• Journal of Astronomy and Space Sciences
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• v.23 no.4
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• pp.337-344
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• 2006

KVN simulation, which is focused on evaluating the impacts of KVN to geodetic VLBI network, was performed. The KVN is under construction with three radio telescopes VLBI system for radio astronomy and space geodesy. To distinguish the impacts of KVN on global and local scale networks, we designed two different sizes of VLBI networks, namely, KVN-Asia and KVN-Pacific. While the former consisted of Far East Asia region VLBI stations, the latter consisted of pacific region VLBT stations. The primary purpose of our simulation is quantitative evaluation of KVN impacts before and after the participation of KVN in the previous two virtual networks. We selected two different sets of parameters to be estimated in the simulation as indices of evaluating estimation precision: station coordinates and EOPs. The station coordinates are evaluating index for KVN-Asia and the EOPs are another evaluating index for KVN-Pacific. From the simulation results of comparisons between evaluating indexes, 50% and 20% of maximum improvements for KVN-Asia and KVN-Pacific were anticipated respectively. We expect that the space geodetic use of KVN will be focused on the several promising research fields which are proposed through the simulation results.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.8
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• pp.7-18
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• 1999

We have designed and tuilt the quasioptical system for the dual channel receiver which is used for the simultaneous observation of the cosmic radio with 100GHz band and 150GHz band. The quasioptical system has been widely used to guide the beam for the millimeter and submillimeter waves. A Gaussian distribution of field and power transverse to their axis of propagation allow the simple and elegant theory of Gaussian quasioptics. Using the theory of Gaussian beam, we introduced the analysis of image beam which is applied for a wide range of frequency. In order to guide two beams from the Cassegrain antenna simultaneously, the quasioptical system and its components for the dual channel receiver were designed by using the image beam method. We have checked the characteristics of the quasioptical components and the system by using the heam measurement system, which is made by us. The quasioptical system has been installed in the dual channel receiver on the Cassegrain antenna. The performance of this system has been finally confimed through the successful simultaneous observation with two bands of the cosmic radio.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.7
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• pp.678-684
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• 2009

Many researches on the GNSS integer ambiguity resolution methods for precise positioning and attitude determination applications have been done. However, by the time invariant property of the integer ambiguity, the reuse of integer ambiguity without performing time consuming integer search procedure is possible. In this paper, a new efficient integer ambiguity propagation method is proposed. The initial integer ambiguity can be determined using the famous LAMBDA method and it is propagated with the propagation method. The proposed method can reconfigure the integer ambiguity using the previous epoch's integer ambiguity and new carrier phase measurements under environmental variations such as geometry changes, signal blockage and reacquisition. Experiments with real measurements show the proposed method can determine an integer ambiguity effectively.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.10
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• pp.918-926
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• 2007

Military aircrafts usually operate at the area with lots of threats such as radars and surface-to-air missiles. Aircraft also faces with the unexpected or pop-up threats. Under this environment, a safe flight path should be generated to lead a mission successful. In this paper, a new path planning algorithm is proposed to provide less dangerous flight path efficiently. Of many path planning algorithms, a potential method is considered, because it has advantages of computation efficiency and smooth path generation. Trajectory generation under the condition of maximum range is studied so that the aircraft may reach the target area without refueling. The algorithm to cope with an unexpected situation is also proposed by adopting the concept of initial direction vector, additional force, and a new mapping function. The performance of the proposed algorithms is demonstrated for SEAD (Suppression of Enemy Air Defences) mission by numerical simulation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.12
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• pp.1076-1083
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• 2017

This paper discusses the error estimation in radar measurement data obtained while tracking a launch vehicle. It is known that typical radar measurement data consist of the true positional or orientation information on the vehicle being tracked, random noise and a deterministic bias due to radio refraction. Unlike previous research works, this paper proposes a tracking-error (mainly bias) estimation method solely based on the single radar measurement with no aid of other measurement such as GPS. The proposed method has been verified with real measurement data obtained while tracking the KSLV-I launch vehicle.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.7
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• pp.497-504
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• 2020

