• 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.

• Journal of Aerospace System Engineering
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• v.4 no.4
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• pp.37-43
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• 2010

Need for agile satellites increases for performing various mission due to increase of satellite image applications and users. This paper performs attitude maneuver analysis by using Satellite Tool Kit(STK) made by AGI. In order to automate the STK analysis process, a MATLAB program is developed to generate STK input data and to process STK output data. Five attitude maneuver modes are analyzed and attitude angle variation and required torques are calculated.

• Aerospace Engineering and Technology
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• v.13 no.2
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• pp.18-28
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• 2014

We assume that two control moment gyros are installed for space qualification in a satellite with four reaction wheels, and study the high agile maneuver method. Using high torque control moment gyros, we reduce the satellite's attitude error. After that, we activate reaction wheels to control remaining attitude error. This proposed method can avoid singularity problem of control moment gyros, and do not require gimbals' angle to calculate torque command. Through numerical simulations, we show that our method's agile performance is similar to previous method and reduce the reaction wheels' required momentum.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.9
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• pp.806-813
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• 2016

For satellite attitude control and maneuver, normally four reaction wheels are used through pyramid configuration. However, if satellite's moment of inertia is large or available reaction wheels' capability is small, we can consider using five reaction wheels. In this case, we should think the arrangement of wheels and their operation method. Active SAR satellite requires high agile maneuver about roll axis to achieve looking angle change. In this research, we study the operation method of five reaction wheels configuration for fast roll maneuver.

• International Journal of Aeronautical and Space Sciences
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• v.8 no.2
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• pp.37-43
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• 2007

Coordination of multiple UAVs is an essential technology for various applications in robotics, automation, and artificial intelligence. In general, it includes 1) waypoints assignment and 2) trajectory generation. In this paper, we propose a new method for this problem. First, we modify the concept of the standard visibility graph to greatly improve the optimality of the generated trajectories and reduce the computational complexity. Second, we propose an efficient stochastic approach using simulated annealing that assigns waypoints to each UAV from the constructed visibility graph. Third, we describe a method to detect collision between two UAVs. FinallY, we suggest an efficient method of controlling the velocity of UAVs using A* algorithm in order to avoid inter-UAV collision. We present simulation results from various environments that verify the effectiveness of our approach.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.9
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• pp.53-59
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• 2006

Need for agile satellite increases for performing various mission due to increase of satellite image applications and users. In high resolution satellite TDI (time delay and integration) method is adopted in order to improve SNR. But image quality can be degraded by satellite maneuver. In this paper requirements for remote sensing in high resolution satellite with agility are extracted and an approach to operate the agile satellite to perform the missions are proposed. The proposed approach in this paper will be applicable to system level design and analysis.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.4
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• pp.709-718
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• 2017

This paper proposes the guidance laws for an agile turn of air-to-air missiles during the initial boost phase. Optimal solution for the agile turn is obtained based on the optimal control theory with a simplified missile dynamic model. Angle-of-attack command generating methods for completion of agile turn are then proposed from the optimal solution. Collision triangle condition for non-maneuvering target is reviewed and implemented for update of terminal condition for the agile turn. The performance of the proposed method is compared with an existing homing guidance law and the minimum-time optimal solution through simulations under various initial engagement scenarios. Simulation results verify that transition to homing phase after boost phase with the proposed method is more effective than direct usage of the homing guidance law.

• Journal of Mechanical Science and Technology
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• v.19 no.9
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• pp.1695-1705
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• 2005

Reaction wheels and thrusters are commonly used for the satellite attitude control. Since satellites frequently need fast maneuvers, the minimum time maneuvers have been extensively studied. When the speed of attitude maneuver is restricted due to the wheel torque capacity of low level, the combinational use of wheel and thruster is considered. In this paper, minimum time optimal control performances with reaction wheels and thrusters are studied. We first identify the features of the maneuvers of the satellite with reaction wheels only. It is shown that the time-optimal maneuver for the satellite with four reaction wheels in a pyramid configuration occurs on the fashion of single axis rotation. Pseudo control logic for reaction wheels is successfully adopted for smooth and chattering-free time-optimal maneuvers. Secondly, two different thrusting logics for satellite time-optimal attitude maneuver are compared with each other: constant time-sharing thrusting logic and varying time-sharing thrusting logic. The newly suggested varying time-sharing thrusting logic is found to reduce the maneuvering time dramatically. Finally, the hybrid control with reaction wheels and thrusters are considered. The simulation results show that the simultaneous actuation of reaction wheels and thrusters with varying time-sharing logic reduces the maneuvering time enormously. Spacecraft model is Korea Multi-Purpose Satellite (KOMPSAT)-2 which is being developed in Korea as an agile maneuvering satellite.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.6
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• pp.543-552
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• 2011

Control Moment Gyro(CMG) is one of the most efficient momentum exchange devices for satellite attitude control and CMG is very essential device for agile satellite. In this study, the essential dynamic equation for the design of gimbal motor and wheel motor is summarized. The development process of SGCMG hardware for agile small satellite system, the description of developed hardware and its performance test results are presented. Test result shows that the developed hardware model can produce an output torque more than 1.2Nm as designed. Other test items are max. torque, gimbal bandwidth, minimum torque, torque error, gimbal rate error.

• International Journal of Aeronautical and Space Sciences
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• v.7 no.2
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• pp.14-25
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• 2006

This paper is focused on designing an implementable control law to perform spacecraft various missions using momentum exchange devices such as reaction wheels(RWs) and control moment gyros(CMGs). A compact equation of motion of a spacecraft installed with various momentum exchange devices is derived in this paper. A hybrid control law is proposed for precision attitude control of agile spacecraft. The control law proposed in this paper allocates control torque to the CMGs and the RWs adequately to satisfy the precision attitude control and large angle maneuver simultaneously. The saturation problem of reaction wheels and the singularity problem of control moment gyros are considered. The problems are successfully resolved by using the proposed hybrid closed loop control law. Finally, the proposed hybrid control law is demonstrated by numerical simulations.