Trace species measurement on unmanned atmospheric research craft suitable for interplanetary travel is a demanding application for optical sensing techniques. Yet optical techniques offer many advantages including high-precision, fast response, and strong species selectivity. Balloonsonde, kite, unmanned aerial vehicle (UAV), or glider deployment demands that optical sensors meet stringent size, weight and power requirements. Vista Photonics proposes to construct rugged, compact, low-power optical sensor prototypes capable of selectively determining isotopic-resolved hydrocarbons at Titan-relevant concentrations. The sensor will be demonstrated in Phase II by airborne measurement of CO2 and water vapor on Earth. The enabling technology for meeting stringent NASA mission requirements is a new rugged, compact, and lightweight optical path length enhancement cell that recovers the established sensitivity of high-performance optical absorption detection techniques on a platform with no moving parts. The proposed spectrometer will be capable of detecting multiple species with little additional weight or power penalties.