• Journal of Astronomy and Space Sciences
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• 제31권3호
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• pp.247-264
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• 2014

In this paper, a brief but essential development strategy for the lunar orbit determination system is discussed to prepare for the future Korea's lunar missions. Prior to the discussion of this preliminary development strategy, technical models of foreign agencies for the lunar orbit determination system, tracking networks to measure the orbit, and collaborative efforts to verify system performance are reviewed in detail with a short summary of their lunar mission history. Covered foreign agencies are European Space Agency, Japan Aerospace Exploration Agency, Indian Space Research Organization and China National Space Administration. Based on the lessons from their experiences, the preliminary development strategy for Korea's future lunar orbit determination system is discussed with regard to the core technical issues of dynamic modeling, numerical integration, measurement modeling, estimation method, measurement system as well as appropriate data formatting for the interoperability among foreign agencies. Although only the preliminary development strategy has been discussed through this work, the proposed strategy will aid the Korean astronautical society while on the development phase of the future Korea's own lunar orbit determination system. Also, it is expected that further detailed system requirements or technical development strategies could be designed or established based on the current discussions.

• Journal of Astronomy and Space Sciences
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• 제37권1호
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• pp.1-9
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• 2020

Frozen orbit is an attractive option for orbital design owing to its characteristics (its argument of pericenter and eccentricity are kept constant on an average). Solar sails are attractive solutions for massive and expensive missions. However, the solar radiation pressure effect represents an additional force on the solar sail that may greatly affect its orbital behavior in the long run. Thus, this force must be included as a perturbation force in the dynamical model for more accuracy. This study shows the calculations of initial conditions for a lunar solar sail frozen orbit. The disturbing function of the problem was developed to include the lunar gravitational field that is characterized by uneven mass distribution, third body perturbation, and the effect of solar radiation. An averaging technique was used to reduce the dynamical problem to a long period system. Lagrange planetary equations were utilized to formulate the rate of change of the argument of pericenter and eccentricity. Using the reduced system, frozen orbits for the Moon sail orbiter were constructed. The resulting frozen orbits are shown by two 3Dsurface (semi-major, eccentricity, inclination) figures. To simplify the analysis, we showed inclination-eccentricity contours for different values of semi-major axis, argument of pericenter, and values of sail lightness number.

• Journal of Astronomy and Space Sciences
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• 제29권4호
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• pp.413-422
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• 2012

In recent years, a number of missions have been planned and conducted worldwide on the planets such as Mars, which involves the unmanned robotic exploration with the use of rover. The rover is an important system for unmanned planetary exploration, performing the locomotion and sample collection and analysis at the exploration target of the planetary surface designated by the operator. This study investigates the development of mobility system for the rover ground model necessary to the planetary surface exploration for the benefit of future planetary exploration mission in Korea. First, the requirements for the rover mobility system are summarized and a new mechanism is proposed for a stable performance on rough terrain which consists of the passive suspension system with 8 wheeled double 4-bar linkage (DFBL), followed by the performance evaluation for the mechanism of the mobility system based on the shape design and simulation. The proposed mobility system DFBL was compared with the Rocker-Bogie suspension system of US space agency National Aeronautics and Space Administration and 8 wheeled mobility system CRAB8 developed in Switzerland, using the simulation to demonstrate the superiority with respect to the stability of locomotion. On the basis of the simulation results, a general system configuration was proposed and designed for the rover manufacture.

• 천문학회보
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• 제44권2호
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• pp.42.3-42.3
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• 2019

We translate Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA) ultraviolet (UV) multi-channel images into another UV single-channel image using a deep learning algorithm based on conditional generative adversarial networks (cGANs). The base input channel, which has the highest correlation coefficient (CC) between UV channels of AIA, is 193 Å. To complement this channel, we choose two channels, 1600 and 304 Å, which represent upper photosphere and chromosphere, respectively. Input channels for three models are single (193 Å), dual (193+1600 Å), and triple (193+1600+304 Å), respectively. Quantitative comparisons are made for test data sets. Main results from this study are as follows. First, the single model successfully produce other coronal channel images but less successful for chromospheric channel (304 Å) and much less successful for two photospheric channels (1600 and 1700 Å). Second, the dual model shows a noticeable improvement of the CC between the model outputs and Ground truths for 1700 Å. Third, the triple model can generate all other channel images with relatively high CCs larger than 0.89. Our results show a possibility that if three channels from photosphere, chromosphere, and corona are selected, other multi-channel images could be generated by deep learning. We expect that this investigation will be a complementary tool to choose a few UV channels for future solar small and/or deep space missions.

