The transition from old space to new space along with increasing commercialization has a major impact on space flight, in general, and on electric propulsion (EP) by ion thrusters, in particular. Ion thrusters are nowadays used as primary propulsion systems in space. This article describes how these changes related to new space affect various aspects that are important for the development of EP systems. Starting with a historical overview of the development of space flight and of the technology of EP systems, a number of important missions with EP and the underlying technologies are presented. The focus of our discussion is the technology of the radio frequency ion thruster as a prominent member of the gridded ion engine family. Based on this discussion, we give an overview of important research topics such as the search for alternative propellants, the development of reliable neutralizer concepts based on novel insert materials, as well as promising neutralizer-free propulsion concepts. In addition, aspects of thruster modeling and requirements for test facilities are discussed. Furthermore, we address aspects of space electronics with regard to the development of highly efficient electronic components as well as aspects of electromagnetic compatibility and radiation hardness. This article concludes with a presentation of the interaction of EP systems with the spacecraft.

The $2s_{1/2}\mathrm{\text{−}}2p_{1/2}$ energy splittings $\Delta E_L$ of the lithiumlike ions ${}_{79}{}^{197}\mathrm{A}\mathrm{u}^{76+}$, ${}_{82}{}^{208}\mathrm{P}\mathrm{b}^{79+}$, and ${}_{92}{}^{238}\mathrm{U}^{89+}$ have been measured at the Experimental Storage Ring, utilizing low energy dielectronic recombination. The resonance energies in total 41 different $1s^{2}2p_{1/2}n{l}_{j^{\prime }}$ ($n\ge 20$) autoionizing Rydberg states populated in the dielectronic capture process have been determined. The $2s_{1/2}\to 2p_{1/2}$ excitation energies have been obtained by extrapolation of these resonance energies to the associated series limits $n\to \infty$. The combined analysis of the experimental data for all three ions yields $\Delta E_L=216.134(96)\mathrm{e}\mathrm{V}$ for ${\mathrm{A}\mathrm{u}}^{76+}$, 230.650(81) eV for ${\mathrm{P}\mathrm{b}}^{79+}$, and 280.516(99) eV for ${\mathrm{U}}^{89+}$.

Neutral ${\mathrm{C}}_{60}$ is well known to exhibit a giant resonance in its photon absorption spectrum near 20 eV. This is associated with a surface plasmon, where delocalized electrons oscillate as a whole relative to the ionic cage. Absolute photoionization cross-section measurements for ${\mathrm{C}}_{60}^{+}$, ${\mathrm{C}}_{60}^{2+}$, and ${\mathrm{C}}_{60}^{3+}$ ions in the 17–75 eV energy range show an additional resonance near 40 eV. Time-dependent density functional calculations confirm the collective nature of this feature, which is characterized as a dipole-excited volume plasmon made possible by the special fullerene geometry.