Trajectory Modeling of Grad Rocket with Low-cost Terminal Guidance Upgrade Coupled to Range Increase through Step-like Thrust-curves

The paper shows a full 6 DOF modeling for a GRAD rocket in Earth’s non-inertial frame. For numerical purposes the modeling is limited to flat Earth approximation. The full motion equations are shown and all terms are explained together with the aerodynamics parameters for the entire flight envelope. Non-linear interpolation is used for aerodynamic coefficients and their derivatives. We present the typical dispersion factors due to rocket production inaccuracies, launch condition variability and atmospheric factors and their relative influence on a guidance implementation package. Next we present a 6 DOF modeling with various step-like thrust-curves while maintain the same total impulse delivered by the original motor. The influence of the step size on the range of the GRAD rocket is investigated together with the dispersion influence. We show that significant range increase can be obtained while using the same propulsion unit with a step-like thrust-curve modification. We also investigate the influence of the step-like thrust-curve on dispersion of such a rocket and the technological possibilities to implement our solution. In the last part of the paper we present a terminal guidance concept 122 mm rockets. A preliminary requirement for IMU units to be used for terminal guidance is shown together with the general guidance algorithm for several trajectories. Performance expectations are shown through the analysis of the IMU units performance as well as flight dynamics of the 122 mm rockets.