Parameterized Modelling of Stage Separation of Launch Vehicles with Modelica

In order to improve launching capability and performance, almost all launch vehicles in active service contain two or more stages. During the launch process, it is of vital importance to gradually reduce the weight of the launch vehicles by separating and jettisoning spent stages which have burned out its propellant. The separation process between the stages plays a crucial role in guaranteeing the safety of the launch vehicles and ensuring a successful launch. Consequently, it is essential for launch vehicle designers to well understand the stage-separation dynamics which is quite complex and affected by many system parameters. To evaluate the impact of the system parameters on the stage-separation mission, a parameterized model is established for a two-stage launch vehicle using the Modelica language along with the software MWorks. As representative parameters to evaluate, the mass-center positions of the first and second stages, both the positions and directions of the active forces, the residual thrusts, the positive thrusts, the retro thrusts, the masses and moments of inertia of the two stages, are all taken into account for dynamic analysis. The parameterized Modelica model is built by exploiting the idea of the equation-based causal modelling to numerically simulate the stage-separation process and evaluate the influence of the parameters on the system responses. Simulation results based on representative case studies indicate that the separation process of the first and second stages can be well described by the Modelica model. Besides, a comparison with Adams software demonstrates the results of the Modelica model agree well with those obtained using Adams.