This paper is a continuation of [1] and [2] in which the methods for calculation of the inside ballistic characteristic (IBC) of rocket engine taking into account the non-stationarity of speed combustion for hard fuel are considered. We describe and fundament the physico-mathematical model of non-stationary combustion of hard propellants. We obtain the analytical dependence of the speed of combustion from pressure which will be used when developing methods for calculating the IBC of rocket engines operating in non-stationary regime.

solid propellants, burning speed, physico-mathematical model, condensed phase, rocket engine, inside ballistic characteristics, gas dynamic, chemical reaction.