• Journal of the Korea Institute of Military Science and Technology
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• v.10 no.2
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• pp.12-20
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• 2007

The aiming ability is a key to improve the accuracy performance of the gun pointing system in the ground military vehicle. This paper describes the new detection method of chatter vibration using disturbance acceleration in the pointing structure. In order to analysis the vibration trends of the pointing system occurred while the vehicle driving, acceleration data obtained from vehicle was processed by using data processing algorithm with moving average and Hilbert transform. The specific mode constants of acceleration were obtained from various disturbances. Vehicle velocity, road condition and property of pointing structure were considered as factors which make the change of vibration trend in vehicle dynamics. Finally, back propagation neural networks have been applied to the pattern recognition of the classification of vibration signal in various driving conditions. Results of signal processing were compared with other condition result and analysed.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.227.2-227.2
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• 2012

대구경 고해상도 광학탑재체의 광구조부는 주반사경과 부반사경 등을 포함한 주요 광학부품들과 검출기를 포함한 초점면 조립부 등을 고정 지지해주는 부분으로, 발사시 전달되는 진동 및 우주 열환경하에서의 길이 안정성을 광학성능 범위내로 유지하여야 한다. 광학탑재체의 성능에 가장 큰 영향을 미치는 것은 주반사경과 부반사경의 광축방향의 길이 안정성으로, 광학탑재체의 작동 온도범위 내에서 수 마이크로미터 내외로 안정성이 요구된다. 이를 실현하기 위하여 주반사경과 부반사경의 간격은 열 및 흡습에 둔감한 탄소섬유 강화수지 복합재로 되어 있는 경통 구조물로 설계, 제작된다. 제작된 경통구조물의 길이 안정성을 검증하기 위해서는 별도의 정밀 측정장치가 필요하게 된다. 본 논문에서는 이러한 길이 안정성 측정장치에 대해 기술한다. 온도에 대해 변화가 거의 없는 (CTE<0.1ppm/K) Zerodur 소재의 막대 구조물을 기준 스케일로 삼았고, 이를 지지하기 위해 Invar 소재의 구조물을 사용 하였다. 주반사경의 베젤부위와 부반사경의 접속부위의 변위 변화를 세점에서 측정하여 길이 안정성을 측정할 수 있게 하였다.

• Proceedings of the Optical Society of Korea Conference
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• 2003.07a
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• pp.140-141
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• 2003

인공위성 카메라는 발사 시 발생하는 하중조건(진동, 충격 등)과 우주 환경(무중력, 진공, 복사 등)하에서 카메라 내부의 각종 광학부품과 그를 지지하는 구조물의 변형으로 인해 광학적 성능 전반에 큰 영향을 받는다. 특히 높은 신뢰성이 요구되는 고해상도 지구관측용 광학카메라의 경우 광학적 현상과 기계적 현상을 동시에 체계적으로 고려하는 광기계 해석 및 설계(opto-mechanical analysis and design)가 필수적이다. 그 중에서도 목표로 하는 광학적 성능을 얻기 위한 위성용 카메라 주반사경의 설계기술이 가장 중요한 부분에 속한다. (중략)

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.7
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• pp.637-646
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• 2010

A time-domain panel method based on the potential flow theory and the time-stepping method is developed to predict the steady/unsteady aerodynamic characteristics of FM07, which is the BWB (Blended-wing body) type MAV. In the aerodynamic analyses, we used two types of the initial model(Case I) and the improved model(Case II), which is moved the gravity center toward the rear and has larger aspect ratio. In the steady aerodynamic analyses, it is revealed that improved model has higher lift to drag ratio(L/D) and more stable pitch characteristic than those of the initial model. In the unsteady aerodynamic analyses for sudden acceleration motion similar to the launch phase of MAV, it seemed that there is a rapid increase of the lift coefficient after the launch and unsteady results are good agreed compare with steady results in just a few times. In the analysis for pitch oscillation motion, which is occurred at the cruise condition of the FM07, it shows that unsteady aerodynamic coefficients looped around steady results and the improved model has more sensitive aerodynamic characteristics.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.40.2-40.2
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• 2010

