Real-time estimation of projectile roll angle using magnetometers: in-lab experimental validation

Abstract

The knowledge of the roll angle of a projectile is decisive to apply guidance and control law. For example, the goal of ISL£s project GSP (Guided Supersonic Projectile) is to change the §ight path of an airdefence projectile in order to correct the aim error due to the target manoeuvres. The originality of the concept is based on pyrotechnical actuators and onboard sensors which control the angular motion of the projectile. First of all, the control of the actuators requires the precise control of the roll angle of the projectile. To estimate the roll angle of the projectile, two magnetometers are embedded in the projectile to measure the projection of the Earth magnetic ¦eld along radial axes of the projectiles. Then, an extended Kalman ¦lter (EKF) is used to compute the roll angle estimation. As the rolling frequency of the GSP is about 22 Hz, it was easy to test the navigation algorithm in laboratory. In a previous paper [1], the In-Lab demonstration of this concept showed that the roll angle estimation was possible with an accuracy of about 1• . In this paper, the demonstration is extended to high-speed roll rate, up to 1000 Hz. Thus, two magnetometers, a DSP (Digital Signal Processor) and a LED (Light Eminent Diode), are rotated using a pneumatic motor; the DSP runs an EKF and a guidance algorithm to compute the trigger times of the LED. By using a high-speed camera, the accuracy of the method can be observed and improved. GUIDED SUPERSONIC PROJECTILEFor ground-based air defence gun systems to be e¨ective, the ability to hit the target is a prerequisite. To achieve high hit probability performance against manoeuvring air targets, such as attack helicopters, cruise missiles, or unmanned air vehicles, the basic point is to ¦re projectiles having short times of §ight. However, this solution is limited by the performance of the gun.

Experimental Validation¹

“…The two blocks ("roll estimation" and "attitude estimation") are based on EKF. The details of theses filters are given in [2], [5] and [6]. First, this method has been tested on simulation and then on in-flight recorded data.…”

Real-Time Estimation for Roll Angle of Spinning Projectile Based on Phase-Locked Loop on Signals from Single-Axis Magnetometer

“…Another attitude determination system [ 18 ] used three magnetometers aligned with body coordinate system assisted by angular rate sensors to figure out all three Euler angles. ARL achieved accuracy within 5° in roll angle measurement and ISL even did better in experimental validation [ 19 ] after compensation. However, in all these research above, the precision is affected by conventional algorithm of magnetic measurement, more than one magnetic sensor and based on the amplitude of magnetic sensors’ output.…”

Spinning projectile’s attitude measurement using intersection ratio of magnetic sensors

“…The projectile attitude determination method using the earth's magnetic field has the advantage of low cost, strong shock resistance, no cumulative error, high reliability, etc. [4][5][6] The use of magnetometers to obtain orientation information is not a new idea and has been ultilized in various types of flight vehicles in recent researches, from satellites to UAVs. 7,8 Typically, an algorithm is employed to determine a solution for the Direction Cosine Matrix(DCM), Euler angles, or quaternions of the vehicle on basis of a set of magnetometer measurements.…”