Electric Propulsion Technology Research Articles

Electric Propulsion in Space: Technology and Geopolitics

ABSTRACT During the 20th Century and within the first decade of the 21st, electric propulsion (EP) has played an important role in space activities, and its importance has not ceased to increase significantly in the last 15 years. The potential benefits of using EP on a bigger scale could be immense, reducing the cost of future space missions. The main hypothesis of this paper is that EP will play an increasingly important role in the system of international space relations in the coming decades with deep scientific, commercial, and geopolitical implications. To prove this, we examine the historical evolution, relevance, and future applications of such a propulsion system. Although there is extensive technical literature on EP, only a few works analyze electric space propulsion from an interdisciplinary perspective. On the contrary, much of the available information only provides an atomized, unipolar, and fragmented approach to the phenomenon. To fill this gap, this study presents an integrated analysis of the evolution, relevance, and trends of EP technologies, as well as their geopolitical implications in the space domain. The results obtained constitute a crucial contribution to the analysis of space propulsion from an interdisciplinary – socio-technological – perspective.

Development of Carbon Composite Blades within the Context of the Experimental Validation of a CFD-Based Design Tool for Contra-Rotating, Electric Fan Engines

Electric propulsion systems have emerged as a disruptive technological approach towards achieving sustainable and climate-neutral aviation. To expand the operational envelope of such propulsion units in terms of altitude and velocity, an enclosing duct and counter-rotating rotors to enhance efficiency can be utilized. In this study, an iterative CFD-based design tool developed for these novel propulsion systems is utilized to design a reference engine, having a classic rotor–stator configuration. Being the key component of this propulsor, a manufacturing process for composite blades is presented. This effort aims to make state-of-the-art technology accessible to smaller research projects, promoting the widespread adoption of electric propulsion technology in the aviation sector. By experimental investigations of the blade elongation both in tensile tests and engine operation, measuring the tip clearance with a high-speed camera, this process could be validated to facilitate the transferability of research. Finally, the performance of the manufactured engine is measured by a five-hole miniature probe, not only in design point but also in off-design operation. The results indicate that a substantial reduction in discrepancies between initial specifications, subsequent CFD simulations, and experimental investigations compared to conventional design tools relying on empirical formulations can be achieved due to the CFD-based approach. This allows the CFD-based tool to be validated for designing scalable contra-rotating fan engines.

Design Exploration of a Distributed Electric Propulsion Aircraft Using Explainable Surrogate Models

Distributed electric propulsion in aircraft design is a concept that involves placing multiple electric motors across the aircraft’s airframe. Such a system has the potential to contribute to sustainable aviation by significantly reducing greenhouse gas emissions, minimizing noise pollution, improving fuel efficiency, and encouraging the use of cleaner energy sources. This paper investigates the impact and relationship of turbo-electric propulsion component characteristics with three performance quantities of interest: lift-to-drag ratio, operating empty weight, and fuel burn. Using the small- and medium-range “DRAGON” aircraft concept, we performed design exploration enabled through the explainable surrogate model strategy. This work uses Shapley additive explanations to illuminate the dependencies of these critical performance metrics on specific turbo-electric propulsion component characteristics, offering valuable insights to inform future advancements in electric propulsion technology. Through global sensitivity analysis, the study reveals a significant impact of electrical power unit (EPU) power density on lift-to-drag ratio, alongside notable roles played by EPU-specific power and applied voltage. For operating empty weight, EPU-specific power and voltage are highlighted as critical factors, while turboshaft power-specific fuel consumption notably influences fuel burn. The analysis concludes by exploring the implications of the insights for the future development of turbo-electric propulsion technology.

Study on a hybrid-produced magnetic-field Hall thruster

The increasing interest in all-electric, low-Earth orbit satellite constellations has stimulated the rapid development of electric propulsion technology, particularly low-power Hall thrusters. In this study, the difficulties in magnetic field design were analyzed in low-power Hall thrusters, and a new and efficient hybrid production technique is proposed. Hybrid production combines the advantages of coil and permanent magnet production; the main magnetic field is generated by permanent magnets, and the regulating magnetic field is generated by coils in parallel. Accordingly, a prototype of a 600-W hybrid-produced magnetic field Hall thruster, HPHT-600, was designed and tested. The HPHT-600 has a small size (channel outer diameter 54 mm), light weight (1.2 kg), low area–volume ratio (0.148), and low magnetic power. In addition, it exhibits a power envelope of 300–1000 W and a total efficiency of 53.5 % at the discharge voltage of 300 V, anode volume flow rate of 35 sccm, and total specific impulse of 1900 s at 500 V and 20 sccm.

