Deployment requirements for deorbiting electrodynamic tether technology

In the last decades, green deorbiting technologies have begun to be investigated and have raised a great interest in the space community. Among the others, electrodynamic tethers appear to be a promising option. By interacting with the surrounding ionosphere, electrodynamic tethers generate a drag Lorentz force to decrease the orbit altitude of the satellite, causing its re-entry in the atmosphere without using propellant. In this work, the requirements that drive the design of the deployment mechanism proposed for the H2020 Project E.T.PACK\u2014Electrodynamic Tether Technology for Passive Consumable-less Deorbit Kit\u2014are presented and discussed. Additionally, this work presents the synthesis of the reference profiles used by the motor of the deployer to make the tethered system reach the desired final conditions. The result is a strategy for deploying electrodynamic tape-shaped tethers used for deorbiting satellites at the end of their operational life

Deorbit kit demonstration mission

In Low Earth Orbit, it is possible to use the ambient plasma and the geomagnetic field to exchange momentum with the Earth's magnetosphere without using propellant. A device that allows an efficient momentum exchange is the electrodynamic tether (EDT), a long conductor attached to the satellite. EDT technology has been demonstrated in several past missions, being the Plasma Motor Generator mission (NASA 1993) one of the most successful. Nevertheless, it is not until today that reality has imposed a strong need and a concrete use case for developing this technology. In March 2019, the European Commission project Electrodynamic Tether technology for PAssive Consumable-less deorbit Kit (E.T.PACK) started the design of a new generation EDT. After completing the design phase, the consortium manufactured and is currently testing a Deorbit Kit Demonstrator (DKD) breadboard based on EDT technology. The objective of E.T.PACK is to reach Technology Readiness Level equal to 4 by 2022. The DKD is a standalone 24-kg satellite with the objective to demonstrate the performances of the improved EDT solution and validate its ultra-compact deployment system. The DKD is composed of two modules that will separate in orbit extending a 500-m long tape-like tether. The deployed bare-Aluminium tether will capture electrons from the ambient plasma passively and the circuit will be closed with the ionospheric plasma by using an active electron emitter. E.T.PACK tether will take advantage of several novelties with respect to the mission flown in the past that will allow to optimize the system volume and mass. Once successful demonstrated in orbit, the team plans to develop a suite of EDT systems capable of deorbiting satellites between 200 and 1000 kg from an altitude up to 1200 km in a few months. The work presents the current design status of the de-orbit kit demonstrator breadboard, the simulations of the system deorbit performances and the development approach.This work was supported by the European Union's Horizon 2020 Research and Innovation Programme under grant agreement No.828902 (3M€ E.T.PACK project) and No.101034874 (100K€ BMOM project). SG is supported by an Industrial Ph.D funded by Comunidad de Madrid (135K€ IND2019/TIC17198). The team has recently got 2.5M€ additional financial support from European Union (ETPACK-F project No. 101058166) for the manufacturing and qualification of the In Orbit Demonstration (IOD) by the end of 2025

Validation of enabling technologies for deorbiting devices based on electrodynamic tethers

The increasing number of man-made objects in near-earth space is becoming a serious problem for future space missions around the Earth. Among the proposed strategies to face this issue, and due to the passive and propellant-less character, electrodynamic tethers appear to be a promising option for spacecraft in low Earth orbits thanks to the limited storage mass and the minimum interface requirements to the host spacecraft. This work presents the roadmap that the Electrodynamic Tether Technology for Passive Consumable-less Deorbit Kit (E.T.PACK) is following to develop a prototype of a deorbit device based on electrodynamic tether technology with Technology Readiness Level 4 by the end of 2022. The paper illustrates the roadmap of the activities carried out at the University of Padova, where software and hardware have been prepared to validate some of the critical elements of the deorbit device. Specifically, the software tools include: (a) the software called “DEPLOY” that allows the computation of a reference trajectory for the deployment of the tether and the completion of sensitivity analysis of the deployment trajectory to key error sources; (b) the software called “FLEXSIM” that predicts the performances of electrodynamic tethers as a function of the system configuration employed; and (c) the software called “FLEX” that includes the dynamical effects of tether flexibility and provides important information on the dynamic stability of the system during deployment and deorbiting phase. The paper describes in detail the three software tools and provides results of a simulation showing how it is possible to deorbit a 24-kg satellite from an initial orbital altitude of 600 km in less than 100 days using a 500-m long tape-like bare tether. The team has also developed laboratory mock-ups and performed experimental activities to: (a) determine the tether mechanical properties; (b) test the functionality of mechanisms used to deploy the tether; (c) test the functionality of the attitude control assembly used during the deployment phase; and (d) validate a passive damper designed for dissipating the longitudinal oscillations of the tether and thus guarantee the stability of the system during both deployment and deorbiting phase. The paper provides a description of both the laboratory setup and the experimental activities performed to validate EDT technologies, including the damping capability of a compact passive-damping mechanism, showing how it can reduce consistently the peak forces up to about 80%

Orbital performance of small satellite deorbiting kit based on electrodynamic tape/tethers

