• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.7
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• pp.610-615
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• 2014

Filterbanks have been widely used in the field of multi-channel signal processing for their simple efficient implementation architectures. Especially, the polyphase DFT(Discrete Fourier Transform) filterbank is the most preferred filterbank for the uniform spaced multi-channel processing due to its simplicity. In frequency hopped communication systems, however, the use of the polyphase DFT filterbank is limited due to its undesirable transient response from hop-to-hop transitions. In this paper, the transient response of polyphase DFT filterbanks in the hop-to-hop transition was analyzed, and the efficient methods to overcome such a problem was proposed. Simulation results showed that the proposed schemes could resolve this issue efficiently.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.1
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• pp.79-85
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• 2008

Generally Solid Rocket Motor(SRM) has advantages like this - safety, simplicity and flexibility in design and manufacturing process. However, once propellant grain shape and nozzle throat area are determined, modification of thrust magnitude is nearly impossible. Recently, methods for controlling the thrust magnitude of SRM are vigorously developed. This paper predicts internal ballistic performance variation, especially thrust of SRM by means of Linear Approximation according as chamber pressure or nozzle throat area is changed. The results predicted by the proposed method are good agreement with the those of exclusive Ballistic Performance Prediction Program(SPP).

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.11
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• pp.1094-1103
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• 2008

A fuel specific detonation wave in a pipe propagates with a predictable wave velocity. This internal detonation wave speed determines the level of flexural wave excitation of pipes and the possibility of resonant response leading to a large displacement. In this paper, we present particular solutions of displacements and the resonance conditions for internally loaded pipe structures. These analytical results are compared to numerical simulations obtained using a hydrocode(multi-material blast wave analysis tool). We expect to identify potential explosion hazards in the general power industries.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.3
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• pp.230-236
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• 2012

The purpose of this research is to determine the calibration constants of the wind speed measurement systems required to calculate the wind tunnel velocity in the test section. In the present work, the aerodynamic calibration tests of the test section were conducted in the Agency for Defense Development's Low-Speed Wind Tunnel. The test speed ranged from 10 to 100 m/s with a reference pitot-static pressure probe. The validity of the calibration results was evaluated by comparing them with the previous calibration constants. The calibration results show that fair to good agreement is obtained with resonable accuracy.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.3
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• pp.248-252
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• 2007

This article is related to the possibility for continuous operation of a liquid rocket engine when a portion of cryogenic propellant in the pipeline is vaporized. As a result of experimental studies imitating the formation of vapors in the flow, we confirmed the possibility of full gas-phase condensation in case temperature of cryogenic liquid is lower than it's saturation temperature in the pipeline. Empirical equation allowing to calculate a nonequilibrium condensation region in the steady flow of cryogenic liquid was obtained as a non-dimensional form and the fields of practical application were suggested.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.11
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• pp.747-754
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• 2022

An experimental study was carried out to control a shock-induced boundary layer separation by utilizing the supersonic sweeping jet from the fluidic oscillator. High-speed schlieren, surface flow visualization, wall pressure measurement and precise Pitot tube measurement were applied to observe the influences of the location and the supply pressure of the fluidic oscillator on the characteristics of the oblique-shock-induced boundary layer separation. The characteristics of the separation control by the present supersonic fluidic oscillator was quantitatively analyzed by comparing with a conventional control method utilizing an air-jet vortex generator.

• Bulletin of the Korean Space Science Society
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• 2009.10a
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• pp.31.3-31.3
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• 2009

