Study On Three-dimensional Trajectory Optimization And Online Guidance For Combined-cycle Based Reusable Launch Vehicle

With the development of astronautical technology and more and more diversified and frequent space mission,the requirement for economy,safety,reliability,and carriage capacity has become unprecedentedly important to launch vehicles.Based on a kind of reusable launch vehicle that horizontally takes-off/lands with combined-cycle air-breathing propulsion(CRLV),this dissertation researches on a series of key technologies,which are mainly about: 1)modeling of the CRLV,including equations of motion,overall parameters design,and trajectory optimization;2)synergistic optimization of overall parameters and ascent trajectory;3)optimization of ascent three-dimensional(3D)trajectory in consideration of great deviation in launch time;4)online guidance in the glide phase under the effect of multiple uncertainties.These problems are detailed as follows.On the basis of analysis on reusable launch vehicles that take-off/land horizontally,the overall scheme of the CRLV is proposed in consideration of its characteristics.The scheme comprises the profile of flight,the overall configuration,overall parameters,and aerodynamic parameters.In addition,in view of the fact that the CRLV climbs and accelerates with the combined cycle-based propulsion in the ascent phase,the mathematical models of the air-breathing engine that has different working-modalities are proposed based on thermodynamic principles as well as the interaction between the propulsion performance and trajectory states.With the requirement of ascent trajectory optimization,representative parameters that have great effect on the propulsion,such as thrust parameters and modality switch parameters,are picked out and incorporated into the optimization problem.Finally,several important coordinate systems and the corresponding relations of transformation are represented to describe the motion of the CRLV;then the equations of motion of CRLV are given in a polar coordinate system.In order to settle the complicated nonlinear coupling among the thrust,flight states,and the performance index as well as multi-constraints on flight states and environment derived from the propulsion,a new angle-of-attack(AOA)profile is proposed to design the ascent trajectory.On this profile,the AOA and its angular rate can be analytically calculated.Therefore,the AOA constraints derived from different propulsion modalities can be satisfied in the predesign of the profile and thus are removed from the optimization models,making the optimal ascent traje-ctory easier to obtain.Then the original trajectory optimization problem is converted into a parameter optimization problem that has fifteen unknowns.Solving such an optimization problem,in which a large number of optimization parameters exist and both the physical significances and the numerical ranges of these optimization parameters are far different,is quite challenging.To settle this,an improved particle swarm optimization(PSO)method is proposed in this dissert ation.Based on analysis on the convergence of PSO,a dynamic weight and a turbulence operator are proposed to improve the searching capacity of PSO.In addition,a multiple swarm parallel-searching strategy and a dynamic population are proposed to solve the problem.One of the most outstanding characteristics of CRLV is the lateral maneuver capacity in the ascent phase.This kind of capacity affords CRLV the superiority in flexibility in comparison with traditional launch vehicles.Taking the restrictions on both observation of ground stations and illumination of Sun for payload into consideration,the mathematic models of the launch window are proposed to confirm the opportunity of launch.In addition,on the purpose of revising launch time,longitudinal and lateral trajectories are decoupled by respectively designing a longitudinal profile and a lateral maneuver strategy.The longitudinal part aims to shape the orbit,while the lateral motion aims to revise the orbital RAAN and inclination.Then the ascent 3D trajectory optimization problem is converted into a parameter searching problem with four variables.To quickly obtain the optimal ascent 3D trajectory and guarantee the accuracy of the solution,a hybrid optimization method is proposed based on PSO.Results of simulation demonstrate the capacity of CRLV in extension of launch window.The return phase is the key to the reusability of CRLV.The glide phase generally forms the majority of the return phase and is researched in this dissertation.To be flexible to different scenarios and be resistant to various uncertainties and disturbances,an online guidance law is proposed in the glide phase.First,analytical equations of motion are deduced in the glide phase based on an altitude profile;then path constraints and the performance index are also analytically represented without numerical integration of the dynamics.In addition,a new concept of virtual target is proposed to design the lateral motion.Based on the analytical dynamics,the virtual target is analytically confirmed to revise the cross-range in order to control the dissipation in velocity.Different from other online guidance laws,the guidance law proposed in this dissertation relies on neither prediction of terminal states nor pre-design of AOA and bank angle.As a consequence,the proposed law requires less on-board computational cost.More outstandingly,the proposed law doesn't require a trajectory tracking controller or a large amount of off-line calculation.The proposed law can easily meet the terminal altitude,position,and flight path angle and can guarantee the optimality of the trajtectory.