Electric propulsion for lifeboat

This paper presents the integration of the electric propulsion technology in the lifeboat maneuvering system to enhance efficiency, reliability and sustainability. The present lifeboat propulsion system often relies on the internal combustion engine which requires fuel to propel and also has various challenges to face such as emissions, maintenance, and overall environmental impact. This paper delves into the design, economics, ergonomics, engineering challenges and performance assessments associated with the successful implementation of electric propulsion for lifeboats. Special emphasis is given to the research and development of lightweight, high-capacity energy storage systems (ESS) and efficient electric motors which are suitable for the maritime emergency evacuation applications. The features of electric propulsion (EP), such as reduced harmful emissions, lowering maintenance requirements and improving maneuverability draws more attention for this research field. The paper also explores the integration of green energy sources such as solar and wind that can be used to supplement the electric propulsion system which enhance the autonomy and sustainability of the lifeboat during emergencies. This work focuses on the overall advancement of maritime emergency safety equipment and will also help in contributing to make maritime services more eco-friendly by offering a comprehensive analysis of electric propulsion integration in lifeboats, providing insights for further future developments.

Investigation of the Effect of Magnetic Field and Propellant on Hall Thruster’s Stability via a 0D Model

Hall thrusters are plasma-based devices that have established themselves as one of the most attractive and mature electric propulsion technologies for space applications. These devices often operate in a regime characterized by low frequency, large amplitude oscillations of the discharge current, which is commonly referred to as the ‘breathing mode’. The intensity of these oscillations depends on the thruster’s design and operating conditions and can reach values of the order of the average discharge current, posing issues for the thruster’s performance and for coupling with the driving electronics. A 0D model of the thruster discharge was developed to investigate the core physical mechanisms leading to the onset and sustenance of the breathing mode. The model was found to be capable of reproducing oscillations with characteristics in line with those observed in the breathing mode. In this work, we extend the use of the 0D model to investigate the effect of the magnetic field intensity and of different propellants on the system stability.

Payload Optimization for EnVision Mission Using an Electric Propulsion Module for Interplanetary Transfers

This paper presents a study on the feasibility of using electric propulsion (EP) for interplanetary transfer in the context of an Earth–Venus mission. Extensive research has been conducted on EP modules for Mars missions, demonstrating their potential for faster mission times and greater flexibility compared to all-chemical propulsion (CP) systems. However, there is a notable gap in our understanding regarding EP systems for Venus missions, despite the unique and challenging environment that Venus presents. This study aims to bridge that gap by evaluating the performance of an EP module compared to a conventional all-CP spacecraft, which serves as the backup mission for the EnVision mission by the European Space Agency. The objectives of the study include identifying key drivers for the EP module’s preliminary design, analyzing tradeoffs and challenges associated with EP systems, and evaluating the feasibility of achieving payload mass delivery. The results reveal that the all-EP spacecraft delivers a higher payload mass compared to the all-CP EnVision mission, highlighting the superiority of EP over CP for interplanetary missions. This research provides valuable insights into the potential advantages of EP systems for future interplanetary missions and emphasizes the necessary design considerations when utilizing EP technology.

