Design, realization and characterization of a free-floating platform for flexible satellite control experiments

Experimental verification of numerical models is a key aspect in all scientific and technological disciplines, yet space systems can be particularly hard to test on ground: in fact, a terrestrial mock-up replicating the orbital dynamics should be in a gravity-free environment. One of the most common approaches to (at least partially) realize this condition, consists in free-floating systems, in which the friction between an experimental platform and the working surface is almost completely removed. The vertical axis is still subject to gravity, and only 3 degrees of freedom (two horizontal translations and one rotation about the vertical axis) are available to replicate the orbital behavior. Our research group had been developing since 2012 a free-floating platform named PINOCCHIO (Platform Integrating Navigation and Orbital Control Capabilities Hosting Intelligent Onboard). The need to investigate with higher accuracy the attitude control problem for flexible satellites called for the design, realization and characterization of a new platform with enhanced performance. This paper describes the main components of the system, including the pressure air system, the navigation and communication system, the GNC architecture and relevant hardware. The attention is specifically on the characterization of the subsystems' performance. The physical (mass, moment of inertia), control (thrusters' torque and force) and IMU characteristics are experimentally measured with the associated uncertainty level. The accuracy of the VICON system in static and dynamic conditions is also characterized, obtaining a 100 micrometers-level resolution for external measurement of rigid and elastic displacements; this information is fundamental for performing tests of fine pointing control algorithms for flexible and agile satellites. The proposed characterization methodology and associated results could be of interest for university and industry laboratories intended to develop new free-floating platforms.