Detection of Hypergolic Fuels with a Chemicapacitive Sensor Array S. T. Hobson, S. Cemavolic, S. V. Patel, M. L. Warburton, and T. E. Mlsna Seacoast Science Inc., Carlsbad, California 92011, USA Accurate and reliable detection of hypergolic fuels is a vital component to the Kinetic Energy Interceptor (KEI) module of the U. S. Missile Defense Agency. Seacoast Science has developed a sensor that uses micromachined capacitors to measure the dielectric constant of a group of selectively absorbing materials. The interaction between target analyte and polymer modifies the dielectric properties (capacitance) of the material. Using an array of commercially available polymers, functionalized polysiloxanes and polycarbosilanes of varying architecture (starburst, hyperbranched, and dendritic) both substituted and unsubstituted hydrazines (hydrazine, monomethyl hydrazine, and unsymmetrical dimethylhydrazine) and nitrogen dioxide (nitrogen tetroxide mimic) were detected in the in the presence of water vapor or hydrocarbons as interferrents. Introduction There is a growing threat of foreign enemy states and terrorist organizations acquiring ballistic missile technology to use or threaten to use against the United States or our allies. Because of the instability of certain rogue nations and terrorist agents, the threat of massive retaliation may not be a sufficient deterrent (1). Part of the MDA’s proposed protection scheme is the Kinetic Energy Interceptor (KEI) to be used in the Boost Phase Defense. For the KEI system, the ideal missile design uses a liquid fuel initiator (monomethyl hydrazine (MMH) – fuel; nitrogen tetroxide – oxidizer). The overarching goal of this research was to satisfy the concerns of the current policy of the United States Navy (USN) that prohibits these chemicals on USN vessels. A detection system that addresses the concerns of the USN both from the possible explosion danger and the toxic adverse effects from MMH would assist in this process. A chemical sensor suite based on microelectromechanical capacitor technology that allows for alarm detection of high levels (LEL) of hypergolic compounds within the canister and missile nose and a fixed sensor array that will detect MMH and NO 2 at toxic (PEL) levels might enable MDA to eventually field the KEI on USN platforms. MEMS-based Chemicapacitve Sensor Array The core technology detailed herein is a sensor array or an “electronic nose.” This term can encompass many different types of sensor technologies (2) with a common goal, namely the mimicry of mammalian olfaction (3). The receptors in the nasal cavities of mammals do not detect individual chemicals selectively, but use many, perhaps thousands of types, of partially selective receptors, which absorb the chemicals being inhaled (4, 5). These receptors may respond strongly, weakly, or not at all, resulting in patterns, which the brain learns to identify as a specific odor. Many chemicals will make these receptors fire; the key is that the relative intensities are different for different odors.