• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.10
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• pp.745-752
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• 2020

A numerical study was carried out to evaluate the aerodynamic characteristics of the supersonic grid fins installed on SpaceX Falcon 9. The unit-grid-fin concept was utilized for more efficient and simpler 3-D steady flow calculations. Pre- and post-correction processes that accounted the interference effects by the angle of attack of the missile, the influences of the outer frame of the grid fin and the connecting rods were improved in the study, and it was demonstrated that the present correction method was more accurate as compared to previous studies. Finally, the present approach was applied to evaluate the aerodynamic characteristics in transonic/supersonic flights of SpaceX Falcon 9 with various angle of attacks.

• Journal of Korean Ophthalmic Optics Society
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• v.12 no.4
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• pp.133-139
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• 2007

Although the physiological roles of calretinin have not been established, it may simply work as a calcium buffer or may actively work in calcium-mediated signal transduction. Calretinin plays a little role in the transport and physiological buffering of calcium in the adult photoreceptor cells, bipolar cells and horizontal cells of the human retina. We identified the calretinin-immunoreactive neurons in the inner nuclear cell layer and ganglion cell layer and the distribution pattern of the labeled neurons in the retina of a bat, Rhinolophus ferrumequinum, in this study. We observed the existence of calretinin-immunoreactive AII amacrine cell in the inner nuclear layer and ganglion cells in the ganglion cell layer of bat retina through this study. This observation must be significant along with our previous studies as we need to study for more understanding about the unsolved issue of a bat vision and the unique behavioral aspects of bat flight maneuverability.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.9
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• pp.843-854
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• 2009

For preparing Korean lunar missions, optimal Earth-Moon transfer trajectory is designed using continuous low thrust. Using both constant and variable low thrusting method, "End-to-End" mission analysis is made from beginning of the Earth departure to the final lunar arrival. Spacecraft's equations of motion is expressed using N-body dynamics including the gravitational effects due to the Earth, Moon, Sun and also with Earth's $J_2$ effects. Planets' exact locations are computed accurately with JPL's DE405 ephemeris. As a results, optimal thrust steering angle's characteristics are discovered which showed almost tangential direction burns at the near of central planets. Also, it is confirmed that variable low thrusting method is more efficient than constant thrusting method, and can save about 5% of fuel consumption. Presented algorithm and various results will give numerous insights into the future Korea's Lunar missions using low thrust engines. Also, it is expected to be used as a basis of more detailed mission analyzing tool.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.6
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• pp.1-6
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• 2002

Micro engine that includes Micro scale combustor is fabricated. Design target was focused on the observation of combustion driven actuation in MEMS scale. Combustor design parameters are somewhat less than the size recommended by feasibility test. The engine structure is fabricated by isotropic etching of the photosensitive glass wafers. Electrode is formed by electroplating of the Nickel. Photosensitive glass can be etched isotropically with almost vertical angle. Bonding and assembly of structured photosensitive glass wafer from the engine. Combustor size was determined to be 1mn scale. Piston in cylinder moves by fuel injection and reaction. In firing test, adequate engine operation including ignition, flame propagation and piston motion was observed. Present study warrants further application research on MEMS scale internal combustion power units.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.9
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• pp.103-113
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• 2004

The satellite is exposed to the severe vibration environments such as random vibration environments such as random vibration, acceleration, shock, and acoustics during launch ascent and transportation. It is also faced with various space environments such as thermal vacuum, radiation and microgravity during the mission life. The satellite should be designed, manufactured, assembled and tested to be able to endure in these harsh environments. This paper addresses the results of the structural and thermal design and analyses for the HAUSAT-1 picosatellite which is scheduled to launch in the first quarter of 2005 by Russian launch vehicle "Dnepr". The qualification vibration and thermal vacuum tests have been conducted and passed at the satellite level to ensure that the HAUSAT-1 mechanical system was designed to be stable with enough margin.

