Electric Propulsion Research Articles

Additive manufacturing of ceramic single and multi-material components–A groundbreaking innovation for space applications too?

The main advantages of ceramic materials are their excellent thermal, chemical, and mechanical properties. They also have a much lower density than metals, making them ideal for lightweight construction, which can also be interesting for space components. However, ceramics have not been widely used due to their low ductility and the challenges of mechanical processing using conventional methods like milling and turning. Additionally, integrating different functions into a single component has been limited.The introduction of additive manufacturing (AM) technologies has revolutionized this field. It is now possible to manufacture highly complex ceramic components with unprecedented functionality. By hybridizing different manufacturing technologies and materials, additional functions such as electrical contacts, sensors, and actuators can be directly integrated, leading to improved manufacturing costs and component properties.Three different demonstrator examples are presented in this paper to give a first impression of what will be possible in the field of space applications in the future. These examples are a ceramic igniter, a ceramic reactor for thermal decomposition of H2O2, and a ceramic aerospike engine.

An Innovative Mechanical Approach to Mitigating Torque Fluctuations in IC Engines during Idle Operation

Internal combustion engines have been a major contributor to air pollution. Replacing these engines with electric propulsion systems presents significant challenges due to different countries’ needs and limitations. An active, purely mechanical solution to the problem of irregular torque production in an alternative internal combustion engine is proposed. This solution uses an actuator built on a camshaft and a spring, which stores and returns energy during the engine operating cycle, allowing torque production to be normalized, avoiding heavy flywheels. Designed for control throughout the engine’s duty cycle, this system incorporates a cam profile and a spring mechanism. The spring captures energy during the expansion stroke, which is then released to the engine during the intake and compression strokes. Simple, lightweight, and efficient, this system ensures smoother and more consistent engine operations. It presents a viable alternative to the heavy and problematic dual-mass flywheels that were introduced in the 1980s and are still in use. This innovative approach could significantly enhance the performance and reliability of alternative internal combustion engines without notable energy losses.

Distributed Hybrid Electric Propulsion Aircraft Design Based on Convex Optimized Power Allocation Management

In order to ensure that aircraft have medium and long-range flights, enhanced aerodynamic performance, and reduced fuel consumption, this paper presents an original Distributed Hybrid Electric Propulsion Aircraft (DHEPA) design scheme and proposes a novel power allocation management method based on convex optimization. Firstly, by taking the Tecnam P2006T general-purpose aircraft as a reference, key components of DHEPA are selected and modeled. Then, a power allocation management method for DHEPA is proposed on the basis of convex optimization, which takes the minimum fuel consumption as the performance index to realize the reasonable power allocation of the battery and engine, while avoiding sliding into the local optimum of allocation. Finally, momentum theory and numerical simulation methods are used to analyze the aerodynamic enhancement effect of the propeller on the wing in the DHEPA, and a dynamics method is utilized to calculate the dynamics performance of the aircraft at several important stages. The results show that, compared with the reference aircraft, the lift of the DHEPA is increased by 46%. Under typical sectors, the DHEPA has a higher rate of climb and maximum leveling off speed at cruise, and a significantly lower fuel consumption.

A High Step-Down SiC-Based T-Type LLC Resonant Converter for Spacecraft Power Processing Unit

A spacecraft power processing unit (PPU) is utilized to convert power from solar arrays or electric batteries to the payload, including electric propulsion, communication equipment, and scientific instruments. Currently, a high-voltage converter is widely applied to the spacecraft PPU to improve power density and save launch weight. However, the high voltage level poses challenges such as high step-down ratios and high power losses. To achieve less conduction loss, a SiC-based T-type three-level (TL) LLC resonant converter is proposed. To further broaden the gain range and achieve high step-down ratios, a variable frequency and adjustable phase-shift (VFAPS) modulation scheme is proposed. Meanwhile, the steady-state time-domain model is established to elaborate the operation principles and boundary conditions for soft switching. Furthermore, the optimal resonant element design considerations have been elaborated to achieve wider gain range and facilitate easier soft switching. Furthermore, the numerical solutions for switching frequency and phase shift (PS) angle under each specific input could be figured out. Finally, the effectiveness of this theoretical analysis is demonstrated via a 500-W experimental prototype with 650∼950-V input and constant output of 48-V/11-A.

