Sierra Engineering Inc. (Sierra) believes that the subject triaxial liquid propellant swirl injector has the potential to meet many of NASA's Earth-to-Orbit (ETO) propulsion systems goals. The triaxial swirl injector is ideally suited to a wide range of liquid oxidizers and fuels, including hydrogen and a wide range of hydrocarbons. It holds the potential of excellent high-frequency combustion stability characteristics and low injector production cost, similar to a pintle injector. Additionally, the triaxial swirl injector offers the potential for excellent injector and combustion chamber thermal compatibility and outstanding propellant atomization characteristics, both at levels far superior to a pintle injector. The triaxial injector concept is well suited to both main injector and preburner applications. The Phase I SBIR effort focused on understanding the influence design variables have on injector performance. We developed the mechanical design concept for a prototype injector. The proposed Phase II effort will complete the detailed design and analysis of the prototype injector. The test hardware will be fabricated and tested with several propellants. A preliminary design will be developed for a large-scale combustor.