• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.10
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• pp.872-880
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• 2017

Usually, on/off control method is a way to control the thruster. Bang-Bang Control, PWM(Pulse Width Modulator) and PWPF(Pulse Width Pulse Frequency) are widely used as a typical way. When we are designing PWPF, the incorrectly designed parameters($K_m$, ${\tau}$, $U_{on}$, $U_{off}$, $U_m$) make trouble, such as the phase lag, the wasted fuel, the reduced system life. Therefore, the effect of parameters on the system performance should be analyzed before the proper parameters are selected. In this paper, we suggest the PWPF parameters design method by performing a static analysis, and analyze the interactive effects on design parameters by performing a dynamic analysis and simulation.

• Journal of Astronomy and Space Sciences
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• v.26 no.1
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• pp.47-58
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• 2009

In this study, a Hardware-In-the-Loop (HIL) simulator using thrusters is developed to validate the spacecraft attitude system. To control the attitude of the simulator, eight cold gas thrusters are aligned with roll, pitch and yaw axis. Also linear actuators are applied to the HIL simulator for automatic mass balancing to compensate the center of mass offset from the center of rotation. The HIL simulator consists of an embedded computer (Onboard PC) for simulator system control, a wireless adapter for wireless network, a rate gyro sensor to measure 3-axis attitude of the simulator, an inclinometer to measure horizontal attitude, and a battery set to supply power for the simulator independently. For the performance test of the HIL simulator, a bang-bang controller and Pulse-Width Pulse-Frequency (PWPF) modulator are evaluated successfully. The maneuver of 68 deg. in yaw axis is tested for the comparison of the both controllers. The settling time of the bang -bang controller is faster than that of the PWPF modulator by six seconds in the experiment. The required fuel of the PWPF modulator is used as much as 51% of bang-bang controller in the experiment. Overall, the HIL simulator is appropriately developed to validate the control algorithms using thrusters.

• Korean Journal of Food Science and Technology
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• v.41 no.4
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• pp.374-379
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• 2009

In this study, we investigated effects of different packaging materials and methods on physico-characteristics of green pumpkin during storage at $10^{\circ}C$. Whole green pumpkin samples were packaged with polyvinyl chloride film (PVCF), orange coating film (OCF), paraffin film (PF), or paper with paraffin film (PWPF) and stored at $10^{\circ}C$. Weight loss, pH, firmness, browning, and gas composition ($O_2$ and $CO_2$) inside the film packages were evaluated. All characteristics of the unpackaged group (control group, CON) changed rapidly and lost marketability as compared with the packed pumpkin group. The pH values in all of the green pumpkin samples were between 6.38 and 6.67, and decreased with increased storage time. Over the storage time, all packaged pumpkin groups evidenced prevented or retarded deterioration of the green pumpkin samples in terms of appearance, texture, and discoloration. Firmness decreased slightly with increased storage time. Brown color difference were much higher in the controls than in the film-packaged green pumpkin samples, and increased rapidly in the early stages of storage. These results were attributed to reduce respiration rates as a result of elevated carbon dioxide and reduced oxygen levels in the packages. The results of this study demonstrated that the green pumpkin packaged with PWPF and PVCF showed retarded deterioration as compared to the CON, OCF and PF samples in a controlled atmosphere, and thus significant differences were noted according to the packaging material and methods used.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.19 no.4
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• pp.37-43
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• 2011

Lunar exploration program has been prepared with the aim of launch in the 2020's. As part of it, a lunar lander demonstrator has been developed which is the model for verifying all the system, such as structure, propulsion and control system before launch to deep space. After verifying all the system, the demonstrator will be evaluated by flight test. This paper deals with path tracking controller based on thrusters for the demonstrator. For this, first we derive equations of motion according to the allocation of thrusters and design the path tracking controller. The signal generated from the controller is continuous so PWPF(Pulse-Width Pulse-Frequency) modulator is adopted for generating on/off signal. Finally MATLAB simulation is performed for evaluating the path tracking ability and the final landing velocity.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.9
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• pp.55-63
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• 2003

An attitude control system using reaction thrusters for the upper stage of a launch vehicle is considered. The thruster configuration (position and direction) determines control system response, fuel consumption, effective torque and system fault tolerance. We propose a procedure for finding the optimal thruster configuration with desired control effectiveness over the range of selected torque commands. An optimization technique called Particle Swarm Optimization is used for the numerical experiments. The validity of the solution is checked through computer simulations.