• 한국추진공학회지
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• 제22권2호
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• pp.138-151
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• 2018

본 논문에서는 재사용 발사체와 발사체의 회수과정에서 사용된 기술에 대해 소개하고 분석한다. 이를 위하여 세계 각국의 재사용 발사체를 조사하였으며 발사체 회수 부분에 따라 기술을 분류하였다. 특히, 실제 비행에 성공한 Space X의 Falcon 9과 Blue Origin의 New Shepard의 회수과정을 중심으로 조사하였으며 비행 조건에 따라 적용된 기술들을 분석하여 특징들을 나열하였다. 이를 통하여 추후 한국형 발사체가 발사 비용을 절감하기 위해 사용할 수 있는 재사용 기술들에 대해 소개하고자 한다.

• Advances in aircraft and spacecraft science
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• 제3권3호
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• pp.351-366
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• 2016

Macroperforations improve the sound absorption performance of porous materials in acoustic cavities and in waveguides. In an acoustic cavity, enhanced noise reduction is achieved using porous materials having macroperforations. Double porosity materials are obtained by filling these macroperforations with different poroelastic materials having distinct physical properties. The locations of macroperforations in porous layers can be chosen based on cavity mode shapes. In this paper, the effect of variation of macroporosity and double porosity in porous materials on noise reduction in an acoustic cavity is presented. This analysis is done keeping each perforation size constant. Macroporosity of a porous material is the fraction of area covered by macro holes over the entire porous layer. The number of macroperforations decides macroporosity value. The system under investigation is an acoustic cavity having a layer of poroelastic material rigidly attached on one side and excited by an internal point source. The overall sound pressure level (SPL) inside the cavity coupled with porous layer is calculated using mixed displacement-pressure finite element formulation based on Biot-Allard theory. A 32 node, cubic polynomial brick element is used for discretization of both the cavity and the porous layer. The overall SPL in the cavity lined with porous layer is calculated for various macroporosities ranging from 0.05 to 0.4. The results show that variation in macroporosity of the porous layer affects the overall SPL inside the cavity. This variation in macroporosity is based on the cavity mode shapes. The optimum range of macroporosities in poroelastic layer is determined from this analysis. Next, SPL is calculated considering periodic and nodal line based optimum macroporosity. The corresponding results show that locations of macroperforations based on mode shapes of the acoustic cavity yield better noise reduction compared to those based on nodal lines or periodic macroperforations in poroelastic material layer. Finally, the effectiveness of double porosity materials in terms of overall sound pressure level, compared to equivolume double layer poroelastic materials is investigated; for this the double porosity material is obtained by filling the macroperforations based on mode shapes of the acoustic cavity.

• Advances in aircraft and spacecraft science
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• 제6권2호
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• pp.117-144
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• 2019

High Altitude and Long Endurance (HALE) aircraft are capable of providing intelligence, surveillance and reconnaissance (ISR) capabilities over vast geographic areas when equipped with advanced sensor packages. As their use becomes more widespread, the demand for additional range, endurance and payload capability will increase and designers are exploring non-conventional configurations to meet the increasing demands. One such configuration is the joined-wing concept. A joined-wing aircraft is one that typically connects a front and aft wings in a diamond shaped planform. One such example is the Boeing SensorCraft configuration. While the joined-wing configuration offers potential benefits regarding aerodynamic efficiency, structural weight, and sensing capabilities, structural design requires careful consideration of elastic buckling resulting from the aft wing supporting, in compression, part of the forward wing structural loading. It has been shown already that this is a nonlinear phenomenon, involving geometric nonlinearities and follower forces that tend to flatten the entire configuration, leading to structural overload due to the loss of the aft wing's ability to support the forward wing load. Severe gusts are likely to be the critical design condition, with flight control system interaction in the form of Gust Load Alleviation (GLA) playing a key role in minimizing the structural loads. The University of Victoria Center for Aerospace Research (UVic-CfAR) has built a 3-meter span scaled and flexible wing UAV based on the Boeing SensorCraft design. The goal is to validate the nonlinear structural behavior in flight. The main objective of this research work is to perform Ground Vibration Tests (GVT) to characterize the dynamic properties of the scaled flight vehicle. Results from the experimental tests are used to characterize the modal dynamics of the aircraft, and to validate the numerical models. The GVT results are an important step towards a safe flight test program.

