• Bulletin of the Korean Space Science Society
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• 2008.10a
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• pp.35.3-36
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• 2008

The ground-based spacecraft simulator is a useful tool to realize various space missions and satellite formation flying in the future. Also, the spacecraft simulator can be used to develop and verify new control laws required by modern spacecraft applications. In this research, therefore, Hardware-in-the-loop (HIL) simulator which can be demonstrated the experimental validation of the theoretical results is designed and developed. The main components of the HIL simulator which we focused on are the thruster system to attitude control and automatic mass-balancing for elimination of gravity torques. To control the attitude of the spacecraft simulator, 8 thrusters which using the cold gas (N2) are aligned with roll, pitch and yaw axis. Also Linear actuators are applied to the HIL simulator for automatic mass balancing system to compensate for the center of mass offset from the center of rotation. Addition to the thruster control system and Linear actuators, the HIL simulator for spacecraft attitude control includes an embedded computer (Onboard PC) for simulator system control, Host PC for simulator health monitoring, command and post analysis, wireless adapter for wireless network, rate gyro sensor to measure 3-axis attitude of the simulator, inclinometer to measure horizontality and battery sets to independently supply power only for the simulator. Finally, we present some experimental results from the application of the controller on the spacecraft simulator.

• Proceedings of the KIEE Conference
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• 2001.11c
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• pp.53-56
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• 2001

In this paper we discuss a direct satellite broadcasting system for vehicle. The proposed satellite-steering algorithm and controller based on it are designed for a communication and broadcasting system which uses the Mugungwha satellite. The Mugungwha satellite that the proposed system should steer is a geostationary orbit device. The satellite-steering algorithm computes azimuth and elevation with reference to a stationary point on earth. This is extended to a real satellite steering algorithm that considers position and attitude. Real moving position and attitude are represented by latitude, longitude, roll, pitch and yaw. To apply these five pieces of information to the reference satellite steering algorithm, we introduce Euler's degree coordinates that express independently the rotation of each axis relative to an axis. There are two ways a basic algorithm of the antenna of a vehicle can track and orient to satellite. One way is a feedback loop method for broadcasting gain, while the other is a feedback loop method for position and attitude of a vehicle. In the present paper, we design a controller of satellite broadcasting system for a vehicle using an algorithm that combines the two methods. We performed a simulation and experiment to prove effectiveness.

• International Journal of Ocean System Engineering
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• v.4 no.1
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• pp.19-28
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• 2014

The tension leg platform (TLP) is a vertically moored structure with excess buoyancy. The TLP is regarded as moored structure in horizontal plan, while inherit stiffness of fixed platform in vertical plane. In this paper, a numerical study using modified Morison equation was carried out in the time domain to investigate the influence of nonlinearities due to hydrodynamic forces and the coupling effect between surge, sway, heave, roll, pitch and yaw degrees of freedom on the dynamic behavior of TLP's. The stiffness of the TLP was derived from a combination of hydrostatic restoring forces and restoring forces due to cables and the nonlinear equations of motion were solved utilizing Newmark's beta integration scheme. The effect of tethers length and wave characteristics such as wave period and wave height on the response of TLP's was evaluated. Only uni-directional waves in the surge direction was considered in the analysis. It was found that for short wave periods (i.e. 10 sec.), the surge response consisted of small amplitude oscillations about a displaced position that is significantly dependent on tether length, wave height; whereas for longer wave periods, the surge response showed high amplitude oscillations about that is significantly dependent on tether length.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.47 no.3
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• pp.19-27
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• 2010

KSLV(Korea Space Launch Vehicle)-I is designed as a launch vehicle to enter a 100 kg-class satellite to the LEO(Low-Earth Orbit). Attitude angles of the upper-stage, including roll, pitch and yaw are controlled by cold gas thruster system using nitrogen gas. The thruster for the KSLV-I is the main pneumatic valve in the RCS(Reaction Control System). In this paper, the design, function tests, and environment tests of the thruster for KSLV-I are described. The developed thrusters are experimentally evaluated and successfully passed the required qualification and acceptance tests.

