Model of Current Collection to Small Breaches in Electrodynamic-Tether Insulation

Future electrodynamic-tether missions are expected to be long duration (from several months to years); hence, these missions can expect possibly significant performance degradation due to breaches in tether insulating material caused by hazards such as mi-crometeoroids. In order to accurately predict this performance degradation, the collection of plasma current to these small breaches must be characterized. We have performed a series of plasma chamber experiments on simulated tether samples with holes in the outer insulation to determine I–V characteristics. The samples are fabricated from stainless-steel wire insulated with conventional shrink or Teflon tubing, and of annealed copper wire. Various sizes of breaches (holes) have been inserted in the insulation. The sizes of the holes, their number, and their spacing have been varied. The influence of the spacing on the current–voltage characteristic is compared to a developed model. The samples are connected to an electrometer so the I–V characteristic can be measured. Ionospheric-level plasma is generated with a low energy plasma source system running on argon. These results, while directly applicable to electrodynamic tethers, are also important for any insulated wiring on spacecraft that runs the risk of being impacted by micrometeoroids or small orbital debris.