Orbit Design And Control Algorithm Of Asteroid Explorer

With the development of science and technology, aviation and space activitiesflourish all over the world. From the first exploration of the Moon to the detectionof the Venus and Mars, extraterrestrial planetary explorations have never stopped.Since the study of near-Earth asteroids has the unique value in technology andastronomy, it has become a new focus of all the countries which attribute a lot to theaviation. Because of the irregular gravity field of the irregular asteroid, traditionalmethods are no longer applicable so that the modeling of the gravity field of theasteroid and the research of orbital dynamics become critical.This paper aims to analyze the modeling of the gravity field of the irregularasteroids and its dynamics. The following sections have been presented.Firstly, two kinds of frame coordinate systems usually used in the paper areintroduced, with which the kinematic equations and conversions of asteroidexplorer’s orbits are given. For irregular asteroids, the modeling and calculation ofthe gravitational field are conducted and two models of spherical harmonicsfunction and polyhedron model are compared.Secondly, the control of asteroid explorer’s hover is discussed. For the hover inthe body-fixed coordinates, two hover projects are proposed based on the linearperturbation kinematics equations: sliding mode control law and Tight control lawwith small perturbation. When the deviation is large, sliding mode control law isused, in order to achieve fast approaching. Otherwise, if the deviation is small, theTight control law is a better choice, in order to avoiding great thrust control andreducing the energy consumption.Finally, an analysis of the equilibrium point near the asteroid and a stabilitycriterion of the equilibrium point were given, an analytical solution based on afirst-order linear motion model was given for the research of the characteristicsaround the equilibrium point, above all, the instability reason of the equilibriumpoint was discussed. An nominal orbit at the equilibrium point of the Halo orbit wasdesigned based on the first-order analytical solution. Besides, a Halo orbit keepingcontrol law based on continuous low thrust and minimum modulus principle wasdesigned, according to the linearity error kinematic equations. Detector can achievethe nominal orbital motion and orbit maintenance under the control law designedpreviously.