External Plasma-Breathing Magnetohydrodynamic Spacecraft Propulsion*

The hazard posed by space debris has the potential to severely dampen future space prospects. Though mitigation strategies such as satellite deorbiting and active debris removal exist, both are hindered by significant technical and economic challenges, such as the need for high Delta-V budgets. Atmosphere-breathing spacecraft propulsion has gathered attention due to its potential to avoid onboard propellant storage, but current implementations involve major architectural modifications. In this context, an external magnetohydrodynamic (MHD) propulsion system is proposed as a low-footprint alternative that avoids major spacecraft redesign by adopting an external patch configuration. It is found that the mass and power requirements scale linearly with the mass of the spacecraft, and that both passive and active drag components exist, and are of similar magnitude. Adopting a first-order analysis scheme, the effective specific impulse (defined as impulse generated per unit device mass) of the MHD conductive propulsion system is found to be 13-15 km/s in polar and near-polar orbits and above 30 km/s in equatorial orbits over a period of 2.5 years. Power consumption per unit thrust on the order of 5-20 W/mN is found. The power and propellant mass requirements are thus similar or slightly lower than electric propulsion options such as Hall effect thrusters and magnetoplasmadynamic propulsion, with power consumption being of the same order as other atmosphere-breathing options. Drawbacks of conductive MHD propulsion, such as those associated with the necessity of strong magnetic fields for operation, are also discussed.