The technical innovation proposed here is the application of an alternative hydrocarbon fuel densified propylene, in combination with liquid oxygen (LOX) that has the potential to enhance the performance of a proposed Nano / Micro Launch Vehicle (NMLV) enough such that a simple two-stage, pressure-fed configuration will be sufficient for orbital missions. Besides eliminating the third stage, the absence of turbopumps reduces hardware costs, improves overall system reliability and simplifies engine start-up. This project addresses Section 1.2.5 of the Technology Area 1 Roadmap as it raises the TRL of both a non-toxic alternative hydrocarbon fuel (propylene) and also propellant densification (subcooling propylene) to increase vehicle mass fraction performance. Programmatic innovation makes it possible to bring this propulsion technology to a TRL of 6 by the end of Phase II in the form of a 5K lbf-LOX/propylene first stage engine. This will be accomplished by leveraging an ongoing NMLV development program that has already produced a flight-proven LOX/ethanol 4.5K lbf-thrust engine that features a long-duration silica-phenolic ablative chamber.