Trend Research on Maritime Autonomous Surface Ships (MASSs) Based on Shipboard Electronics: Focusing on Text Mining and Network Analysis

The growing adoption of electric propulsion systems in Maritime Autonomous Surface Ships (MASSs) necessitates advancements in shipboard electronics for safe, efficient, and reliable operation. These advancements are crucial for tasks such as real-time sensor data processing, control algorithms for autonomous navigation, and robust decision-making capabilities. This study investigates research trends in MASSs, using bibliographic analysis to identify policy and future research directions in this evolving field. We analyze 3363 MASS-related articles from the Web of Science database, employing co-occurrence word analysis and latent Dirichlet allocation (LDA) topic modeling. The findings reveal a rapidly growing field dominated by image recognition research. Keywords such as “datum”, “image”, and “detection” suggest a focus on collecting and analyzing marine data, particularly with deep learning for synthetic aperture radar imagery. LDA confirms this, with “image analysis and classification research” as the leading topic. The study also identifies national and organizational leaders in MASS research. However, research on Arctic routes lags behind that on other areas. This work provides valuable insights for policymakers and researchers, promoting a deeper understanding of MASSs and informing future policy and research agendas regarding the integration of electric propulsion systems within the maritime industry.

Ion–surface interactions in plasma-facing material design

A multi-scale simulation framework for ion–solid interactions in plasma-exposed materials provides crucial insight into advancing fusion energy and space electric propulsion. Leveraging binary-collision approximation (BCA) simulations, the framework uniquely predicts sputter yields and analyzes material transport within volumetrically complex materials. This approach, grounded in the validated BCA code TRI3DYN, addresses key limitations in existing models by accurately capturing ion–solid interaction physics. A case study is presented, highlighting the framework’s ability to replicate experimental sputter yield results, underscoring its reliability and potential for designing durable materials in harsh plasma environments. Insights into sputtering transport phenomenology mark a significant advancement in material optimization for improved resilience in plasma-facing applications.

New Design of an Electrical Excavator and Its Path Generation for Energy Saving and Obstacle Avoidance

This study’s goals are divided into two categories. The first is to design and build an excavator equipped with parallel electrical linear actuators. The second is to generate and test a PSO-based and a PFM-based path for this excavator in order to save energy by reducing energy consumption, improve the digging accuracy by minimizing the deviation between the desired and dug surfaces of the ground, and prevent colliding with subsurface objects. For this purpose, computer vision was employed to improve monitoring and verification. Five types of experiments were carried out in this investigation. The first two and the other three examined the impact of energy conservation in PSO- and PFM-based path generation, respectively. Finally, the results from these experiments were compared to identify and show the effect of optimal path generation.

Robust Control Based on Adaptative Fuzzy Control of Double-Star Permanent Synchronous Motor Supplied by PWM Inverters for Electric Propulsion of Ships

This study presents the development of an adaptive fuzzy control strategy for double-star PMSM-PWM inverters used in ship electrical propulsion. The approach addresses the current and speed tracking challenges of double-star permanent magnet synchronous motors (DSPMSMs) in the presence of parametric uncertainties. Initially, a modeling technique employing a matrix transformation method is introduced, generating decoupled and independent star windings to eliminate inductive couplings, while maintaining model consistency and torque control. The precise DSPMSM model serves as the foundation for an unknown nonlinear backstepping controller, approximated directly using an adaptive fuzzy controller. Through the Lyapunov direct method, system stability is demonstrated. All signals in the closed-loop system are ensured to be uniformly ultimately bounded (UUB). The proposed control system aims for low tracking errors, while also mitigating the impact of parametric uncertainties. The effectiveness of the adaptive fuzzy nonlinear control system is validated through tests conducted in hardware-in-the-loop (HIL) simulations, utilizing the OPAL-RT platform, OP4510.