• 천문학회보
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• 제44권2호
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• pp.42.2-42.2
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• 2019

Korea Astronomy and Space Science Institute (KASI) has been developing a next-generation coronagraph (NGC) in cooperation with NASA to measure the coronal electron density, temperature, and speed using four different filters around 400 nm. To demonstrate technology for the measurement through the 2017 total solar eclipse across the USA, KASI organized an expedition team to demonstrate the coronagraph measurement scheme and the instrumental technology. The observation site was in Jackson Hole, Wyoming, USA. We built an eclipse observation system, so-called Diagnostic Coronal Experiment (DICE), which is composed of two identical telescopes to improve a signal to noise ratio. The observation was conducted with 4 wavelengths and 3 linear polarization directions according to the planned schedule in a limited total eclipse time of about 140 seconds.Polarization information of corona from the data was successfully obtained but we failed to get the coronal electron temperature and speed information due to a low signal-to-noise ratio of the optical system. In this study, we report the development of DICE and observation results. TSE observation and analysis by using our own developed instrument gave an important lesson that a coronagraph should be carefully designed to archive the scientific purpose. This experience through TSE observation will be very useful for a success of NASA-KASI joint missions called the Balloon-borne Investigation of the Temperature and Speed of Electrons in the Corona (BITSE) and COronal Diagnostic EXperiment (CODEX).

• Journal of Positioning, Navigation, and Timing
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• 제12권4호
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• pp.437-445
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• 2023

A space system refers to a network of sensors, ground systems, and space-craft operating in space. The security of space systems relies on information systems and networks that support the design, launch, and operation of space missions. Characteristics of space operations, including command and control (C2) between space-craft (including satellites) and ground communication, also depend on wireless frequency and communication channels. Attackers can potentially engage in malicious activities such as destruction, disruption, and degradation of systems, networks, communication channels, and space operations. These malicious cyber activities include sensor spoofing, system damage, denial of service attacks, jamming of unauthorized commands, and injection of malicious code. Such activities ultimately lead to a decrease in the lifespan and functionality of space systems, and may result in damage to space-craft and, lead to loss of control. The Cybersecurity Adversarial Tactics, Techniques, and Common Knowledge (ATT&CK) matrix, proposed by Massachusetts Institute of Technology Research and Engineering (MITRE), consists of the following stages: Reconnaissance, Resource Development, Initial Access, Execution, Persistence, Privilege Escalation, Defense Evasion, Credential Access, Discovery, Lateral Movement, Collection, Command & Control, Exfiltration, and Impact. This paper identifies cybersecurity activities in space systems and satellite navigation systems through the National Institute of Standards and Technology (NIST)'s standard documents, former U.S. President Trump's executive orders, and presents risk management activities. This paper also explores cybersecurity's tactics attack techniques within the context of space systems (space-craft) by referencing the Sparta ATT&CK Matrix. In this paper, security threats in space systems analyzed, focusing on the cybersecurity attack tactics, techniques, and countermeasures of space-craft presented by Space Attack Research and Tactic Analysis (SPARTA). Through this study, cybersecurity attack tactics, techniques, and countermeasures existing in space-craft are identified, and an understanding of the direction of application in the design and implementation of safe small satellites is provided.

• 한국항공우주학회지
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• 제48권6호
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• pp.419-429
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• 2020

다수의 무인항공기를 이용하여 표적을 탐색 및 추적하는 임무를 수행하는데 있어서 무인항공기의 운용 대수, 비행고도 등 운용 조건뿐만 아니라, 각 비행체들이 어떤 알고리즘을 이용해 비행경로를 결정하느냐에 따라 그 임무에 대한 성과는 크게 달라질 수 있다. 다만 이러한 표적 탐색 임무에서 자율 비행 무인항공기의 운용 방법이 어떠할 때 가장 효과적이며 효율적인지에 대한 연구는 미흡한상태이다. 본 연구에서는 플로킹 이론을 기반을 둔 다양한 자율비행 알고리즘을 활용하여, 다수의 무인 항공기가 서로 충돌을 회피하면서 표적을 탐지하는 임무를 기반으로 비행 시뮬레이션을 수행하고 그 결과를 분석하여, 표적 탐지 임무에서의 다수의 무인항공기를 제어할 수 있는 보다 효율적/효과적인 방안을 제시하였다.

