Modeling And Attitude Control For Strap-On Launch Vehicle With POGO Vibration

The attitude stability is important issue to launch mission, which not only reflects the design level of launch vehicle but determines a country’s ability to enter space. The POGO vibration will happen in liquid-fueled rocket is taken for coupling effect of propulsion system and its longitudinal vibration system, which might affects the stability of attitude motion. However, there is a crucial problem for the new Chinese strap-on launch vehicle should face:cascade launch vehicle with one-dimensional beam structure is an inaccu-rate approximate model and not for modelling the strap-on launch vehicle. To overcome such drawbacks, this dissertation concentrates on dynamics modelling method of multi-body system for strap-on launch vehicle, frequency-selective and structure-preserving model reduction algorithm for large-scale dynamical systems, hybrid system description for multibody system of strap-on launch vehicle with continuous process and discrete pro-cess POGO vibration, and attitude control strategy with steady-state tracking error bound. The major research contents and results of this dissertation are shown as follows:The unstable POGO vibration of new Chinese launch vehicle resulted from cou-pling effects among rigid motion, elastic vibration, fuel sloshing and engine pulsation, which greatly influence on attitude control system. The structure-propulsion-POGO vi-bration coupling loop of launch vehicle is set up through the multibody system modeling method which is determined by rigid body segment, imaginary hinge, effects of internal and external force, and three-dimensional topology structure. While the small deviation attitude dynamics model of launch vehicle multibody system is established, and its cor-rectness have been further confirmed by using engineering software of virtual prototyping technology. Finally, by comparing with concentrated mass dynamic model of launch ve-hicle, numerical simulations are done to illustrate the effectiveness of multibody system modeling method.A model reduction algorithm for large-scale dynamical systems of strap-on launch vehicle have to be introduced for solving unmanageably large demands on computational resources. The characteristics of two type of reduction algorithms which singular value decomposition and Krylov subspace theory are presented comprehensively. Furthermore, an iterative SVD-Krylov model reduction algorithm is proposed which not only ensure stability-preserving for the reduction model, but is easy to realize and helpful for obtain- ing small error norm, thus solving the problem of traditional reduction methods destroy the dynamical properties of second-order system in vibration equations. By constructing block matrix of controllability and observability Gramians, the reduction model has the ability to maintain second-order structure and closely approximates the original system in the specified frequency range. Finally, by completing program turning mission, numer-ical simulations are done to illustrate the effectiveness of the proposed model reduction algorithm.Description method of hybrid system is used in researching hybrid characteristics of the structure-propulsion-POGO vibration coupling loop of the launch vehicle. For the attitude stability analysis of launch vehicle which take into account POGO vibration with continuous process and discrete process, description method of hybrid system can reflects impulse change of state better. A type of input-state stability (ISS) for impulsive hy-brid systems is developed, and its ISS Lyapunov function is proposed which of impulsive sequences satisfying the fixed dewell-time condition. When the information of POGO vibration with time delay has a characteristic of stochastic sequence, a stochastic delayed impulsive system of neutral-type is proposed. Furthermore, by constructing the Lyapunov-Krasovskii function and Ito formula for the impulsive hybrid system, the sufficient con-ditions for asymptotically stability of the system are established. Finally,the numerical simulations of attitude stabilization illustrate the effectiveness of the proposed sufficient conditions.For high-precision requirement of attitude keeping, a Slotine form of integral sliding-mode control is designed based on boundary layer method. Furthermore, unlike most of the existing approach, an appropriate saturation function to suppress chattering is designed and achieved acceptable steady-state tracking error without repetition simulation test. For the attitude control problem relative POGO vibration with Brovnian jumping stochastic sequence and neutral-type time-delay state, a finite time arrival sliding mode control strat-egy is designed based on the sufficient condition for asymptotically stochastic stability. The controller can realizes fast convergence of state to desired attitude error bound while being robust against unstable POGO vibration. Finally, the numerical simulations illus-trate that the method can suppress POGO vibration and keep high pointing precision.