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... (above 800 km of altitude), the LWT takes advantage of the magnetic drag and reduces drastically the area-time product. Although it is unclear whether a coating with a low enough work function (W) is feasible with actual ceramic materials (see Sec. 3), the historical evolution of low-W materials suggest that such achievement may not be far (see Fig. 2 in Ref. ...
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... as required for the EDT-D (see top panel in Fig. 5). The hollow cathode is jointly developed with a custom propellant supply system which includes all necessary components from filling valve to storage tanks to pressure reducer and passive flow control and is small enough to be integrated into the electron emitter module of the EDT-D shown in Fig. 2. Another electron emitter that is being considered is a cold Electron Field Emitter (EFE) based on carbon nanotubes (see bottom panel in Fig. 5). This design was recently evaluated within a 1400 h endurance test and has shown good emission characteristics with acceleration voltages below 1 kV, a power demand of roughly 1 W/mA and an ...
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... It provides a state-of-the-art baseline for low-power propulsion. The EDT is currently at the technology demonstration stage and is envisaged for low-power propellant-free orbit raising and lowering, and passive attitude control via gravity gradient stabilisation [77]. It is one of few technologies capable of combined orbit and attitude control in LEO. ...
Solar sails are an attractive technology for propellant-free propulsion, especially in small satellites with tight power and mass budgets. Several recent missions have shown promising applications of solar sails for nanosatellite orbital control in low Earth orbit (LEO). They enable easier access to and removal from high-altitude orbits. Since solar radiation pressure produces torques in addition to forces, a solar sail can also be used for low-power attitude control. Few missions have exploited this effect. In response, this paper proposes a new nanosatellite mission concept, only achievable by combined orbit-attitude control via solar sail: the sunflower mission, for high-altitude wide-area Earth observation. A realistic sail design meeting the mission requirements is obtained via parametric analysis and comprehensive review of past missions. A pyramid-shaped sail is proposed for the mission, and its advantages and drawbacks are analysed. The dynamics are evaluated using a high-fidelity numerical simulator with all relevant physical perturbations in LEO. The imaging objectives are successfully achieved over a multi-year duration. The sail also provides propellant-free orbit insertion from a low-altitude launch orbit, and fast de-orbit at end-of-life. It uses less power and has a smaller stowed size than several competitor technologies for orbit-attitude control of LEO nanosatellites.
... The third and final technology is the electrodynamic tether. This is a device for low-power, fuel-free orbit raising and lowering, currently at the technology demonstration stage [52]. It also provides passive attitude control via gravity gradient stabilisation. ...
Solar sails are a practical and attractive technology for low-power propulsion. While solar sailing itself requires no power, power is usually needed for attitude control. Small satellites are especially well-suited to solar sailing due to advances in the stowability of deployable reflective structures. Studies and flight experiments to date have mainly focused on solar sail applications for orbit control, using low Earth orbit (LEO) as a convenient proving ground. However, solar radiation pressure (SRP), which enables solar sailing, could also be used for low-power attitude control. This remains an untapped resource in current LEO solar sail missions and could provide mass and power savings, hence increasing the budgets available for other systems. In response, the present simulation study evaluates candidate methods to achieve both orbit and attitude control of general small satellites via solar sail. Firstly, a design trade is conducted to determine the required properties of the sail including its shape, via parametric analysis. A right-square pyramid naturally emerges as the best candidate. Secondly, the orbit-attitude control performance is assessed via a high-fidelity orbit-attitude simulation platform. A novel sunflower-type mission concept is proposed, where the sail provides passive attitude control in pitch and yaw, for applications such as Earth remote sensing. Thirdly, the costs and benefits of the pyramidal sail are compared to other technologies for low-power orbit-attitude control in LEO. It is hoped that this work will help to create new pathways for small satellite solar sailing in LEO.
