State Tracking and Control of a Lifted Autonomous Space Vehicle During the Atmospheric Re-Entry Phase: a Lyapunov Approach

The paper presents the tracking and control of a selected set of state variables for a technological demonstrator re-entry vehicle, during the final phase of its descent towards the Earth. The aerodynamic has been treated as bi-dimensional (within the vertical plane) and the system is modeled as a rigid body. A complete analysis of the possible control solutions has been done, in terms of both control variables and actuators. A controller has been synthesized by applying the Lyapunov asymptotic stability theory: different Lyapunov functions have been implemented and the best one is here proposed. From the actuators point of view, a configuration requirement limits their selection to aerodynamic actuators such as elevons. According to the settled Lyapunov function, taking into account the actuators saturation, the selected state variables - the angle of attack, the Mach number and the pitch angular velocity - are correctly tracked, while the remaining are tracked with a dynamic gap. A comparison with a Proportional Integrative controller showed the benefits of the Lyapunov approach. Moreover, the implemented law turns out to be robust according to the initial condition vector variation. All aerodynamic data come from simulations done according to a possible configuration of the first Unmanned Space Vehicle (USV) Italian prototype, currently under development under the CIRA procurement; the PRORA-USV project is focused on testing a new reentry vehicle completely unmanned.