Design of a Satellite Simulator for Close Range Rendezvous and Docking Using Innovative APF Guidance

In recent times the number of space missions has grown significantly, hence increasing the number of orbiting satellites and consequently space debris. In this context, In-Orbit Servicing (IOS) aims to solve this problem by extending the life of spacecrafts and eventually de-orbiting them once they become obsolete. The purpose of this thesis is to develop an orbital simulator for small satellites (100 ÷ 150 kg) in LEO orbit, capable of accurately reproduce rendezvous and docking manoeuvers. In the future, the developed simulator will be used to test and train Autonomous Navigation (AN) and guidance algorithms developed with AI techniques. In this thesis, a realistic In-Orbit Servicing scenario between a chaser and a target satellite is presented as a case study. The simulated mission consists in two phases: a close range rendezvous phase in which, after scanning its surroundings, the chaser locates the target and moves to a holding point located at 500m from it (either in V-bar or R-bar); a second phase in which the chaser performs the final approach and docks to the target. In particular, two methods for the final approach will be presented. In the first case, a classical approach will be considered, the chaser will perform a fly-around manoeuver moving from V-bar to a R-bar holding point and will then start a cone approach until docking is acquired; in the second case, an innovative APF guidance algorithm, in which the obstacle is shaped like the keep-out zone, will be considered. The actuation system is composed by thrusters for position control and both thrusters and reaction wheels for attitude control. The control system relies on a PID controller for closed loop control, whereas an open loop control is used for the classical approach. While the target is considered to be fixed and unperturbed, the chaser is affected both by disturbing forces and moments; in particular the effects of J2, gravity, solar pressure, albedo and atmospheric drag are considered. The chaser is considered to be equipped with a set of various sensors for the attitude and position data. Their signals will be filtered by means of Extended Kalmn Filters (EKF). The sensors set is divided in absolute sensors (Earth horizoin sensors, magnetometer, sun sensor, GPS and IMU) and relative sensors (camera and LiDAR). The scenario is simulated in the MATLAB/Simulink enviroment and a combination of Phyton and Blender is used to simulate the camera image acquisition.