• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.5
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• pp.115-124
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• 2018

Thermal protection materials (TPMs) are very crucial for the survival of any re-entry space vehicles. One of the systems used for rigorous validation of TPMs is an enhanced Huel type segmented arc-heated plasma wind tunnel. A 0.4 MW class arc-heated plasma wind tunnel has been constructed at Chonbuk National University which is capable of producing high enthalpy supersonic flow. In this paper we have studied the characteristics of plasma flow according to power and mass flow parameters.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.577-587
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• 2004

A coaxial pulsed plasma thruster (PPT) with a Teflon cavity was designed, and its performance characteristics were examined varying stored energy, cavity length and capacitance. The PPT was tested as the entire system including the discharge circuit, and the results were explained with both the transfer efficiency and the acceleration efficiency. The transfer efficiency is defined as the fraction of energy in capacitors supplied into plasma, and the acceleration efficiency as the fraction of energy supplied into plasma converted to thrust energy. To estimate these efficiencies, the equivalent plasma resistance was defined and calculated using energy conservation during discharge. The equivalent plasma resistance proportionally increased with cavity length, and therefore the current peak increased with decreasing cavity length. The energy density calculated by the transfer efficiency was increased with decreasing cavity length. As a result, higher acceleration efficiency and lower transfer efficiency were obtained with shorter cavity length. Accordingly, there was an optimal cavity length for the thrust efficiency. The specific impulse and the impulse bit per unit stored energy ranged from 390 s and 50 $\mu$ Ns/J for a cavity length of 34 mm to 825 s and 11 $\mu$ Ns/J for a cavity length of 4 mm when the stored energy was fixed to 21.4J. Thus, it was showed that the performance of this PPT approached that of electromagnetic-acceleration-type PPT with decreasing cavity length. The PPT achieved thrust efficiencies of 10-12% at 21.4 J and 6-7% at 5.35 J at cavity lengths between 14 mm and 29 mm.

• Current Industrial and Technological Trends in Aerospace
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• v.7 no.2
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• pp.76-84
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• 2009

In this review an attempt is made to give the background to the current trends in foreign developments in the ceramic matrix composites for space vehicles. The lightweight and high temperature specific modulus properties of ceramic composites have continued to develop for designing advanced propulsion structures and for increasing space vehicle performances. Those applications require advanced materials with good resistance to high temperatures, to oxidation environments and to mechanical stresses. The advantages of ceramic matrix composites are the low specific weight, the high specific strength over a wide temperature ranges, and their good damage tolerance compared to tungsten, pyrographites and polycrystalline graphites. Due to these advantages ceramic matrix composites are currently used in rocket engine chamber, nozzle, solar array, radar antenna, mirror support structures, hypersonic leading edge articles, heat shields, reentry vehicle nose tips, and radiators for spacecraft. Various processes are discussed together with examples of current application so that some of the advanced technologies can be possibly applied to Korean space technology.

• Publications of The Korean Astronomical Society
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• v.30 no.1
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• pp.11-16
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• 2015

First light galaxies have predictable linear clustering, and are expected to produce fluctuations with a characteristic spatial power spectrum, which peaks at an angular scale of ~ 10 arcminutes and in the $1-2{\mu}m$ spectral regions. The Cosmic Infrared Background ExpeRiment 2 (CIBER2) is a dedicated sounding rocket mission for measuring the fluctuations in the extragalactic infrared background light, following up the previous successful measurements of CIBER1. With a 28.5 cm telescope accompanied with three arms of camera barrels and a dual broadband filter on each H2RG (${\lambda}_c=2.5{\mu}m$) array, CIBER2 can measure 6 bands of wide field ($1.1{\times}2.2$ degrees) up to 3 AB magnitudes deeper than CIBER1. This project is leaded by California Institute of Technology/Jet Propulsion Laboratory, collaborating internationally with Institute of Space and Astronautical Science in Japan, Korea Astronomy and Space Science Institute, Korea Basic Science Institute, and Seoul National University. The Korean team is in charge of 1) one H2RG scientific array, 2) ground station hardware and software, 3) telescope lenses, and 4) flight and test bed electronics fabrication. In this paper, we describe the detailed activities of the Korean participation as well as the current status of the CIBER2 project.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.192-192
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• 2017

In this paper we showed the application of European Space Agency's C-band Sentinel-1 Synthetic Aperture Radar (SAR) imagery to identify land subsidence in a heavily groundwater pumping area. We used the repeat pass satellite interferometry method in combination with persistent scattering (PS) interferometric technique to generate and analyze twenty-eight interferograms for the period October 2014 to November 2016. The interferometry results show that land subsidence is more pronounced in the urban areas. Excessive groundwater pumping in the study area is believed to be the main reason for land subsidence. The results are compared with the subsidence rate measured by GPS as reported in other studies and with the mean change in total water storage field of GRACE solutions provided by the Jet Propulsion Laboratory (JPL), the German Research Centre for Geosciences (GFZ) and the Center for Space Research (CSR). The comparison shows persistently decreasing trends during the period of study. A strong reliance of the trend of land subsidence on the temporal decline in total water storage proposes that much of the land subsidence can be attributed to heavy pumping of the groundwater.

