Asteroid hazard mitigation : deflection models and mission analysis

Small celestial bodies such as Near Earth Objects (NEOs) have become a common subject of study because of their importance in uncovering the mysteries of the composition, formation and evolution of the solar system. Among all asteroids, NEOs have stepped into prominence because of two important aspects: they are among the easiest celestial bodies to reach from Earth, in some cases with less demanding trajectories than a simple Earth-Moon trajectory and, even more meaningful, they may pose a threat to our planet. The purpose of this thesis is to provide a comprehensive insight into the asteroid hazard problem and particularly to its mitigation. Six different concepts are fully described; specifically models for nuclear interceptor, kinetic impactor, low-thrust propulsion, mass driver, solar collector and gravity tug are developed and their efficiency is assessed for a complete set of different types of hazardous celestial objects. A multi-criteria optimization is then used to construct a set of Pareto-optimal asteroid deflection missions. The Pareto-optimality is here achieved not only by maximizing the deflection of the threatening object, but also by minimizing the total mass of the deflection mission at launch and the warning time required to deflect the asteroid. A dominance criterion is also defined and used to compare all the Pareto sets for all the various mitigation strategies. The Technology Readiness Level for each strategy is also accounted for in the comparison. Finally, this thesis will also show that impulsive deflection methods may easily catastrophically disrupt an asteroid if the required energy for a deflection reaches a certain limit threshold. A statistical model is presented to approximate both the number and size of the fragments and their initial dispersion of velocity and then used to assess the potential risk to Earth posed by the fragmentation of an asteroid as a possible outcome of a hazard mitigation mission.