Investigation of Deorbiting Systems using Passive Electrodynamic Propulsion

In the last decade, the continuous and alarming growth of space debris prompted many space agencies all over the world to adopt debris mitigation strategies. Present guidelines indicate the need to deorbit new satellites launched into low Earth orbit (LEO) within 25 years from their end of life. At present, a space-proven technology suitable to carry out a complete deorbit utilizes classical chemical propulsion. However, a deorbit maneuver by means of chemical rocket strongly affects the satellite propulsion budget, thus limiting the operational life of the satellite. These issues bring the need to develop innovative deorbiting technologies. One of these consists in using electrodynamic tethers that, through its interaction with the Earth ionosphere and magnetic field, can take advantage of Lorentz forces for deorbiting. Previous studies have shown the effectiveness of such a technology to deorbit LEO satellites from different altitudes and inclinations in a relatively short time. This work addresses some of the issues of deorbit systems based on electrodynamic tether systems. First, a passive elastic-viscous damping device installed at the attachment point of the tether to the spacecraft is studied to damp the low and yet continuous injection of energy into the system produced by Lorentz forces that, in the long run, can bring the tether to instability. Second, the issues related to the in-orbit deployment of a tape-shaped tether from a non-tumbling spacecraft are attacked to find simple and effective solutions. The chosen strategy is to deploy a tethered tip mass following a pre-determined flight path fed forward to a linear proportional-derivative closed-loop control operated by a brake system mounted on the deployer reel. Lastly, an optimization process for bare electrodynamic tether systems has been developed. The analysis focuses on the deorbiting performances of electrodynamic tether systems from LEO high ranking hot spot regions (e.g., sun-synchronous orbits), and includes a realistic mass budget of a deorbiting system suitable for small satellites

Orbital debris mitigation through deorbiting with passive electrodynamic drag

The increase of orbital debris and the consequent proliferation of smaller objects through fragmentation are driving the need for mitigation strategies. The issue is how to deorbit the satellite with an efficient system that does not impair drastically the propellant budget of the satellite and, consequently, reduces its operating life. We have been investigating, in the framework of a European-Community-funded project, a passive system that makes use of an electrodynamics tether to deorbit a satellite through Lorentz forces. The deorbiting system will be carried by the satellite itself at launch and deployed from the satellite at the end of its life. From that moment onward the system operates passively without requiring any intervention from the satellite itself. The paper summarizes the results of the analysis carried out to show the deorbiting performance of the system starting from different orbital altitudes and inclinations for a reference satellite mass. Results can be easily scaled to other satellite masses. The results have been obtained by using a high-fidelity computer model that uses the latest environmental routines for magnetic field, ionospheric density, atmospheric density and a gravity field model. The tether dynamics is modelled by considering all the main aspects of a real system as the tether flexibility and its temperature-dependent electrical conductivity. Temperature variations are computed by including all the major external and internal input fluxes and the thermal flux emitted from the tether. The results shows that a relatively compact and light system can carry out the complete deorbit of a relatively large satellite in a time ranging from a month to less than a year starting from high LEO with the best performance occurring at low orbital inclinations

REGULUS CubeSat Propulsion System: In-Orbit Operations

A robust, versatile, and cost-effective propulsion system to provide wide mobility to small satellite platforms and nanosatellite deployers. A Plug&Play propulsion system designed to be easily integrated into different satellite platforms and to match customer\u27s requirements, with minimal customization efforts and costs

REGULUS Iodine Electric Propulsion System Integration in CubeSats’ Platforms and Testing

REGULUS is an electric propulsion (EP) system for CubeSats at TRL8 and now waiting for the IoD flight in late 2020. REGULUS system is provided for integration with all electronics, fluidic line, iodine tank and structures for total mass below 3 kg. Thanks in particular to the Magnetically Enhanced RF Plasma Thruster (MEPT) technology and the use of iodine propellant, the system can provide 3000Ns of total impulse in a 93.8 x 95.0 x 150.0 mm volume performance, fitting in a 1.5U Cubesat. REGULUS includes the whole propulsion package for integration in CubeSats and MicroSats as well as small CubeSat carriers. The system is composed by the thruster, the electronics (PPUs and PCU) the fluidic line and the tank. The main features of REGULUS are the presence of a simple architecture, a thruster with no neutralizer and grids, no high DC-voltage PPU and the use of solid iodine as propellant, that can be substituted with Xenon fluidic line and tank when required. Its first mission will be onboard of Unisat-7 by GAUSS. The flight will take place in late 2020 in a Soyuz flight. During the mission, REGULUS will allow Unisat-7 to perform an orbit descending maneuver, drag compensation in VLEO and decommissioning

