• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.40.3-41
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• 2009

인류가 위성을 발사하기 시작하면서 수많은 우주파편이 발생하게 되었고 이로 인하여 우주파편 환경은 날이 갈수록 심각해지고 있다. 우주공간을 비행하는 우주물체는 분쇄된 파편, 임무 관련 파편, rocket body 그리고 운용위성으로 구분된다. U.S. Space Surveillance Network에 따르면 10cm 이상 크기를 갖는 물체는 현재 13,000개가 넘는다고 알려지고 있고 질량만 해도 6,000톤이 넘는다. 이런 우주파편 환경으로 인하여 우주파편 간의 충돌, 우주파편과 운용위성 간의 충돌 또는 운용위성 간의 충돌에 대한 우려가 꾸준히 제기되어왔고, 불행하게도 2009년 2월 10일 Iridium 33과 Cosmos 2251 위성이 고도 790km 부근에서 충돌하여 1,300여개의 우주파편이 발생했다. 또한 2007년에 중국이 고도 860km 부근에서 750kg에 해당하는 자국의 위성(FY-1C)을 미사일로 격추시킴에 따라 2500여개의 우주파편이 발생하여 저궤도의 우주파편 환경을 더욱 심각하게 만들고 있다. 운용위성과 우주파편과의 충돌 가능성을 분석하기 위해서는 우주파편 및 위성의 궤도정보를 알아야 한다. 이를 위해서 NORAD(North American Aerospace Defense Command)에서 제공하는 TLE(Two Line Element)가 주로 이용된다. 하지만 관측 및 궤도 결정 특성상 수 km의 오차를 포함하므로 궤도정보의 공분산이 크다는 단점이 있으므로 충돌 분석을 수행하는데 있어 한계가 있다. 이 논문은 충돌분석 수행에 있어 TLE 정보만을 이용한 경우뿐만 아니라 정밀궤도와 TLE를 동시에 이용한 경우를 비교함으로써 충돌 불확실성의 해소방안을 제시할 계획이다.

• Journal of Astronomy and Space Sciences
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• v.24 no.2
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• pp.135-144
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• 2007

Space environment becomes more hazardous for satellite because of increasing number of space debris. This research is to analyze collision hazards between KOMPSAT 3 in low-earth orbit and space debris generated by the explosion of FengYun satellite on the January 11, 2007. Based on the observed data of the space debris from FengYun satellite, the mass and number distribution of the debris are estimated including undetectable debris from the explosion of FengYun satellite. The spatial density and flux for the space debris can be calculated according to size. This study also brings out the analysis for the assessment of collision probability and damage probability. The algorithm developed in the current paper can be used to estimate the level of risk due to space debris for the satellites that will be launched in the future.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.2
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• pp.156-165
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• 2015

A survivability-analysis program has been developed to analyze the ground collision risk of atmospheric reentry objects, such the upper stages of a launch vehicle or satellites, which move at or near the orbital velocity. The aero-thermodynamic load during the free fall, the temperature variation due to thermal load, and the phase shift after reaching the melting point are integrated into the 3 degree-of-freedom trajectory simulation of the reentry objects to analyze the size and weight of its debris impacting the ground. The analysis results of the present method for simple-shaped objects are compared with the data predicted by similar codes developed by NASA and ESA. Also, the analysis for actual reentry orbital objects has been performed, of which results are compared with the measurement data.

• Journal of the Korea Society for Simulation
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• v.29 no.3
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• pp.1-8
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• 2020

When enemy drones infiltrate large urban areas, various forms of great republics are deployed in large areas to respond. Due to the characteristics of a large number of government-run aircraft, the residual coal, other than the hit bullet, falls into various sizes of debris after its own explosion. The damage rate was analyzed by dividing the debris into anti-aircraft guns and guided weapons by deriving four factors: critical speed, fragmentation mass, initial speed of debris, and object collision speed, which can cause damage to human life as the debris falls to the ground. In the future, the North is expected to infiltrate the capital city of Seoul by operating unmanned aerial vehicles, which are asymmetric forces, and the damage could be minimized by setting up pre-fatal and fire-restricted zones to minimize casualties between responses.

