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This paper illustrates how risk for the Navy Lightweight Exo-Atmospheric Projectile (LEAP) Technology Demonstration program was reduced using hardware-in-the-loop (HWIL) testing of the GPS/INS function in JHU/APL's Navigation and Guidance System Integration Laboratory (NAVSIL) facility. Under LEAP, a new STANDARD Missile based interceptor and a shipboard weapon system was built to demonstrate the potential of integrating the required technologies to defend against tactical ballistic missiles in outerspace (prior to atmospheric reentry). The LEAP system used an integrated GPS/INS package to provide accurate knowledge of interceptor attitude as well as position and velocity, which were critical to pointing the Kinetic Kill Vehicle at the target. The mission contained both high acceleration and high velocity while demanding high accuracy attitude estimates at the end of the short flight. The NAVSIL facility provided a high-fidelity HWIL approach to testing missile guidance systems that utilize GPS/INS guidance. Precise control and repeatability were provided for the two primary sensor inputs: GPS RF and the inertial measurements with instrument errors. HWIL tests were driven by high-fidelity all-digital 6-DOF missile motion simulations that accurately generated the translational and attitude dynamics in all phases of the mission from pre-launch through to the target. Real-time antenna pattern simulation was implemented to assess impact of signal level effects on GPS receiver performance. An innovative real-time technique was employed to simulate the frequency shift induced in the GPS receiver oscillator due to high-g forces, thus allowing accurate laboratory assessment of the receiver's ability to track, reacquire,a nd accurately navigate under g load. The resulting responsive high-fidelity HWIL testing capability provided critical support to development of the GPS/INS package and an independent assessment of expected GPS/INS performance during the mission.
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