Trajectory control system for the LAICAnSat-3 mission

This work presents the trajectory control system for the LAICAnSat-3 mission. The LAICAnSat project was established at the University of Brasilia for creating a low cost educational platform for conducting experiments at high and low altitudes. LAICAnSat previous stages include two launches of balloon-sats (LAICAnSat-1 and LAICAnSat-2). These two launches allowed the test of a preliminary system, which included a broad sensor suite (a high performance camera, temperature, pressure, humidity, UV light level, altitude, position, speed, heading, and acceleration sensors) and a communication and tracking system. The trajectory control of the LAICAnSat-3 is active during its descent phase. The goal of the guidance is to autonomously land the vehicle in a prescribed area. The directional control of the vehicle is provided by a paraglider, which is steered laterally by a servo motor that pulls the lines of the canopies. The system does not have a glide slope control, therefore the only controllable trajectory is the one on the horizontal plane; the vertical motion is assumed constrained by gravity and by the lift to drag ratio of the vehicle. Trajectory planning is based on a kinematic model of the vehicle and foresees the implementation of a series of trajectory paths of maximum control deflection that guarantees to remain in a bounded area. The reference heading is tracked by a PID controller, implemented in the on-board computer of the LAICAnSat. Simulations have been performed to assess the robustness of the designed controller to disturbances like wind gusts. The on-board computer is a board designed ad-hoc for this mission. It includes a micro-controller, environmental and inertial sensors, data storage capability, a multi-GNSS module, and the interfaces with the other subsystems of the vehicle. The multi-GNSS module provides position and heading information, which are used both on ground to track the flight and on-board to provide the feedback to the PID.