• 한국항공우주학회지
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• 제38권12호
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• pp.1184-1194
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• 2010

달 착륙과 이륙은 착륙선의 자세 및 고도에 따라서 몇 가지 단계로 나누어져 있다. 따라서 최적의 착륙선 궤적을 생성하기 위해서는 각 단계에 맞는 구속 조건과 제어 값이 필요하다. 착륙과 이륙의 최적궤적생성은 연료소모 및 자세변화율을 최소화 하는 가격함수를 이용하여 최적화를 수행하였다. 본 논문에서는 궤적을 생성하는 최적제어 문제의 풀이 방법을 직접적인 접근방식중의 하나인 Gauss pseudo-spectral을 사용하였고, 이 문제로 착륙선의 기준 궤적과 상태 및 제어 값을 생성하였다.

• 한국항공우주학회지
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• 제39권5호
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• pp.408-415
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• 2011

달착륙은 크게 궤도이탈 단계, 동력하강 단계로 구성되어지며, 동력하강단계는 Braking, Approach, Final landing phase의 세부 3단계로 나누어진다. 본 논문에서는 동력하강 세부 3단계의 최적경로를 통하여 달착륙선의 착륙 제어를 수행하기로 한다. 우선 Gauss pseudo-spectral 방법을 통하여 기준 궤적을 생성하였고, 고도와 각 방향의 속도오차를 이용하여 PID 제어기를 생성하였다. 마지막으로 Matlab의 Simulink를 이용하여 달착륙선의 착륙단계 시스템을 구성하고 이를 이용하여 시뮬레이션을 수행하였다.

• International Journal of Aeronautical and Space Sciences
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• 제10권1호
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• pp.112-121
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• 2009

This paper deals with supersonic air-breathing missile system. A supersonic air-breathing missile system has very complicated and incoherent thrust characteristics with respect to outer and inner environment during operation. For this reason, the missile system has many maneuver constraints and is allowed to operate within narrow flight envelope. In this paper, trajectory optimization of the missile is accomplished. The trajectory optimization problem is formulated as a discrete parameter optimization problem. For this formulation, Legendre Pseudo-Spectral method is introduced. This method is based on calculating the state and control variables on Legendre-Gauss-Lobatto (LGL) points. This approach helps to find approximated derivative and integration quantities simply. It is shown that, for this trajectory optimization, trend analysis is performed from thrust characteristics on various conditions so that the trajectory optimization is accomplished with fine initial guess with these results.

• International Journal of Aeronautical and Space Sciences
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• 제16권2호
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• pp.264-277
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• 2015

This article investigates various transcription techniques for the Legendre pseudospectral (PS) method to compare the pros and cons of each approach. Eight combinations from four different types of collocation points and two discretization methods for dynamic constraints, which differentiate Legendre PS transcription techniques, are implemented to solve a carefully selected test set of nonlinear optimal control problems (NOCPs). The convergence property and prediction accuracy are compared to provide a useful guideline for selecting the best combination. The tested NOCPs consist of the minimum time, minimum energy, and problems with state and control constraints. Therefore, the results drawn from this comparative study apply to the solution of similar types of NOCPs and can mitigate much debate about the best combinations. Additionally, important findings from this study can be used to improve the numerical efficiency of the Legendre PS methods. Three PS applications to the aerospace engineering problems are demonstrated to prove this point.