Survivability Testing a Gun Hard MEMS IMU/GPS Navigation System

This paper describes a series of evaluation tests on a combined MEMS IMU/GPS navigation unit, culminating in a survivability trial conducted using a specially modified 155mm projectile. The trial consisted of a 20,000g launch and subsequent soft recovery. The unit is an ultra tightly coupled GPS/MEMS IMU integrated navigation system, incorporating a gun hard MEMS IMU, a ruggedized C/A code GPS receiver and processor card. The IMU uses a vibrating structure gyroscope that has sold over 10 million units worldwide and MEMS accelerometers. The unit incorporates the Modular Integrated Navigation Kalman (MINK) Filter, specifically designed to calibrate MEMS IMUs and developed from the extensive experience gathered in the design and calibration of MEMS IMUs. The unit has been developed at sites in Plymouth UK and Jerusalem, Israel with the final evaluation method developed in Singapore. In order to prove gun hardness, the system has been exposed to non-operational launch shocks of over 20,000 times the force of gravity. This has been achieved using an Aerobutt facility in Northumberland, UK and at the Alkantpan (Vastrap) firing range in the Northern Cape region of South Africa. The Aerobutt facility is an 85mm mortar system with a restrictive air soft recovery system. In South Africa the system was fired from a 45 caliber 155mm G5 howitzer, with the recovery of the round in soft sand. To support the G5 howitzer test firings, an experimental slug projectile has been designed and built in Singapore, which provides an internal housing for the test sample, with a removable cover to allow removal of the test sample after the firing. The integrated IMU/GPS system is at an advanced stage of development; the test plan has encompassed the following steps: Component level testing of the receiver and inertial sensors Initial integrated system performance evaluation tests conducted in a road vehicle at Plymouth UK, around a variety of environments where GPS is masked or unavailable. Aerobutt testing, including multiple repeat firings; demonstrating that units could remain operational following successive firings at up to 22,000g. Fully representative firings from the G5 howitzer, where the samples survived shock levels of 20,000g. Integrated system performance testing conducted on units recovered following firing. Results are presented for these evaluations, considering sensor and oscillator stability, data and time retention, and navigation accuracy.