Effects on roll rate of mass and aerodynamic asymmetries for ballistic re-entry bodies

"Symmetrical" ballistic-type re-entry bodies have been observed to exhibit erratic roll behavior during flight. This unpredicted behavior can have adverse effects on performance by producing excessive loads and dispersion. To explain the observed phenomena, roll characteristics produced by several types of mass and aerodynamic asymmetries were determined by numerical solution of the equations of motion and by a simplified analytical solution. The asymmetries considered included lateral displacement of the center of gravity and center of pressure, inclination of the principal longitudinal axis to the body geometrical center line, unequal pitch and yaw moment of inertia about the principal axes, and asymmetric aerodynamic moments. All types of asymmetries, except for the inclination of the principal axis, produced significant roll torque, and various combinations of these asymmetries produced roll-rate histories similar to those observed on flight records.