Investigation of Deorbiting Systems using Passive Electrodynamic Propulsion

In the last decade, the continuous and alarming growth of space debris prompted many space agencies all over the world to adopt debris mitigation strategies. Present guidelines indicate the need to deorbit new satellites launched into low Earth orbit (LEO) within 25 years from their end of life. At present, a space-proven technology suitable to carry out a complete deorbit utilizes classical chemical propulsion. However, a deorbit maneuver by means of chemical rocket strongly affects the satellite propulsion budget, thus limiting the operational life of the satellite. These issues bring the need to develop innovative deorbiting technologies. One of these consists in using electrodynamic tethers that, through its interaction with the Earth ionosphere and magnetic field, can take advantage of Lorentz forces for deorbiting. Previous studies have shown the effectiveness of such a technology to deorbit LEO satellites from different altitudes and inclinations in a relatively short time. This work addresses some of the issues of deorbit systems based on electrodynamic tether systems. First, a passive elastic-viscous damping device installed at the attachment point of the tether to the spacecraft is studied to damp the low and yet continuous injection of energy into the system produced by Lorentz forces that, in the long run, can bring the tether to instability. Second, the issues related to the in-orbit deployment of a tape-shaped tether from a non-tumbling spacecraft are attacked to find simple and effective solutions. The chosen strategy is to deploy a tethered tip mass following a pre-determined flight path fed forward to a linear proportional-derivative closed-loop control operated by a brake system mounted on the deployer reel. Lastly, an optimization process for bare electrodynamic tether systems has been developed. The analysis focuses on the deorbiting performances of electrodynamic tether systems from LEO high ranking hot spot regions (e.g., sun-synchronous orbits), and includes a realistic mass budget of a deorbiting system suitable for small satellites.La continua ed allarmante crescita del numero di detriti spaziali avvenuta negli ultimi dieci anni ha spinto le agenzie spaziali di tutto il mondo ad adottare specifiche strategie di mitigazione. Le attuali linee guida internazionali indicano la necessità di far deorbitare i nuovi satelliti lanciati in orbita terrestre bassa (LEO) entro 25 anni dalla fine della loro vita operativa. Attualmente, i sistemi basati sulla propulsione chimica costituiscono l'unica tecnologia spaziale collaudata adatta ad effettuare un deorbiting completo di un satellite. Tuttavia, l'utilizzo di razzi per una manovra deorbitante richiede un considerevole quantitativo di propellente, andando ad influenzare fortemente il budget di massa del satellite, limitandone così la vita operativa. Ciò porta alla necessità di sviluppare tecnologie innovative per il rientro a fine vita di satelliti. Una di queste consiste nell'utilizzo di fili elettrodinamici che, attraverso l'interazione con la ionosfera e il campo magnetico terrestre, sfruttano le forze di Lorentz per effettuare il rientro. Studi precedenti hanno dimostrato l'efficacia di tale tecnologia per il deorbiting di satellite in LEO da diverse altezze e inclinazioni orbitali in un tempo relativamente breve. Questo lavoro di tesi affronta alcuni dei problemi caratteristici dei sistemi di deorbiting basati su sistemi a filo elettrodinamico. Innanzitutto, è stato studiato l'impiego di un sistema viscoelastico passivo da installare in corrisponenza dell'interfaccia tra filo e satellite. Questo sistema è stato ideato per smorzare il flusso di energia prodotto dalle forze di Lorentz che continuamente entra nel sistema e che, a lungo andare, può portare il tether all'instabilità dinamica. In secondo luogo, si è affrontato il problema relativo al dispiegamento in orbita di un filo a forma di nastro (tape tethers) da un veicolo spaziale il cui assetto è noto. La strategia scelta è quella di dispiegare dal satellite-base un sub-satellite seguendo una traiettoria predefinita, facendo uso di un sistema di controllo in retroazione lineare proporzionale-derivativo operato da un impianto frenante montato sull'albero del sottosistema di dispiegamento. Infine, è stato sviluppato un processo di ottimizzazione per sistemi a filo elettrodinamico. L'analisi si concentra sulle prestazioni dei sistemi elettrodinamici per il deorbiting di satelliti di piccola taglia (Small Satellites) da orbite LEO appartenenti a regioni sensibili (ad esempio, le orbite polari eliosincrone). Il processo di ottimizzazione è anche in grado di fornire un mass budget realistico del sistema di rientro

