Research On Entry Guidance And Control Algorithm For Glide Vehicle

Entering earth’s atmosphere with hypersonic speed, glide vehicle is unpowered duringentry phase. With a relatively high lift-to-drag ratio, glide vehicle possesses strongmaneuverability. In addition, the entry guidance and control system can control the flighttrajectory through changing the direction of lift. However, the design of entry guidance andcontrol system is not easy because of the vehicles’ various flight missions, long time flight,and rapidly changing speed, position, and flight environment.This dissertation presents new entry guidance and control methods for glide vehicle.The research focuses on onboard trajectory planning, trajectory tracking guidance andattitude control. It can be mainly divided into the following four parts:First of all, a novel three dimensional autonomous entry guidance for glide vehiclesatisfying geographic constraints and other path constraints is proposed. The guidance iscomposed of a trajectory planner and a trajectory tracker. The reference trajectorygenerated onboard by trajectory planner can be divided into initial descent phase and glidephase. The initial descent phase is designed in consideration of a nominal angle of attackand an appropriate constant bank angle. And the trajectory planning for glide phaseconsiders both longitudinal and lateral movement. Regards to the design of longitudinalsub-planner, the dissertation encourages it should obtain the desired reference trajectorythrough interpolating between the upper boundary and the lower boundary of entry corridorin the plane of drag-versus-energy. While the drag profile specifies the magnitude of bankangle, the lateral sub-planner decides the sign of bank angle. In addition, the lateralsub-planner utilizes two-reverse mode to achieve waypoint constraints and dynamicheading error corridor to overcome no-fly zone constraints. In the process of drawingsatisfactory reference trajectory, the longitudinal planer and lateral sub-planner areiteratively employed so that the reference trajectory could completely fulfill all pathconstraints. In terms of trajectory tracking, a novel tracking law based on active disturbancerejection control is introduced. After adaptability tests and the testing of Monte Carlosimulations, the entry guidance approach prove to be capable of adjusting to finish variousentry missions and of helping the glide vehicle reach the prescribed target point precisely while satisfying geographic constraints.Secondly, to improve system’s robustness and the accuracy of entry guidance, atrajectory tracking guidance algorithm based on indirect Legendre pseudo-spectral methodand receding horizon control is introduced. At first, the author converts the problem oftracking trajectory based on the obtained reference trajectory to a problem of regulating thetrajectory state, which becomes essentially an optimal control problem of a linear timevarying system. Then, a robust guidance law combines the benefits of indirect Legendrepseudo-spectral method and receding horizon control method is applied to solve theproblem. The above work is tested by a3-degree-of-freedom numerical simulation for theentry of suborbital glide vehicle. The results indicate that the designed trajectory trackingguidance is of good robustness in the presence of various initial uncertainties andaerodynamic parameter disturbances.Thirdly, this dissertation researches on the finite-time attitude control problem forglide vehicle with redundant actuators in consideration of planet uncertainties and externaldisturbances. At first, feedback linearization technique is used to cancel the nonlinearitiesof motion equations and to construct a basic mode for attitude controller. Then, the basicmode is integrated with two kinds of time-varying sliding mode control methods separately.In each case, disturbance observer is introduced to further enhance the control performanceand system robustness. It is worth noting that one method is designed based on boundarylayer technique; the other is a novel second-order sliding model control method.Furthermore, this dissertation advocates an approach of optimal control allocation whichcan distribute torque commands to aerodynamic actuators and on-off reaction controlsystem actuators after the attitude controller confirms torque commands. Finally, thefinite-time stability analyses are carried out to examine the closed-loop systems of thementioned two methods, respectively. Both time-varying sliding mode control methodsprove to be robust to uncertainties and disturbances and free of influence of chatteringphenomenon. Moreover, the proposed second-order sliding mode control performanceshigher control accuracy.Last but not least, to cope with flight faults during entry, this dissertation proposes anew scheme which is actively tolerant to the faults challenging glide vehicle. The scheme is designed by collaborating fault detection method and attitude controller reconfigurationmethod. On the basis of the dynamic model in consideration of the faults, a nonlinear faultdetection observer is created to observe and reflect faults immediately. Moreover, with thehelp of control technologies concerning both self-adaptation and sliding mode, it is realizedthat the attitude controller would automatically switch to the proposed self-adaptive slidingmode control if any fault is detected. After comparing the proposed active fault-tolerantcontrol method and traditional control method, the researcher finds that the proposedmethod is of satisfactory control performance despite flight faults.