Numerical Prediction of Aerodynamic Noise for a Propeller-wing Configuration and an Investigation of Pitch Effect

Driven by the sustainable and eco-friendly vision of aviation, Distributed Electric Propulsion (DEP) technology has received much attention for its high aerodynamic efficiency. Simultaneously, lower noise emissions from DEP configurations are desired and therefore it is important to investigate the aerodynamic noise features, which include but are not limited to the noise generation mechanism and the effect of propeller-propeller/wing interactions. This paper focuses on a numerical approach, which is suitable for industrial practice, for predicting the aerodynamic noise of propeller-wing configurations. A generic DEP configuration is employed, consisting of a Mejzlik 2-blade propeller installed on the leading edge of a NACA0018 airfoil. A hybrid method of computational aeroacoustics has been performed in the present simulations, where aeroacoustics in the near field is solved by coarse-grid compressible large-eddy simulations and then the acoustic far field is calculated by the Ffowcs-Williams Hawkings analogy. The influence of grid resolution is studied based on Pope's criterion M and satisfactory results are achieved at a moderate mesh count as compared to the experimental measurements. Further simulations are conducted to investigate the effect of propeller pitch on the aerodynamic performance, noise generation and propeller-wing interactions.

Time- and Energy-Saving Potentials of Efficient Urban Air Mobility Airspace Structures

Novel electric propulsion technology has given rise to thinking about urban air mobility in a new way with its expected high degree of operational flexibility. The designs of electric vertical takeoff and landing configurations are determined by their mission profile, which we found to be oversimplified at many points in the current scientific literature. There is a gap of understanding in how mission profiles impact travel time and energy demand. In this paper, we review various mission designs, formulate a five-segment flight profile (including vertical ascent, climb, cruise, descent, and vertical approach), and apply it on a fleet level of up to 200,000 urban air mobility trips. The demand data originate from the Upper Bavaria region study, OBUAM. In a sensitivity study, we vary the cruise altitude, the height of the vertical flight segments, and the climb and descent angles for two vehicle configurations: a fixed-wing tilt-rotor concept, and a multicopter concept. The main findings for the fixed-wing concept are that the height of the vertical flight segments and the cruise altitude should be as low as possible, and small climb angles (below 7 deg) should be avoided. The multicopter concept, however, is penalized by fast forward flight while being comparatively insensitive to both the cruise altitude and height of the vertical flight segments. Furthermore, we found a tradeoff between time- and energy-optimal flights with the a energy-optimized climb/descent angle at around 10 deg.

Elliptical Orbit Design Based on Air-Breathing Electric Propulsion Technology in Very-Low Earth Orbit Space

Very-low Earth orbit (VLEO) space below 200 km is essential for high-quality communications and near-Earth space environment detection. Due to the significant atmospheric drag, orbital maintenance is required for spacecraft staying here. Based on air-breathing electric propulsion (ABEP) technology, this paper analyzed the orbital boundary conditions of the spacecraft under the constraints of parameters including slenderness ratio, thrust-to-power ratio, drag coefficient, and effective specific impulse. The energy balance is the key constraint for low VLEO orbits, which is determined by the drag coefficient, slenderness ratio, and thrust-to-power ratio. Under the existing technical conditions, the lowest circular orbit (along the terminator) is about 170 km. An elliptical orbital flight scheme is also analyzed to reach a 150 km perigee. A half-period control method was proposed based on the on–off control method for the elliptical orbit, which could enable the spacecraft to maintain a stable 150–250 km elliptical orbit.

A multi-objective variable-specific impulse maneuvers optimization methodology

The problem of optimizing variable-specific impulse electric propulsion maneuvers is presented, proposing a novel multi-objective methodology for the computation of near-optimal planetocentric solutions. The methodology relates a parameter expressing the instantaneous maneuvering efficiency, or thrust effectivity, with the specific impulse through an arbitrary parametric function. The parameters of this function are determined by a multi-objective genetic algorithm, which minimizes propellant consumption and maneuver duration. The study includes the analysis of several scenarios, with the results demonstrating that the methodology can be successfully employed in the context of space mobility of small satellites. The findings reveal that variable-specific impulse maneuvers can achieve improvements exceeding 17% in both propellant mass and maneuver duration compared to a constant-specific impulse case. Consequently, the resultant Pareto fronts showcase enhanced trade-offs and more favorable solutions for the optimization problem. The results highlight the significance of this optimization methodology for electric propulsion technologies with throttling capabilities, particularly in systems with near-constant propulsive efficiency.

