Observability-Based Space Noncooperative Target Motion Estimation

This study proposes a complete method for estimating the relative motion parameters of noncooperative targets in space and analyzes the system observability for the optically autonomous relative navigation problem of noncooperative targets in space. First, using the installation offset of the onboard monocular camera, a relative navigation system model is established herein by observing the three feature points of the target using the line-of-sight direction of the feature points as the measurement information and combining the target's relative orbital dynamics, attitude kinematics, and dynamics. Second, the system observability is analyzed based on the system observability matrix and combined with the null-space theory. The conditions under which the system does not satisfy the observability are analyzed through the definition of observability. An iterative extended Kalman filter based on this system model is then derived to realize the complete estimation of the target relative position, relative velocity, target attitude, angular velocity, inertia ratio, and position of the feature points under the target body frame. Finally, the effect of the camera offset on the system observability is analyzed through a numerical simulation. The results verify that an appropriate camera offset can make the monocular relative navigation system fully observable. The only existing unobservable state variable is found at 0 camera offset.