Development of a solid rocket motor design tool and application in spin-up motors

Kurzfassung

The aim of this work is to design a system of spin-up motors (SUMs) for a sounding rocket as part of a strategy chosen by the German Aerospace Center (DLR) to reduce dispersion of their vehicles. SUMs are small solid rocket motors (SRMs) mounted on the boost adapter between two stages to provide a roll motion to the sounding rocket by applying a controlled torque around its longitudinal axis. A design tool is created in Python with the aim to compute the geometry and the performance of a SUM unit and of the spin-up system. The chosen propellant formulation is composed by ammonium perchlorate (AP) as oxidizer, hydroxyl terminated polibutadiene (HTPB) as binder and aluminum powder as fuel. Through a Monte Carlo simulation, the impact of the uncertainties of the empirical coefficients a and n of the Vieille/Saint-Roberts law on the behaviour of performance variables is assessed. An optimization study is performed to obtain the geometrical properties of the motor. The results of the design tool match the ones of the validation cases and meet the requirements imposed by DLRs Mobile Rocket Base (MORABA). However, minor discrepancies due to the simplifications present in the tool emerge from the comparison of the ideal model to experimental data in the transient phases of ignition and tail-off. The tool is also used with two green propellants based on ammonium nitrate (AN) and ammonium dinitramide (ADN) as oxidizers to check the feasibility of these compounds to replace AP. A preliminary design and calculation of the dimensions of the structural components of a SUM unit is accomplished and finally a model on the computer aided design (CAD) software CATIA V5 is generated, as a first step towards the future construction of a spin-up system.