Experimental estimation of the amount of residual slag remaining inside orbital insertion stage solid rocket motor

Several technical reports have raised concerns about the ejection of a significant amount of residual slag from a solid rocket motor (SRM) at the end of combustion, which contributes to the growing space debris problem. The E-31 static firing test has demonstrated a remarkable reduction in residual slag by using advanced propellant with improved aluminum combustion efficiency. E-31 will be adopted for orbital insertion stage for Japan’s upcoming flagship solid propellant launcher known as Epsilon S. Experimental findings have validated that in SRMs that selects a propellant that can achieve such high aluminum combustion efficiency, the acceleration sensitivity to aluminum/alumina particles flying inside the combustion chamber drops to a level that cannot be distinguished from the range of variations. Consequently, contrary to the past technical reports, the estimated quantity of residual slag inside the SRM during flight is considered to have a minimal adverse impact on the orbital environment.