MIRIS 우주관측카메라는 과학기술위성 3호의 주탑재체로서 $0.8{\sim}2.0{\mu}m$의 근적외선영역에서 우주배경복사와 우리은하 평면의 Pa-$\alpha$ survey 관측을 목적으로 한다. 이러한 임무를 수행하기 위해 MIRIS 우주관측카메라에는 MCT(HgCdTe) IR 검출기가 사용되고 6개의 필터를 장착할 수 있는 필터휠이 설계되었으며, 열잡음을 줄이고 원하는 SNR을 얻기 위해 모두 100K 이하로 냉각이 요구된다. 효과적인 냉각 및 저온유지를 위해서 외부의 열을 1차적으로 차단하는 Cryostat 외부용기와 100K 이하로 냉각되는 내부 Cold Box의 이중구조를 가지는 Dewar가 설계 되었다. 내부 Cold Box의 냉각은 소형 stirling cooler로 이루어지고 외부의 열 유입량이 Cooler의 냉각용량을 넘지 않도록 설계하였다. Cryostat 외부용기는 radiation cooling으로 냉각되어 200K 이하의 온도를 유지하며 내부 Cold Box로의 열유입을 최소화하기 위해 GFRP(Glass Fiber Reinforced Plastic) 단열 지지대와 MLI(Multi Layer Insulation)가 사용된다. 또한 100K으로 냉각시 필터고정부와 Cold Box 구조에서 일어날 수 있는 구조적인 피로도를 줄이고 열변형에 의한 문제를 방지하기 위한 고려가 설계에 포함되었다. FM(Flight Model)은 고진공 환경의 우주공간에서 문제가 발생하지 않도록 설계되었다. 또한 EQM 진동시험결과를 토대로 발사환경에서 발생하는 강한 진동을 견딜 수 있도록 FEM(Finite Elements Method) 구조해석을 통하여 필터고정부에 flexible structure 설계와 완충제를 추가하고 필터휠 구동부와 harness 고정부 및 cooler 지지부를 비롯한 전체 구조물에서 충분히 진동을 극복할 수 있도록 설계하였다.

• Aerospace Engineering and Technology
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• v.5 no.2
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• pp.143-148
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• 2006

This article summarizes the results of sea transportation load measurements, which will be used as the reference to the sea transportation environment condition for the launch vehicle of KSLV-I. KSLV-I will be transported by Sea from Pusan to the NARO space center in Gohung, Chunnam province. Since the vibration load condition during sea transportation is considered as one of the important design parameters of KSLV-I and its transportation means, it is necessary to directly measure the environmental condition of sea transportation loads prior to establish the sea transportation plan in detail. This material includes the measured data of 3-axis linear accelerations and 3-axis angular rates on the board of a barge-ship, which is towed by a tug boat during shipping operation. This barge-ship is same class with one which will actually carry KSLV-I. The results show that the measured load condition during sea transportation is not severer than the reference data of MIL-STD-810F and Zenit-3SL launch system.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.2
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• pp.75-82
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• 2022

Nondestructive method to predict buckling load for the propellant tank of launch vehicle should be evaluated. Vibration correlation technique can predict the global buckling load of unstiffened cylindrical structure with geometric initial imperfection using correlation of natural frequency and compressive load from compressive test below the buckling load. In this study, vibration and buckling tests of a thin metal unstiffened propellant tank model subjected to internal pressure and compressive loads were performed and the test results were used for VCT to predict global buckling load. For the vibration test of thin structure, non-contact excitation method using a speaker was used. The response was measured with piezoelectric polymer(PVDF) sensor. Prediction results of VCT were compared with the measured buckling load in the test and the nondestructive global buckling load prediction method was verified.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.7
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• pp.929-935
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• 2013

This paper presents the results of sizing optimization of ahat-shaped stiffener on a rectangular stiffened panel. The stiffened panel is subjected to impact loading by a projectile with a velocity of 1500-2500 m/s. To determine the size of the hat-shaped stiffener, sizing optimization was performed. The sizing optimization consists of three functions: objective, constraint, and design functions. The objective function is used to maximize the fundamental frequency of the stiffened panel. The constraint function is that the stiffener volume is less than 10% of the plate volume. The design function is the dimensions of the hat-shaped stiffener. By using the stiffened panel with the optimized hat-shaped stiffener, a hypervelocity impact was simulated, and the velocity and kinetic energy on the optimized stiffener was obtained. To evaluate the impact reduction on the stiffened panel, the velocity and kinetic energy of the projectile was normalized and compared.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.2
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• pp.172-180
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• 2016

A cubesat classified as a pico-satellite typically uses commercial-grade components that satisfy the vibration and thermal environmental specifications and goes into mission orbit even after undergoing minimum environment tests due to their lower cost and short development period. However, its reliability exposed to the physical environment such as on-orbit thermal vacuum for long periods cannot be assured under minimum tests criterion. In this paper, we have analysed the reliability and life prediction of the failure mechanisms of the cubesat mission board during its service life under the launch and on-orbit environment by using the sherlock software which has been widely used in automobile fields to predict the reliability of electronic devices.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.7
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• pp.635-640
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• 2015

In this paper, we report a non-explosive separation device for a small satellite which utilize a shape memory alloy actuator. Based on previous research, we try to increase the reliability of the proposed device by changing some components. It enables the proposed device to activate under high preload. Also, we confirm it generates low shock which is main advantage of non-explosive separation device. Finally, vibration test which mimics launching environment and thermal vacuum test which mimics space environment are carried out respectively. After each environment test, we confirm the proposed device is successfully activated. Conclusively, we develop a non-explosive separation device which can activate with low shock under high preload after shock and environment tests(vibration and thermal vacuum tests).