Study On The Terminal Guidance Law For Exo-Atomospheric Spacecraft Based On Strapdown Seeker

In response to the threat of ballistic missile, many countries such as the United States and Russia strengthen the study of the missile defense system. Especially, the United States have built up a multistatic and hierarchical missile defense system. As an important part of the missile defense system, the exo-atomospheric interceptor adopts high-precision terminal guidance laws to guarantee the interception precision.Terminal guidance laws adopted by the traditional exo-atomospheric spacecraft are dependent on the infrared seeker, and proportional navigation is always adopted. However, with the emergence of strapdown seeker, its advantages like low cost and light weight, make the strapdown guidance a hot research topic in the field of military. But the strapdown seeker can only measure relative angle of sight, can't directly access to the line of sight angular rate, so the proportional navigation and other traditional guidance laws cannot be applied. Therefore, this thesis focuses on the study of the terminal guidance of the exo-atomospheric spacecraft according to the characteristics of the strapdown seeker. The main research content includes the following several aspects:First of all, the definition of relevant coordinate systems and transformation relations are studied, and the dynamic models of the center of mass and around the center of mass are set up. At the same time, according to the principle of strapdown seeker, its measuring model is deduced. These models provide theoretical basis for follow-up studies on the terminal guidance and the attitude control system design.Because the traditional methods such as pursuit guidance law and proportional navigation are the design basis for a new strapdown guidance law, the classical guidance law is studied and analyzed. On this basis, take the characteristics that only the relative angle information can be measured by the strapdown seeker, into consideration, the strapdown correction pursuit guidance and strapdown proportional navigation, which are applicable to exo-atomospheric spacecraft, are deduced. Considering the nonlinear factors, the nonlinear strapdown guidance law is presented. Based on the specific layout scheme of orbit control engines, the PWPF modulation method is studied, finally the theory is studied by simulation.Based on strapdown seeker measurement information, the nonlinear filtering method is used to estimate the line of sight angular rate information, and by applying the angular rate to proportional navigation the terminal guidance of exo-atomospheric spacecraft can be realized. So, first, set up the mathematical model between angle of sight and line of sight angular rate, as the measurement equation of the filter; and describe the change of angular rate with the first-order markov model, as the state equation of the filter; then, based on the extended Kalman filter method, the line of sight angular rate can be estimated. Apply the estimated angular rate to proportional navigation, and conduct simulation research.Finally, the attitude control system of exo-atomospheric spacecraft is designed. Appling the attitude control system to the strapdown guidance law and the LOS angular rate estimation method respectively, the simulation of six degrees of freedom is conducted, and the precision of the guidance law and control method is estimated.