Military Targeting Systems and the Development of Inertial Systems
Problem
Military targeting systems require maximum accuracy at all times and under all conditions. These systems can be hand-held or mounted on various vehicles or weapons, but they all must perform reliably and consistently in order to meet the needs of the warfighter.
Heading and elevation are critical factors in accurate targeting systems. The complex nature of these systems can present significant challenges in achieving maximum accuracy quickly, reliably, and repeatedly. Magnetic disturbances, whether produced by external sources or internal to the targeting system, can cause considerable errors in the output of conventional digital magnetic compasses (DMCs).
A complete inertial system that integrates MEMS-based inertial sensors, magnetometers, and advanced algorithms to process and fuse sensor data is required to overcome the difficulties inherent to traditional DMCs in complex applications such as targeting systems. All of this must be accomplished in a small, lightweight package with minimum power consumption, the ever present demands of SWaP-C – small Size, light Weight, low Power, and low Cost.
Solution
Over the past several years Sparton De Leon Springs, FL, has developed an in-depth understanding of the complexity, the challenges, and the requirements of military targeting systems. The Company’s line of inertial sensor systems offers complete and integrated solutions that not only deliver accurate heading and platform attitude data, but many additional features.
Leading-edge MEMs-based gyros allow for heading stability in the presence of transient magnetic disturbances. These tri-axial gyros and accelerometers provide inertial data that eliminates the need for an additional inertial measurement unit (IMU).
Sparton’s proprietary AdaptNavTM sensor fusion algorithm provides real-time optimization of sensor performance in varying magnetic and dynamic operating environments. It provides real-time platform “noise” characterizations used for drift compensation of heading, pitch, and roll when systems are in electrically or mechanically “noisy” environments. Sparton’s NorthTekTM embedded programming platform provides limitless output customization as well as additional processing capability that can be utilized to offload various system integrator processing requirements. NorthTekTM can be thought of as a new way for customers to write custom apps that can be downloaded to the inertial sensor system.
Conventional digital magnetic compasses require a complex and cumbersome “in-field” calibration process. This calibration, commonly referred to as a “Kabuki Dance,” is not embraced by most users, including the military. It is often performed improperly, incompletely, or not at all. This results in diminished sensor performance and poor overall accuracy, in not just target applications, but others as well.
Sparton developed a new calibration mode that utilizes the motion of the host device to collect and process calibration measurements in real-time. This “adaptive calibration” mode dramatically simplifies the calibration procedure while maintaining good overall performance and accuracy. While not designed to totally eliminate the manual in-field calibration, adaptive calibration frees the user from the periodic calibrations necessary, but not always performed, to keep a system at optimal performance.
Sparton AdaptCalTM utilizes a proprietary calibration algorithm that provides continuous 3D adaptive in-field calibration with hard and soft magnetic interference compensation. Instead of requiring the traditional, and complex, “12-point” calibration, the AdaptCalTM learns while in use, continuously calibrating the platform’s magnetic properties.
Simple and fast in-field calibration ensures rapid system availability and maximum accuracy. Multiple data outputs for calculation of heading accuracy Figure of Merit (FOM) and in-field calibration quality. An optional “strapped down” precision mount with a flex cable connection provides optimum accuracy and allows for flexibility in positioning the device within the targeting system’s housing.
In fact, AdaptCalTM, FOM, and the precision mount option were all specifically developed by Sparton working with targeting system integrators. Sparton has an established history of a willingness and flexibility to work with customers and end users in the development of technological improvements and product modifications. They call this Voice of the Customer (VOC) and they do listen.
All of this is achieved in a form factor of almost 12g and consumes only 60 mW. This is not a conventional DMC. It is truly a state-of-the-art, integrated sub-system that provides heading, pitch, roll, and inertial data outputs while minimizing size, weight, power, and cost.
Application
The U.S. military is challenging companies to develop handheld tactical laser rangefinders small enough for soldiers to carry that will help detect, identify, and pinpoint targets day or night, in good weather or bad.
The desired systems should weigh no more than three pounds and provide improved integrated night-vision capability, internal selective availability anti-spoofing module (SAASM) GPS, and both magnetic and non-magnetic heading capability. The newest equipment requires reduced size, weight, and power usage – all at a lower cost.
Sparton’s AHRS products are a critical component in meeting these SWaP-C demands as well as the desired performance capabilities.
Summary
Sparton has worked closely with prime contractors on technological advancements and product enhancements. This willingness to be flexible, to think outside the box, to modify and improve products for the specific application of military targeting highlights Sparton’s desire to be disruptive – disruptive in its products and their features as well as disruptive in the success of the partners with whom they work.
The Sparton AHRS-M2
The Sparton AHRS-M2 is a micro-sized, light weight, low power Attitude Heading Reference System with a revolutionary built-in adaptive-calibration mode. Sparton AdaptCal™ provides continuous 3D adaptive in-field calibration while Sparton’s AdaptNav™ sensor fusion algorithms allow the system to provide accurate attitude and heading outputs.
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