GALCIT Colloquium

High-performance reusable rocket engines are essential to proposed low-cost heavy lift launch vehicles that will enable next generation launch economics. Current development efforts are focused on oxidizer-rich and full-flow staged combustion engines, which offer advantages in fuel efficiency. However, these engines subject materials to extreme operating conditions, involving cryogenic temperatures, extreme temperature swings, high heat fluxes, and ultra-high-pressure oxygen. These conditions give rise to a host of catastrophic failure modes, from oxidation-assisted fatigue to strain-ratcheting induced rupture to metal fires. The success of these new reusable propulsion systems thus depends on advances in the processing, design, and application of robust materials specifically tailored to withstand such extreme environments. In this talk, I will share insights from our investigation into the underlying mechanisms of frictional ignition, one of the failure modes of greatest concern in oxidizer-rich turbopumps and the root cause of several recent launch failures (Sea Launch's NSS-8 and Orbital's Orb-3). We have assessed the role of oxide tribolayer breakdown in frictional ignition using high-speed sliding experiments, postmortem characterization of recovered specimens, continuum mechanics modeling of sliding contacts, and thermochemical calculations of the structure and stability of oxide tribolayers. Our results reveal why certain superalloys are intrinsically ignition-resistant, suggesting approaches to material design and selection for high-pressure oxygen environments.