Modeling, Design And Analysis Of Large Strap-on Launch Vehicle's Attitude Control System

Attitude control is a key technology for the development of large strap-on launch vehicle. With the background of Chinese new strap-on launch vehicle, this dissertation studies the attitude control problem of large strap-on launch vehicle from four aspects including modeling of attitude dynamics, controller design, the influence of the complex three dimensional elastic vibration, and engine's vibration on the attitude control system.The main contens are summarized as follows:1. The characteristics and disadvantages of the attitude dynamic model of traditional strap-on launch vehicle are summarized and analyzed. Based on the given particular attiude dynamic model and the usage method of mode data, its characteristics and the reasons of applicability for our traditional strap-on launch vehicles are summarized and analyzed; the limitation of the model is also analyzed.2. A general attitude dynamic model of strap-on launch vehicle is established. 1) Taking into account a strap-on launch vehicle with arbitrary amounts of boosters, propellant boxes and engines, based on the dynamics of flexible multibody system, the nonlinear dynamic model is derived by Lagrange's equations in real coordinates and quasi coordinates. After introducing the proper predigestion and linearization, the attitude dynamic model in the form of small windage is obtained. 2) The appropriate model for a new strap-on launch vehicle is obtained by using the attitude dynamic model in common currency and its correctness is validated. 3) Based on the new model, the relations among rigid body movement, liquid sloshing, elastic vibration and engine vibration are analyzed particularly. The differences of the new model and traditional model are discussed.3. A new design method of strap-on launch vehicle's attitude controller based on Inverse Nyquist Array method is proposed. 1) The degree of coupling among three channels is analyzed by employing the theory of diagonal dominance. 2) Attitude controller is designed by Inverse Nyquist Array method, and the validity is validated by variable parameter time domain simulation. 3) Based on the analytical results of the three channel's coupling characteristics, simplified attitude dynamic model which is fit for single channel design in frequency domain are given, and their rationality is analyzed.4 The influence of complex three dimensional elastic vibration on attitude control system is studied. Based on the new model founded in this dissertation ,four new problems which are not considered in traditional analysis are studied following: 1)The influence of three dimensional modes with booster's obvious local deformation on the control system. 2) The influence of longitudinal components of strap-on launch vehicle's three dimensional modes on attitude control system. 3) The influence of over loading on both attitude motion and the body's vibration. 4) The influence of inertial coupling between rigid body motion and rocket's vibration on attitude control system;5. The influence of engine vibration on strap-on launch vehicle's attitude control system is studied. 1) Two characteristics of engine vibration equations are analyzed, the influence of engine vibration on design method of controller is studied and the model is simplified. 2) The influence of engine vibration on attitude control system ,in particular, the influence of engine vibration on the stability of rocket's elastic modes is studied. The resonance mechanism between engine vibration and rocket's elastic modes is analyzed based on simplified model. 3)The computation of resonance frequency boundary which causes the instability of the system is studied, the compute method is given, as an example, the resonance frequency boundary of a new strap-on launch vehicle is computed. The time domain simulation validates the correctness of the results. The influence of engine vibration damping on resonance frequency is analyzed.This research expands the theory of launch vehicle's attitude dynamic modeling and the theory of controller design. The influence of strap-on launch vehicle's complex three dimensional elastic vibration and engine vibration on attitude control system is studied systemically. The attiude dynamic model, the analytical and simulation results obtained in this dissertation are valuable for our country's new strap-on launch vehicle's design.