Investigating Electrodynamic Tether Behavior Under Varying Parameters to Optimize Design and Performance

The recent change in space safety and orbital debris policy, reducing the allowed de-orbiting time for spacecraft from 25 years to 5 years, has sparked a significant interest in developing efficient systems for rapid de-orbiting. Various traditional and non-traditional methods have been proposed, including chemical and electric thrusters, drag sails, and plasma brakes. Among these, the concept of electrodynamic tethers (EDTs) has emerged as a promising solution for applications such as fuel-less propulsion for de-orbiting, station-keeping, orbital maneuvering, and power generation. Despite extensive research, there remains a lack of comprehensive resources for engineers on the design of EDT systems for end-of-life missions. This study addresses the design challenges associated with utilizing EDTs for different spacecraft, emphasizing the need to evaluate their performance and feasibility in various orbital regimes. It delves into the fundamentals of electrodynamic systems, analyzing orbital parameters and tether characteristics critical to the design process, and outlines the performance metrics of EDT systems. The aim is to demonstrate how operating conditions and desired outcomes define the characteristics of an EDT system. By considering multiple criteria and trade-offs, this work provides detailed design considerations for mission-specific passive EDT systems for end-of-life missions. Additionally, the study explores the use of active tether systems for station-keeping application. Mission scenerios for different spacecraft sizes are used to asses the feasibility of utilizing EDT systems for station-keeping. The EDT performance using power efficiency metrics is compared with the propuslion system onboard the mission considered. The results show that EDT system are beneficial for LEO application for all spacecraft size but the efficiency reduces for VLEO. For smaller spacecraft sizes like cubesats, other propulsion systems may be more advantageous. An experimental investigation was also conducted in a plasma chamber to analyze and compare the electron current collection of a cylindrical electrodynamic tether under various conditions. The current-voltage (I-V) characteristics were examined using different simulated plasma environments, tether materials, plasma densities, and tether biasing levels. The experiment utilized plasma gases Hydrogen, Oxygen, and Room Air to simulate the plasma conditions within a plasma chamber simulating plasma densities ranged from 10^14 to 10^15 particles per m^3 . Alongside tungsten aluminum solid tether samples, the I-V characteristics of Aracon braided tether sample is used in the experiment. The analysis revealed that the I-V characteristics vary depending on the specific plasma gas used, highlighting the significant influence of plasma ions on current collection. This suggests that the performance of EDTs will depend on the dominant ion species at different altitudes. The comparison between experimental data and theoretical Orbital-Motion-Limited (OML) models showed that tethers exposed to air and oxygen plasma displayed values more consistent with theoretical predictions, particularly at higher biases, with the aracon sample showing especially favorable results. Among the tether materials tested, the aracon sample performed better in oxygen and air plasma, while aluminum showed superior performance in hydrogen plasma. This indicates that the choice of tether material is crucial and highly dependent on the dominant ions in the environment. This work explores the variables and provides a comprehensive analysis of the factors that influence the performance of electrodynamic tether systems in space applications aiming to improve the understanding of tether-plasma interactions for enhanced EDT system design.