... Another contact-based promising ADR technology for a long time has been the use of the Electrodynamic tether, which works on the principle of the drag thrust produced by the flow of electrons through the length of the tether in the presence of the Earth's magnetic field that helps de-orbit the system. Even though this technology would be simple, lightweight, and propellant-less, there are certain disadvantages and risks involved that cannot be eliminated such as very low Technology Readiness Level (TRL), possibility of severing, risk of collision with operation satellites, additional tension control for tumbling debris and tug safety [4][5][6]. In lieu of using only a tether, another integrated technology emerged, a tethered net could also be suitable for non-cooperative spinning objects. ...
Low Earth Orbit is exceptionally constrained by the increasing number of satellites, increasing collision risks that might lead to significant losses in technological advancement. Hence, it is imperative to develop techniques such as Active Debris Removal (ADR) to preserve the usability of the space environment surrounding Earth. A promising ADR technique consistent with contactless operation constraints, which is undergoing rapid development, is known as the Ion Beam Shepherd (IBS). This revolves around using a highly collimated ion beam to continuously exert a force at a close range on the debris to achieve a highly controlled deorbiting. However, to date, no demonstration mission has proven this concept in space. This paper presents a survey of the main research works in the subject of IBS ADR missions along with multiple comparative analyses between alternative architectures for an in-orbit demonstration mission that could potentially increase the Technology Readiness Level (TRL) of IBS capabilities for small satellites in LEO. Particular attention is given to the mission’s critical elements, such as state-of-the-art electric propulsion, techniques for collision avoidance, methods for reconstructing the dynamics of non-cooperative targets, and hazardous effects connected to IBS. The most critical risks are investigated in this paper and discussed in detail. Impulse transfer misalignment resulting in tumbling of the target, contamination risk, problems with acquiring the target based on the visual sensor inaccuracy, attitude control error in the approaching phase, and electric propulsion reliability are studied here from different angles.
... Due to those considerations, EDTs offer a solution that, specifically for LEO satellites and spent stages, is potentially very competitive among the alternative technologies currently used for end-of-life deorbiting missions, hence providing a propellant-free and fully-green device that offers a safe preservation of the space environment. The European Commission funded in 2018 with 3 M€ the project E.T. PACK, that is a 45-month H2020 Future Emerging Technologies FET-OPEN project with the objective of developing an electrodynamictether-based Deorbit Kit (DK) with TRL equal to 4. The E.T.PACK consortium has recently finished the design of a Deorbit Kit Demonstrator (DKD) prototype and is carrying out the manufacturing and testing phases of its elements [59]. The DKD consists of a 12U CubeSat with a total mass of 24 kg, that incorporates the key technologies to be validated in space. ...
... The DKD consists of 2 modules connected together [59]: the Deployment Mechanism Module (DMM), that hosts the 500-m tape tether and the Deployment Mechanism (DM), and the Electron Emitter Module (EEM), that hosts the Electron Emitter, an active device that provide the emission of electrons in the plasma environment in order for the current to be established through the tether. Each module is completely independent with its own power, communication, data handling and attitude control subsystems. ...
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%.
... Typical lengths, widths and thicknesses of state-of-the-art EDTs are in the order of a few kilometers, few centimeters and several tens of microns. Tether mass and volume represent a 5% and 3% of the total mass and volume of the Electrodynamic Tether Device (EDT-D) [14]. As an example, E.T.PACK originally estimated a 3-km long, 2.5-cm wide and 40-m thick tape tether for a 1000-kg satellite [14,15] while the tape adopted for the future 24-kg demo mission is only 500-m long. ...
... Tether mass and volume represent a 5% and 3% of the total mass and volume of the Electrodynamic Tether Device (EDT-D) [14]. As an example, E.T.PACK originally estimated a 3-km long, 2.5-cm wide and 40-m thick tape tether for a 1000-kg satellite [14,15] while the tape adopted for the future 24-kg demo mission is only 500-m long. ...
... Consequently, it is of key importance for the tethered system to take full advantage of its capability to carry out simple avoidance maneuvers [16]. In addition to that, it is recommended that EDT-based deorbit devices have GPS receivers at both modules to know the position vector of the two tether ends [14]. ...
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%.