• 한국위성정보통신학회논문지
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• 제6권1호
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• pp.37-44
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• 2011

2010년 6월 26일에 발사된 통신해양기상위성(천리안)은 Ka-대역 위성통신, 정지궤도 해양관측, 그리고 기상관측을 위한 탑재체를 가지고 있다. 정지궤도상의 위성을 효과적으로 운용하기 위해서 위성 임무운영 개념을 정립하여 이를 위성관제시스템의 개발 초기 단계부터 적용하였다. 천리안 위성의 임무운영은 일별, 주별, 월별 그리고 계절별 운영으로 구분된다. 위성의 일별운영은 임무계획, 명령계획 및 전송, 원격측정 데이터 처리 및 분석, 위성 거리측정 및 궤도결정, 위성의 궤도 및 이벤트 예측, 그리고 휠 오프로딩 파라미터 계산으로 구분된다. 위성의 주별 운영으로는 화요일에 남북방향 위치유지조정, 목요일에 동서방향 위치유지조정으로 구분된다. 월별운영으로는 위성의 온보드 오실레이터를 갱신하기 위한 비행역학 파라미터 계산과 위성으로의 전송이 수행되며 계절별 운영으로 봄과 가을에는 지구가 태양을 가리는 식에 관련된 위성운영을 수행한다. 이 논문에서는 통신해양기상위성이 발사된 후 약 3개월에 걸친 궤도 내 시험 기간 중에 이루어진 위성관제시스템의 주요 기능들에 대한 운영검증을 기술한다. 이 기간 중에 위성관제시스템의 대부분 기능이 성공적으로 검증되었으며 천리안 위성관제시스템은 위성의 설계 수명기간인 7년 또는 위성이 수명을 다하는 그 이후까지 계속 사용될 예정이다.

• Advances in aircraft and spacecraft science
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• 제5권2호
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• pp.225-237
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• 2018

The difficulties of satellite vibration testing are due to the commonly expressed qualification requirements being incompatible with the limited performance of the entire controlled system (satellite + interface + shaker + controller). Two features cause the problem: firstly, the main satellite modes (i.e., the first structural mode and the high and low tank modes) are very weakly damped; secondly, the controller is just too basic to achieve the expected performance in such cases. The combination of these two issues results in oscillations around the notching levels and high amplitude beating immediately after the mode. The beating overshoots are a major risk source because they can result in the test being aborted if the qualification upper limit is exceeded. Although the abort is, in itself, a safety measure protecting the tested satellite, it increases the risk of structural fatigue, firstly because the abort threshold has been already reached, and secondly, because the test must restart at the same close-resonance frequency and remain there until the qualification level is reached and the sweep frequency can continue. The beat minimum relates only to small successive frequency ranges in which the qualification level is not reached. Although they are less problematic because they do not cause an inadvertent test shutdown, such situations inevitably result in waiver requests from the client. A controlled-system analysis indicates an operating principle that cannot provide sufficient stability: the drive calculation (which controls the process) simply multiplies the frequency reference (usually called cola) and a function of the following setpoint, the ratio between the amplitude already reached and the previous setpoint, and the compression factor. This function value changes at each cola interval, but it never takes into account the sensor signal phase. Because of these limitations, we firstly examined whether it was possible to empirically determine, using a series of tests with a very simple dummy, a controller setting process that significantly improves the results. As the attempt failed, we have performed simulations seeking an optimum adjustment by finding the Least Mean Square of the difference between the reference and response signal. The simulations showed a significant improvement during the notch beat and a small reduction in the beat amplitude. However, the small improvement in this process was not useful because it highlighted the need to change the reference at each cola interval, sometimes with instructions almost twice the qualification level. Another uncertainty regarding the consequences of such an approach involves the impact of differences between the estimated model (used in the simulation) and the actual system. As limitations in the current controller were identified in different approaches, we considered the feasibility of a new controller that takes into account an estimated single-input multi-output (SIMO) model. Its parameters were estimated from a very low-level throughput. Against this backdrop, we analyzed the feasibility of an LQG control in cancelling beating, and this article highlights the relevance of such an approach.

