Asteroid Control via Neutral Beam Emitting Spacecraft

Abstract

Automated surveys along with population models have determined that tens of thousands Near Earth Objects (NEOs) exist and regularly cross over the Earth's orbit. While none of the currently discovered NEOs are predicted to impact Earth, many have yet to be discovered. We propose using neutral beam equipped spacecraft to deflect an asteroid from an Earth impact trajectory. Neutral beams are created through global neutralization of ion beams via recombination reactions and contain no charged particles. This thesis focuses on the design and testing of a unique neutral beam thruster and its application to planetary defense. The first contribution of this thesis focuses on the efficacy of using low-thrust propulsion to de-spin and deflect sub-kilometer sized asteroids. The second contribution of this thesis demonstrates that neutral beams, a technology typically used to heat tokamak plasmas, can be scaled for keV electric propulsion for spacecraft. The third contribution of this thesis is that a method has been developed to conduct thrust measurements for sub-Newton propulsion on a hanging pendulum thrust stand during thermal drift. For the fourth contribution of this thesis analytical expressions for a low power neutral beam are derived and simulations are conducted to design a unique gas diffusion neutralizer. The experimental performance is validated against both the analytical expressions and simulation data. Using neutral beams for mitigating the hazard of sub-kilometer asteroids is possible within current and near-term technology. The gas diffusion neutralizer designed is applicable to other gridded ion thrusters with only minor modifications needed. This thesis presents the experimental methods for neutral beam characterization including assembly of the diagnostics. The improvements in testing on a hanging pendulum thrust stand allow for more rapid characterization of the thrust performance of sub-Newton thrusters. The analytical expressions and simulations developed by this work have been confirmed by experimental data and demonstrate the viability of neutral beam propulsion. Future work in this field could investigate deflection mission design, alternate ion sources, gas diffusion neutralizer material choices, ion deflection subsystems, and higher energy ion beams.