Novel In-flight Coarse Alignment of Low-cost Strapdown Inertial Navigation System for Unmanned Aerial Vehicle Applications

Kalman filtering-based in-flight alignment heavily relies on coarse alignment to obtain a sound initial attitude; otherwise the subsequent fine alignment cannot achieve a reliable and satisfying result. In order to strengthen the rapid response capability, it is necessary to have an integrated system combining an airborne global navigation satellite system (GNSS) with strapdown inertial navigation system (SINS) to implement coarse alignment on a moving base. Due to complicated flight dynamics and strict load constraints of UAVs, in-flight coarse alignment is much more difficult than ground coarse alignment. Moreover, the introduction of a low-cost micro-electro-mechanical system-based SINS (MEMS-SINS) with high noise, which is suitable for UAV applications with advantages in cost-effectiveness, lightweight, miniature design, low power consumption and survivability, makes it more challenging. In this paper, a novel in-flight coarse alignment aided by GNSS is derived to obtain the initial attitude based on quaternion. Velocity and its differential information from GNSS and specific forces from MEMS-SINS are compared to obtain an analytical solution for the initial angles. A flight test is conducted to test the new algorithm. The results indicate it can achieve 11.5 deg (1·) accuracy for heading, and 5.7 deg (1·) accuracy for level angles (i.e., roll and pitch). As a nice in-flight coarse alignment, it can guarantee accurate and reliable fine alignment afterward.