Indirect Optimization of Asteroid Deflection Missions with Electric Propulsion

An indirect method, which exploits the theory of optimal control, is applied to optimize a kinetic impactor mission for the deflection of an Earth-crossing asteroid. The trajectory of the deflecting spacecraft from Earth escape to asteroid deviation is determined to maximize the miss distance at the asteroid's closest approach to the Earth. A procedure to find mission opportunities is developed and applied to both ballistic and electric propulsion trajectories. The optimization method proves to be robust and efficient. A large number of deflection opportunities are found with limited computational effort. The comparison of results shows the benefit that the use of electric propulsion can provide with respect to ballistic trajectories; high-performance trajectories, which move far from the sun and become retrograde, are enabled. Counterintuitive effects related to asteroid inclination are also highlighted.