Research On Control Technology Of Reentry For Reusable Launch Aircraft

The reentry of Reusable Launch vehicle begins at the altitude of120km,7Mach number, and endsat the altitude of25km,2.5Mach number. The flight envelope is big, and the dynamic changes rapidly.In the reentry process, The RLV has experienced the low pressure, the middle pressure and the highpressure. Accordingly, the RLV has used the RCS control, the composite control and the aerodynamiccontrol, which are the mainly problem researched by this thesis.In the early reentry, the RLV only used RCS. Compared with the conventional actuator, RCS showsthe discrete characteristic, which is a chanllenge to the continuous system’s control. So we use the pulsewidth modulation algorithms to modulate the continuous control value into the discrete control value, inorder to make RCS output the equivalent torque with continuous torque. And based on the discretecontrol theory, the stability of the RCS control system is analyzed. At the same time, the RCS controlsystem introduces the control dead zone. Through the selection of the dead zone, the RCS flow and theopen frequency of RCS are reduced.The RCS control exit when the control-ability of aerodynamic control surface satisfies therequirement of flight task, and only the aerodynamic control used. Because of the high angle of attackand Mach number when the RLV in the reentry flight, the aerodynamic characteristics of the RLV arecomplex and the lateral coupling is severity, which leads the problems such as the dutch roll instabilityand roll reverse. According to the analysis of the aerodynamic characters, a control strategy called“rudder controls roll control, aileron arguments the Dutch roll.” is put forward for the lateral control.The composite control is in the middle of reentry control. Through analysis and compare theaerodynamic control ability and the flight requirement, the switching time of composite control isresearched. There are RCS and aerodynamic actuator on composite control. In order to reduce the use ofRCS, The composite control law is mainly on aerodynamic control law，and RCS is taken as theauxiliary actuator. On this principle, the composite control law is designed. There is also the problem ofcomposite distribution. And this thesis introduce the strategy of control dead zone and control-weighted,which can reduce the RCS flow and ensure the control performance.Last, this thesis builds the RLV simulation flat roof, and the monte-carlo method is used tosimulation. The results show that the control strategy can ensure the attitude control performance andthe RCS flow in the reasonable range.