• 대한기계학회논문집B
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• 제34권2호
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• pp.213-218
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• 2010

인공위성 적외선 탑재체의 열싱크 역할을 위해, 액체헬륨을 이용하여 극저온패널(가로 약 800 mm, 세로 약 700 mm)을 4.2 K까지 냉각시키는 시스템을 설계, 개발, 검증하였다. 유효직경 8 m, 유효 깊이 10 m의 대형열진공챔버에서 검증된 본 냉각시스템은 500리터 용량의 액체헬륨용기 두 개(극저온 패널로의 액체헬륨 또는 저온헬륨가스 주 공급용기 및 주공급용기로의 재충진용기)를 사용하였는데, 목표인 극저온패널의 냉각 및 온도제어는 주 공급용기 내부의 미세압력조절을 통해 액체헬륨 공급유량을 제어함으로써 이루었다. 극저온패널에 공급된 후 배기되는 저온 헬륨가스는 특별히 설계, 제작된 사중진공배관의 제3층을 흐르며 열차단막의 역할을 수행함으로써, 액체헬륨 공급 라인인 제1층(중심배관)으로의 열유입을 최소화하였다. 극저온패널을 상온에서 40 K(합성표준불확도 194 mK)까지 냉각시키는데 약 3시간이 소요되었으며, 20 W의 열을 발산하는 극저온패널을 40 K 주변 온도에서 1 K 이내의 온도균일도를 가지며 유지할 수 있었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 1999년도 제17회 학술발표회 논문개요집
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• pp.211-211
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• 1999

Titanium nitride (TiN) thin films have useful properties including high hardness, good electrical conductivity, high melting point, and chemical inertness. The applications have included wear-resistant hard coatings on machine tools and bearings, decorative coating making use of the golden color, thermal control coatings for widows, and erosion resistant coatings for spacecraft plasma probes. For all these applications as feature sizes shrink and aspect ratios grow, the issue of good step coverage becomes increasingly important. It is therefore essential to manufacture conformal coatings of TiN. The growth of TiN thin films by chemical vapor deposition (CVD) is of great interest for achieving conformal deposition. The most widely used precursor for TiN is TiCl4 and NH3. However, chlorine impurity in the as-grown films and relatively high deposition temperature (>$600^{\circ}C$) are considered major drawbacks from actual device fabrication. To overcome these problems, recently, MOCVD processes including plasma assisted have been suggested. In this study, therefore, we have doposited Ti(C, N) thin films on Si(100) and D2 steel substrates in the temperature range of 150-30$0^{\circ}C$ using tetrakis diethylamido titanium (TDEAT) and titanium isopropoxide (TIP) by pulsed DC plamsa enhanced metal-organic chemical vapor deposition (PEMOCVD) method. Polycrystalline Ti(C, N) thin films were successfully grown on either D2 steel or Si(100) surfaces at temperature as low as 15$0^{\circ}C$. Compositions of the as-grown films were determined with XPS and RBS. From XPS analysis, thin films of Ti(C, N) with low oxygen concentration were obtained. RBS data were also confirmed the changes of stoichiometry and microhardness of our films. Radical formation and ionization behaviors in plasma are analyzed by optical emission spectroscopy (OES) at various pulsed bias and gases conditions. H2 and He+H2 gases are used as carrier gases to compare plasma parameter and the effect of N2 and NH3 gases as reactive gas is also evaluated in reduction of C content of the films. In this study, we fond that He and H2 mixture gas is very effective in enhancing ionization of radicals, especially N resulting is high hardness. The higher hardness of film is obtained to be ca. 1700 HK 0.01 but it depends on gas species and bias voltage. The proper process is evident for H and N2 gas atmosphere and bias voltage of 600V. However, NH3 gas highly reduces formation of CN radical, thereby decreasing C content of Ti(C, N) thin films in a great deal. Compared to PVD TiN films, the Ti(C, N) film grown by PEMOCVD has very good conformability; the step coverage exceeds 85% with an aspect ratio of more than 3.