Enabling ultra-small sensor spacecraft for the space environment using small-scale electrodynamic tethers

In this paper we investigate an approach that appears to scale to the small size needed for femtosatellite (commonly called "ChipSats") drag make-up and even orbit raising with the added benefit of being propellantless. The approach uses a short, semi-rigid electrodynamic tether (EDT) for propulsion, which keeps the overall ChipSat mass low and provides enough thrust to overcome drag in LEO. We report on our trade studies to assess the feasibility of using the EDT for ChipSat propulsion. We have analyzed the EDT anode's ability to draw current from the ionosphere and thereby generate thrust. We then traded this performance against the tether mass and material, electron emitter and collector types, and power needed to determine the EDT's capability of overcoming atmospheric drag forces. The results reveal that an insulated tether only a few meters long and tens of microns in diameter could provide milligram to 100 gram-level ChipSats with complete drag cancellation and even the ability to change orbit. The EDT system described here might be considered inefficient in terms of the power required for thrust. However, the received solar power is sufficient and the EDT is propellantless, so we believe the EDT still provides a viable approach for propulsion. We also explore the assumption that the gravity gradient force aligns the tether along the local vertical and find that this assumption needs further investigation. A more complete systems design and analysis is continuing.