Propulsion Technology Research Articles

The azimuthal currents in the ion-driven magnetic nozzle

Ion-driven magnetic nozzles (Ti > Te) are designed as intrinsic parts of cutting-edge propulsive technologies such as variable specific impulse magnetoplasma rockets (VASIMRs) and applied-field magnetoplasmadynamic thrusters. Employing a two-dimensional axisymmetric particle-in-cell (PIC) code, in the ion-driven magnetic nozzle, the compositions and distributions of azimuthal currents in different axial regions are investigated under various inlet ion temperatures Ti0 and found to differ dramatically from that in the electron-driven magnetic nozzles. Previously reported to be all paramagnetic and vanishing under a high magnetic field, the azimuthal currents resulting from the E × B drift are shown to turn diamagnetic and sustain a considerable magnitude when Ti0 is considered. The previously reported profile of diamagnetic drift current is altered by the introduction of inlet ion temperature, and the paramagnetic part is significantly suppressed. Moreover, a wide range of paramagnetic currents appear downstream due to the inward detachment of ions, which can also be reduced by increasing inlet ion temperature. Albeit considered in this paper, the azimuthal currents resulting from grad-B and curvature drift are still negligible in all cases of interest. The magnitude of diamagnetic azimuthal currents increases with amplifying Ti0, indicating a clear physical image of energy transformation from ion thermal energy to the directed kinetic energy through electromagnetic processes in the magnetic nozzle. Additionally, the magnetic inductive strength also has noticeable impacts on the azimuthal currents, the current magnitude tends to decrease as the magnetic field increases, and over-increment of it may result in larger divergence angles and lower nozzle efficiency.

Combined Heat Shield and Solar Thermal Propulsion System for an Oberth Maneuver

A powered gravity assist around the sun, also known as an Oberth maneuver, has the potential to achieve a solar system escape velocity of 20 astronomical units (AUs) per year, which is desirable for an interstellar mission. Unfortunately, current heat shields and propulsion technology struggle to outperform an unpowered Jupiter gravity assist, let alone 20 AUs/year, due to unfavorable mass tradeoffs. We are therefore developing an unconventional approach that simultaneously addresses the need for high specific impulse and close proximity to the sun: convert the heat of the sun into usable thrust by passing a propellant through the heat shield. To demonstrate the concept of a combined heat shield and solar thermal propulsion system, we designed and fabricated a prototype and exposed it to a 20-sun solar simulator. The reflective yttria-stabilized zirconia coating and helium gas flow maintained a temperature of 339 K. With a dark chrome oxide coating facing the simulator, it generated 1.3 N of thrust at a flow rate of and a temperature of 516 K. The agreement between theory and the experiment suggests that an escape velocity of 15 AUs/year is attainable at a mass ratio of two and a perihelion of 2.5 solar radii.

A prescribed time attitude control method based on thrust vector control (TVC) nozzle for solid propulsion satellite

With the development of on-orbit missions, solid propulsion technology is applied to the rapid orbital maneuver of satellites. During solid propulsion maneuver, the position change of the mass center caused by the fuel consumption and the installation error of thruster have brought serious attitude disturbances. For this problem, a novel prescribed time attitude control method is proposed in this paper. Firstly, a dynamics model of the solid propulsion micro-satellite is established, while the thrust direction is adjusted by the thrust vector control (TVC) nozzle. Then, a constraint boundary function is constructed to characterize the strict fixation of the thruster operating time and an adaptive fuzzy observer is developed to quickly estimate the lumped model uncertainties. Using the backstepping method, a novel prescribed time attitude control strategy regardless of initial conditions is designed. Simulation results show that the designed controller can achieve the prescribed time convergence of satellite attitude during solid propulsion orbital maneuver, effectively.

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.

Multi-physics coupling analysis on neutronics, thermal hydraulic and mechanics characteristics of a nuclear thermal propulsion reactor

As a highly developmental potential propulsion technology, nuclear thermal propulsion (NTP) technology has characteristics of high power and high specific impulse. A large number of relevant studies for NTP reactor have been carried out, but most studies only focused on the overall reactor performance parameters, ignoring the core reactivity safety and local assembly behavior safety. In this study, a cross-scale neutronics, thermal hydraulic and mechanics coupling model of the core-assembly is established by using three-dimensional Monte Carlo code and commercial CFD program to analyze three aspects: reactor control response security characteristics, heat release homogeneity of reactor and thermal hydraulic parameters. By means of value comparison of control system, three-dimensional power flattening and sensitivity analysis of single variable thermal–hydraulic parameter, the thermal hydraulic temperature safety and mechanical thermal stress safety of assemblies are significantly improved under control safety and inherent safety, which proves the importance of the neutronics, thermal hydraulic and mechanics characteristic balance.This paper can provide a theoretical basis for study on the assembly multi-physics behavior and safety characteristics of NTP reactors.

