Ballistic characteristics of bi-plateau solid propellants

The burning rate of solid propellants that are used for rocket propulsion usually increases with increasing pressure. Bi-plateau propellants exhibit two inflections in burning rate curve as pressure is increased. This experimental research is aimed at understanding the unusual combustion mechanisms that control the bi-plateau burning rate. The burning rate and the burning surfaces characteristics of four ammonium perchlorate/hydroxylterminated polybutadyene propellants were investigated to draw conclusions about the combustion phenomena. An ultrasonic pulses-echo system measured the burning rates at pressures from 100 to 5000 psi and initial propellant temperatures of 20{dollar}spcirc{dollar}C and 60{dollar}spcirc{dollar}C. Scanning electron microscopy and electron dispersion spectroscopy diagnostics characterized extinguished propellant surfaces. The results showed evidence of a binder melt layer that correlated with the propellant burning rate suppression. The extent of the melt layer showed strong correlation with the level of ballistic additive and the combustion pressures. Compared to the nominal propellant without additive at 1500 psi, the burning rate was augmented by 75% with the additive; by 375% with the additive and a lower coarse/fine ratio of oxidizer; and by 275% with additive and a different binder curative.