OPTIMAL POWER PARTITIONING BETWEEN ELECTRIC THRUSTERS FOR SPACE TRAJECTORIES

Subject of this thesis is the design of a space robotic mission to the asteroid 433 Eros. The mission aims to grab a boulder from its surface and transport it inside the Earth's influence sphere. This work was inspired by NASA's Asteroid Redirect Mission (ARM), which was cancelled in 2017 due to lack of funding, and whose purpose was to transfer a boulder from the surface of a Near-Earth asteroid (NEA) to a stable lunar orbit, where it could be further analyzed both by robotic probes and by a future manned mission. The propulsion system used for the theorized mission consists of three autonomous ion thrusters fully adjustable in magnitude and direction of thrust. Furthermore, during the return flight an Earth gravity assist is used to increase the mass of boulder that the spacecraft can transport towards Earth. The following chapters will analyze the interplanetary phase of this mission and, specifically, an optimization of the interplanetary trajectories will be carried out. An indirect method will be used to formulate the possible optimal combinations of the powers of the three engines, where, in the context of electric propulsion, the thrust and flow rate of the propellant are linked by a cubic dependence on the input power. The trends of the power, the thrust and the specific impulse of the optimal case will be compared with the case in which the power is distributed in such a way as to have a thruster always at maximum power and with the case in which the power is distributed uniformly. Finally, the results obtained from the asteroid Eros (Near-Earth asteroid) will be compared with those obtained from the sub-kilometer asteroid "2008ev5".