Significant Development Potential of the Solid Oxide Fuel Cell for the Technical Progress of the Marine Main Propulsion Plant in the Context of Energy Conservation and Emission Reduction

The International Maritime Organization (IMO) has proposed a series of strict pollutant emission regulations and carbon emission reduction targets, and the shipping industry is seeking new types of the marine main propulsion plant with advantages of high-efficiency and low-emission. Among the possible alternatives, the marine electric propulsion technology whose electric power source is fuel cell has gained sufficient attentions. At present, the worldwide research of the marine applications for fuel cell supplying propulsion power focuses more on the proton exchange membrane fuel cell (PEMFC) with low power instead of other types of fuel cell, and a series of research projects have achieved concrete results such as the industrialized marine fuel cell system or practical demonstration application. But the development trends of the application of the marine fuel cell supplying propulsion power are from the small boat to the great ship, from the navigating zone with low environmental complexity such as coastal water, inland waters to the ocean with complex navigation conditions. Thus, the power demand of the marine fuel cell in the future will show steady growth, which will create more development opportunities for the solid oxide fuel cell (SOFC) with the advantages of higher power, greater efficiency, long life span and fuel diversity. Although some challenges exist, the solid oxide fuel cell with significant development potential can certainly lead the technical progress of the marine main propulsion plant in the context of energy conservation and emission reduction.

Analysis on the working mode of electric propulsion system

At present, the electromagnetic propulsion technology and the electrostatic propulsion technology are more mature than before. With the increase of available power on the spacecraft, the performance can be better improved. This paper mainly reviews the electric propulsion technology for long-term space travel. It can be concluded that, compared to traditional chemical rocket systems, electric propulsion systems are more suitable for long-term space missions and have the ability to transport relatively heavy objects in space.

An atmosphere-breathing propulsion system using inductively coupled plasma source

CubeSats have attracted more research interest recently due to their lower cost and shorter production time. A promising technology for CubeSat application is atmosphere-breathing electric propulsion, which can capture the atmospheric particles as propulsion propellant to maintain long-term mission at very low Earth orbit. This paper designs an atmosphere-breathing electric propulsion system for a 3 U CubeSat, which consists of an intake device and an electric thruster based on the inductively coupled plasma. The capture performance of intake device is optimized considering both particles capture efficiency and compression ratio. The plasma source is also analyzed by experiment and simulation. Then, the thrust performance is also estimated when taking into account the intake performance. The results show that it is feasible to use atmosphere-breathing electric propulsion technology for CubeSats to compensate for aerodynamic drag at lower Earth orbit.

Exploring the Green-Oriented Transition Process of Ship Power Systems: A Patent-Based Overview on Innovation Trends and Patterns

The shipping industry has accelerated the transformation of its carbon emission reduction and decarbonization, and relevant patents are rapidly increasing, but the industry still lacks consensus on the low-carbon development route of ship propulsion technology. We used the Derwent Innovation Index to collect the global patent information on ship power systems between 1965 and 2022 and proposed a new patent information mining framework. It is used for the dynamic tracking and analysis of global technology correlation characteristics, hot technology topics, and competitive situations. The findings indicate that: (1) the innovation of ship power systems is more radical and concentrated in the fuel field represented by LNG technology, whereas technical innovation in the field of pure electric propulsion is more scattered. Small tonnage ships, underwater operations, and recreation technology are among its innovation hotspots. (2) Pure electric propulsion technology is dominated by combined innovation with other propulsion methods (hybrid propulsion technology) and Chinese universities have recently begun to lead this technology. (3) Fuel cells and remote control have become innovation hotspots. Fuel cell technology, which combines electric, fuel, and hybrid power technology, is now on the cutting edge of innovation and has the potential for disruptive innovation.

Theoretical Research on Magnetic Confinement Mechanism of Applied-Field Magnetoplasmadynamic Thruster

Since the invention of rockets, mankind has been constantly trying to explore the universe. It was not until the beginning of the last century that electric propulsion technology was introduced. With the same weight of fuel consumed as chemical propulsion, electric propulsion technology can transport a spacecraft to a more distant universe. With its excellent performance in terms of specific impulse and thrust, the MPDT (MagnetoPlasmaDynamic Thruster) is garnering significant attention in the field of electric propulsion. Recent research has focused on improving its propulsion performance and service life. Due to the complexity of its working mechanism, there is no perfect explanation for it. Further analysis of its working mechanism may lead to a solution to the improvement of certain significant performance aspects such as thrust. An ideal magnetic fluid model of the MPDT is established based on the MHD method, and the working mechanism is analyzed and summarized according to simulations and experiments. The results of the analysis indicate that reducing the size of the cathode could significantly improve the thruster’s performance.