• Journal of the Korean Ceramic Society
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• v.41 no.3
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• pp.210-215
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• 2004

Porous ceramics for water-permeable paving brick was prepared by the sintering of mixed materials comprising of sewage sludge ash, waste porcelain fragment, waste glaze and low-grade clay at 1,000$^{\circ}C$ for 2 h, and the physical $.$mechanical properties, the permeability and the freeze-thaw resistance of specimens with preparation parameters were investigated. The physical mechanical properties were increased in specimens while porosity and permeability were decreased with increasing sewage sludge ash content and sintering temperature on the properties of specimens showed the opposite results. The bulk density, porosity, compressive strength and permeability (passed charge) of 30A60F specimens with 30 wt% of sewage sludge ash content, waste porcelain fragment size with 1∼2 mm and sintered at 1,000$^{\circ}C$ for 2 h were 2.17, 46.2%, 221 kgf/$\textrm{cm}^2$ and 3,150 coulombs, respectively. The permeability was increased with increasing waste porcelain fragment size, however compressive strength was decreased. The freeze-thaw resistance of 30A60F specimen with 1∼2 mm of fragment size was superior to that of the other specimens. The 30A60F specimens can be used for the water-permeable paving brick with the high permeability and adequate strength. The heavy metals included in the all specimens showed lower than the standard level.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.4
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• pp.354-363
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• 2012

Now there are a lot of expired satellites or space debris around the earth orbit and they threaten the operating satellites and manned space missions. KOMPSAT-2 that scheduled to operate the mission by July, 2013 also has to consider the space debris. This paper introduces the '25 years rules' that must be re-entered within 25 years after the space mission for LEO satellites and describes the removal trajectory design that satisfies the '25 years rules' and minimizes fuel consumption. And this paper suggests monte-carlo simulation for risk analysis that causes the approaching object to the removal trajectory. The result shows that the collision probability of worst case presents 6.0741E-07 and it need to more analysis about precise satellite safety during removal maneuver because there is no information about the object size that approaching to the satellites.

• Bulletin of the Korean Space Science Society
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• 2004.04a
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• pp.77-77
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• 2004

인공위성은 정상궤도에 들어선 후부터 수명을 다하는 시기까지 각종 복사, 열(온도차), 고진공, 미세중력, 미세운석과 우주파편 등에 의해 영향을 받게 된다. 특히, 위성체에 미치는 열환경은 위성이 궤도를 그리며 운동하는 동안 태양과 지구로부터의 복사량의 크기 및 분포에 따라 결정되는데, 약 5,50$0^{\circ}C$의 흑체온도를 갖고 있는 태양과 -27$0^{\circ}C$의 심우주는 위성체에서 태양이 비추는 부분과 반대편과의 온도를 극한으로 만들게 된다. (중략)

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.22-23
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• 2000

강한 레이저 펄스에 의해 만들어진 플라즈마를 사용하여 연엑스선(soft X-ray, 10-300 $\AA$) 광원을 얻으려는 노력은 주로 고체나 기체 표적에 대한 것이었다. 최근에 이르러 기체의 단열 팽창에서 생기는 원자 송이(atomic cluster)를 표적으로 하는 연구 결과들이 발표되었다. $^{(1).(2)}$ 원자 송이는 국소적으로는 고체에 가까운 밀도를 가지고 있어서 효율적으로 레이저 에너지를 흡수하는 반면, 전체적으로는 기체 상태에 있기 때문에 파편이 적고, 기체의 압력과 온도를 변화시킴으로써 송이의 크기를 조절할 수 있다. (중략)

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.12
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• pp.829-838
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• 2022

This study conducts Hypervelocity Impact(HVI) simulations considering space objects with various shapes and different impact angles. A commercial nonlinear structural dynamics analysis code, LS-DYNA, is used for the present simulation study. The Smoothed Particle Hydrodynamic(SPH) method is applied to represent the impact phenomena with hypervelocity. Mie-Grüneisen Equation of State and Johnson-Cook material model are used to consider nonlinear structural behaviors of metallic materials. The space objects with various shapes are modeled as a sphere, cube, cylinder, and cone, respectively. The space structure is modeled as a thin plate(200 mm×200 mm×2 mm). HVI simulations are conducted when space objects with various shapes with 4.119 km/s collide with the space structures, and the impact phenomena such as a debris cloud are analyzed considering the space objects with various shapes having the same mass at the different impact angles of 0°, 30° and 45° between the space object and space structure. Although space objects have the same kinetic energy, different debris clouds are generated due to different shapes. In addition, it is investigated that the size of the debris cloud is decreased by impact angles.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.5
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• pp.615-622
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• 2020

Frangible bullets, which are shredded after impact on a target, reduce the possibility of both ricochet and unexpected injury in shooting training and in mission acts in dams, nuclear power plants, and cultural properties. Reducing the levels of hazardous materials in shooting ranges, such as lead, has become an important agenda for the government and environmental groups. In this study, the shape of a frangible bullet was designed for efficient shredding, and the safety and reliability were confirmed by actual firing under different process conditions. In addition, the physical characteristics, such as compaction pressure, density, and frangibility of each process, were compared by analyzing the microstructure of the sintered frangible bullet. The experiment revealed the smallest fragmentation after impact on the target under the following conditions: Cu-Sn 85:15; sintering temperature, 600℃; sintering time, one hour. Further development of the process conditions and experimental methods will contribute to the performance and environmental improvement of a frangible bullet.