• Aerospace Engineering and Technology
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• v.8 no.2
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• pp.122-126
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• 2009

KSLV(Korea Space Launch Vehicle)-I is designed as a launch vehicle to enter a 100 kg-class satellite to the LEO(Low-Earth Orbit). Attitude angles of the upper-stage, including roll, pitch and yaw are controlled by cold gas thruster system using nitrogen gas. To verify the flow rate of the gas charging system and to prepare a nitrogen gas charging scenario, the development of a gas charging simulator for RCS(Reaction Control System) is required. This paper describes the orifice design, development, and test of the gas charging simulator for RCS of KSLV-I.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.252-255
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• 2008

In this study, the characteristics of crossing a river of Ground Armored Vehicle (GAV) were evaluated by numerical method and real size tests. 3-D hybrid mesh systems were constructed by 3-D models of the GAV, and a commercial software, FLUENT, was used in numerical analysis. In order to deal with multi-phase problem (air and water), Volume Of Fluid (VOF) method was used, and Moving and Deforming Mesh (MDM) was adapted for unsteady motion of GAV. There were two steps in this research. Firstly, stability of the GAV which cruised a river was evaluated by changing several shapes of water-proof-front-wing of the GAV in steady state, and compared results (free surface shape and drag value in 10km/h) with those of real size tests. Secondly, results of unsteady analysis considering weight and moment of inertia of the GAV were presented. There were showed a maximum velocity with a designed water jet and dynamic stability including pitch, roll, and yaw moment. Based on these results, the optimal shape of water-proof-front-wing of the GAV was determined for a proto-type of the GAV.

• Journal of Astronomy and Space Sciences
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• v.29 no.4
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• pp.389-395
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• 2012

The problem of spacecraft attitude control is solved using an adaptive neuro-fuzzy inference system (ANFIS). An ANFIS produces a control signal for one of the three axes of a spacecraft's body frame, so in total three ANFISs are constructed for 3-axis attitude control. The fuzzy inference system of the ANFIS is initialized using a subtractive clustering method. The ANFIS is trained by a hybrid learning algorithm using the data obtained from attitude control simulations using state-dependent Riccati equation controller. The training data set for each axis is composed of state errors for 3 axes (roll, pitch, and yaw) and a control signal for one of the 3 axes. The stability region of the ANFIS controller is estimated numerically based on Lyapunov stability theory using a numerical method to calculate Jacobian matrix. To measure the performance of the ANFIS controller, root mean square error and correlation factor are used as performance indicators. The performance is tested on two ANFIS controllers trained in different conditions. The test results show that the performance indicators are proper in the sense that the ANFIS controller with the larger stability region provides better performance according to the performance indicators.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.7
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• pp.659-666
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• 2016

Magnetic disturbance is one of the main factors that deteriorate the accuracy of orientation estimation methods based on inertial/magnetic sensor signals. This paper proposes a parallel Kalman filter(KF) that explicitly detects magnetic disturbances and thus can accurately estimate 3D orientation in magnetically disturbed environments. Due to the parallel nature of the proposed KF, even severe magnetic disturbances only affect yaw estimation, while roll and pitch values remain accurate. Consequently, the proposed KF can be effectively used in various applications that involve magnetically inhomogeneous environments, such as robots, ships, and planes.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.2
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• pp.47-55
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• 2012

This work deals with dynamic analysis of a monorail system with magnetic caterpillar where magnets are embedded inside each articulated element of the caterpillar, augmenting traction force of main rubber wheels to climb up slope up to 15 degree grade. Considerations are first given to determine stiffness of the primary and secondary suspension springs in order for the natural frequencies of car body and bogie associated with vertical, pitch, roll and yaw motion to be within generally accepted range of 1-2 Hz. Equations for calculating magnetic force needed to climb up given slope are derived, and a magnetic caterpillar system for 1/6 scale monorail is designed based on the derivation. To assess the hill climbing ability and cornering stability, and make sure smooth operation of the side and vertical guiding wheels which is critical for safety, a multibody model that takes into account of every component level design characteristics of car, bogie, and caterpillar is set up. Through hill climbing simulation and comparison with measurement of the limit slope, the validity of the analysis and design of the magnetic caterpillar system are demonstrated. Also by studying the curving behavior, maximum curving speed without rollover, functioning of lateral motion constraint system, the effects of geometry of guiding rails are studied.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.1
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• pp.82-87
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• 2002

The attitude determination in LEO Satellite like KOMPSAT is one of the most important issues for Sun-Acquisition. Particularly, in KOMPSAT, the roll axis direction can be determined since the sun sensor gives the information on the Euler angle for pitch and yaw axes in Sun-Acquisition mode. In other words, it is the problem to determine the two unknown axes direction with one axis knowledge. This paper proposes a new effective method for attitude determination of general LEO satellites when one axis information is avilable and proves its usefulness throughout the simulation.