• International Journal of Aeronautical and Space Sciences
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• v.12 no.2
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• pp.149-155
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• 2011

The viscous flow in an axisymmetric nozzle was analyzed while accounting for the mesh sizes in both in the free stream and the boundary layer. The Navier-Stokes equations were resolved using the finite volume method in order to determine the supersonic flow parameters at the exit of the converging-diverging nozzle. The numerical technique in the aforementioned method uses the flux vector splitting of Van Leer. An adequate time stepping parameter, along with the Courant, Friedrich, Lewis coefficient and mesh size level, was selected to ensure numerical convergence. The boundary layer thickness significantly affected the viscous flow parameters at the exit of the nozzle. The best solution was obtained using a very fine grid, especially near the wall at which a strong variation of velocity, temperature and shear stress was observed. This study confirmed that the boundary layer thickness can be obtained only if the size of the mesh is lower than a certain value. The nozzles are used at the exit of the shock tube in order to obtain supersonic flows for various tests. They also used in propulsion to obtain the thrust necessary to the displacement of the vehicles.

• International Journal of Aeronautical and Space Sciences
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• v.13 no.2
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• pp.170-187
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• 2012

Recent years have seen an outpour of revived interest in the use of airships for a number of applications.Present day developments in materials, propulsion, solar panels, and energy storage systems and the need for a more eco-oriented approach to flight are increasing the curiosity in airships, as the series of new projects deployed in recent years show; moreover, the exploitation of the always mounting simulation capabilities in CAD/CAE, CFD and FEA provided by modern computers allow an accurate design useful to optimize and reduce the development time of these vehicles.The purpose of this contribution is to examine the different aspects of airship development with a review of current modeling techniques for airship dynamics and aerodynamics along withconceptual design and optimization techniques, structural design and manufacturingtechnologies and, energy system technologies. A brief history of airships is presented followed by an analysis of conventional and unconventional airships including current projects and conceptual designs.

• Journal of Astronomy and Space Sciences
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• v.28 no.4
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• pp.291-298
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• 2011

The atmospheric infrared sounder (AIRS) sensor loaded on the Aqua satellite observes the global vertical structure of atmosphere and enables verification of the water vapor distribution over the entire area of South Korea. In this study, we performed a comparative analysis of the accuracy of the total precipitable water (TPW) provided as the AIRS level 2 standard retrieval product by Jet Propulsion Laboratory (JPL) over the South Korean area using the global positioning system (GPS) TPW data. The analysis TPW for the period of one year in 2008 showed that the accuracy of the data produced by the combination of the Advanced Microwave Sounding Unit sensor with the AIRS sensor to correct the effect of clouds (AIRS-X) was higher than that of the AIRS IR-only data (AIRS-I). The annual means of the root mean square error with reference to the GPS data were 5.2 kg/$m^2$ and 4.3 kg/$m^2$ for AIRS-I and AIRS-X, respectively. The accuracy of AIRS-X was higher in summer than in winter while measurement values of AIRS-I and AIRS-X were lower than those of GPS TPW to some extent.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.4
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• pp.44-52
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• 2002

Aerodynamic characteristics of a flapping airfoil in low Reynolds number flows are numerically studied using the unsteady, incompressible Navier-Stokes flow solver with a two-equation turbulence model. For more efficient computation of unsteady flows over flapping airfoil, the flow solver is parallel-implemented by MPI programming method Unsteady computations are performed for low Reynolds number flows over a NACA four-digit series airfoils. Effects of pitching, plunging, and flapping motion with different reduced frequency, amplitude, thickness and camber on aerodynamic characteristics are investigated. Present computational results yield a better agreement in thrust at various reduced frequency with experimental data.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.4
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• pp.565-578
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• 2016

A probabilistic based systems approach is addressed in this study for the reliability prediction of solid rocket motors (SRM). To achieve this goal, quantitative Failure Modes, Effects and Criticality Analysis (FMECA) approach is employed to determine the reliability of components, which are integrated into the Fault Tree Analysis (FTA) to obtain the system reliability. The quantitative FMECA is implemented by burden and capability approach when they are available. Otherwise, the semi-quantitative FMECA is taken using the failure rate handbook. Among the many failure modes in the SRM, four most important problems are chosen to illustrate the burden and capability approach, which are the rupture, fracture of the case, and leak due to the jointed bolt and O-ring seal failure. Four algorithms are employed to determine the failure probability of these problems, and compared with those by the Monte Carlo Simulation as well as the commercial code NESSUS for verification. Overall, the study offers a comprehensive treatment of the reliability practice for the SRM development, and may be useful across the wide range of propulsion systems in the aerospace community.