Current plans for large LEO constellations envisage the launch and the transit of thousands of small-size satellites in clustered orbits. As recommended by international guidelines, spacecraft shall implement post mission disposal strategies, to mitigate the hazard they pose on the space debris environment. In particular, all new satellites in LEO are expected to deorbit within 25 years from their end of life. Among the proposed deorbiting technologies, electrodynamic tethers appear to be a promising and reliable option; in this context the European Commission is currently funding the project E.T.PACK – Electrodynamic Tether Technology for Passive Consumable-less Deorbit Kit in the framework of the H2020 Future Emerging Technologies FET Open program. The project focuses on the design of a disposal kit for LEO satellites, that can be activated at spacecraft end of life to perform autonomous re-entry. In this work we investigated the orbital performance of the proposed disposal kit as a function of host spacecraft mass and operational orbit. It is shown that the electrodynamic tether option can be attractive compared to deorbit systems based on traditional (e.g., chemical propulsion) and other alternatives (e.g., neutral-drag sails)

An in-line damper for tethers-in-space oscillations dissipation

The dynamical stability of tethered systems can be strongly affected by deployment strategies and environmental disturbances and consequently energy dissipation strategies are implemented to reduce oscillation amplitudes. Among the possible solutions for passive dissipation, in-line dampers consist in small mechanisms employing viscous-elastic devices or electromagnetic damping systems. In this work a CubeSat-mission-sized in-line damper is presented and the ground testing to verify its working principle is introduced. The mechanism is designed for a 500-m tape tether deployment mission but can be easily scaled to other operational configurations. The effectiveness of this solution is assessed through a campaign of numerical simulations, that are also employed to calculate the damper main design drivers. The ground tests of a scaled prototype confirm the numerical results and indicate that the in-line damper influences positively the dynamics of a deployment manoeuvre by reducing the peak tensile loads and the deviations from the nominal deployment profile

Test of tethered deorbiting of space debris

Current investigations on space tethers include their application to space debris deorbiting, specifically on the set of manoeuvres performed by a chaser tug to change the orbital parameters of a target body. Targets can be cooperative spacecraft at the end of their life or uncontrolled objects such as defunct satellites without clearly available capturing interfaces. In this latter case, a link joining tug and target may be misaligned with the target body inertia axes, influencing the attitude of both bodies; in case of rigid links, torques transmitted during tugging operations may overcome the tug attitude control system. This issue is clearly less significant in case of non-rigid connections, such as tethers; furthermore, with such connections the chaser can remain at a safe distance from the target during the whole deorbiting operation. On the other side, the initial phase of tethered space debris removal manoeuvres can be influenced by transient events, such as sudden tether tension spikes, that may cause longitudinal and lateral oscillations and, in case of resonance with the target attitude dynamics, could represent a serious issue for tug safety. In this paper it is proposed to provide the tug with a tether deployer mechanism capable to perform reel-in and reel-out, smoothing loads transmission to the target and damping oscillations. This concept is validated through a representative test campaign performed with the SPAcecRraft Testbed for Autonomous proximity operatioNs experimentS (SPARTANS) on a low friction table. A prototype of the deployer is manufactured and the deployment and rewind of a thin aluminium tape tether is proven. Test results include the verification of the tether visco-elastic characteristics with the direct measurement of spikes and oscillations and the estimation of the proposed system damping capabilities

Experimental and numerical fracture analysis of the plain and polyvinyl alcohol fiber-reinforced ultra-high-performance concrete structures

In this paper, a new procedure for manufacturing the plain and polyvinyl alcohol (PVA) fiber-reinforced ultra-high-performance concrete (UHPC) is introduced to improve its workability and to reduce its shrinkage behavior. To determine its fracture characteristics, a series of three-point bending tests are performed with the notched beam structures made of the produced UHPCs. In addition, with the rising demand for time and cost saving design methodologies associated with R&D experimentation for many industrial materials, such as UHPC structures, numerical modelling and simulation have become an essential tool. Therefore, a relevant discrete-level numerical modelling approach based on bond-based peridynamics is proposed to predict the fracture behaviors of the UHPC and UHPC-PVA structures. In the proposed method, the structures are discretized by uniform meshless nodes linked by standard peridynamic bonds, and then the bonds are randomly associated with mechanical and fracture parameters of the UHPC and PVA materials according to their corresponding volume fractions. With this approach, the reinforcement of the PVA fibers on the UHPC materials is expressed by the bonds with the parameters of PVA materials, which greatly simplifies the modelling process of randomly distributed PVA fibers reinforced UHPC structures. The comparison between numerical and experimental results validates the effectiveness and accuracy of the present method

Impact risk assessment of deorbiting strategies in low earth orbits

Various strategies are currently investigated for deorbiting satellites at the end of life to comply with the 25-year rule adopted by several space agencies. A suitable indicator of the “damage risk” due to a collision with other orbiting objects should consider not only the impact cross section of the bare spacecraft but also the additional cross section of the deorbiting device and should make a distinction between low and high energy-density impacts, respectively, with soft and hard parts of the deorbiting device. This paper presents advancements made in the last few years in electrodynamic tether technology finalized at revising the soft-impact damage risk presented by these deorbiting devices to other objects in Low-Earth Orbit (LEO) when updated deorbit performance analysis and state-of-the-art design parameters are adopted. It is found that, thanks to their collision avoidance capability and the novel tape-like geometry, bare electrodynamic tethers, besides being very competitive at reducing the hard-impact risks, are reliable devices in reducing soft-impact risks