Ph.D Thesis

Ph.D StudentSegal Shai
SubjectVision-Based Control of Relative Spacecraft Attitude
DepartmentDepartment of Aerospace Engineering
Supervisors PROF. Pinchas Gurfil
DR. Avishy Carmi
Full Thesis textFull thesis text - English Version


With the development of distributed space system technology, the ability to model, estimate and control relative motion between spacecraft has become crucial for successful operation of multiple satellites. Moreover, in cases where the spacecraft are non-cooperative, such as on-orbit servicing or tracking resident space objects, the relative navigation problem becomes far more challenging due to the lack of cross-link communication or a priori information. This research addresses modeling, estimation and control related to the relative navigation problem both in the cooperative and non-cooperative setups.

The first part of this work, presents a new a kinematically-coupled spacecraft relative motion model. In contrast to the traditional non-linear point-mass and linear Clohessy-Wiltshire models, which describe the translational motion between the center-of-masses of the spacecraft, in this model equations of motion are derived to model the relative motion between any two arbitrary points on the spacecraft. The model is constructed by including the effect of relative rotation on relative translation. Numerical simulations illustrate that this effect is important for tight formation flying and rendezvous.

The second part of this work deals with the vision-based relative state estimation problem between two non-cooperative spacecraft. Using two cameras mounted on a chaser satellite, the relative state with respect to a target satellite, including the position, attitude, and rotational and translational velocities, is estimated. The new approach employs a stereoscopic vision system. It is shown that, even in the non-cooperative case, there is information that can be extracted pertaining to the relative attitude and target structure. The performance of the new filtering algorithm is validated by Monte-Carlo simulations and in a laboratory experiment conducted at the Technion's Distributed Space Systems Laboratory.

Finally, new methods for vision-based satellite attitude control aimed at space-based optical tracking of resident space objects (RSOs) are developed. An Earth-orbiting chaser satellite equipped with either one or two body-fixed cameras can successfully track an RSO provided that the target is kept within the camera field-of-view. Two control architectures are presented for the cases of monocular and stereoscopic vision. The stability of the developed control laws are substantiated based on Lyapunov's direct method and demonstrated using Monte-Carlo  simulations.