• Aerospace Engineering and Technology
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• v.8 no.1
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• pp.108-116
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• 2009

This paper considers the trajectory design problem for a lunar orbiter when launched by KSLV-II. KSLV-II puts its kick motor stage and lunar orbiter into a low earth orbit, and then the kick motor stage performed the translunar injection. To simulate more realistic situations, TLI (Trans-Lunar Injection) and LOI (Lunar Orbit Injection) maneuvers are modeled as finite burns. The feasibility of the lunar mission by KSLV-II are confirmed by the numerical results that show the reasonable required-velocity and propellant usage.

• Journal of Astronomy and Space Sciences
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• v.27 no.3
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• pp.195-204
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• 2010

The optimal Earth-Moon transfer trajectory considering spacecraft's visibility from the Daejeon ground station visibility at both the trans lunar injection (TLI) and lunar orbit insertion (LOI) maneuvers is designed. Both the TLI and LOI maneuvers are assumed to be impulsive thrust. As the successful execution of the TLI and LOI maneuvers are crucial factors among the various lunar mission parameters, it is necessary to design an optimal lunar transfer trajectory which guarantees the visibility from a specified ground station while executing these maneuvers. The optimal Earth-Moon transfer trajectory is simulated by modifying the Korean Lunar Mission Design Software using Impulsive high Thrust Engine (KLMDS-ITE) which is developed in previous studies. Four different mission scenarios are established and simulated to analyze the effects of the spacecraft's visibility considerations at the TLI and LOI maneuvers. As a result, it is found that the optimal Earth-Moon transfer trajectory, guaranteeing the spacecraft's visibility from Daejeon ground station at both the TLI and LOI maneuvers, can be designed with slight changes in total amount of delta-Vs. About 1% difference is observed with the optimal trajectory when none of the visibility condition is guaranteed, and about 0.04% with the visibility condition is only guaranteed at the time of TLI maneuver. The spacecraft's mass which can delivered to the Moon, when both visibility conditions are secured is shown to be about 534 kg with assumptions of KSLV-2's on-orbit mass about 2.6 tons. To minimize total mission delta-Vs, it is strongly recommended that visibility conditions at both the TLI and LOI maneuvers should be simultaneously implemented to the trajectory optimization algorithm.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.12
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• pp.950-958
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• 2013

The Lunar orbiter is expected to be inserted into a ~300km low Earth orbit using Korea Space Launch Vehicle-II(KSLV-II). After the states are successfully determined with obtained tracking data, the Trans Lunar Injection(TLI) burn has to be done at appropriate epoch to send the lunar orbiter to the Moon. In this study, we describe in detail the mission scenario of the Korean lunar orbiter from the launch at NARO Space Center to lunar orbit insertion(LOI) stage following direct transfer trajectory. We investigate the launch window including launch azimuth, delta-V profile according to TLI and LOI burn positions. We also depict the visibility conditions of ground stations and solar eclipse duration to understand the characteristics of the direct transfer trajectory. This paper can be also helpful not only for overall understanding of ${\Delta}V$ trend by changing TOF and coasting time but for selecting launch epoch and control parameters to decrease fuel consumption.

• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.40.2-40.2
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• 2009

이 연구에서는 달천이(TLI: Trans Lunar Injection) 및 달포획(LOI: Lunar Orbit Injection) 기동 시 대전 지상국의 가시성을 고려한 최적의 임무를 설계하였다. TLI 기동은 탐사선이 지구 주차궤도에서 지구-달 천이궤적으로 진입하기 위하여 주어지는 기동이며, LOI 기동은 탐사선이 지구-달 천이궤적에서 달의 중력권으로 진입하기 위하여 주어지는 기동이다. TLI 및 LOI 기동 시 대전 지상국에서의 가시성의 확보는 실제적인 미래 한국의 달 탐사를 대비하였을 때 중요한 요소이다. 따라서 이 연구에서는 TLI 및 LOI 기동 시 대전 지상국에서의 가시성을 모두 고려하여, 최소연료로 지구 주차궤도에서 달 임무궤도 진입까지의 모든 단계에 대해 임무설계를 실시하였다. TLI 및 LOI 기동 시 추력은 순간 추력(Impulsive thrust)로 가정하였으며, KSLV-II 발사체의 성능을 적용하여 설계하였다. 임무 설계 시 태양, 지구, 달의 섭동력을 고려한 N체 운동 방정식을 탐사선에 적용하였으며, 지구의 비대칭 중력장, 태양 복사압, 달의 J2 섭동에 의한 영향도 고려하였다. JPL의 정밀 천체력인 DE405를 사용하였고, 상용 소프트웨어인 SNOPT(Spares Nonlinear OPTimizer)를 이용하여 비행 궤적의 최적해를 도출하였다. 임무 설계 결과를 통해, 대전 지상국의 가시성을 고려한 TLI 및 LOI 기동의 크기에 의한 임무설계의 분석을 수행하였다. 또한 최적화된 달 탐사 임무의 단계별 기동의 크기와 지구-달 천이 궤적의 형상 및 다양한 임무 요소들의 해석을 도출하였다.

