Research On Orbit Design And Optimization Of Asteroid Exploration Mission

When the deep space exploration activites continues moving forward, it has become the inevitable trend to perform the exploration of asteroids which have unique scientific value. Binary asteroid system is a special form of the asteroid groups and about 16% of near-earth asteroids and main belt asteroids belong to binary asteroid system, which are the preferred target of the future China asteroid sample return mission.In this thesis, the asteroid low-thrust transfer orbit design and optimization, the weak gravitational binary asteroid system gravity field modeling and the dynamic characteristics near the binary asteroid system are studied based on the potential engineering background of the asteroids exploration and defense. First of all, the preliminary design of the low-thrust transfer orbit is conducted by use of the exponential sinusoid and the genetic algorithm. Then, the optimization of the low-thrust transfer orbit is performed by the Radau pseudo-spectral method and the sequential quadratic programming(SQP) algorithm. The key of low-thrust transfer orbit preliminary design is to solve the flight time constraint equation. An improved exponential interpolation method is put forward which has good computational efficiency and high calculation precision. Secondly, the sphere-sphere model, the ellipsoid-sphere model and the improved restrictive ellipsoid-ellipsoid model are adopted for the gravitational field modeling, and the corresponding complexity and precision of the three models increase gradually. Next, the changes of the Lagrangian points and the stability regions of the triangle Lagrangian points are compared among the three models of the binary asteroid system. For different gravitational field models, the integral link is introduced into the calculation process too much if the elliptic integral is used to calculate the gravitational potential energy, which will greatly increase the amount of calculation and the difficulty of calculation. Therefore, the second degree and order spheric harmonic function model is adopted in this paper to calculate the gravitational potential energy, which has high calculation efficiency and has not integral link. Finally, the flow function method is used to calculate and analysis the collinear Lagrangian point Lyapunov orbits and its invariant manifolds of the binary asteroid system for the three different models, which doesn't need to approximate analytical solution as the iterative initial value and calculate the state transition matrix, and is easy for programming. On the basis of the Lyapunov orbits and its invariant manifolds, using the progressive and directivity of the invariant manifolds, this paper designs the capture and escape trajectories of the binary asteroid system for the three different models; and with the aid of the invariant manifolds and its heteroclini connections, this paper also use the poincare section method to design the low energy transfer trajectories between the different collinear Lagrangian point Lyapunov orbits for the three different models of the binary asteroid system.