Engineers at the Raytheon Co. Missile Systems segment in Tucson, Ariz., are upgrading the AIM-9X Sidewinder air-to-air missile to extend the weapon's range and address obsolescence issues. The AIM-9X is a relatively short-range, infrared, heat-seeking missile that equips most jet fighters, fighter-bombers, and other offensive combat aircraft, and is used to shoot down enemy aircraft close by. The AIM-9X works by homing in on an enemy aircraft's hot engine exhaust. The U.S. Naval Air Systems Command at Patuxent River Naval Air Station, Md., will award a sole-source contract to Raytheon to perform missile upgrades on the AIM-9X.