• Bulletin of the Korean Space Science Society
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• 2008.10a
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• pp.25.3-26
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• 2008

The direct way to the moon is to start from the parking orbit by using impulsive thruster In previous domestic research, the direct way has been studied by using a single impulsive shot. However, when a single impulsive shot occurs to go into a Translunar orbit, gravity losses occur because thruster is not impulsive shot but the finite burns and it causes the gravity losses. To make up for the weak point of a single impulsive shot, this paper divides TLI (Trans Lunar Injection) into several small burns. Therefore, departure loop trajectory and the Translunar trajectory. This method is useful not only to reduce the gravity losses but also to check the condition of satellite. By using this method, this paper demostrates the optimized trajectory from Earth parking orbit to lunar mission orbit which minimizes the fuel, and the SNOPT (Sparse Nonlinear OPTimizer software) is used to find optimal solution. Also, this paper provides lunar mission profile which includes the mission schedule when TLI, LOI (Lunar Orbit Insertion) maneuvers occur, a mount of fuel when thruster is used and other mission parameters.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.1
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• pp.69-77
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• 2012

After lunar explorations were restarted in 1990s, the world space advanced countries have been competing actively to preoccupy the Moon from the 2000s. Korea has been also conducting precedent study on lunar exploration to carry out that by ourselves in 2020. This study analyzed delta-V of various Earth-Moon transfer trajectories for minimization of fuel consumption. Through the simulation, the best Earth-Moon transfer trajectory for Korean lunar mission is suggested and it will be used as useful materials of Korean lunar mission.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.162.2-162.2
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• 2012

한국형 발사체 KSLV-2의 발사능력을 고려하면 달 탐사선의 총 무게는 약 550kg이 된다. 따라서 달 탐사선에 탑재할 수 있는 탑재체 무게를 최대화하기 위해서는 지구에서 달로 가는 천이궤적을 가장 효율적으로 설계하여 연료 소모량을 최소화하여야 한다. 본 연구에서는 최근에 달 탐사 천이궤적으로 가장 많이 사용되고 있는 Weak Stability Boundary 천이궤적에 관해 연구를 수행하였다. Weak Stability Boundary 천이궤적은 지구로부터 출발한 후 원지점 약 1.4 km(지구-태양의 L1 점 근처)까지 비행한 후 태양풍을 통해 에너지를 얻어 근지점 거리를 지구-달 거리만큼 증가시켜 LOI(Lunar Orbit Injection)시 ${\Delta}V$를 최소화하여 달 궤도에 들어가는 방법이다. Weak Stability Boundary 천이방법의 TLI(Trans Lunar Injection) 값은 직접천이 방법의 TLI 값보다 더 크지만 달 궤도 진입에 필요한 LOI ${\Delta}V$값은 25% 정도 덜 든다는 장점이 있다. 이 방법은 일본의 Hiten 탐사선이 최초로 사용하였으며, 달에 도착하기까지 수개월이 걸리는 단점이 있다. Weak Stability Boundary 천이궤적 시뮬레이션을 통해 최대로 절약할 수 있는 연료 소모량을 확인할 수 있었으며, 다른 천이방법들과의 장단점 비교를 통해 한국형 달 탐사선의 지구-달 천이궤적 후보로 사용 될 수 있음을 확인하였다.

• Journal of Astronomy and Space Sciences
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• v.38 no.2
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• pp.145-155
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• 2021

In this work, preliminary launch opportunities from NARO Space Center to the Sun-Earth Lagrange point are analyzed. Among five different Sun-Earth Lagrange points, L1 and L2 points are selected as suitable candidates for, respectively, solar and astrophysics missions. With high fidelity dynamics models, the L1 and L2 point targeting problem is formulated regarding the location of NARO Space Center and relevant Target Interface Point (TIP) for each different launch date is derived including launch injection energy per unit mass (C3), Right ascension of the injection orbit Apoapsis Vector (RAV) and Declination of the injection orbit Apoapsis Vector (DAV). Potential launch periods to achieve L1 and L2 transfer trajectory are also investigated regarding coasting characteristics from NARO Space Center. The magnitude of the Lagrange Orbit Insertion (LOI) burn, as well as the Orbit Maintenance (OM) maneuver to maintain more than one year of mission orbit around the Lagrange points, is also derived as an example. Even the current work has been made under many assumptions as there are no specific mission goals currently defined yet, so results from the current work could be a good starting point to extend diversities of future Korean deep-space missions.

• 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.