• Journal of Aerospace System Engineering
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• v.16 no.5
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• pp.62-69
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• 2022

EHA (Electro-Hydrostatic Actuator) is more energy efficiency than a centralized hydraulic system. In particular, the EHA used for aircraft has a redundant design in preparation for failure scenario. Also, due to the aircraft's internal space limitation, the actuator's length must be optimized. Therefore, a series configuration of double rod and single rod cylinder is advantageous. However, due to the asymmetry of the cross-sectional area of the piston, the force fighting phenomenon between the two cylinder areas occurs during redundant operation with a general control system. In this paper, the force fighting phenomenon of redundant EHA was simulated. A controller with load compensation and a force control-based position controller as a method to suppress its stimulation

• Korean Journal of Optics and Photonics
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• v.35 no.5
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• pp.210-217
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• 2024

We investigate the effects of mid-spatial frequency wavefront errors on the modulation transfer function (MTF) of optical imaging systems such as airborne cameras and astronomical telescopes. To reduce the prediction error of the MTF, an improved Shannon approximation is proposed. The Shannon approximation is useful for low-order wavefront errors, but it has limitations in predicting MTF with high-order wavefront errors, especially those caused by mid-spatial frequency errors from the manufacturing process of aspheric optical components. In this study, we analyze the impacts of concentric ring-shaped mid-spatial frequency wavefront errors on the MTF using MATLAB and Code V simulations and propose a method to improve the Shannon approximation, which has a new correction factor (K-factor).

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.4
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• pp.403-414
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• 1997

The distribution of the space debris caused by any source affects the DBS & FSS wave propagation for satellite communication. In this paper, the normalized expansion coefficients are evaluated with varying the volume distribution density of space debris and the operating frequency, and then the attenuation and phase shift are calculated by using the normalized expansion coefficients. Conclusively, the attenuation and phase shift are mostly affected with the real and imaginary part of the amplitude function, respectively, which represented by electric field component of the Bessel function. The results of this paper adapted for the design of the link budget for satellite communication system and the reconsideration of space environment as the space debris increses by geometric progression.

• Journal of Satellite, Information and Communications
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• v.7 no.3
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• pp.78-85
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• 2012

This paper takes precautions proposals against prospective disasters from the space weather maximum in 2013. The space weather maximum could wreak havoc in this world. A geomagnetic space storm sparked by a solar eruption like the one that flared toward earth is bound to strike again and could wreak havoc across the modern world. Despite of the fact that not only researches by colleges and institutions current researches have been focusing on warning systems of space communication and the earth network systems, but also management and control systems are not situated for the space weather blasters. The purpose of the study is that the damage reduces methods implementation on the ultimate space weather communication systems by above lists proposed type analysis. In result, the implementation of the communication disaster management systems deals with the smart IT converged GIS analysis on the flare, solar proton event, geomagnetic storm to the effects of the geomagneticsphere, ionosphere and troposphere from solar maximum. This research can provide affective methods for the saving lives and property protections that implementation of the disaster prediction and disaster prevention systems adapts smart IT systems and converged high tech information systems using decision making support systems of the GIS methodology.

• Journal of Space Technology and Applications
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• v.2 no.1
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• pp.41-51
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• 2022

CubeSat is a satellite platform that is widely used not only for earth observation but also for space exploration. CubeSat is also used in magnetic field investigation missions to observe space physics phenomena with various shape configurations of magnetometer instrument unit. In case of magnetic field measurement, the magnetometer instrument should be far away from the satellite body to minimize the magnetic disturbances from satellites. But the accommodation setting of the magnetometer instrument is limited due to the volume constraint of small satellites like a CubeSat. In this paper, we investigated that the magnetic field interference generated by the cube satellite was analyzed how much it can affect the reliability of magnetic field measurement. For this analysis, we used a reaction wheel and Torque rods which have relatively high-power consumption as major noise sources. The magnetic dipole moment of these parts was derived by the data sheet of the manufacturer. We have been confirmed that the effect of the residual moment of the magnetic torque located in the middle of the 3U cube satellite can reach 36,000 nT from the outermost end of the body of the CubeSat in a space without an external magnetic field. In the case of accurate magnetic field measurements of less than 1 nT, we found that the magnetometer should be at least 0.6 m away from the CubeSat body. We expect that this analysis method will be an important role of a magnetic cleanliness analysis when designing a CubeSat to carry out a magnetic field measurement.

• Proceedings of the Korea Contents Association Conference
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• 2003.11a
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• pp.367-372
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• 2003

In the framework of Lorentzian warped products, we study the Friedmann - Robertson - Walker cosmological model to investigate non-smooth curvatures associated with multiple discontinuities involved in the evolution of the universe. In particular we analyze non-smooth features of the spatially flat Friedmann-Robertson-Walker universe by introducing double discontinuities occurred at the radiation- matter and matter-lambda phase transitions in astrophysical phenomenology.

