Meet the teams: PoliTethers team

The dynamics of fixed-length tethered-systems (SatLeash – Experiment)

University	Politecnico di Milano, Department of Aerospace Science and Technologies (PoliMi-DAER), Italy
Endorsing professor	Michèle Lavagna Politecnico di Milano, Italy
ELGRA mentor	Ann Delahaye QinetiQ Space
Team	Andrea Bellanca Riccardo Benvenuto Paolo Lunghi Vincenzo Pesce Simone Flavio Rafano Carnà

Space tethers are long cables, made of high strength fibers strands, used to connect two or more end-bodies in orbit. Many applications have been proposed for space tethers, and among them the team is focusing on Active Debris Removal and space transportation using the tethered-tug concept, i.e. two objects, one passive and one active, connected by a flexible link, the motion of the system being excited by the active spacecraft thrusters.

Because of their overall flexibility and when placed in a zero-g environment, tethered-systems undergo a complicated set of three-dimensional librations and vibrations. Therefore, it is necessary to study their three-dimensional behavior in microgravity and to this end, parabolic flights are the most suited facilities for both time-span and available test area.

Experiment Design

Tethered system will play a crucial part in future missions. Hence, validated models, simulation tools and stabilizing control laws, describing tethered-tugs orbital and attitude dynamics, are considered of primary importance to design future missions.

Whiplashes or bounce-back effects are an example of these highly complex dynamics. Therefore, PoliMi-DAER has developed simulation models to describe the tethered-satellite-systems dynamics and design their control. The experiment goals are the validation of these models and the implementation of control laws to stabilize the system, avoiding whiplashes or bounce-back effects. The team is proposing to fulfill these objectives by testing a reduced-scale tethered floating system, released and retrieved with different conditions. Its three-dimensional trajectory will be reconstructed using stereo-cameras and acceleration sensors. Different tether stiffness will be tested as well as different control strategies.

Use of tethers in space