Spacecraft Medium Voltage Direct-Current (MVDC) Power and Propulsion System

This paper introduces a medium voltage direct-current (MVDC) system for large spacecraft megawatt-scale (MW) power and propulsion systems intended for interplanetary transport, including missions to the Moon and Mars. The proposed MVDC system includes: (i) A nuclear electric propulsion (NEP) that powers a permanent magnet (PM) generator whose output is rectified and connected to the MVDC bus. (ii) A solar photovoltaic (PV) source that is interfaced to the MVDC bus using a unidirectional boost DC-DC converter. (iii) A backup battery energy storage system (BESS) that connects to the MVDC bus using a bidirectional DC-DC boost converter. (iv) A dual active bridge (DAB) converter that controls the power to the spacecraft’s electric thruster. The NEP serves as the main power source for the spacecraft’s electric thruster, while the solar PV and BESS are intended to provide power for the payload and spacecraft’s low-voltage power system. The paper will (i) provide a review of the spacecraft MVDC power and prolusion system highlighting state-of-the-art main components, (ii) address the control of boost converters for the PV and BESS sources and the DAB converter for the thruster, and (iii) propose an uncertainty and disturbance estimator (UDE) concept based on current control algorithms to mitigate MVDC instability due to unpredictable factors and external disruptions. The proposed UDE can actively estimate and compensate for the system disturbance and uncertainty in real time, and thus, both the system tracking performance and robustness can be improved. Simulation studies have been conducted to substantiate the efficacy of the proposed schemes.

Functional analysis of speed, battery pack capacities and chargers of small electric ships

Electric propulsion refers to propulsion using a combination of an electric motor and batteries. Electric motors powered by batteries represent a significant solution within the broader context of sustainability, energy efficiency, and technological advancement. As energy containers, batteries are characterized by low energy and power density and are currently not considered suitable for use on large displacement ships. Consumption of electric ships depends on numerous factors and the performance of the vessel's energy system requires great attention. The basic limitations are the ship’s size and speed, the built-in capacity of the batteries, charging infrastructure, and sailing distance. These limitations are discussed and justified in two case studies in which the existing diesel-powered ships are replaced with electric ones.

On the critical parameters for feasibility and advantage of air-breathing electric propulsion systems

In recent years, air-breathing electric propulsion emerged as a potential enabling technology for long-duration space missions in Very Low Earth Orbit (VLEO). In this work, we show how the complex relation between mission environment, spacecraft configuration, and propulsive performance can be associated to a single requirement for full air-breathing drag compensation, which becomes less stringent for higher VLEO orbits. The impact of the spacecraft shape and size on the performed analysis is then evaluated and the results compared with conventional electric propulsion solutions with stored propellant, showing how the adoption of air-breathing propulsion becomes more advantageous, from a volume and mass fraction perspective, when the spacecraft scale is reduced.

Optimal combined impulsive/low-thrust trajectories for asteroid deflection via kinetic impact

This work considers the trajectory optimization of a kinetic impactor spacecraft, which is sent to collide with a threatening near-Earth asteroid. It is assumed that Earth departure is done impulsively, by the upper stage of a launch vehicle, and is then followed by low-thrust electric propulsion until impact. For a given spacecraft, all of the important decision parameters, such as the date of departure, the direction of the hyperbolic departure, the thrust program, i.e. the history of the low-thrust pointing angles, and the date of impact are all chosen by the optimizer to maximize the perigee radius of the asteroid at its closest approach. Normally a trajectory optimization problem of this type would need to be described by many hundreds of decision parameters, e.g. if formulated to be solved by an optimization package (such as GPOPS) using nonlinear programming. We show that a successful and accurate optimization of the mission is possible using the heuristic method, particle swarm, and only 16 decision parameters, and present results for the deflection of 99942 Apophis at its 2029 close approach.

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.

Study on the compatibility between iodine and common aerospace materials

Iodine has proven to be a promising alternative to xenon as a propellant for Hall and ion thrusters. High atomic mass and favourable ionization characteristics, comparable to xenon in terms of propulsive performance, together with lower cost compared to xenon makes it an attractive option. However, its reactivity and corrosive nature raise concerns. Tests to assess material compatibility and determine whether thruster components are susceptible to corrosion are unavoidable for its safe adoption as a propellant. This paper describes the main results of an experimental campaign aimed at a qualitative assessment of the compatibility with iodine of different materials. The study included more than fifteen materials that find application in electric propulsion devices, such as cathodes, thrusters and feeding systems, including ceramics such as LaB6, polymers, iron and aluminum alloys, and graphite. The specimens were exposed to iodine vapor environments at temperatures reaching approximately 200 °C for extended periods (from three to over 30 h) or were directly exposed to liquid iodine. The experimental setup and results of morphological and elementary analyses are presented and discussed. The research provides some insights into the viability of using iodine as a propellant and the potential challenges associated with its corrosive properties.

