specific axis by changing installed skew angle of wheels. Two proposed methods are applied to large angle maneuvers of satellite. Improvement of control performance and feasibility for applying to commercial satellite attitude control are demonstrated by numeric simulations.