• Journal of Astronomy and Space Sciences
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• 제19권4호
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• pp.395-402
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• 2002

The NORAD type Two Line Element (TLE) was obtained from the osculating orbital elements by an iterative approximation procedure. The mathematical model was presented and computer program was developed for the conversion. The osculating orbital elements of the KOMPSAT-1 were converted into the NORAD TLE. Then the effect of the SGP4 atmospheric drag coefficient ($B^*$) was analyzed by comparison of the orbit propagation results with different $B^*$ values.

• 한국자동차공학회논문집
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• 제16권1호
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• pp.29-36
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• 2008

In this paper, the orbital forming analysis of an automotive hub bearing was studied to predict forming performances using the explicit finite element method. To find an efficient solution technique for the orbital forming, axisymmetric finite element models and 3D solid element models were solved and numerically compared. The time scaling and mass scaling techniques were introduced to reduce the excessive computational time caused by small element size in case of the explicit finite element method. It was found from the numerical simulations on the orbital forming that the axisymmetric element models showed the similar results to the 3D solid element models in forming loads whereas the deformations at the inner race of bearing were quite different. Finally the strains at the inner race of bearing and the forming forces to the peen were measured for the same product of the numerical model by test, and were compared with the 3D solid element results. It was founded that the test results were in good agreements with the numerical ones.

• 소성∙가공
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• 제14권1호
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• pp.29-36
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• 2005

In this paper, a useful rigid-plastic finite element method with various numerical schemes is presented for simulation of an orbital forming process. A new approach to reduce volume change during simulation is presented and an approximation method to reduce computational time is also presented. An actual orbital forming process found in a bearing making industry is simulated by the presented approach. The simulated results of the orbital forming process are compared with the experimental results.

• Journal of Mechanical Science and Technology
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• 제20권2호
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• pp.177-184
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• 2006

An orbital design method of the formation initialization based on the relative orbital element method is presented. It firstly constructed the relative motion equation of the satellite formation flying in terms of the leader and followers' orbital elements. Then the equation was simplified when the orbit eccentricity of the leader satellite was small. And according to the satellites' mission, a general design method for the relative trajectory was proposed. The advantage of this method is that one can get a very simple analytical formula of each follower satellite's orbital elements when the orbital eccentricity of the leader satellite is zero. The simulation results show that the method is effective.

• 한국항공우주학회지
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• 제30권7호
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• pp.123-129
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• 2002

본 논문은 실제 저궤도 위성에서 GPS를 이용하여 궤도를 추정하는 연구 결과를 담고 있다. 우리별 3호의 GPS 수신기가 실제 측정한 3차원 위치 및 속도 정보를 이용하였으며, 추정 알고리즘으로는 실시간 계산을 위한 확장 칼만필터와 후처리를 위한 스무더를 사용하였다. 스무더는 확장 칼만필터를 통과한 값을 이용하여 다시 역으로 추정하는 과정을 거치게 되므로 전체적으로 안정화된 추정값을 제공한다. 본 논문에서는 스무더를 적용한 추정값을 이용하여 우리별 3호의 케플러 궤도 요소를 계산하고, 분석하였다.

• Journal of Astronomy and Space Sciences
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• 제28권1호
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• pp.37-54
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• 2011

Two semi-analytic solutions for a perturbed two-body problem known as Lagrange planetary equations (LPE) were compared to a numerical integration of the equation of motion with same perturbation force. To avoid the critical conditions inherited from the configuration of LPE, non-singular orbital elements (EOE) had been introduced. In this study, two types of orbital elements, classical Keplerian orbital elements (COE) and EOE were used for the solution of the LPE. The effectiveness of EOE and the discrepancy between EOE and COE were investigated by using several near critical conditions. The near one revolution, one day, and seven days evolutions of each orbital element described in LPE with COE and EOE were analyzed by comparing it with the directly converted orbital elements from the numerically integrated state vector in Cartesian coordinate. As a result, LPE with EOE has an advantage in long term calculation over LPE with COE in case of relatively small eccentricity.

• 한국정밀공학회지
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• 제27권4호
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• pp.27-32
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• 2010

This paper presents an investigation into the pinhead forming process with the objective of finding the optimal forming conditions. In order to this, the orbital forming analysis of a heading MIG was carried out using the explicit finite element method. Relationships between temperature by forming of load and stresses, rake angle by forming final shape and stress distribution were investigated through analysises in order to find an efficient solution. As a result, the higher temperature and orbital rake angle were the better forming conditions.

• 천문학회보
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• 제7권
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• pp.3.1-3.1
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• 1982

• Journal of Astronomy and Space Sciences
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• 제29권3호
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• pp.287-293
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• 2012

Satellite operating agencies are constantly monitoring conjunctions between satellites and space objects. Two line element (TLE) data, published by the Joint Space Operations Center of the United States Strategic Command, are available as raw data for a preliminary analysis of initial conjunction with a space object without any orbital information. However, there exist several sorts of uncertainties in the TLE data. In this paper, we suggest and analyze a method for estimating the uncertainties in the TLE data through mean, standard deviation of state vector residuals and covariance matrix. Also the estimation results are compared with actual results of orbit determination to validate the estimation method. Characteristics of the state vector residuals depending on the orbital elements are examined by applying the analysis to several satellites in various orbits. Main source of difference between the covariance matrices are also analyzed by comparing the matrices. Particularly, for the Korea Multi-Purpose Satellite-2, we examine the characteristics of the residual variation of state vector and covariance matrix depending on the orbital elements. It is confirmed that a realistic consideration on the space situation of space objects is possible using information from the analysis of mean, standard deviation of the state vector residuals of TLE and covariance matrix.

• 대한원격탐사학회지
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• 제15권2호
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• pp.119-130
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• 1999

현재 전 세계적으로 많은 위성관제 및 위성영상데이터 수신처리 지상국에서 저궤도 위성의 추적 및 위성과의 통신을 위하여 NORAD 궤도데이터를 사용하고 있다. 공신력있는 북미우주방위사령부(NORAD)에서는 거의 매일 주기로 수천개의 지구 주회 물체를 관측하여 그 궤도데이터를 인터넷을 통해 전 세계로 공개하고 있으며, 이 데이터를 사용한 위성 궤도 예측은 지상국에서 위성과 통신하기에 충분한 추적정확도를 제공한다. 하지만 고해상도 지구관측 위성의 임무수행을 위해서는 위성의 위치결정 정확도의 중요성 때문에 평균 궤도정보인 NORAD 데이터를 사용하는 대신 자체 위성 관측 및 추적시스템을 운영한다. 우리별 3호의 지상국인 경우 자체 위성 추적시스템이 없는 관계로 위성과의 통신 뿐 아니라 영상촬영 및 처리를 위한 궤도정보를 NORAD 데이터에 의존하고 있다. 본 논문에서는 이러한 NORAD 데이터를 이용하여 위성의 위치를 예측 또는 결정함으로써 고해상도 지구관측 위성이 원하는 지역을 얼마나 정확히 촬영할 수 있는지, 그리고 생성되는 영상 카탈로그의 위치는 실제 촬영된 위치와 얼마나 달라질 수 있는지를 실험, 분석한다.