Estimation For Motion Parameters Of A Free-floating Body In Space

The capture of free-floating bodies in space is a particularly critical part of space missions,and is essential for space activities such as assisting spacecraft access to orbit,spacecraft maintenance in orbit,refuelling,debris removal and towing the derelict spacecraft out of orbit.Ensuring the safe and reliable on-orbit capture of non-cooperative targets in space is therefore an important challenge in space missions.If the structural characteristics,attitude,angular velocity and inertial information of the space non-cooperative target can be accurately obtained before capture,it will be very beneficial for the subsequent direct capture and on-orbit mission operations.This thesis focuses on the on-orbit capture of space free-floating bodies,and considers the characterisation and study of the motion parameters of space free-floating bodies when the priori information of the target is unknown.The main research elements are as follows:(1)For the complex motion of a free floating body in space,the thesis defines the reference coordinate system to be used,establishes the attitude kinematics and dynamics equations of a non-cooperative target in space,classifies and analyses the typical target motion states according to the angular momentum and kinetic energy relationship.Also,the theoretical knowledge of the relevant optimisation theory and vision used in subsequent chapters is presented.(2)In the problem of angular velocity estimation of spatially free-floating bodies,an inter-frame matching algorithm is designed for the motion state of uniaxial spin of spatially free-floating bodies.The algorithm sifts out unstable and short-lived features through the inter-frame transfer of feature information,and builds a global and continuously stable feature database.A model function is then generated based on the constraints of the target motion model and transformed into an optimisation problem to solve for angular velocity.(3)In the problem of estimating other kinematic parameters of a spatially free floating body in a tumbling state,the tumbling state of the target is simulated with the help of a multi-body dynamics simulation system,using the sensor module to output each state parameter,including angular velocity,angular acceleration and attitude quaternion.The angular momentum conservation theorem and the attitude dynamics formulation are then used to estimate the rotational inertia ratio and angular momentum direction of the free-floating body in space.