• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.9
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• pp.843-854
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• 2009

For preparing Korean lunar missions, optimal Earth-Moon transfer trajectory is designed using continuous low thrust. Using both constant and variable low thrusting method, "End-to-End" mission analysis is made from beginning of the Earth departure to the final lunar arrival. Spacecraft's equations of motion is expressed using N-body dynamics including the gravitational effects due to the Earth, Moon, Sun and also with Earth's $J_2$ effects. Planets' exact locations are computed accurately with JPL's DE405 ephemeris. As a results, optimal thrust steering angle's characteristics are discovered which showed almost tangential direction burns at the near of central planets. Also, it is confirmed that variable low thrusting method is more efficient than constant thrusting method, and can save about 5% of fuel consumption. Presented algorithm and various results will give numerous insights into the future Korea's Lunar missions using low thrust engines. Also, it is expected to be used as a basis of more detailed mission analyzing tool.

• 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.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.1
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• pp.17-23
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• 2020

Upper stage of launch vehicle mainly injects a lunar explorer from low earth orbit to the moon at a distance of 380,000 km. In foreign lunar explorer, the upper stage is separated from the explorer after the explorer is injected into the earth-moon transfer trajectory, and the lunar explorer then uses on-board propellant to carry out mid-course correction maneuvers and lunar orbit insertion maneuvers. This study describes a newly presented small liquid upper stage. Using a small liquid upper stage with a wet mass of 2.9 tonnes, the lunar explorer not only can be injected earth-moon transfer trajectory but also can be performed lunar orbit insertion. This study provides acceptable mass range of the lunar explorer and the scope of acceptable mission range also describes based on the launch from Naro Space Center.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.4
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• pp.357-367
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• 2008

Preparing for future Korean Lunar missions, preliminary Lunar mission design software is developed using a impulsive thrusting method. Developed software is capable of design and analysis every required mission phases to design Lunar mission, including the Earth departure, Lunar transfer, Lunar arrival and mission operation phases. Also, assuming that KSLV-II is selected as a launch vehicle, future Korean Lunar explorer's mass budget is estimated based on driven optimal trajectory characteristics. Tracking analysis is also performed using Deep Space Network including angle geometry analysis between Earth - Moon - Lunar explorer - Sun which are very important for communication, solar panel pointing strategy and eclipse analysis when Lunar missions are under designing phase.

• Aerospace Engineering and Technology
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• v.7 no.1
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• pp.91-98
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• 2008

Since the 1st space race between the United States and Soviet Union during the 1960s, we are competing 2nd space race to occupy the Lunar territory. Since the United States announced to construct the Lunar Base by the end of 2020, ED, Japan, and China launched Lunar explorers successfully. Even India is planning to launch a Lunar explorer in 2008. Korean government also announced that the Korea will launch first Lunar explorer in 2020. In this research Lunar mission trajectory design which will be fundamental data for Lunar mission with variable low thrust and Lunar mission trajectory which has a similar mission specification to SMART-1 are presented.

• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.39.4-40
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• 2009

