Power harvesting of vertical and spinning electrodynamic tethers in deorbiting scenarios for optimal and constrained conditions

The power generation by ElectroDynamic Tether (EDT) systems in deorbiting scenarios is studied. A semi-analytical model is developed to estimate the deorbit time and the harvested power for a bare EDT equipped with a cathode and an electrical load interposed between them to harvest the power. A key element of the model is the impedance of the load, which is investigated numerically to find the value that maximizes the harvested power as a function of two dimensionless parameters involving the tether length and the cathode potential drop. A parametric analysis varying EDT length, spacecraft mass, and orbit inclination was conducted with the semi-analytical model — using an analytical expression for the optimal impedance to speed up computation — to assess the performance of vertical and spinning EDTs. A 2-km-long vertical EDT at 35° of inclination deorbits 500 kg from 800 km of altitude in around 37 days while producing an average power of 126 W. A spinning EDT with the same length and initial altitude can deorbit a 1000-kg satellite from Sun-synchronous orbit in 166 days while providing 57 W. The results were benchmarked with a simulation campaign using the BETsMA v2.0 software, which relaxed some of the hypotheses of the semi-analytical model. The software was also used to study the impact on the performance, i.e., deorbit time and harvested power, of mission constraints like maximum current at the cathode and maximum impedance. The numerical results show that limiting the maximum current at the cathode to a third of the maximum value during the full simulation without any constraint increases the deorbit time by less than 20% while keeping the harvested power almost invariant.