Rapid evolution of miniaturized, automatic, robotized, function-centered devices has redefined space technology, bringing closer the realization of most ambitious interplanetary missions and intense near-Earth space exploration. Small unmanned satellites and probes are now being launched in hundreds at a time, resurrecting a dream of satellite constellations, i.e., wide, all-covering networks of small satellites capable of forming universal multifunctional, intelligent platforms for global communication, navigation, ubiquitous data mining, Earth observation, and many other functions, which was once doomed by the extraordinary cost of such systems. The ingression of novel nanostructured materials provided a solid base that enabled the advancement of these affordable systems in aspects of power, instrumentation, and communication. However, absence of efficient and reliable thrust systems with the capacity to support precise maneuvering of small satellites and CubeSats over long periods of deployment remains a real stumbling block both for the deployment of large satellite systems and for further exploration of deep space using a new generation of spacecraft. The last few years have seen tremendous global efforts to develop various miniaturized space thrusters, with great success stories. Yet, there are critical challenges that still face the space technology. These have been outlined at an inaugural International Workshop on Micropropulsion and Cubesats, MPCS-2017, a joint effort between Plasma Sources and Application Centre/Space Propulsion Centre (Singapore) and the Micropropulsion and Nanotechnology Lab, the G. Washington University (USA) devoted to miniaturized space propulsion systems, and hosted by CNR-Nanotec—P.Las.M.I. lab in Bari, Italy. This focused review aims to highlight the most promising developments reported at MPCS-2017 by leading world-reputed experts in miniaturized space propulsion systems. Recent advances in several major types of small thrusters including Hall thrusters, ion engines, helicon, and vacuum arc devices are presented, and trends and perspectives are outlined.

As a vehicle reenters or travels through the atmosphere at hypersonic velocities, the shock-heated air surrounding the vehicle becomes weakly ionized. This plasma layer causes an important systems operation problem known as communications blackout or radio blackout. At sufficiently high plasma density, the plasma layer either reflects or attenuates radiowave communications to and from the vehicle. In this paper, we study the application of electric and magnetic fields to reduce the plasma density. Specifically, an E B crossed-field configuration is proposed. Both analytical and numerical results suggest that significant reduction of the plasma density is possible at large altitudes. For instance, plasma density reduction by a factor of 10 is predicted in the case of 81 kmand a magnetic field of about 0.1 T. Theoretical results suggest that significant reduction of the plasma density is possible, enabling radio communication across the plasma layer. The benefit of the reduced plasma density in terms of electromagnetic wave absorption across the plasma layer is estimated.Michael Keidar, Minkwan Kim and Iain D. Boy

Minkwan Kim, Michael Keidar, and Iain D. Boy

Radio blackout that occurs during hypersonic reentry flight is an important issue for the operation of the vehicle. Since the radio blackout problem is caused by a high plasma number density around a vehicle, it is necessary to manipulate the plasma to allow communication. We suggest a configuration of an E B layer as a reentry blackout mitigation method. The suggestedE Blayer configuration with a two-dimensional magnetic field is simulated using the thermalized potential model and the Poisson-like model in order to illustrate the effectiveness of this approach as a mitigation method. The numerical model uses a magnetohydrodynamics approximation and is solved using a finite volume method with a Riemann solver. The results of the numerical model are assessed using available experimental results.Astrong plasma density reduction is obtained when the high electric and magnetic fields are applied near the cathode. The manipulated plasma region provides a possibility to communicate through a plasma layer during a reentry blackout.Minkwan Kim and Iain D. Boyd and Michael Keida

The sheath shape in a cylindrical electrode system is simulated by using a 2-D fluid model. The cylindrical electrode system introduces an electron-depleted region, i.e., a sheath. The generated sheath may suggest a possible approach to the communication blackout problem that occurs for a reentry vehicle, in hypersonic flight or during laser interaction with a target. This approach can work if the electron-depleted sheath region extends over the vehicle surface up to the peak of the plasma density which is typically few centimeters. In addition, for efficient communication, the sheath region should be larger than the physical size of an antenna. To estimate the size of the plasma sheath, the electron number density and the potential distribution near the cylindrically shaped electrodes are presented, and the plasma sheath is indicated.