Abstract

The sensitivity of the initial guess in terms of optimizer based on an hp-adaptive pseudospectral method for solving a space maneuver vehicle's (SMV) trajectory optimization problem has long been recognized as a difficult problem. Because of the sensitivity with regard to the initial guess, it may cost the solver a large amount of time to do the Newton iteration and get the optimal solution or even the local optimal solution. In this paper, to provide the optimizer a better initial guess and solve the SMV trajectory optimization problem, an initial guess generator using a violation learning differential evolution algorithm is introduced. A new constraint-handling strategy without using penalty function is presented to modify the fitness values so that the performance of each candidate can be generalized. In addition, a learning strategy is designed to add diversity for the population in order to improve the convergency speed and avoid local optima. Several simulation results are conducted by using the combination algorithm; simulation results indicated that using limited computational efforts, the method proposed to generate initial guess can have better performance in terms of convergence ability and convergence speed compared with other approaches. By using the initial guess, the combinational method can also enhance the quality of the solution and reduce the number of Newton iteration and computational time. Therefore, the method is potentially feasible for solving the SMV trajectory optimization problem.

Highlights

  • Trajectory optimization problems for re-entry vehicles have been investigated widely by some researchers [1]–[4]

  • This paper presents a combinatory approach that uses the violation learning differential evolution (VLDE) algorithm and the hp-adaptive pseudospectral method

  • To solve the space maneuver vehicles (SMV) trajectory optimization problem using numerical methods, the continuous-time SMV trajectory optimization problem needs to be transformed to an nonlinear programming problems (NLPs) and the discretization method used in this paper is the hp-adaptive pseudospectral method

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Summary

INTRODUCTION

Trajectory optimization problems for re-entry vehicles have been investigated widely by some researchers [1]–[4]. It is more challenging to solve the re-entry problem by using indirect methods, since in an indirect method, first-order necessary conditions for optimality should be derived from the original optimal control problem according to the calculus of variations so that the Hamiltonian boundary-value problem can be constructed This process usually becomes costly due to the complexity of the dynamic model and path constraints. The NLP solver will start at an infeasible point where most of the constraints are violated (i.e., cannot be satisfied) meaning the number of the Newton iteration will be increased To tackle this problem, this paper presents a combinatory approach that uses the violation learning differential evolution (VLDE) algorithm and the hp-adaptive pseudospectral method. Based on the definition of violation degree and satisfactory degree, a proper fitness function is designed that does not contain penalty factors or weight coefficients Because of these advantages, the VLDE approach is applied to solve the SMV trajectory planning problem.

PROBLEM DESCRIPTION
SMV Dynamic Model
Re-Entry Process Constraints
Objective Function of Trajectory Optimization
HP-ADAPTIVE PSEUDOSPECTRAL METHOD
TRAJECTORY OPTIMIZATION PROBLEM BASED ON THE VLDE METHOD
Violation Degree of Constraints
Fitness Function With Violation Degree
Evolutionary Strategies
Learning Strategy
Optimization by the VLDE Algorithm
Simulation Parameter Setting
10 Iter 10 Iter 10 Iter 10 Iter 10
Numerical Simulation
Analysis of the Simulation Result
Dispersion Models
CONCLUSION
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