In leak monitoring of launch vehicles, detection of low concentrations of hydrogen and other fuels is important to avoid explosive conditions that could harm personnel and damage the vehicle. Dependable vehicle operation also depends on the timely and accurate measurement of these leaks. The fuels include hydrogen and hydrocarbons while simultaneous knowledge of oxygen is important to determine if there is an explosive condition. Using the sensing technologies elsewhere on this webpage, leak detection arrays which measure hydrogen, hydrocarbons, and oxygen in a single package are being developed in the Next Generation Launch Technology program. The goal of this work is a system with the surface area of a postage stamp which simultaneously measures both fuel and oxygen with power and telemetry. A prototype MEMS-based leak detection sensor system which integrates hydrogen, oxygen, and hydrocarbon sensors into a single package has been achieved. Measuring hydrogen/hydrocarbons (fuel) and oxygen can give an appraisal of whether there is an explosive condition in a given region. The accompanying “smart” sensor package contains all required analog and digital electronics, including CPU, memory, and communications devices. [Click here] for an enlarged view of the microsystem and packaging. This basic hardware approach is being matured for [Crew Launch Vehicle (SLI)]. Further system development is planned to produce a complete, stand-alone leak detection system that can be placed in a number of locations.