Development of Mid‐Way Testing Contingencies for Solid Rocket Motor Processing

Abstract

AbstractPolyurethane based composite solid propellant (CSP) having aluminium as fuel and ammonium perchlorate (AP) as oxidizer is used in present day solid rocket motors (SRMs). Mechanical and burn rate properties of CSP are wholly dependent on the composition and packing fraction of bimodal AP. Any process deviation or anomalous behavior of propellant slurry at the end of pre/final mixing will result in unacceptable mechanical and ballistic properties leading to rejection of these mixes. Hence, it becomes essential to investigate for possible causes of anomalous behavior such as incorrect content and Coarse/Fine AP ratio (CAP/FAP), contamination with foreign materials, etc. Though suitable test procedures are already available for homogeneity/composition analysis and in vogue, there is no regular test procedures in case of interchange of raw materials of different formulations, to check for contamination of pre‐mixes and to verify AP content in the mixes after mixing the curing agent. Herein, simple contingency procedures have been developed to estimate CAP/FAP in the pre‐mix and AP content in pre/finalmix slurries. The CAP (before its use in premix and after CAP/FAP estimation) was examined using a particle size and shape analyzer and an optical microscope. Contamination checks were also carried out on the samples of premixes usingFT‐IR and DSC. In addition, propellant samples cured under standard conditions were checked for possible deviations with respect to expected mechanical, interfacial, physical and ballistic properties. Conclusions drawn from the investigation can be used to clear the pre/final mix batches for further processing.It is to be noted that these cost‐saving contingency procedures will hereafter form part of analytical testing routines during the processing of solid propellant segments.