Attitude and Trajectory Estimation for Small Suborbital Payloads

Sammanfattning: Sounding rockets and small suborbital payloads provide a means for research in situ of the atmosphere and ionosphere. The trajectory and the attitude ofthe payload are critical for the evaluation of the scientific measurements and experiments. The trajectory refers the location of the measurement, while the attitude determines the orientation of the sensors.This thesis covers methods of trajectory and attitude reconstruction implemented in several experiments with small suborbital payloads carried out by the Department of Space and Plasma Physics in 2012–2016.The problem of trajectory reconstruction based on raw GPS data was studied for small suborbital payloads. It was formulated as a global least squares optimization problem. The method was applied to flight data of two suborbital payloads of the RAIN REXUS experiment. Positions and velocities were obtained with high accuracy. Additionally, wind up rates were obtained, which match the measurements from onboard angular rate sensors.Based on the trajectory reconstruction technique, atmospheric densities, temperatures, and horizontal wind speeds below 80 km were obtained using rigid free falling spheres of the LEEWAVES experiment. An iterative method was applied using the relation between the retrieved accelerations and the velocities and the densities. The dependence of the drag coefficient on the flow characteritics calls for the iterative approach. The uncertainties of the results are lower at low altitudes. Comparison with independent data indicates that the results are reliable for densities below 70 km, temperatures below 50 km,and wind speeds below 45 km.Attitude reconstruction of suborbital payloads from yaw-pitch-roll Euler angles was studied, using measurements of magnetic fields and angular velocities. The Euler angles were established by two methods: a global optimization method and an Unscented Kalman Filter (UKF) technique. The comparison of the results shows that the global optimization method provides a more accurate fit to the observations than the UKF.Improving the results of the falling sphere experiments requires understanding of the attitude motion of the sphere. An analytical consideration was developed for a free falling and axisymmetric sphere under aerodynamic torques. Due to the displacement between the center of mass and the geometric center, the motion can generally be defined as a superposition of precession andnutation. These motion phenomena were modeled numerically and compared to flight data.