Mesa Photonics, in collaboration with the College of Optics and Photonics (CREOL) at the University of Central Florida, proposes to develop a spacesuit gas sensor based upon its Enhanced Raman Gas Sensor (ERGS) technology. The goal a moisture tolerant, drop-in replacement for the current CO2 sensor. Preliminary work achieved detection sensitivities for CO2, CH4, O2, and N2 of 1000, 300, 1000 and 1500 ppm, respectively. ERGS reports gas partial pressures directly and can operate tolerate pure oxygen. The response to all gases is linear from 0 to 100%. No consumable supplies are required and ERGS is self-calibrating. The ERGS technique is compact and robust and has low electrical power requirements. Its detection performance and physical characteristics make it well suited as a flight-capable system spacesuit gas sensor. ERGS detects gases by recording the Raman spectrum of a gas mixture flowing through a short length (~50 cm) of hollow-core photonic crystal fiber (HC-PCF). Sensitivity is more than 800 times better than conventional Raman spectroscopy since the gas and light confinement increases the Raman interaction length. This proposed STTR project is designed to bring ERGS technology from its current TRL 6 to TRL 8 or 9 at the end of Phase II. Phase I work by Mesa Photonics includes improving ERGS optical design, verifying gas measurement accuracy over a wide range of mixture compositions and total pressures, and testing response to condensing moisture. The CREOL team will design custom HC-PCF that is better matched to ERGS wavelength requirements and, possibly, have a larger diameter hollow core. In Phase II, Mesa will build, test, and deliver a prototype gas that will include custom fiber produced at CREOL based on the hollow-core designs from Phase I. The Phase II prototype will have a similar footprint to the existing Extravehicular Mobility Unit (EMU) gas sensor.