Influence of Nozzle Radiation on Solid Rocket Motors Tail-Off Thrust

The aims of this work are focused on the evaluation of the solid rocket motor residual thrust and on the impact of thermal protection properties on such thrust. Indeed, tail-off thrust of solid rocket motors upper stages can last tens of seconds after motor burn-out, affecting the performance of the rocket on sequencing of stage separation. Hence, the knowledge of the tail-off thrust profile is fundamental to properly design wait times and separation systems total impulse of a multi-stage launcher. Therefore, although it has been shown in the past that pyrolysis gases responsible for the residual thrust are mostly produced by alumina molten slag deposited next to the nozzle nose within the combustion chamber, this study is aimed at suggesting that the portion of the nozzle within the combustion chamber can act as the main radiative heat source leading to thermal protection material ablation, and then to residual thrust production. An analysis of an actual solid rocket motor has been performed in the direction of proving the effectiveness of the overall procedure. Then a sensitivity analysis with respect to the quantities identifying the thermal protection properties has been computed in order to evaluate the impact of such variations on the residual thrust profile.