• 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 of Propulsion Engineers
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• v.25 no.1
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• pp.29-41
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• 2021

The PID controller with fin angle and thrust as control input was designed based on the aerodynamic data of scramjet system. Flight simulation following a given trajectory which strike the target point after climb and cruise with constant dynamic pressure was conducted. After that, the required thrust for the climb and cruise was calculated and the required fuel flow rate for the hydrogen fuel dual mode scramjet combustor was analyzed. The combustor analysis of this study which conducted on integrated model of independently developed inlet, combustor, nozzles and external aerodynamic models, laying the foundation for the integrated design of the air breathing hypersonic system.

• Journal of KIISE:Databases
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• v.31 no.2
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• pp.150-162
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• 2004

Moving objects have characteristics that they change continuously their positions over time. The movement of moving objects should be stored on trajectories for processing past queries. Moving objects databases need to provide spatio-temporal index for handling moving objects queries like combined queries. Combined queries consist of a range query selecting trajectories within a specific range and a trajectory query extracting to parts of the whole trajectory. Access methods showing good performance in range queries have a shortcoming that the cost of processing trajectory Queries is high. On the other hand, trajectory-based index schemes like the TB-tree are not suitable for range queries because of high overlaps between index nodes. This paper proposes new TR(Trajectory Riving)-tree which is revised for efficiently processing the combined queries. This index scheme has several features like the trajectory preservation, the increase of the capacity of leaf nodes, and the logical trajectory riving in order to reduce dead space and high overlap between bounding boxes of nodes. In our Performance study, the number of node access for combined queries in TR-tree is about 25% less than the STR-tree and the TB-tree.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.3
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• pp.274-279
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• 2010

The present work is to analyze the longitudinal static stability and the drop trajectory of fighter aircraft's external fuel tank, of which horizontal fin is modified as the 20% scale down size compared with the original one. The analytical results to the pitching stability of external fuel tank using a thin airfoil's aerodynamic force data show the corresponding tendency to results of wind tunnel experiment. Results of trajectory simulation by the 6 degree of freedom equations of motion, comparing with drop trajectories of wind tunnel experiment, are shown that aircraft's attitude affects strongly on horizontal movement but not on the vertical movement. Those results give the reliability to aircraft safety when the external fuel tank with the 20% reduced horizontal fins is released from aircraft based on the flight manual.

• 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 Korean Society of Transportation
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• v.18 no.3
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• pp.29-39
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• 2000

Position of stop line according to left turn trajectory at intersections was studied. The Purpose of this study is to suggest a design guideline of left turn trajectory at intersections which is related to the Position of cross road stop line. Distance from the curb line to the stop line at each lane was calculated and discussed for various combination of road widths. Three design vehicle type and three control radii were considered. Setbacks of stop line from the curb line are Proportional to the control radius which depends on type of design vehicle. 8m, lim and 19m setback for control radius of 12m, 15m and 23m were calculated respectively as their maximum value. This result will be helpful to Paint the road marking on the Pavement which is usually difficult to fit to the designated radius. Field study of the effect of left turn trajectory on flow rate and safety was conducted. It was approved that improperly designed left turn trajectory decreases left turn capacity and increases conflicts among left turn flows of the adjacent lane.

• Korean Journal of Optics and Photonics
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• v.24 no.3
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• pp.125-134
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• 2013

In case of the optical camera system with an infinite object distance, optical designs different from previous systems are required to speed up the auto-focus. As the number of lens groups is increased due to this, the conventional analytic method found it difficult to calculate the locus, and even the one-step advanced calculation method also had the trouble of taking a lot of time. In this paper, we suggested an analytic method for calculating the zoom loci by analyzing movement of one or two groups for situations corresponding to the given back focal length and effective focal length after taking a spline interpolation for each lens group. With this method, we would not only calculate the analytic zoom loci without iterations in every optical system without placing a limit on the group number at the zoom lens systems with the infinite object distance, but we would also show the utilities of this method through many examples.

• Journal of IKEEE
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• v.25 no.4
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• pp.766-769
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• 2021

In order to perform tasks such as design, control, optimization, and prediction of flight vehicle trajectories based on machine learning techniques including deep learning, a certain amount of flight vehicle trajectory data is required. However, there are cases in which it is difficult to secure more than a certain amount of flight vehicle trajectory data for various reasons. In such cases, synthetic data generation could be one way to make machine learning possible. In this paper, to explore this possibility, we generated and evaluated synthetic flight vehicle trajectory data using time-series generative adversarial neural network. In addition, various ablation studies (comparative experiments) were performed to explore the possibility of using synthetic data in the aircraft trajectory prediction task. The experimental results presented in this paper are expected to be of practical help to researchers who want to conduct research on the possibility of using synthetic data in the generation of synthetic flight vehicle trajectory data and the work related to flight vehicle trajectories.

• Journal of Astronomy and Space Sciences
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• v.26 no.2
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• pp.171-186
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• 2009

Various Earth-Moon transfer trajectories are designed and analyzed to prepare the future Korea's Lunar missions. Minimum fuel trajectory solutions are obtained for the departure year of 2017, 2020, 2022, and every required mission phases are analyzed from Earth departure to the final lunar mission orbit. N-body equations of motion are formulated which include the gravitational effect of the Sun, Earth and Moon. In addition, accelerations due to geopotential harmonics, Lunar J2 and solar radiation pressures are considered. Impulsive high thrust is assumed as the main thrusting method of spacecraft with launcher capability of KSLV-2 which is planned to be developed. For the method of injecting a spacecraft into a trans Lunar trajectory, both direct shooting from circular parking orbit and shooting from the multiple elliptical intermediate orbits are adapted, and their design results are compared and analyzed. In addition, spacecraft's visibility from Deajeon ground station are constrained to see how they affect the magnitude of TLI(Trans Lunar Injection) maneuver. The results presented in this paper includes launch opportunities, required optimal maneuver characteristics for each mission phase as well as the trajectory characteristics and numerous related parameters. It is confirmed that the final mass of Korean lunar explorer strongly depends onto the initial parking orbit's altitude and launcher's capability, rather than mission start time.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.3
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• pp.207-212
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• 2010

This paper presents a spiral descending path and a landing guidance law for net-recovery of a fixed-wing unmanned aerial vehicle. The net-recovery landing flight is divided into two phases. In the first phase, a spiral descending path is designed from an arbitrary initial position to a final approaching waypoint toward the recovery net. The flight path angle is controlled to be aligned to the approaching direction at the end of the spiral descent. In the second phase, the aircraft is guided from the approaching waypoint to the recovery net using a pseudo pursuit landing guidance law. Six degree-of-freedom simulation is performed to verify the performance of the proposed landing guidance law.