Flexible rockets exhibit coupled structural and flight-dynamics behavior that can degrade stability and control if not properly modeled. This article reviews modeling approaches for structural flexibility, fluid–structure interaction, actuator/servo dynamics, and sensor placement; derives equations of motion for a flexible multibody launch vehicle; describes linearization and modal reduction techniques; details typical simulation workflows; and presents example results illustrating stability margins, bending modes, and guidance–control interactions. Recommendations for validation and guidance for software implementation are provided.
The accelerometer at station ( x_sens ) reads: [ a_meas = a_rigid + \sum_i=1^N \phi_i(x_sens) \ddot\eta_i ] This corrected acceleration is fed to the guidance, navigation, and control (GNC) system. dynamics and simulation of flexible rockets pdf
When the engine gimbals, the thrust vector rotates, but the thrust frame is attached to a flexible nozzle. The local angle of the engine relative to the vehicle centerline must include the elastic slope at the gimbal point. Time update loop (pseudo): initialize state q, qdot,
initialize state q, qdot, t=0
while t < t_final:
update mass/inertia from mass_properties(t)
compute aerodynamic forces f_aero = aero(t, state)
compute slosh forces f_slosh = slosh(t, state)
compute control inputs u = control(t, state)
assemble M, C, K, f_total
solve M * q̈ = -C*q̇ - K*q - f_total
integrate state using implicit solver (e.g., Newmark-beta or implicit Runge-Kutta)
t += dt