견우와 직녀의 사랑 이야기가 얽혀 있는 두 별은 여름철을 대표하는 별들로서 중국 문화권에서는 지난 수 천 년 동안 매우 인기가 높은 별이었다. 두 별은 중국의 춘추전국시대의 노래를 모아 놓은 시경(詩經)에 이미 등장하고 있고, 서기 408년에 조성된 고구려의 덕흥리 고분 속에 있는 벽화에도 그려져 있다. 고려시대에는 이 별들에 대한 국가적인 제사를 지냈으며, 조선 시대에는 칠월칠석에 국왕이 신하들과 어울려 잔치를 베풀고 칠석시(七夕詩)를 지어서 책으로 편찬하는 일도 있었다. 한편 견우성은 주로 농사와 관계된 별점을 가지고 있었고, 시각제도와 긴밀한 관계가 있는 28宿(수)의 하나였으므로 천문학자들이 지속적으로 관심을 갖고 관측한 별이다. 그러한 관측의 결과는 고려사, 조선왕조실록, 승정원일기 등에 다수가 남아 있다. 그런데 동양 천문학에서 이미 널리 다루어졌던 문제 가운데 하나는, 바로 이 문학적 견우성과 천문학적 견우성이 일치하지 않는다는 것이다. 지금 일반 시민들에게 견우성은 독수리자리의 알테어(Altair)로 알려져 있다. 그러나 모든 사서와 고대 천문서 및 천문도가 지칭하는 견우성은 염소자리의 다비(Dabih)라는 별이다. 견우성이 28宿(수)의 하나라는 사실은 그 별(별자리)이 황도와 백도 근처에 있어야 함을 의미한다. 따라서 알테어는 적위가 높아서 도저히 28宿(수)에 속할 수가 없다. 게다가 알테어는 은하수 속에 들어가 있으므로, 견우와 직녀가 은하수를 사이에 두고 마주보고 있다는 일반적인 설화와도 어긋난다. 그럼에도 불구하고, 현재 대다수의 서적과 매체, 그리고 일반인을 대상으로 한 행사와 천문관에서 상영되는 프로그램들에는 모두 알테어를 견우성으로 하여 설명하고 있다. 이러한 불일치는 상당한 혼란을 초래하고 있는 상황이다. 이 연구에서는 이러한 불일치가 천문학적인 견우성과 인문학적인 견우성의 불일치로 보고, 이 문제를 실증적으로 접근해 본다. 즉, 고려사, 조선왕조실록, 승정원일기에 실려 있는 견우성 엄폐 관측 기록을 조사하여 한국사에서 전문 천문학자들은 어느 별을 견우성이라고 보아왔는지 알아보고, 또한 일반인들이 지은 시문에는 어떤 별을 견우성으로 여겼는지 고찰한다. 아울러 역사적으로 이 문제에 대한 선인들의 생각을 짚어보고, 중국과 일본의 학자들은 이 문제를 어떻게 바라보고 있는지를 살핀 다음, 마지막으로 현실적으로 이 문제를 어떻게 해결할 수 있는지 고찰해 본다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.12
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• pp.1028-1036
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• 2018

KARI plans to launch Korea Pathfinder Lunar Orbiter (KPLO) to the Moon by December 2020 for the first step of the Korea Lunar Exploration Project. This orbiter will be launched to obtain lunar exploration technologies and science data in advance before launching a main orbiter and a lunar probe. This paper describes the verification of thermal design for the orbiter. It is exposed to more extreme thermal environment than that of low Earth orbit satellite due to the heavy infrared emission of the Moon. Accordingly, a thermal design considering this environment is needed to maintain the temperature of payloads and components equipped in the orbiter within operating temperature range in all orbits. We performed the thermal analysis for Earth-Moon transfer orbit, lunar mission orbit and lunar eclipse required for thermal design verification of the lunar orbiter. As a result, this thermal design met the design requirements.

• Aerospace Engineering and Technology
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• v.6 no.1
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• pp.109-113
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• 2007

In this paper, the design process of the High Voltage Power Supply for RLG(Ring Laser Gyroscope) is described. The specification for High Voltage Power Supply(HVPS) is proposed. Also, The analysis of Flyback converter topology is explained. The Design for the HVPS is composed of the inverter circuit, feedback control circuit, high frequency switching transformer design, and voltage doubler circuit.

• Current Industrial and Technological Trends in Aerospace
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• v.6 no.2
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• pp.133-142
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• 2008

We study the possibility of entering into helicopter market with respect to demand, industry structure and infrastructure. In conclusion, it is possible to enter into it based on domestic demand if we complement some technology, financial assistance system and helicopter operation related regulation. Strategy is made for helicopter industry to be a growth driver and then we suggest five projects to carry out it. Those are lasting creation of helicopter demand, possession of core part material and competitive technology, construction of airworthiness certification system and infrastructure for activation of helicopter operation, improvement of financial assistance system and finally strengthening policy modulation between civil, army, and government.