Transfer Trajectory Design And Optimization Of Near-Earth Asteroid Sample Return Mission

The asteroid sample return mission is a hot spot for deep space exploration.Trajectory design is an essential part of research.This paper studies the design of transfer trajectory of the near-Earth asteroid sample return mission.The design of the heliocentric direct transfer orbit is studied using the 2-impulse transfer and 3-impulse transfer model.The following aspects are studied:(1)The classic Lambert 2-impulse transfer algorithm and 3-impulse transfer model are established.By optimizing the launch window,escape status and maneuver time,the optimal transfer to asteroid is obtained.(2)The transfer trajectory in chemical thrust with dry mass of the spacecraft as the optimization objective is innovatively designed.Combining with the launch energy of the launch vehicle,the transfer trajectory to asteroid is solved by optimizing the dry mass of the spacecraft.Using this method,it can raise the dry mass of the spacecraft effectively and expand the selection range of the asteroids.(3)Multiobjective optimization models of transfer time and dry mass,transfer time and velocity increment are established.NSGA-?algorithm is employed.It effectively allocates the transfer time and the time spent on the asteroid to make mission design more flexible.The design of the heliocentric transfer trajectory to asteroids with large inclination and eccentricity using gravity assist is studied.The model of using deep space maneuvers and gravity assist is established.Launch window,flight sequence are numerically optimized to obtain the velocity increment of sample return transfer trajectory.By establishing and solving the gravity-assist model with deep space maneuver,the velocity increment for trajectory transfer is effectively reduced.The design of geocentric escape trajectory with lunar gravity assist(LGA)is studied.According to the different level of launch energy and numbers of LGA,the following research contents are carried out :(1)For launch with high energy,the basic model of single LGA escape transfer using forward patch method and backward patch method is established.By using the method of backward patch,several conclusions are drawn.The launch energy can be reduced effectively,while the velocity increment of optimal heliocentric transfer can't be decreased.The constraints on DLA of direct launch can be released to some degree.By taking spacecraft dry mass as the optimization objective,LGA can effectively raise the dry mass of transferring to some asteroids.(2)For launch with low energy,several double LGA types such as resonance,backflip and coplanar are established using geometric properties of conics and Kepler orbital characteristics.Models of double LGA escape transfer using chemical thrust and low thrust for heliocentric trajectory are established.The effects of using different double LGA types are compared.The transfer scheme is derived,which uses double LGA escape with two as the resonance ratio.(3)For launch with low energy,aiming at the problem that transfer velocity increment of LGA escape with chemical thrust for heliocentric trajectory is large,the model of impulse-aided LGA escape transfer is established,which effectively reduces the launch energy of the launch vehicle and velocity increment for transfer,hence increasing spacecraft dry mass and injecting more mass into mission orbit.