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 variety of hydrocarbons. It holds the potential of excellent high-frequency combustion stability characteristics, low injector production cost, and deep throttling capabilities similar to a pintle injector. Additionally, this injector offers the potential for excellent thermal compatibility and outstanding propellant atomization characteristics. The concept is well suited for both main chamber and preburner applications. This Phase I SBIR focuses on developing prototype mechanical designs and the supporting analysis necessary to justify fabrication and testing during a follow-on Phase II effort.