SatLeash - Parabolic flight validation of tethered-tugs dynamics and control for reliable space transportation applications

The SatLeash experiment investigates the dynamics and control of tow-tethers, for space transportation. Understanding tethered towing objects in space is becoming an active research field for its range of applications. Many missions, such as Active Debris Removal, LEO satellites disposal, low-to-high energy orbit transfer and even asteroids retrieval could employ this technology. Space tugs, made of a passive orbiting target interconnected through a flexible link to an active chaser the thrusters of which excite the stack dynamics, open new challenges for guidance and control design. A wave-based control, using tension feedback, is selected as effective method to stabilize the system during tensioning and release phases. The team exploits a multibody dynamics simulator developed at PoliMi-DAER-to describe tethered-satellite-systems dynamics and synthetize their control. This is considered of primary importance to design future missions. The experiment, selected to fly in microgravity conditions by the ESA FlyYourThesis! 2016 programme, focuses on validating the adopted models and verifying the implemented control law. A reduced-scale tethered floating test bed, equipped with a stereovision system to reconstruct its 3D trajectory, has been developed for the parabolic flight campaign. Different tether stiffness have been tested as well as control schemes to verify their effectiveness in reducing bouncing-back effects. Developed models and control laws, together with numerical and experimental simulation results are presented in the paper.