Design and optimization of ion propulsion drone

Electric propulsion technology is widely used in many kinds of vehicles in recent years, and aircrafts are noexception. Technically, UAVs are electrically propelled but tend to produce a significant amount of noise andvibrations. Ion propulsion technology for drones is a potential solution to this problem. Ion propulsion technologyis proven to be feasible in the earth’s atmosphere. The study presented in this article shows the design of EHDthrusters and power supply for ion propulsion drones along with performance optimization of high-voltage powersupply for endurance in earth’s atmosphere.

Design and optimization of ion propulsion drone

Electric propulsion technology is widely used in many kinds of vehicles in recent years, and aircrafts are no exception. Technically, UAVs are electrically propelled but tend to produce a significant amount of noise and vibrations. Ion propulsion technology for drones is a potential solution to this problem. Ion propulsion technology is proven to be feasible in the earth’s atmosphere. The study presented in this article shows the design of EHD thrusters and power supply for ion propulsion drones along with performance optimization of high-voltage power supply for endurance in earth’s atmosphere.

Aircraft Distributed Electric Propulsion Technologies—A Review

Global transportation has shifted toward electromobility to achieve net-zero emission, and in the next few decades, commercial electric aircraft is likely to become a reality. This transition has embarked on through the existing more electric aircraft (MEA), and the ultimate goal will be potentially achieved by hybrid-electric and all-electric airliners, along with green fuels, such as green hydrogen or supercritical CO2 (sCO2) and its potential Gg CO2 equivalent elimination—with or without combustion. Electric propulsion replaces conventional jet propulsors with electric fans powered by electric generators rotated by an engine, a combination of generators and energy storage, or just energy storage. An appealing idea is to distribute the electric fans along the aircraft wings or tails to improve aerodynamics, boost energy efficiency, and reduce carbon emissions and acoustic noise. Focusing on distributed electric propulsion (DEP) systems, this article reviews the state-of-the-art advancements in aircraft electrification. Three major DEP categories, i.e., turboelectric, hybrid-electric, and all-electric propulsion technologies, are investigated. Although all of them utilize electric fans as propulsors, their system structures and power generation stages are different. Hence, comprehensive considerations are required to optimize the DEP system designs. Starting with the multifarious electrical system architectures proposed in the literature, a thorough review is conducted including the system parametric specifications, design considerations of power converters, the power electronics devices’ characteristics in cryogenic conditions, and various energy storage systems. This review aims to provide a reference to researchers, engineers, and policy-makers in aviation to accelerate the progress toward future net-zero emissions.

Ion-induced electron emission by keV-range energy indium ions: Influence of material and geometry

This work provides measurements of the ion-induced electron emission yield caused by keV-range energy indium ions (3–8 keV). In our experiment, the ion sources, fueled with indium, are based on the working principle of field-emission electric propulsion (FEEP) technologies. The measured yields are given for different material properties (plain structure vs foam) and geometries (flat surface vs conical). Study outcomes show that electrons induced by keV-range indium ions can lead to overestimating the measured ion current by 30%–200% depending on the collector materials and geometry. We spotlighted that molybdenum, tungsten, and stainless steel 316L have relatively low yields compared to aluminum 2017A. Moreover, it is possible to lower down a specific material yield by two-thirds when using a foam structure. Finally, it is shown that off-axis ion influence on a collector increases the resulting electron emission yield. In the case of an indium-FEEP thruster, ion-induced electron emissions are a major perturbation when measuring ion current. Mainly, due to the energy range of ions studied, yields retrieved are orders of magnitudes larger than what is usually measured when studying the plume of an electrostatic electric propulsion system. It is, therefore, strongly recommended to use a so-called Faraday cup to study the ion beam from an indium-FEEP thruster as the probe’s close architecture allows us to greatly mitigate these perturbations.