• Aerospace Engineering and Technology
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• v.3 no.1
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• pp.126-133
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• 2004

Photogrammetry, as its name implies, is a 3-dimensional coordinate measuring technique that uses photographs as the fundamental medium for metrology. In the last few years the accuracy of photogrammetry has increased dramatically thanks to the rapid advance of digital camera manufacturing technique. This paper discusses photogrammetric measurement of the interface surface of MSC(Multi-Spectral Camera), which is a main payload of KOMPSAT-2. Total 24 paper targets on the objective surfaces and two scale bars calibrated with high accuracy were used for measurement, and multiple images were taken from 11 different camera angles by using a spacecraft rotation dolly. As a result of analysis, 3D coordinates of each targeted point were obtained and the flatness value based on the selected reference plane was calculated and compared with the pre-determined requirement. The technique acquired by this study is expected to be used for the 3D precise measurement of ultra-light weight and inflatable space structures such as a satellite antenna and a solar array.

• Polymer(Korea)
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• v.39 no.2
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• pp.346-352
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• 2015

Polyalphaolefin (PAO) is a synthetic lubricant that is superior to mineral-based lubricants in the terms of physical and chemical characteristics such as low pour point, high viscosity index (VI), and thermal and oxidation stability. Several kinds of PAOs have been synthesized by using 1-pentene, 1-hexene, 1-octene, or 1-dodecene as monomer with three kinds of aluminum-based Lewis acid catalysts via cationic polymerization. The control of the catalytic performance and physical properties of PAO such like molecular weight, kinematic viscosity, pour point, and viscosity index was done by changing polymerization parameters. The alkyl aluminum halide-based catalysts show better catalytic activity than that of the conventional $AlCl_3$ catalyst. The microstructure of PAO was investigated by means of TOF-MS (time of flightmass spectroscopy) analysis in order to elucidate the correlation between the performances of the lubricant (VI, pour point) and the molecular structure of PAO. The VI of PAO increases with increases in the carbon number of ${\alpha}$-olefin. In other words, the performances of PAO as a lubricant strongly depended on the branch length of PAO.

• Journal of Hydrogen and New Energy
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• v.23 no.3
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• pp.250-255
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• 2012

In this paper, the development and performance analysis of a fuel cell-powered unmanned aerial vehicle is described. A fuel cell system featuring 1 kW proton exchange membrane fuel cell combined with a highly pressurized fuel supply system is proposed. For the higher fuel consumption efficiency and simplification of overall system, dead-end type operation is chosen and each individual system such as purge system, fuel supply system, cooling system is developed. Considering that fluctuation of exterior load makes it hard to stabilize fuel cell performance, the power management system is designed using a fuel cell and lithium-ion battery hybrid system. After integration of individual system, the performance of unmanned aerial vehicle is analyzed using data from flight and laboratory test. In the result, overall system was properly operated but for more duration of flight, research on weight lighting and improvement of fuel efficiency is needed to be progressed.

• Current Industrial and Technological Trends in Aerospace
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• v.9 no.1
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• pp.3-14
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• 2011

The current space activities are soaring ever since the first human flight to outer space 50 years ago and the first satellite launch 54 years ago. 74 space launch vehicles were launched in 2010, up from average 66 yearly in 2000s, and 900 operational satellites are currently in orbit around Earth. Space has become a worthwhile investment for governments as space assets become vital to national social, economic, and technological development as well as contributing their national defense and security program. The world governments' investments on space programs have reached a historical peak of $71.5 billion in 2010. However, the growth of government funding for space has slowed down posting only a 2% growth rate since 2009 while 9 % compound annual growth rate experienced by world's space expenditures between 2004 and 2009. Korea invested $158 million in 2011, experienced strong decrease with a 16% compound annual growth rate since 2008. In this paper the current statuses of world governments' funding for space program and space market were presented and the current issues on the Korean space budget policy were reviewed.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.2
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• pp.126-131
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• 2010

The purpose of this study is to assess the condition of composites used in aircraft under varying temperature environment with ultrasound guided wave technique. Investigation of crucial influential factor on the composite health monitoring related to aircraft operational environments such as the number of thermal cycles and temperature deviation between ground level and flight altitude has been of a great concern for aircraft safety issue. In this study, ultrasonic guided wave health monitoring scheme is proposed to evaluate composite specimens damaged with the thermal fatigue simulating aircraft operational condition. Guided wave dispersion curves are used to select right modes which show a promising sensitivity to each different thermal fatigue damage level. The present approach can be also implemented as one of on-lines health monitoring tools for aircraft.