4.2 State Estimator

In order for Ranger NBV to fly autonomously, it must be able to measure its position and attitude along with the associated rates. This information is extracted from data produced by various vehicle sensor systems, and then assembled into a single vector. This state vector has 13 elements.


(4.12)

The first three elements describe the estimate of the Cartesian position of the vehicle's origin with respect to the neutral buoyancy tank reference frame. The origin chosen for the tank at SSL lies at the surface of the water in the center of the tank. The x, y, and z axes point North, East, and Down, with distances measured in meters. The next three elements describe the velocity of the vehicle's origin in the tank frame (m/s). The next four elements represent the vehicle's attitude. This attitude is parameterized in the form of a quaternion. The final three elements describe the vehicle's angular velocity (rad/s) described in the vehicle reference frame.
This thesis focuses on controlling Ranger NBV's attitude. At this time, sensors for measuring vehicle position are still under development, so the vehicle's position and linear velocity are unknown. This section describes the equations used in the formation of the attitude and angular velocity portions of the vehicle state vector.