There are a number of pressing problems mankind is facing today that could, at least in part, be resolved by space systems. They include capabilities for fast and far-reaching telecommunication, surveying of resources and climate, and sustaining global information networks, to name but a few. Not surprisingly, increasing efforts are now devoted to building a strong near-Earth satellite infrastructure, with plans to extend the sphere of active life to orbital space and later, to the Moon and Mars if not further. This demands novel and more efficient means of propulsion. At present not only heavy launch systems are still based on thermodynamic principles but satellites and spacecraft still rely on gasbased thrusters or chemical engines to move. Similarly to other transportation systems where electrical platforms expand rapidly, space propulsion technologies are also experiencing a shift towards electric thrusters which do not feature limitations intrinsic to thermodynamic systems. Most important, electric and plasma thrusters promise virtually any impulse ultimately limited by the light speed. Not surprisingly, consolidated efforts in this field could be seen, and all-electric space systems are becoming closer to reality. In this paper we briefly outline the most recent successes in the development of plasma-based space propulsion systems, and present our view on future trends, possibilities and challenges.

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Hollow cathodes are electron sources used for the gas ionization and the beam neutralization in both ion and Hall effect thrusters (HETs). A reduction of power and propellant consumption from the cathode is particularly needed in small satellite applications, where power and mass budgets are inherently limited. Concurrently, the interest in high-power HETs is increasingly fostered for a number of space applications, including final positioning and station-keeping of Geostationary Earth Orbit (GEO) satellites, spacecraft transfers from Low Earth Orbit (LEO) to GEO, and deep-space exploration missions. As such, several hollow cathodes have been developed and tested at Sitael, each conceived for a specific power class of thrusters. A numerical model was used during the cathode design to define the geometry, in accordance with the thruster unit specifications in terms of discharge current, mass flow rate, and lifetime. Lanthanum hexaboride (LaB6) hollow cathodes were successfully developed for HETs with discharge power ranging from 100 W to 20 kW. Experimental campaigns were carried out in both stand-alone and coupled configurations, to verify the operation of the cathodes and validate the numerical model. The comparison between experimental and theoretical results are presented, offering a sound framework to drive the design of future hollow cathodes.