Real time estimation of projectile roll angle using magnetometers: In-flight experimental validation

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 flight path of an air-defence 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 field along radials axes of the projectiles. Then, an extended Kalman filter is used to compute the roll angle estimation. As the rolling frequency of the GSP is about 22 Hz, it is easy to test the navigation algorithm in laboratory. So in previous papers ([1],[5]) the in-lab demonstration of this concept shows that the roll angle estimation was possible with an accuracy of about 1° at 22 Hz. In this paper, the demonstration is extended to in-flight test, with a roll rate about 35 Hz. Thus, two magnetometers, a DSP and a LED (to simulate a thruster) are embedded inside the projectile; the DSP runs an extended Kalman filter and a guidance algorithm to compute the trigger times of the LED. By using a high speed camera (a trajectory tracker), we can observe that the LED is switch on at the target angle.