Prediction of Delivered Specific Impulse of Solid Rocket Motor

Abstract

Prediction of delivered specific impulse ; a key factor of the internal ballistic features of solid propellant rocket motors; except knowledge of fundamental theories on rocket propulsion, requires also collection of certain technical data on some similar design solutions of real rocket motors. In this way a time shortening and decrease of development costs of a new rocket motor and a corresponding solid propellant grain are achieved. Selection of an optimal, but not only satisfactory design of the solid propellant grain, comprises application of logical order in the design process, estimation of structural requirements and internal ballistic performances, inclusion more accurate solid propellant performances, as well as calculation of solid propellant grain configuration and stress analyses of the rocket motor structure and solid propellant grain. A mathematical model which describes most physical and chemical phenomena taking place in the rocket motor, and which are crucial for ballistic and structural design of solid propellant rocket motors, is presented. The model calculates combustion chamber pressure, thrust and combustion gases flow rate through the nozzle during the burning time, based on all necessary input data for 2D solid propellant grains configurations. Losses in the combustion chamber and nozzle and their influence on performances of the nozzle and generated specific impulse are analyzed. A modular computer program for prediction the idealized internal ballistic performances of solid propellant rocket motors has been developed. • ISP2001 – Calculation the theoretical performances of solid propellants. • CHEM – Rapid Calculation of the internal ballistic properties. • Semi empirical relations for losses predictions – Calculation the losses in the combustion chamber and nozzle. • PFRED – Designing the solid propellant grain with following geometrical shapes: segmented core,C-slot,Moon burner,End burner. regression of burning surface for cylinder with internal burning surface, cylinder with internal-external burning surfaces, multiple cylinders with internal-external burning surfaces and star grain have also been discussed. Calculation of chamber pressure and thrust, propellant weight and thrust coefficient are done as functions of burning time. • AeroIsp –Calculation of Delivered specific impulse as per required inputs for comparison to the semi empirical calculations substracted from theoratical specific impulse. Particular modules are verified with similar program solutions as well as with experimental results obtained from standard ballistic rocket test motors and experimental rocket motors. Analysis of results has shown that the established model enables very good accuracy of prediction the double base solid propellant rocket motors features in cases where influence of combustion gases flow on burning rate is not significant.