A technique was developed for analysis on sonic boom created by supersonic flight and for prediction of its sound level and atmospheric propagation characteristics. It is of great importance to anticipate sound level of sonic boom because it causes environmental issue. For that purpose, the simplified sonic-boom prediction method was applied to calculate sound pressure according to physical properties and flight information of the object and distance to measurement site, in this study. Propagation characteristics of shock wave emanated from a flying object was analyzed by using line-of-sight vector and ray tracing method which dealt with refraction of wave due to atmospheric density distribution along altitude. Predicted results agreed well with measured data from real flight.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.47-47
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• 2010

APT(Asian-Pacific Telecommunity)는 아시아-태평양지역 국가의 공동이익을 도모하기 위하여 결성된 아-태지역 전파협의체 조직으로, WRC(세계전파통신회의)회의에서의 아-태지역 주관청의 공동이익을 얻기 위해 APG(APT Conference Preparatory Group for WRC)회의를 연간 1회의 비율로 개최하고 있다. WRC-12회의에 대비하여 결성된 APG-12 회의가 2010년 3월 태국 방콕에서 개최되었으며, 전파천문업무 보호 및 22 GHz 대역 달탐사, 38 GHz 대역 Space-VLBI운용대역과 관련된 WRC-11 의제 1.6, 1.11, 1.12 등에 대해 활발한 토론이 있었다. WRC-12 의제 1.12는 항공이동국이 ASTRO-G와 같은 차세대 space-VLBI의 우주연구업무에 유해한 간섭을 줄 수 있으므로, 항공이동업무의 간섭으로부터 37-38GHz대역의 우주연구업무를 보호하기 위한 연구의제이다. 따라서 한국천문연구원에서는 KVN과 일본국립천문대(ASTRO-G)간의 원활한 국제 공동VLBI연구를 위해, WRC회의에서 최종적인 규정개정을 함에 있어서 필요한 아-태지역 국가의 공동의견을 창출하기 위한 APT회의에서 주도적인 역할을 담당하고 있다. 본 발표에서는 APG-12 3차 회의에 제출한 우리나라의 기고서 제출 결과 및 동 회의에서의 최종결과 및 향후 대응책에 대해서도 알아보고자 한다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.6
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• pp.515-521
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• 2014

In this paper, we designed axis-displaced Gregorian antenna by using Ray-tracing method. This antenna improves gain, VSWR by rotating the axis of the sub-reflector to get rid of E-field wave returned from sub-reflector to feed horn. Therefore it reduce the sub-reflector size and the volume of antenna. This method is used to track the propagation path for radiation pattern of feed horn from feed horn to sub-reflector, main-reflector and air. We get E-field distribution of this antenna aperture and calculate antenna radiation pattern and optimize the antenna performance. The Ray-tracing Method was verified because the gain, radiation patterns, side lobe level, beam width and return loss of the designed antenna are very similar to CST simulation result and a measured result of the fabricated antenna.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.2
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• pp.118-124
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• 2015

The design of radar absorbing structures(RAS) is a discrete optimization problem and is usually processed by stochastic optimization methods. The calculation of radar cross section(RCS) should be decreased to improve the efficiency of designing RAS. In this paper, an efficient method using impedance matching is studied to design RAS for minimizing RCS. Input impedance of the minimal RCS for the specified wave incident conditions is obtained by interlocking physical optics(PO) and optimizations. Complex permittivity and thickness of RAS are designed to satisfy the calculated input impedance by a discrete optimization. The results reveal that the studied method attains the same results as stochastic optimization which have to conduct numerous RCS analysis. The efficiency of designing RAS can be enhanced by reducing the calculation of RCS.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.3
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• pp.270-278
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• 2014

This paper describes an improvement of space objects orbit prediction. To screen possible collisions between operational satellites and space objects, the TLE (Two-Line Element) was used as pseudo-measurement and than the orbit determination and orbit prediction were performed through the flight dynamics system. For determining the orbits, the state vectors were assumed by a series of TLEs within a certain period. The propagation error was analyzed according to the fitting period and a number of pseudo-observations. In order to find out the improvement of orbit prediction with the proposed method, KOMPSAT-2, 3 having the precise orbit in the meter-level range were first applied. Then the result applied to space objects under the same conditions was analyzed. As a result of the RMS error comparison with the orbit prediction of space object, the precision of orbit prediction was improved by approximately 90% for seven days prediction. The improved orbit prediction of space objects can be utilized in the daily analysis for initial screening of the close space objects at high risk.