• Bulletin of the Korean Space Science Society
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• 2003.10a
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• pp.60-60
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• 2003

과학위성 1호에는 원자외선 분광기를 포함한 다섯 개의 탑재체가 있다. MMS(Mass Memory System)는 이들 탑재체가 수집한 데이터를 대용량 메모리에 저장한 후 지상국으로 보내는 역할을 하며 우주방사선에 의한 메모리 데이터의 오류와 무선 채널을 통한 Downlink 상에서 발생하는 오류를 최소화하기 위해서 소프트웨어적으로 에러를 정정할 수 있는 Reed-Solomon Code를 사용 하였다. 탑재체의 데이터를 저장하기 위한 대용량 메모리는 총 2Gbits로써 8M SRAM, 64M SDRAM, 256M SDRAM의 세 가지로 구성되어 있으며 메모리 여러 개를 하나의 모듈로 만들고 이 모듈이 층으로 쌓여서 MMS에 탑재되어 있다. SRAM에 비해서 집적도가 매우 높은 SDRAM은 공간을 적게 차지하는 장점은 있지만 우주용이 아니므로 그 안정성을 보장할 수 없으므로 우리별 3호에서 성능이 입증된 SRAM과 같이 탑재되었다. 본 연구에서는 MMS의 구조, 동작모드, Spec 및 연구 개발 내용을 소개한다.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.40.3-41
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• 2021

사람들의 우주에 대한 관심이 커지면서 전국 각지에 천문 관측 시설을 갖춘 기관의 수가 점점 늘어나고 있다. 하지만 대부분의 천문 교육은 밤하늘의 천체를 육안으로 관측하는 데에 초점을 맞추고 있어 최신 천문우주 분야의 내용을 공유하는 데에 한계가 있다. 과학동아천문대는 서울의 용산전자상가에 위치한 사설 천문대로서 2013년에 개관한 이래로 도심 속에서 밤하늘을 만날 수 있는 공간으로서 역할을 하고 있다. 우리는 그동안 쌓은 커뮤니티와 자사의 네트워크를 기반으로 천문대가 현재와 같이 단순히 별을 보는 장소에 그치지 않고 천문우주문화를 확산하는 플랫폼이 되도록 변화 시키려고 한다. 이를 통하여 천문우주에 관심 있는 사람들은 더 쉽게 최신 소식을 접하고, 연구자들은 자신의 연구를 수시로 알릴 수 있는 소통의 장을 마련하려고 한다. 이번 발표를 통해 동아사이언스 미래세대 C 플랫폼 본부와 함께하는 과학동아천문대의 새로운 비전을 외부에 처음으로 소개하며 관계자들의 관심과 참여를 요청드린다.

• Annual Conference of KIPS
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• 2024.10a
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• pp.447-450
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• 2024

궤도상 서비싱(On-Orbit Servicing)이란, 우주 공간의 궤도에서 비행하는 인공 물체를 대상으로 상태를 점검 및 수리하거나 궤도 수정 또는 궤도 내 자세 유지, 연료 재급유, 부품 교체, 우주 쓰레기 제거 등을 제공하는 서비스이다. 이는 위성 수명 연장 및 재사용성 증대를 통한 인적, 시간적 비용절감 결과를 가져온다. 이러한 임무를 수행하기 위해서는 대상이 되는 객체를 안전하게 고정하고 유지하는 캡처 및 도킹 과정이 필요하며 데이터는 실시간 모니터링으로 감지한다. 이때, GNC(유도, 항법, 제어) 시스템의 프레임워크는 항공우주 분야에서 우주 비행체가 임무를 수행할 때 필수적인 기능을 통합하고 관리하며 수행하는 구조적 틀을 제공한다. 센서, 알고리즘, 제어기, 항법 장치 등 연관된 하드웨어와 소프트웨어가 유기적으로 작동하도록 구성되어 있으며 비행체가 목표를 정확히 수행하도록 돕는 핵심적인 역할을 한다. 본 논문에서는 기존 궤도상 서비싱의 해외 연구 현황을 파악하여 임무 사례를 통한 GNC 시스템 프레임워크의 분석을 토대로 추후 국내 궤도상 서비싱 GNC 서브시스템 프레임워크 설계 시 적용 방안에는 어떤 것이 있을지에 대하여 연구한 내용을 서술하고자 한다.

• Proceedings of the Korean Institute Of Construction Engineering and Management
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• 2008.11a
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• pp.828-832
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• 2008

In 2004, The U.S president Bush announces space Exploration Vision included in Lunar outpost plan. Following the Space Exploration Vision announced by Bush, NASA made Construction Roadmap and studied space construction varietly to construct Lunar Outpost in 2025. The purpose to construct Lunar outpost is to develop space science and hitech industry and to secure the lunar materials. Especially, Lunar has more than 5billion ton He-3. In this reason, The countries advanced in Space Industry like U.S., Japan, Europe and China is studying space construction to mine Lunar materials and shelter to live. In this paper, We will make definition and necesarity of space construction and research Space Construction research trends to use for the preparation of Korea's space construction roadmap.