• International Journal of Aeronautical and Space Sciences
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• 제16권1호
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• pp.89-101
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• 2015

To satisfy civil aviation requirements using the Global Navigation Satellite System (GNSS), it is important to guarantee system integrity. In this work, we propose a fault detection algorithm for GNSS ephemeris anomalies. The basic principle concerns baseline length estimation with GNSS measurements (pseudorange, broadcasted ephemerides). The estimated baseline length is subtracted from the true baseline length, computed using the exact surveyed ground antenna positions. If this subtracted value differs by more than a given threshold, this indicates that an ephemeris anomaly has been detected. This algorithm is suitable for detecting Type A ephemeris failure, and more advantageous for use with multiple stations with various long baseline vectors. The principles of the algorithm, sensitivity analysis, minimum detectable error (MDE), and protection level derivation are described and we verify the sensitivity analysis and algorithm availability based on real GPS data in Korea. Consequently, this algorithm is appropriate for GNSS regional implementation.

• International Journal of Aeronautical and Space Sciences
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• 제17권2호
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• pp.253-259
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• 2016

The typical method for performing an absolute radiometric calibration of a Synthetic Aperture Radar (SAR) System is to analyze its response, without interference, to a target with a known Radar Cross Section (RCS). To minimize interference, an error-free calibration site for a Corner Reflector (CR) is required on a wide and flat plain or on an area without disturbance sources (such as ground objects). However, in reality, due to expense and lack of availability for long periods, it is difficult to identify such a site. An alternative solution is the use of a Triangular Trihedral Corner Reflector (TTCR) site, with a surrounding protection wall consisting of berms and a hollow. It is possible in this scenario, to create the minimum criteria for an effectively error-free site involving a conventional object-tip reflection applied to all beams. Sidelobe interference by the berm is considered to be the major disturbance factor. Total interference, including an object-tip reflection and a sidelobe interference, is analyzed experimentally with SAR images. The results provide a new guideline for the minimum criteria of TTCR site design that require, at least, the removal of all ground objects within the fifth sidelobe.

• 한국항공우주학회지
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• 제40권5호
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• pp.454-460
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• 2012

무인기의 안정된 통신링크 보장을 위해 오류정정 및 시분할 다중화/역다중화 기능을 갖춘 통신제어기를 FPGA를 이용하여 개발하였다. 아울러 데이터링크의 실시간성을 보장하기 위해 RTOS인 VxWorks를 사용하였다. FPGA를 이용한 통신제어기의 설계는 다양한 입출력 장치의 수정 및 확장이 용이하며, S/W 설계 변경의 유연성을 제공하여 다양한 무인기 시스템에 쉽게 적용이 가능하도록 했다.

• 한국항공우주학회지
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• 제39권2호
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• pp.153-161
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• 2011

한국항공우주연구원에서는 GBAS 기준국의 무결성 감시 알고리즘 개발을 위한 데이터 제공 및 시험을 위하여 무결성 감시 테스트베드를 구축하였다. 개발된 알고리즘의 정확한 구현 및 시험을 위해서는 기반이 되는 시설 및 소프트웨어의 기본 기능이 국제 표준에 부합하게 구현되어 있어야 하므로, 본 논문에서는 현재 구축된 테스트베드의 GBAS 기준국으로서의 기본 기능에 대한 검증시험을 수행한다. 이를 위해 국제적으로 신뢰받고 있는 프로그램인 PEGASUS와의 비교를 통하여 GBAS 보정 정보의 타당성을 확인하였으며, 이를 적용한 사용자 측면에서의 거리 영역 및 위치 영역에서의 데이터 분석을 통하여 시스템의 무결성 및 가용성 성능을 확인하였다.

• 한국항공우주학회지
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• 제37권6호
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• pp.556-561
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• 2009

다양한 비행환경에서 장시간 체공하며 원격 조종되는 무인항공기에서 추진시스템을 신뢰성 있게 운영하는 것은 매우 중요하다. 스마트 무인기의 수직 이착륙 및 전진 비행에 사용 되는 터보축엔진의 정확한 손상진단은 신뢰성과 이용률을 향상시킬 수 있을 것이다. 본 연구에서는 엔진 측정 파라미터들의 변화로부터 퍼지이론을 적용하여 손상된 구성품을 식별한 후 훈련된 신경망 알고리즘을 식별된 손상 패턴에 적용 손상된 양을 정확히 진단할 수 있는 방법을 새로이 제안하였다. 제안된 진단방법은 단일손상은 물론 다중손상도 진단할 수 있다.