이 연구의 목적은 고해상도 합성개구레이더 센서를 탑재한 관측위성의 운용요구사항에 맞춰 임무기간 동안 관측 목표지역을 주기적으로 반복하고 지상궤적을 $\pm2km$ 범위 내에서 안정성을 갖도록 유지 조정하는 궤도제어 알고리즘 연구를 수행하는데 있다. 기존에 수행되어 왔던 지상궤적에 대한 오차를 해석적으로 계산하여 궤도를 유지 조정하는 방법이 아닌 기준궤도에 대하여 상대좌표계에서 표현된 위성의 실제 접촉궤도를 기준궤도와 직접적으로 비교하여 목표궤적을 유지 조정하는 알고리즘을 연구하였다. 이를 위해 첫째, 고해상도 관측위성의 운용요구사항을 만족하는 계획된 목표궤도인 기준궤도를 설계하였다. 기본적으로 기준궤도는 임무 설계 시 완전한 주기성이 고려된 최대한 실제에 가까운 궤도이기 때문에 지구중력장 모델만을 고려하여 간략하게 설계하였다. 둘째, 실제의 인공위성의 궤도는 계획된 기준궤도를 유지해야 하지만 시간에 따라 섭동력의 영향을 받아 계획된 궤도로부터 벗어나게 된다. 기준궤도로부터 실제궤도가 얼마나 벗어나는지에 대한 정량적 분석을 위해 지구 중력장, 달-태양 중력, 대기저항력, 태양복사압, 조석력 등과 같은 다양한 섭동력의 영향에 대한 분석을 수행하였다. 셋째, 반경방향(radial), 진행방향(along-track), 교차방향(cross-track)의 세 방향의 성분으로 구성된 우주공간오차(Space Error) 개념을 적용하여, 투영된 지상궤적에 상응하는 오차를 계산하는 것 보다 안정적으로 오차를 계산하였다. 또한 운용요구사항에 따라 허용된 범위 내에서 궤도를 유지하기 위해 GVE(Gauss Variation Equation)을 이용한 궤도조정을 수행하였다. 섭동력의 분석 결과로부터 지구대기저항력, 달-태양 중력으로 인해 가장 두드러지는 장반경과 궤도이심률의 변화를 조정하기 위해, 임무에 사용되는 추력기의 연료 효율을 고려하여 동결궤도가 유지될 수 있는 최적의 위도이각에서 In-plane에 대한 궤도조정만을 수행하여 장반경과 이심률을 동시에 조정하였다. 지구대기와 태양활동의 영향으로 시간에 따른 장반경의 변화율에 따라 궤도조정 주기를 가지는 것을 알 수 있었고, 이 변화율 때문에 생기는 우주공간오차의 증가를 보정하여 위성의 지상궤적을 목표범위 안에서 유지할 수 있었다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.11
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• pp.984-997
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• 2015

Chang'e-3 consisting of a lunar lander and exploration rover was launched on December 1, 2013 aboard a Long March 3B rocket flying from Xichang space launch center. Chang'e-3 was inserted into the lunar orbit after about a 5-day transit to the Moon and landed on the targeted landing site after orbiting around the Moon for 8 days. The successful landing of the Chang'e-3 gives a lot of help to analyze the future needs of the subsystem technologies and to figure out the trajectory from launch to lunar landing as well as operation sequences in the development of Korean lunar exploration is scheduled. Therefore, the configuration and analysis of overall mission of Chang'e-3 is performed based on the public information from the press and website. As a result, overall mission trajectory is reconstructed by solving boundary condition and then estimating control variable. Visibility status and eclipse status also analyzes so communication and power charge condition is as good as to operate lunar lander. Mass budget of the lander is derived using ${\Delta}V$ according to specific impulse.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.11
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• pp.1021-1032
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• 2011

This paper presents the results of a parametric study for the design of optimal Earth-Moon transfer trajectory using mixed impulsive and continuous thrust. Various types of the optimal Earth-Moon transfer trajectories were designed by adjusting the relative weight between the impulsive and the continuous thrust, and flight time. Two very different transfer trajectories can be obtained by different combination of design parameters. Furthermore, it was found that all thus designed trajectories permit the ballistic capture by the Moon gravity. Finally, the required thrust profiles are presented and analyzed in detail.

• 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 Society for Aeronautical & Space Sciences
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• v.46 no.5
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• pp.402-409
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• 2018

In this paper, we propose a lunar landing scenario of a robotic lunar landing mission and implements an optimal landing trajectory at the powered descent phase based on the proposed scenario. The change of attitude of the lunar lander in the power descent phase affects not only the amount of fuel used but also sensor operation of image based navigation. Therefore, the attitude angular velocity is included in the cost function of the optimal control problem to minimize the unnecessary attitude change when the optimal landing trajectory generates at powered descent phase of the lunar landing. The influence of the change of attitude angular velocity on the optimal landing trajectory are analyzed by adjusting the weight of the attitude angular velocity. Based on the results, we suggest the proper weight to generate the optimal landing trajectory in order to minimize the influence of the attitude angular velocity.