Compact model based on a lumped parameter approach for the prediction of solid propellant micro-rocket performance

The development of a lumped parameter model is described for the performances prediction of a solid propellant micro-scale rocket. A micro-scale rocket consists of a combustion chamber containing the propellant, a converging and a diverging part to accelerate the gas generated by the propellant combustion. The input modelling parameters are the geometrical features of the rockets, the propellant characteristics and the ambient conditions. The output results are the temperature, the pressure, the volumic mass of the gas in the combustion chamber and the resulting thrust as a function of time. To illustrate the computational results, the performances of one micro-rocket investigated at LAAS for micro-propulsion application have been evaluated. The micro-rocket has a throat diameter of 108 mum, a chamber diameter of 850 pm, a chamber length of 1500 mm, a convergent length of 500 mum and a diverging length of 500 mum. The computational results give a chamber pressure of similar to5 bar and a thrust value of similar to3 mN at steady state. To illustrate the capabilities of the model, Section 3.3 discussed two points: The influence of the heat loss on the thrust force; The influence of the diverging part design on the thrust force. Results show that the divergent length has an interest and must be optimised when the external pressure is closed to vacuum, whereas the diverging part length has no effect on the thrust results when the external pressure is atmospheric. (C) 2002 Elsevier Science B.V. All rights reserved.