• 한국항공우주학회지
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• 제38권10호
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• pp.998-1011
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• 2010

본 연구에서는 미래 한국의 달탐사에 대비, 제한추력을 이용한 최적의 지구-달 천이궤적 설계를 수행하였다. 보다 실제적인 임무 시나리오 설계를 위해 달 천이 (Trans Lunar Injection, TLI) 기동에 사용되는 발사체 상단 킥모터의 추력 성능을 제한하였다. 이를 바탕으로 지구 출발부터 달 근접에 이르는 지구-달 천이비행궤적이 설계되었으며, 제한추력을 이용하여 설계된 비행 궤적의 최적화 결과와 순간추력을 이용하여 최적화된 결과가 비교 분석되었다. 만약 순간추력을 이용해 도출된 예비 임무 설계의 결과가 제한추력을 가정한 임무 설계를 위해 응용될 경우, 가정된 제한추력의 크기에 따라 다양한 범위의 기동량의 차이가 발생 할 수 있어 이에 따른 충분한 고려가 이루어져야 함을 확인하였다. 본 연구에서 제시된 제한추력을 이용한 달탐사 임무궤적 설계/해석 결과는 미래 한국의 달탐사를 대비하는데 있어 다양한 사전 지식을 제공할 것이며 장차 상세한 임무설계를 위한 알고리즘의 기반으로 사용될 수 있다.

• 한국항공우주학회지
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• 제38권1호
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• pp.48-57
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• 2010

본 논문에서는 위성 임무 스케줄링을 효율적으로 수행하기 위한 스케줄링 최적화 알고리즘을 타부탐색 알고리즘과 유전 알고리즘을 이용해 디자인하고, 시뮬레이션을 수행한 비교 결과를 기술하였다. 위성 임무 스케줄링은 위성에게 요구된 작업들과 그에 따른 제한사항 및 다양한 변수들을 종합적으로 고려하여 상호간의 시간, 조건 등의 충돌을 회피함과 동시에 위성의 자원을 최대한 활용하여 운용할 수 있는 최적의 작업시간표를 생성하는 것이다. 위성 임무 스케줄링은 동시에 많은 변수를 고려해야 하기 때문에 연산양이 많고, 매 스케줄링 시 마다 동일한 과정을 반복적으로 수행해야 하므로, 스케줄링 최적화 알고리즘과 같은 위성 운영 자동화, 자율화가 요구되는 분야이다. 다양하게 이용되고 있는 두 가지 스케줄링 기법을 위성 임무 스케줄링 최적화에 적용해 보았다.

• 한국항공우주학회지
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• 제45권9호
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• pp.711-723
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• 2017

본 연구에서는 재형상 특성을 지닌 유기적 비행 어레이의 비행 제어 시스템 설계에 대한 내용을 제안하였다. 단일 덕티드팬의 결합과 분리를 기반으로 구성되는 유기적 비행어레이는 주어진 임무나 주변 상황에 대해 유기적으로 어레이 형상을 변화시킬 수 있는 장점을 가진다. 이와 더불어 덕티드팬 비행체 기반이기 때문에 호버링이 가능하여 실내 정찰, 통신 중계, 레이더 재밍과 같은 미션에 유용하게 사용 된다. 비행 어레이의 동역학모델링은 단일 덕티드팬 비행체의 동역학 모델을 기반으로 구성되며, 비선형 제어기법을 적용하기 위해 어파인 형태의 동역학 식에 대한 유도를 수행한다. 비행체 자세 제어를 위해 Backstepping 제어기법을 적용하였으며 PID 제어기법을 통해 위치 제어 루프를 구현한다. 또한 수치 시뮬레이션을 통해 제안 된 제어기가 주어진 상황에서 충분한 성능을 보이는지를 검증하였다.