This contribution presents a short review of electric propulsion (EP) technologies for satellites and spacecraft. Electric thrusters, also termed ion or plasma thrusters, deliver a low thrust level compared to their chemical counterparts, but they offer significant advantages for in-space propulsion as energy is uncoupled to the propellant, therefore allowing for large energy densities. Although the development of EP goes back to the 1960s, the technology potential has just begun to be fully exploited because of the increase in the available power aboard spacecraft, as demonstrated by the very recent appearance of all-electric communication satellites. This article first describes the fundamentals of EP: momentum conservation and the ideal rocket equation, specific impulse and thrust, figures of merit and a comparison with chemical propulsion. Subsequently, the influence of the power source type and characteristics on the mission profile is discussed. Plasma thrusters are classically grouped into three categories according to the thrust generation process: electrothermal, electrostatic and electromagnetic devices. The three groups, along with the associated plasma discharge and energy transfer mechanisms, are presented via a discussion of long-standing technologies like arcjet thrusters, magnetoplasmadynamic thrusters, pulsed plasma thrusters and ion engines, as well as Hall thrusters and variants. More advanced concepts and new approaches for performance improvement are discussed afterwards: magnetic shielding and wall-less configurations, negative ion thrusters and plasma acceleration with a magnetic nozzle. Finally, various alternative propellant options are analyzed and possible research paths for the near future are examined.

There are a number of pressing problems mankind is facing today that could, at least in part, be resolved by space systems. These 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. The realization of these aspirations demands novel and more efficient means of propulsion. At present, it is not only the heavy launch systems that are fully reliant on thermodynamic principles for propulsion. Satellites and spacecraft still widely use gas-based thrusters or chemical engines as their primary means of propulsion. Nonetheless, similar to other transportation systems where the use of electrical platforms has expanded rapidly, space propulsion technologies are also experiencing a shift toward electric thrusters that do not feature the many limitations intrinsic to the thermodynamic systems. Most importantly, electric and plasma thrusters have a theoretical capacity to deliver virtually any impulse, the latter being ultimately limited by the speed of light. Rapid progress in the field driven by consolidated efforts from industry and academia has brought all-electric space systems closer to reality, yet there are still obstacles that need addressing before we can take full advantage of this promising family of propulsion technologies. In this paper, we briefly outline the most recent successes in the development of plasma-based space propulsion systems and present our view of future trends, opportunities, and challenges in this rapidly growing field.

Properties of rotating spokes have been investigated in the plasma discharge of the 200 W-class permanent magnet ISCT200 Hall thruster (HT) in wall-less (WL) configuration under various operating conditions. For comparison purposes, the HT was also operated in the standard configuration. High-speed camera imaging combined with sophisticated image processing allowed the observation of the plasma inhomogeneity dynamics and the determination of characteristics such as mode number, sizes, rotation frequency and propagation velocity. The time varying Xe ⁺ ion azimuthal velocity distribution function has been measured in front of the anode of the WL thruster by means of laser-induced fluorescence spectroscopy in photon-counting regime. Experiments show ions move at the thermal speed on average, yet some ions have a negative velocity, i.e. they rotate in the direction opposite to the E × B drift, in agreement with numerical simulations performed with a 3D-3V PIC code.

Reliable measurements of electron properties are key for the validation of simulations of Hall thrusters and similar plasma sources. In this paper, a recently-developed incoherent Thomson scattering diagnostic is successfully applied to electron property measurement in a low-power Hall thruster discharge. Investigations of electron properties along radial and azimuthal directions in both conventional and magnetically-shielded architectures are performed. The high diagnostic sensitivity gives access to electron property measurements in a plasma environment with densities as low as 10 16 m − 3 . Electron temperatures reaching several tens of eV and drift velocities on the order of 10 6 m s − 3 are measured in the exit plane region. The impact of the magnetic field (intensity and direction) and discharge voltage are investigated.

In this paper, we examine the characteristics of the ISCT100 thruster, a miniature xenon-fueled 100-W permanent magnet Hall thruster (HT) suited for microspacecraft propulsion. The impact of the thruster design upon discharge behavior, ion beam properties, and performances is examined as for two discharge channel geometries as well as two values of the magnetic field strength. Thrust, specific impulse, and efficiency obtained between 50 and 200 W are compared with the ones of other low-power HTs.