Designed Experiment Results for Constituent Effects on NBR Based Solid Rocket Motor Insulation Performance

Solid rocket motor internal insulations are facing serious issues with obsolescence of constituents and the need for improved performance. The design community is at a unique point with a large number of rocket motors requiring reformulation of insulation or design upgrades at the same time. Unfortunately, performance data related to component choice is not generally available to aid development. A study of insulation component materials, conducted at Marshall Space Flight Center over the last four years, used designed experiments to understand the contribution of each material to the performance of a formulation. This report covers work with Nitrile Butadiene Rubber (NBR) based formulations. In-house compounding provided modified formulations allowing for isolation of both individual and synergistic effects. All formulas were tested for mechanical, thermal and producibility properties to evaluate performance.

This presentation will describe the methodology for, and results from, identifying the individual and combined effects of components used in our formulations. Specific properties investigated include, rheology, cure characteristics, density, tensile strength, along with erosion/ablation under various heat loads and flame chemistries. Scale up of several formulas from lab to production size batches was accomplished. We will discuss troubleshooting problems of scale and the new set of designed experiments with Ethylene Propylene Diene Monomer (EPDM) based formulations.