• Advances in aircraft and spacecraft science
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• 제7권3호
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• pp.271-290
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• 2020

The paper describes the analysis of deployment strategies and trajectories design suitable for executing the inspection of an operative spacecraft in orbit through re-usable CubeSats. Similar missions have been though indeed, and one mission recently flew from the International Space Station. However, it is important to underline that the inspection of an operative spacecraft in orbit features some peculiar characteristics which have not been demonstrated by any mission flown to date. The most critical aspects of the CubeSat inspection mission stem from safety issues and technology availability in the following areas: trajectory design and motion control of the inspector relative to the target, communications architecture, deployment and retrieval of the inspector, and observation needs. The objectives of the present study are 1) the identification of requirements applicable to the deployment of a nanosatellite from the mother-craft, which is also the subject of the inspection, and 2) the identification of solutions for the trajectories to be flown along the mission phases. The mission for the in-situ observation of Space Rider is proposed as reference case, but the conclusions are applicable to other targets such as the ISS, and they might also be useful for missions targeted at debris inspection.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제15권8호
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• pp.2805-2826
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• 2021

In most cases, the routing policy of networks shows a preference for a static one-to-one mapping of communication pairs to routing paths, which offers adversaries a great advantage to conduct thorough reconnaissance and organize an effective attack in a stress-free manner. With the evolution of network intelligence, some flexible and adaptive routing policies have already proposed to intensify the network defender to turn the situation. Routing mutation is an effective strategy that can invalidate the unvarying nature of routing information that attackers have collected from exploiting the static configuration of the network. However, three constraints execute press on routing mutation deployment in practical: insufficient route mutation space, expensive control costs, and incompatibility. To enhance the availability of route mutation, we propose an OpenFlow-based route mutation technique called Polymorphic Path Transferring (PPT), which adopts a physical and virtual path segment mixed construction technique to enlarge the routing path space for elevating the security of communication. Based on the Markov Decision Process, with considering flows distribution in the network, the PPT adopts an evolution routing path scheduling algorithm with a segment path update strategy, which relieves the press on the overhead of control and incompatibility. Our analysis demonstrates that PPT can secure data delivery in the worst network environment while countering sophisticated attacks in an evasion-free manner (e.g., advanced persistent threat). Case study and experiment results show its effectiveness in proactively defending against targeted attacks and its advantage compared with previous route mutation methods.

• 한국항공우주학회지
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• 제47권9호
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• pp.665-677
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• 2019

미국은 총 수명주기 비용을 최소화하고 운용 가동률 향상을 위해 총 수명주기 체계관리(TLCSM, Total Life Cycle System Management)를 추진 중이다. 실천전략의 하나로 CBM+(Condition Based Maintenance +)를 새로운 무기체계에 적용할 것을 요구하고 있다. F-35 항공기는 개발단계에서부터 CBM+ 개념 하에서 PHM(건전성 예측 및 관리)을 적용하였다. 본 연구에서는 군수용 고정익 항공기 구성품 PHM 적용을 위하여 기술 동향, 국내 PHM 기술 수준 및 해외 기술발전 추세를 분석하였다. 또한, PHM 기술 요소를 분석하여 군수용 고정익 항공기 기술 요소 획득 로드맵 5단계를 구성하였다.

• Journal of Astronomy and Space Sciences
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• 제38권1호
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• pp.65-82
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• 2021

For the vast majority of geostationary satellites currently in orbit, station keeping activities including orbit determination and maneuver planning and execution are ground-directed and dependent on the availability of ground-based satellite control personnel and facilities. However, a requirement linked to satellite autonomy and survivability in cases of interrupted ground support is often one of the stipulated provisions on the satellite platform design. It is especially important for a geostationary military-purposed satellite to remain within its designated orbital window, in order to provide reliable uninterrupted telecommunications services, in the absence of ground-based resources due to warfare or other disasters. In this paper we investigate factors affecting the robustness of a geostationary satellite's orbit in terms of the maximum duration the satellite's station keeping window can be maintained without ground intervention. By comparing simulations of orbit evolution, given different initial conditions and operations strategies, a variation of parameters study has been performed and we have analyzed which factors the duration is most sensitive to. This also provides valuable insights into which factors may be worth controlling by a military or civilian geostationary satellite operator. Our simulations show that the most beneficial factor for maximizing the time a satellite will remain in the station keeping window is the operational practice of pre-emptively loading East-West station keeping maneuvers for automatic execution on board the satellite should ground control capability be lost. The second most beneficial factor is using short station keeping maneuver cycle durations.

• 천문학회보
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• 제43권2호
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• pp.36.2-36.2
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• 2018

Cosmic reionization era in the early universe was playing a leading part on making the present universe we know. However, we have not been able to reveal the main contributor to the cosmic reionization to date. Faint quasars have been mentioned as the alternative due to the uncertainty of the faint end slope of the quasars luminosity function. With the availability of the deep (~25mag) images from Subaru Hyper Suprime-Cam (HSC) Strategic Program survey, we have tried to find more quasar with low luminosity in the ELAIS-N1 field. Faint quasar candidates were selected from several multi-band color cut criteria based on the track of the simulated quasar at z ~ 5. The Infrared Medium-deep Survey (IMS) and The UKIRT Infrared Deep Sky Survey (UKIDSS) - Deep Extragalactic Survey (DXS) provide J band information which is used to cover the relatively long wavelength range of quasar spectra. To search the reliable candidates with possible Lyman break, medium-band observation was performed by the SED camera for QUasars in EArly uNiverse(SQUEAN) in the McDonald observatory and Seoul National University 4k Camera(SNUCAM) in the Maidanak observatory. Photometric redshifts of the observed candidates were estimated from chi-square minimization. Also, we predicted the importance of the faint quasar to the cosmic reionization from the expected number density of the faint quasar.