Analysis of the separation between the two modules of a tethered satellite system at the start of deployment

Over the past few decades, the increasing issue posed by human-generated space debris has become critical for the accomplishment of forthcoming space missions. Consequently, the space community has shifted its focus towards pioneering environmentally conscious deorbiting technologies. Among these groundbreaking solutions, Electrodynamic Tethers (EDT) emerge as a standout option, showcasing remarkable promise owing to their passive and fuel-free characteristics. Notably, their efficacy in tackling the urgent challenge of space debris within the confines of low Earth orbit (LEO) stands out as a key highlight. The E.T.PACK-F project, funded by the European Innovation Council (EIC), is developing a Deorbit Kit, up to TRL 8 device incorporating Electrodynamic Tether technology. This technology utilizes a long aluminum tape and an electron emitter to generate a Lorentz force, strongly accelerating the deorbiting of end-of-life satellites or spent rocket stages. The presence of an In-Line Damper (ILD) is critical for both mitigating excessive tether libration induced by the Lorenz force during deorbiting and reducing the longitudinal stiffness of the tether line at short lengths. This thesis presents an integrated approach to examining the dynamics of tethered satellite systems, combining accurate simulation techniques with experimental results obtained in representative laboratory conditions. The objective is to provide realistic data on the behavior of the In-Line Damper during the two modules separation phase, offering insights into the challenges and potential solutions for future space debris mitigation technologies. A Matlab program was first developed to simulate the entire dynamics of two modules in the initial separation phase of the tether deployment. Specifically, both modules are represented as rigid bodies with comprehensive 6 degrees of freedom dynamics. The tether is modeled as a series of connected lumped masses, taking into consideration also the elastic and damping effects of the ILD. Concerning the laboratory setup, the unique SPARTANS facility of the University of Padova was adapted to replicate experimentally the dynamics of the ILD during the early separation phase. Specifically, the experimental setup configuration comprises two main components: 1) a satellite mock-up equipped with an air-cushion system for smooth movement on the testing table and four cold-gas thrusters for implementing the initial separation maneuver; 2) a stationary mock-up accommodating the ILD. To precisely measure the relative dynamics between the two mock-ups, a Motion Capture system featuring six infrared cameras was employed. Comparative analysis of the experimental data obtained from various laboratory tests and the results of numerical simulations demonstrated a good level of agreement, confirming that the software simulator effectively captures the realistic physics involved in the early separation maneuver of a tethered system.

OOver the past few decades, the increasing issue posed by human-generated space debris has become critical for the accomplishment of forthcoming space missions. Consequently, the space community has shifted its focus towards pioneering environmentally conscious deorbiting technologies. Among these groundbreaking solutions, Electrodynamic Tethers (EDT) emerge as a standout option, showcasing remarkable promise owing to their passive and fuel-free characteristics. Notably, their efficacy in tackling the urgent challenge of space debris within the confines of low Earth orbit (LEO) stands out as a key highlight. The E.T.PACK-F project, funded by the European Innovation Council (EIC), is developing a Deorbit Kit, up to TRL 8 device incorporating Electrodynamic Tether technology. This technology utilizes a long aluminum tape and an electron emitter to generate a Lorentz force, strongly accelerating the deorbiting of end-of-life satellites or spent rocket stages. The presence of an In-Line Damper (ILD) is critical for both mitigating excessive tether libration induced by the Lorenz force during deorbiting and reducing the longitudinal stiffness of the tether line at short lengths. This thesis presents an integrated approach to examining the dynamics of tethered satellite systems, combining accurate simulation techniques with experimental results obtained in representative laboratory conditions. The objective is to provide realistic data on the behavior of the In-Line Damper during the two modules separation phase, offering insights into the challenges and potential solutions for future space debris mitigation technologies. A Matlab program was first developed to simulate the entire dynamics of two modules in the initial separation phase of the tether deployment. Specifically, both modules are represented as rigid bodies with comprehensive 6 degrees of freedom dynamics. The tether is modeled as a series of connected lumped masses, taking into consideration also the elastic and damping effects of the ILD. Concerning the laboratory setup, the unique SPARTANS facility of the University of Padova was adapted to replicate experimentally the dynamics of the ILD during the early separation phase. Specifically, the experimental setup configuration comprises two main components: 1) a satellite mock-up equipped with an air-cushion system for smooth movement on the testing table and four cold-gas thrusters for implementing the initial separation maneuver; 2) a stationary mock-up accommodating the ILD. To precisely measure the relative dynamics between the two mock-ups, a Motion Capture system featuring six infrared cameras was employed. Comparative analysis of the experimental data obtained from various laboratory tests and the results of numerical simulations demonstrated a good level of agreement, confirming that the software simulator effectively captures the realistic physics involved in the early separation maneuver of a tethered system.