USC Rocket Propulsion Laboratory: Experiences Modeling a Composite Combustion Chamber

The University of Southern California Rocket Propulsion Laboratory is developing a single stage sounding rocket capable of delivering a small electronics payload past the Karman line at 100 km altitude. In order to launch the rocket, the FAA requires extensive ight quali cation testing and analysis of the vehicle. This development and quali cation process includes a full scale static ring of the solid fuel booster to verify propulsion performance and design integrity. The single stage solid motor design incorporates an entirely carbon composite combustion chamber. This unique design is necessary to meet weight requirements on the rocket, but introduces complexities in the structural analysis. The combustion chamber structure is a very long carbon composite tube, the ends of which are sealed with aluminum pressure bulkheads retained with steel dowel pins. Though successfully demonstrated in subscale static and ight testing, this motor case design experienced catastrophic failures during consecutive static rings of ight-scale hardware. Post ight accident investigation was performed in order to identify the root cause failure of these static rings. A high delity model of the thrust chamber accounting for the continuously varying directional properties was built using the Abaqus Uni ed Finite Element Analysis (FEA). The cause of the failure of the rst live ring was determined to be the direct result of loads applied by the thrust stand retention methods. The second livering failed as a result of a buckling failure of the thrust stand. The numerical simulation exonerated the ight motor case design and provided insight into how to x the thrust stand for future testing. Additionally, it a orded the student team the rationale to move forward with the development of ight hardware and the seeking of ight opportunities despite testing anomalies.