Design And Optimization Of Low-thrust Gravity-assist Trajectories

Low-thrust propulsion system is one of the key technologies of the deep spaceexploration in the21st century, which has the advantages of high specific impulse,light weight and high control accuracye etc. The gravity-assist maneuvers canovercome the problem of huge fuel consumption during the long-distance deepexploration.The gravity-assist maneuvers integrated with the low-thrust propulsion is one ofthe important research directions of the deep space transfer trajectories because itcan not only save the fuel consumption but also shorten the exploring taskduration of low-thrust propulsion. The design and optimization of the low-thrustgravity-assist (LTGA) trajectory are researched in this paper base on the featuresof deep space transfer trajectories.First, the basic theories for the preliminary design and optimization of LTGAtrajectories are analyzed and researched. The ephemeris of planets and asteroidsis obtained in the first step. Then, the trajectory dynamical models and thegravity-assist dynamical model are established. The features of each dynamicalmodel are discussed. Besides, the optimization model for each dynamical modelis researched.Second, the preliminary design methods for LTGA trajectories are studied deeply.Based on Shape-Based theories of the exponential sinusoid and inversepolynomial, two significant methods are presented. The jobs done here areprepared for the following task.Then, the optimization methods for LTGA trajectories are researched deeplybased on SQP algorithm. The direct method based on direct collocation and theindirect methods with Sim-Flanagan trajectory model and Multiple Shooting arepresented. The merit and demerit of each method are researched through thesimulation experiments.Finally, Three kinds of the low-thrust transfer trajectory for Apophis explorationare computated and analyzed in detail based on the study contents above. And theoptimal one is chosen.