The projectile GRAM SAASM for ERGM and Excalibur

The Army and the Navy are each developing a GPS guided projectile. The Navy is developing the Extended Range Guided Munition (ERGM), a projectile for a 5" deck-gun. The Army is developing the XM982, now renamed the Excalibur, a projectile for 155-mm platforms such as Crusader and Palladin. These projectiles are to be guided in-flight by a GPS aligned inertial measurement unit (IMU). The distinction between a “guided projectile” and other guided munitions is that a projectile receives most or all of its motive force from a powder charge in a gun barrel. This places the first of a series of severe requirements on the projectile GPS receiver. It must be gun-hardened to survive the shock of gunfire. The range of a projectile, compared to a motor-driven munition, is limited. This means short flight times and requires very fast initial acquisition. High jamming conditions are expected since these are tactical weapons used in a battlefield environment. Collectively, the projectile GPS receiver must have very fast direct-Y acquisition capability that can operate in a high jamming environment. It must also be tightly coupled with the guidance IMU to enhance jammer tolerance during track. The projectile GPS Receiver Application Module (GRAM) must be equipped with a Selective Availability/Anti-Spoof Module (SAASM) for battlefield security. It must draw minimal power to conserve limited on-board battery capacity. Finally and foremost, these guided projectiles must be manufactured in high quantities. The recurring cost of the GPS guidance is a major consideration. This paper describes IEC\´s latest GPS receiver offering that is designed specifically to satisfy these projectile application requirements. The direct-Y acquisition issues, including acquisition correlator and reference oscillator considerations are discussed. The jammer tolerance features and how they interact with acquisition and track are described. The SAASM design is described and the complete GRAM SAASM is described and illustrated