Electric Sail for Near-Earth Asteroid Sample Return Mission: Case 1998 KY26

The electric solar wind sail (E-sail) is an innovative propellantless concept for interplanetary space propulsion that uses the natural solar wind as a thrust source with the help of long, artificially charged tethers. The characteristic property of an E-sail based spacecraft is that the propulsive acceleration scales as the inverse Sun-spacecraft distance, and the thrust vector can be varied within about 30 deg away from radial direction. The aim of this paper is to estimate the transfer times required to fulfill a mission toward the near-Earth asteroid 1998 KY26. In doing so the propulsive acceleration of the E-sail, at a reference distance from the Sun, is used as a performance parameter so that the numerical results are applicable to E-sails of different sizes and different payload masses. The paper shows that the flight time scales nearly linearly with the inverse of the spacecraft maximum propulsive acceleration at 1 astronomical unit from the Sun, when the acceleration is greater than 0.3 mm/s(2). For smaller propulsive accelerations the relationship for the flight time is more involved, because the transfer trajectory is complex and more than one revolution around the Sun is necessary to accomplish the mission. The numerical analysis involves a sample return mission in which the total flight time is parametrically correlated with the starting date for a given E-sail propulsion system.