"The Electric Solar Wind Sail (E-sail) is a recent invention of ultra-efficient propellantless in-space propulsion technology. It uses the solar wind charged ions as natural source for producing spacecraft thrust. The E-sail is composed of a set of long, thin, conducting and positively charged tethers which are centrifugally stretched from the main spacecraft and kept electrically charged by an onboard electron gun powered by solar panels.The E-sail concept is an enabling technology for reducing significantly the time, cost and mass required for spacecraft to reach their destinations. It has been estimated that it has the potential to improve the state of the art of propulsion systems by 2 to 3 orders of magnitude if using the lifetime integrated total impulse versus propulsion system mass as the figure of merit. Furthermore, the E-sail propulsion technology is truly a green propellantless method reducing significantly the mission launch masses and the amount of chemical propellant burnt in the atmosphere. As an electromechanical device it does not need any poisonous, explosive or radioactive substances or dangerous construction procedures.In the proposed project, we develop the key E-sail technologies (tethers, tether reels, spinup and guidance/control method based on gas and FEEP thrusters) to prototype level. The goal is that after the project, the decision to build and fly the first E-sail demonstration mission in the solar wind can be made. As a secondary technological goal, the project will raise the FEEP and gas thruster readiness level for general-purpose satellite attitude control purposes."