Active Nutation and Precession Control for Exoatmospheric Spinning Ballistic Missiles

Abstract

Spinning a ballistic missile is a common practice to stabilize the attitude of the vehicle; however, this requires the vehicle to be accurately balanced to avoid nutation and precession due to axis misalignment. While a missile is spinning, it is subject to nutation attitude behavior depending on the non-diagonal terms of the inertia matrix. Utilizing the onboard Attitude Control System (ACS), the nutation and precession energy can be dissipated to achieve accurate spinning motion. This may be desirable if the vehicle is carrying a sensor package that needs to be pointed accurately. This paper develops the equations of motion for a spinning ballistic missile utilizing the full inertia matrix with non-zero cross products of inertia (POI). The unbalanced condition that is represented by the non-zero cross POI is also evaluated in terms of axis misalignment between principal axis of rotation and geometrical body axis. We present an active nutation control scheme using the missile’s ACS to minimize the nutation and precession angles. A typical nutation control scheme can create an aberration of the precession angle and this interaction is examined with the goal of minimizing both.