Electrodynamic tethers in space: dynamical issues, solutions and performance

Electrodynamic tethers are a promising new technology for a variety of applications ranging from deorbiting of spent satellites and upper stages in low Earth orbits to propellantless propulsion around any planet (inclusive Earth) with a magnetic field and a plasmasphere. However, the continuous application of electrodynamic forces/torques over a relatively long period of time raises dynamical issues related to the tether attitude dynamics that need to be solved for achieving longterm dynamical stability. The paper addresses firstly the fundamentals of the dynamical motion forced by the electrodynamic forces/torques and secondly reviews the techniques used to control the motion generated by those forces/torques. The paper also presents the techniques that were used successfully in simulation to control the dynamics of a tethered system designed for deorbiting spent satellites in low Earth orbits and shows its deorbiting performance at all orbital inclinations. Copyright \ua9 European Space Agenc

Study of dynamical stability of tethered systems during space tug maneuvers

The dynamics of a space tether system composed of one active spacecraft, an uncontrolled large debris (e.g., a defunct satellite), and a visco-elastic tether connecting the two bodies are investigated in this paper. The active spacecraft is assumed to be equipped with a propulsive system for carrying out a tug maneuver that forces the orbital decay of the debris. The dynamical stability and the eigenfrequencies of the tethered system under the action of the thrust are investigated with both numerical and analytical models. A more complex numerical lumped-masses model provides the reference to validate the results hailing from the simplified models. Simplified models of orbital decay, tether, and debris attitude motions were derived using the Clohessy- Wiltshire equations. The results obtained with the simplified models fit very well with those from the lumpedmasses model for a wide range of initial conditions. Thanks to the analytical models two resonance conditions were found, both of them affecting the attitude dynamics of the debris, that could represent a serious issue for the safety of the tug maneuver. Also, an instability mechanism that could induce the dual mass system to rotate around its center of mass under certain conditions was identified. These findings make it possible to pinpoint the set of initial conditions of the tethered system at the beginning of the thrust event that provides a dynamically stable tug maneuver for different configurations of the system (e.g., low/high thrust, stiff/elastic tethers). [Acta Astronautica

Propellantless Technology for the Deorbiting of Small Satellites Mega-Constellations at the End of Life

Deorbiting performance of 200-kg class satellites from different critical altitudes and inclinations using bare electrodynamic tape tethers is discussed. The study leads from the recent interest of several companies worldwide in building of mega-constellations composed of hundreds of microsatellites. Using as input the limited information that can be presently found in open sources, three representative mission scenarios for mega-constellations are studied in this paper considering a constant satellite mass of 200 kg. In the first step, an optimized tether geometry is found using the BETsMA optimization software assuming the spacecraft mass, the starting altitude, and the orbital inclination as inputs. The output of this phase is the conductive tether length, width, and thickness and an estimated cut probability due to hypervelocity impacts during deorbiting. In a second step, the system configuration is further refined by means of extensive numerical simulation campaigns performed with the Flexible Tether Simulator for electrodynamic tethers software that models the tape tether with a discrete number of lumped masses. This accurate simulation code take into consideration both tether longitudinal and lateral modes of vibration and employs the latest Earth magnetic field, ionospheric electron density, and atmospheric models to simulate a realistic in-orbit environment. Moreover, it enables the simulation of tether motion control strategies that can be used to increase the system reliability and efficiency. The final goal of this study is to find a comparatively light system configurations that can perform a complete deorbit of a 200-kg microsatellite in the shortest possible time from different starting altitude and inclinations. The results of the study show that the electrodynamic tether option is attractive compared to deorbit systems based on traditional chemical fuel