Boundary conditions for persistent roll resonance on re-entry vehicles.
Persistent roll resonance on re-entry vehicles can cause catastrophic increases in vehicle angle of attack. This paper analyzes the problem through the physical interpretation of boundary conditions on the roll equation for the occurrence of persistent roll resonance. The result is a rather simple equation that can be used to predict whether or not a particular transient resonance case will become a persistent resonance situation. The boundary equation also implies some of the qualitative effects of various vehicle and trajectory parameters on the probability of occurrence of persistent roll resonance and indicates that a smaller reentry vehicle with low static stability and large ballistic coefficient, undergoing a shallow reentry flight at low altitude, is more likely to experience persistent roll resonance. This, of course, is strongly influenced by the type and magnitude of vehicle asymmetries, which may result from manufacturing tolerances or in-flight changes in heat-shield contour. Linear aerodynamic coefficients and small angles of attack are assummed. Inertial moments due to products of inertia and moments due to the combination of drag and center-of-gravity asymmetry are neglected.