Optimal low-thrust interception of earth-crossing asteroids

The spectacular collision of the Shoemaker-Levy 9 asteroid with Jupiter in July 1994 was a dramatic reminder of the inevitability of such catastrophes in the Earth's future unless steps are taken to develop methods for Earth-approaching object detection and possible interdiction. In this work, optimal (minimum-time) trajectories are determined for the interception of asteroids that pose a threat of collision with the Earth. An impulsive-thrust escape from the Earth is used initially to reduce flight time but is followed with continuous low-thrust propulsion using values of thrust and specific impulse representative of electric motors. The continuous optimization problem is formulated as a nonlinear programming problem using the collocation method in which the differential equations of motion are included as nonlinear constraint equations. The use of low-thrust propulsion after Earth escape is shown to dramatically decrease the mass of the interceptor vehicle at launch.