The method of calculation of non-stationary intra chamber processes in the rocket solid propellant engines based on two approaches is considered. The first approach assumes consideration of products of combustion as mechanical mix, other approach—as the mix which is in chemical equilibrium. For an increase of reliability of the solution of intra ballistic tasks in which the assumption of chemical equilibrium of products of combustion is used, computing algorithms of calculation of structure of products of combustion are changed. In algorithm of the decision system of the nonlinear equations of chemical equilibrium when determining iterative amendments instead of a method of Gauss, the orthogonal QR-method is used. Besides, possibility of application in a task about structure of products of combustion of genetic algorithms is considered.
It is shown that in the tasks connected with forecasting of non-stationary intra ballistic characteristics in rocket solid propellant engines, application of models of mechanical mix and chemically equilibrium structure of products 32of combustion leads to qualitatively and quantitatively coinciding results. The maximum difference of parameters does not exceed 5–10%. In tasks about an exit to the mode of mid-flight rocket engines of solid propellant with high-temperature products of combustion difference in results is more essential, and can reach 20% and more.