• Journal of Aerospace System Engineering
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• v.10 no.4
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• pp.35-40
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• 2016

Mid-course correction maneuvers (MCCMs) are necessary to correct the launch-vehicle dispersion to go to the Moon. There were 3 or 4 MCCMs needed for a direct transfer trajectory. But the strategy for MCCMs of the phasing-loop trajectory is different, because it has a longer trans-lunar trajectory than direct transfer does. An orbiter using a phasing-loop trajectory has several rotations of the Earth, so the orbiter has several good places, such as perigee and apogee, to correct the launch-vehicle dispersion. Although launch dispersion is relatively high, the launch vehicle is not as accurate as we expected. A good MCCM strategy can overcome the high dispersion by using small-magnitude correction maneuvers. This paper describes the phasing-loops sequence and strategy to correct high launch-vehicle dispersions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.3
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• pp.251-256
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• 2018

In the case of a radar repeater that used for the trajectory tracking of a high-speed aircraft, it emits pulses of short width. For phase displacement of these signals a branch type phase shifter is used. The phase on the transmission line is changed by utilizing the variable reactance at the end of the displacement branch transmission line. Further, it is easy to control the high output signal, and there is an advantage that the insertion loss is not large even when the reactance fails. In this paper, we will discuss the fabrication test results of a 400 W class phase shifter that sequentially displaces the phase at $0^{\circ}$, $30^{\circ}$, $60^{\circ}$, $90^{\circ}$.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.1
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• pp.68-77
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• 2018

In order to analyze the overall characteristics of the lunar orbiter, the Variable Coast method, which can be launched everyday, is applied to the 3.5 phasing loop transfer trajectory. The mission scenario for the entire process from launching to entering the lunar orbit is set up and performed simulation by selecting the launch pad and launch vehicle. In particular, the SEM(Satellite-Earth-Moon) angle defined in Earth-Moon rotating frame is an important constraint to comprehensively evaluate the 3.5 phasing loop transfer trajectory. The simulation using SEM angle is analyzed from various viewpoints such as launch epoch, coast duration, perigee altitude and ${\Delta}V$ not only trans-lunar trajectory but lunar orbit insertions and the optimum SEM angle is suggested in this study. It is expected that this results will be helpful to evaluate the characteristics of the 3.5 phasing loop transfer trajectory according to the launch vehicle selection by comparison with Fixed Coast analysis results in the future.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.799-805
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• 1996

In many cases, the magnetic farce model is linearized at the origin in designing the controller of a magnetic bearing system. However. this linear assumption is violated by the unmodeled nonlinear effect such as sensor dislocation and backup bearing dislocation. Therefore, a direct probe into the nonlinear magnetic force model in an active magnetic bearing system is necessary. To analyze the nonlinear magnetic force model of a magnetic bearing system, phase plot analysis which is to plot the numerical solution of the nonlinear equation in several initial points in the interested region is applied. Phase plot analysis is used to observe a nonlinear dynamic system qualitatively (not quantitatively). With this method, we can get much useful information of the nonlinear system. Among this information, a bifurcation graph that represents stability and locations of fixed points is essential. From the bifurcation graph, a stability criterion of magnetic bearing system is derived.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.3
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• pp.218-227
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• 2016

Korean government plans to launch a lunar orbiter and a lander to the Moon by 2020. Before launch these two proves, an experimental lunar orbiter will be launched by 2018 to obtain key space technologies for the lunar exploration. Several payloads equipped in experimental lunar orbiter will monitor the surface of the Moon and will gather science data. Lunar orbiter sends telemetry and receives tele-command from ground using S-band while science data is sent to ground stations using X-band when the visibility is available. Korean deep space network will be mainly used for S and X-band communication with lunar orbiter. Deep Space Network or Universal Space Network can also be used for the S-band during trans-lunar phase when korean deep space network is not available and will be used for the S-band in normal mission orbit as a backup. This paper analyzes a visibility condition based on the combination of various ground antennas and its mask angles according to mission scenario to predict the number of contacts per day and to build an operational scenario for the lunar orbiter.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.12
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• pp.29-35
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• 2008

In this paper, The author present a load current feed-forward compensator by method that improve voltage controller of Step-down Chopper to get stable output voltage to sudden change of load current. To confirm the characteristics of a presented load current feed-forward compensator compared each transfer function of whole system that load current feed-forward compensator is added with transfer function of whole system that existent voltage controller is included using Mason gains formula in Root locus and Bode diagram. As a result the pole of system is improved, extreme point of the wave and system improves, and size of peak value and phase margin of break frequency in resonance frequency confirmed that is good. Therefore, presented control technique could confirm that reduce influence by perturbation and improves stationary state and dynamic characteristics in output of Step-down Chopper.

• Journal of the Economic Geographical Society of Korea
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• v.20 no.3
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• pp.267-286
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• 2017

The main purpose of this paper is to identify the spatiality of North Korea and China border regions through investigating the exceptional characteristics of the regions with the concept of positionality, which allows us to realize the relative position between subject and object. Border regions could be identified appropriately by considering the concept of switching positionality, as it is a kind of multiple space in which its sudden closure and opening should be configured in accordance with geopolitical and geoeconomic changes centering around border line. The main arguments of this research concerned with border regions with the concept of switching positionality are fallen into three. Firstly, changes in border regions should be analyzed by investigating more broader contexts and conjunctural perspectives, and even an internal condition stemmed from locality. Secondly, trajectories of border regions could be analyzed by the assemblages of various powers. Finally, the positionality of economic actors should be examined by identifying dynamic relations between geoeconomics and geopolitics. In particular, the concept of positionality has led to a number of insights into discussions on time-space, and spatiality in relational-dialectical, socio-spatial, and power-topological perspectives. Based upon this concept of positionality, the research has identified exceptional characteristics in North Korea and China border regions. It argues that the exceptionality of the region has stemmed from the intersection between the unstability of geopolitical security and various geoeconomic benefits.