Nonlinear optimal control for robotic exoskeletons with electropneumatic actuators

Nonlinear optimal control for robotic exoskeletons with electropneumatic actuators

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.

Adaptive PMSM Control of Ship Electric Propulsion with Energy-Saving Features

Electric ship propulsion is considered one of the most promising alternatives to conventional combustion systems. Its goal is to reduce the carbon footprint and increase a ship’s maneuverability, operational safety, and reliability. The high requirements for ship propulsion make permanent magnet synchronous motors (PMSMs) an attractive solution due to their characteristics. This paper discusses the control problem of a PMSM based on the input–output feedback linearization method combined with the optimal and adaptive control techniques. The method presented here integrates the parameter tuning process with the optimal design of the baseline controller. Since the load disturbances are treated as an additional unknown parameter, there is no need to introduce an integral action to deal with the resulting steady-state error. An important feature of the designed controller is the so-called energetic optimization of the system; i.e., in addition to the aforementioned adaptive and optimal controller, it has a feature of ensuring zero reactive power consumed by the system. The performed simulations of the machine speed stabilization process confirmed the high efficiency of the proposed controller despite the assumed uncertainty of the system parameters and environmental (load) disturbances. Besides achieving high-quality control, an essential feature of this approach is the elimination of the tuning problem.

Cryogenic thermo-physical properties of additive manufactured materials

Environmentally friendly aviation is one of the great challenges of this century. One promising approach is electric flight, in which an energy carrier (e.g. liquid Hydrogen LH2) and an electric powertrain work together. Within the scope of the joint project AdHyBau, the overarching goal is the development of new additive processes and fibre composite-metal hybrid designs for use in the cryogenic environment of such an electric propulsion system. Additive manufacturing of complex components for use in the cryogenic temperature range down to 20K (LH2) is one essential component in the production. For the design and optimization of the different components it is necessary to know the thermo-physical behaviour of such materials like high purity copper, Ti6Al4V alloy, Al-Mg-Sc alloy, and Inconell 718. The thermo-physical parameters investigated are thermal expansion, thermal & electrical conductivity and heat capacity. Further production-related influences coming from the method used (SLM, DED or Cold-Spray) and orientational dependences are discussed.Supported by the Federal Ministry for Economic Affairs and Climate Action of the Federal Republic of Germany. Grant-No.: 20M1904D.

Lightweight clad bi-metal conductors for cryogenic applications

Lightweight cryogenic conductors are required for applications in electric propulsion, such as cryogenically-fueled electric airplanes and ships. Clad bi-metal conductors allow to consider certain conductor metals that would not be feasible as a single conductor. This includes materials that are chemically reactive and materials that would not have the right mechanical properties to draw wires. The Ashby method is used to compare material combinations systematically. Manufacturing techniques and applications are also discussed. Copper-clad lithium wire stands out as one of the promising new types of clad bi-metal conductors for cryogenic applications.

Experimental study of two-phase cryogenic cooling of aluminum stator conductors using a single slot test configuration

An important goal to enable widespread adoption of electric aircraft propulsion is to develop higher power density motors and generators which are at the same time highly efficient. One way to do this is to use conductors that can carry higher currents and/or generate lower losses. One approach to this is the use of superconducting windings. However, here we focus on very low resistance normal state conductors operating at cryogenic temperatures. The resistivity of both aluminum and copper drops quickly with decreasing temperature, such that the resistivity of Cu drops by about a factor of 7, and that of aluminum by 10, by the time we reach 77 K (LN2). OSU and Hyper Tech have teamed to develop a motor with liquid cryogen cooled aluminum windings (LN2 or LNG cooled). It includes a multi-slot stator with direct cryogen cooling. Here we present the results of a simple “single slot” test which explores the temperature rise of a pair of conductors in a slot directly cooled by LN2. These two aluminum bars are made of 1100 commercial purity Al alloy were placed in parallel with a 1.6 mm gap, which behaved as 120 mm long cryogenic flow channel. Current densities up to 75 A/mm2 were explored, with LN2 flow rates ranging from 1.9 g/s to 6.4 g/s. Thermocouples and voltage taps were used to capture temperature and voltage data during the experiment. As a result, we found stable cooling and operation at these flow rates and current densities, and we characterized the temperature gradient which developed along the conductor bars.