Research On Integrated Position And Attitude Control For Spacecraft Proximity Operations

With the flourishing development of space science and technology,the complexity and diversity of spacecraft on-orbit missions are also increasing.Reliable orbit and atti-tude control is an fundamental assurance for spacecraft to realize all space missions.For traditional single-spacecraft systems,the standard approach is to design the orbit and attitude controllers separately;but in order to implement the emerging multi-spacecraft proximity operation mission,the pursuing spacecraft is generally required to track the relative position and keep attitude synchronize simultaneously with respect to of the target spacecraft.This dissertation aims to solve the problem of integrated relative position-attitude control between the two spacecraft.The theoretical results can provide prerequisites for the successful implementation of proximity operations missions such as fly-around,hovering,on-orbit monitoring or assembly,fuel adding,rendezvous and docking,space confrontation and so on.With the overall goal of achieving integrated relative position-attitude control,and taking into full consideration practical problems such as uncertainties and external disturbances,input constraints,high-precision control and rapid maneuvering,and actuator faults that may be faced in proximity operations missions,several integrated position-attitude control schemes are designed,specified as follows:First of all,the spacecraft proximity operations missions are divided into three phases:orbit adjustment,fly-around and rendezvous and docking.A dynamic com-pensator is introduced to overcome the uncertainty of space disturbance caused by the change of orbit radius and inclination angle.The disturbance suppression problem of relative orbit control is transformed into the global stabilization problem of a special class of nonlinear systems.By applying internal model theory and robust control the-ory,the global asymptotic stability of the closed loop system is guaranteed.Second,a coupled six-DOF relative motion dynamics model is established to de-scribe the problem of integrated position-attitude control for fly-around mission,where the input constraints and external disturbances are considered.A normal controller based on input-state stability is designed.To address the input saturation problem,a novel dead-zone operator based model is introduced.Then,a saturated control scheme is technically proposed by incorporating the adaptive technique into backstepping de-sign,which needs no prior knowledge of the external disturbances'bounds.Then,to solve the position-attitude control for spacecraft rendezvous and docking with system uncertainty and external disturbance,utilizing the non-singular integral ter-minal sliding mode method,a novel finite-time control scheme is technically proposed.Particularly,by employing the adaptive technique,the proposed control strategy enjoys the feature that it avoids requiring the prior knowledge of the lumped system uncer-tainty's bounds.The designed controller is then proved to guarantee the translational and rotational tracking errors locally converge to zero in finite time.Furthermore,the chattering phenomenon is given an effective remedy by resorting to the boundary layer technology.Finally,for the problem of integrated position-attitude control for spacecraft prox-imity operations with actuator faults,the six-DOF dynamic model is improved,so that it can describe the typical actuator fault types including partial loss of energy,contin-uous float,complete failure and stuck.Then,a basic robust fault-tolerant controller is derived to accommodate actuator faults and guarantee global asymptotic stability.Subsequently,a novel adaptive fault-tolerant control scheme is designed that explicitly takes into account the feasible input saturation.Furthermore,the proposed controller is proved to provide fault-tolerant capability despite input saturation and ensures that relative pose tracking errors converge to a neighborhood of the origin.In this dissertation,extensive numerical simulations are carried out to verify the effectiveness of the proposed algorithm for all the aforementioned integrated position-attitude control schemes.