Research On Terminal Guidance And Control For Reentry Vehicles

This dissertation is intended to give a systematic study on the terminal guidanceand control for precise impact of reentry vehicles. The Inertial measurement unit willaccumulate errors after long-time flight. More accurate navigation information will beachieved with combined navigation, using inertia navigation and homing seeker.Furthermore, impact point error will be great guided by standard reentry trajectory iftarget point is changing. Then guidance command should be generated on relativeposition and relative velocity. By thoroughly discussing the theories and technicaldifficulties in terminal guidance and control, this study reaches an abundance of regularconclusions.First, commonly used coordinate system in reentry phase and the transformationmatrix between different coordinate are introduced, the motion equations of reentryvehicle are given. Based on the correlation between Euler angle rates and body anglerates, Euler angle rates are calculated with pseudoinverse and quaternion method whensingularity exists. Guided by optimal guidance law, the angle between velocity vectorand local horizontal and the angle between velocity vector and local vertical plane arecorrelated with elevation/azimuth, and the commanded angle of attack and sideslipangle are derived. In the transformation from attack angle and sideslip angle commandto Euler angle command, the traditional stratrgy relies on inclination angle, flight pathangle and bank angle, a new guidance command generation strategy using relativeposition is researched. Then, a new guidance command combination is generated whichexerts no control effort in roll plane.Based on optimal control theory, this dissertation proposes a new time-to-goestimation algorithm. The terminal miss distance with optimal control effort and thecorrelation between terminal miss and zero-effort-miss are derived. With two differentintercept strategies called point of closet approach and straight collision path, two newequations of time-to-go estimation are given, these two equations make use of theincluded angle between relative position and relative velocity vector. When the includedangle is great, these two equations return less estimation error than traditional first-orderapproximation.Two guidance laws with terminal impact angle constraints are proposed usingadaptive proportional guidance and sliding mode control. The correlation betweeninclination/flight path anlge and elevation/azimuth is constructed based on proportionalguidance. Proper guidance parameter is selected in diving plane and tuming plane, andthe guidance parameter is updated with reentry trajectory. The sliding surface andreaching law for sliding mode in diving plane and turning plane are designed, and suchdesign satisfy the reaching condition for the sliding surface. The needed accelerations in target coordinate are given.To get better tracking performance of attitude command over the reentry phase ofvehicles, this dissertation carries on the use of state-dependent Riccati equation (SDRE)method for attitude controller design of reentry vehicles. SDRE control method employsfactorization of the nonlinear dynamics into a state vector and state dependent matrixvalued function, stability and optimality of SDRE controller are certificated. After theconstruction of SDRE, the solution to Riccatti equation is calculated real-timely withSchur decomposition method. State feedback control law u(x) is derived with linearquadratic regulator (LQR) method. State-dependent coefficients are derived based onreentry motion equations in pitch and yaw channels, and the rudder deflections are gotwith SDRE controller.Based on generalized predictive control(GPC), constrained predictive control isresearched when input, output and control are constrained. Then the solution to optimalinput is got with quadratic programming. Constrained predictive controller is developedbased on the transfer function of the actuator, then the new predictive controller is addedin the attitude control, and better control performance is achieved.At last, the dissertation conducts a hardware-in-the-loop simulation based ondSPACE environment. The actuators and inertial measurement unit are added in thesimulation loop, and guidance command and control output are calculated by on-boardcomputer. dSPACE system has such advantages as changing parameter value onlinely,rapid target prototype and high precision. Control performance are discussed based onsimulation data.To conclude, this dissertation gives a rather complete discussion on issuesconcerning terminal guidance and control both theoretically and pragmatically. Thisresearch work bears great significance in the theory development as well as engineeringpractice.