3-D grain burnback analysis of solid propellant rocket motors: Part 1 – ballistic motor tests

The performance prediction of solid rocket motors is an important phase during the design process and it can be achieved easily if the burnback steps of the solid propellant are known. A method was developed by the authors to analyze and determine the grain burnback of solid propellants in rocket motors. To verify the predictions from the model, subscale ballistic rocket motor tests were performed in this study. An existing rocket motor was modified in terms of insulation, ignition delay, and sealing. Composite propellants containing Aluminum/HTPB/AP were cast into 3-D finocyl grains. Five different finocyl geometries were selected for static firings to obtain different boost and sustain thrust profiles. For all the grains to be tested, finite element stress analyzes were conducted before they were manufactured and fired. Also, X-ray photography of each propellant grain was taken before the test to make sure that the grains were free of cracks and air bubbles. Recorded pressure-time traces from the tests showed that, depending on the requirements of the mission, different boost and sustain profiles could be achieved by changing the geometrical parameters of the finocyl grain. This study supplied a significant knowledge on static firings of rocket motors with complex 3-D grain geometries.