Optimal control of a space-borne laser system for a 100 m asteroid deflection under uncertainties

The paper demonstrates the technical feasibility to deflect a 100 m diameter asteroid using a moderate size spacecraft carrying a 1-20 kW solar-powered class laser. To this purpose, a recent model of the laser ablation mechanism based on the characteristics of both the laser systems and the asteroid has been used to calculate the exerted thrust in terms of direction and magnitude. This paper shows a preliminary deflection uncertainty analysis for two different control logic and assuming different laser mechanism capabilities. In particular, an optimal thrust control direction and fixed laser pointing strategies were considered with two laser optics settings: the first maintaining the focus length fixed and the second able to exactly focus on the surface. Preliminary results show that in general the fixed laser pointing strategy at low power is less able to impart high deflection. Nonetheless, when the power increases, the optimal thrust method produces undesired torques, which reduces the laser momentum coupling as side effects. However, the overall efficiency is higher in the optimal thrust case. Since the collision risk between an impacting asteroid and the Earth depends on the probability distribution of the input uncertainty parameters, it is necessary to study how the overall deflection will be affected. Both aleatory and epistemic uncertainties are taken into account to evaluate the probability of success of the proposed deflection methods.