Toward the Application of Pulse Width Modulated (PWM) Inverter Drive-Based Electric Propulsion to Ice Capable Ships

The current world geopolitical state has driven significant interest in expanding influence in the polar regions. In order to develop new trade routes and defense of these areas, specialized ice-capable vessels are needed. Traditional propulsion technology utilized for these vessels has featured diesel and turbo electric drives with cycloconverter based technology used for speed regulation. Cycloconverter technology has the major disadvantage of characteristic output voltage waveforms that are very non-sinusoidal which induce harmonic rich currents with their resulting negative effects on total power factor and efficiency. There is also the potential to induce harmonic currents that may increase heat production in power cables, stressing insulation and reducing overall component life. Furthermore, sensitive loads such as control system power supplies may also be affected. The output waveform of a PWM drive has harmonic content that is both less severe, and more easily analyzed with current modeling tools. There are significant technical challenges that need to be assessed when considering PWM drive deployment in ice-capable vessels. This is due to the severe load torques, and torque variation imposed on propeller blades during ice-milling operations. To the authors’ knowledge, an analysis of the behavior of vector-controlled PWM drives to this type of service has not been published in the open literature. This paper presents an initial modeling and simulation study that investigates whether such a PWM drive and associated controller may be effective for ice milling and other operational evolutions for these types of ships.

Fire tests with lithium-ion battery electric vehicles in road tunnels

Alternative propulsion technologies, including battery-electric vehicles, are becoming increasingly prevalent. Whilst such vehicles remain a small overall proportion of the vehicle fleet, the combined impact of government policy and technological advances in alternative fuels is expected to accelerate the increase in their numbers in coming years.As a result of these changes, the nature of tunnel safety risk (including the risk of fire) is expected to change over time. The risk implications associated with such vehicles thus requires more detailed consideration. This entails evaluation of incident consequences with particular attention being paid to the impact of fire characteristics and toxic emissions on tunnel users and to the need for specific emergency intervention strategies.In the past, concerns were voiced with respect to the fire safety of the new energy storage device (battery) and the possibility of more difficult firefighting conditions. This resulted in a series of investigations concerning the safety aspects of batteries and battery electric vehicles. However, most of the tests performed merely dealt with battery cells or battery packs. To date, publicly available tests involving actual vehicles remain relatively rare. In 2018, the Austrian Government commissioned a research project concerning the effect of incidents with battery electric vehicles on tunnel safety. This project encompassed fire tests of passenger cars, simulations for heavy duty vehicles, and the impact of incidents with such vehicles on the safety of tunnel users and the tunnel structure.In a series of fire tests, the heat-release and production of (toxic) substances has been evaluated. The burning behaviour of vehicles with different energy storage technologies (i.e. Li-ion batteries, Diesel) was monitored and compared to each other. The heat-release rate and emission of (toxic) substances was measured, and different fire-fighting methods were applied during each test.This paper will focus on the aspect of full-scale fire tests of passenger cars performed in a road tunnel. It should be emphasized that the battery-electric vehicle fire tests presented here were the first of their kind under real road tunnel conditions. This concerns the fire behaviour, but also some new approaches to fighting a BEV fire. All previous tests reported in journals were either carried out in fire halls or only concerned individual battery modules.

Diversity of Physical Processes: Challenges and Opportunities for Space Electric Propulsion

The renewed interest in space exploration has led to the growth in research efforts pertaining to advanced space propulsion systems, including highly efficient electric propulsion systems. Although already tested in space many decades ago and being currently employed on various space platforms and thousands of satellites, these systems are yet to reach their full potential for applications on orbit and in deep space. One specific feature of space electric propulsion is the large diversity of physical processes used in this technology, which is not typical for many other types of propulsion systems used in transport, such as those used by airplanes or automobiles. Various physical processes and mechanisms underpin different electric propulsion technologies and should be integrated to drive the future science and technology of space electric propulsion systems. This opinion article briefly highlights this feature of space electric propulsion and outlines some challenges and opportunities that follow from this diversity.

Systematic Component Investigation of the Steady-State High-Temperature In-Pile Nuclear Thermal Propulsion Experimental Test Bed

A high-temperature, steady-state, in-pile experiment was developed to simulate prototypical nuclear thermal propulsion conditions. The experimental development of the resistively heated test apparatus involved spatially scaling the device to a larger heated region from a previous smaller out-of-pile prototype. A series of tests and investigations were conducted to replicate the smaller out-of-pile system’s success of achieving 2500 K. However, limitations within the larger assembly were identified; specifically, the heater filament design does not scale well. The larger assembly can reliably generate usable temperature levels from room temperature up to those exceeding 1300 K for hours. It can briefly sustain a usable 1800 K. The larger system is achieving temperatures over 2500 K, but these are localized and unable to be monitored in the current design. The achieved temperature levels remain suitable for testing various components considered for a nuclear thermal rocket. However, due to the limitations of the current heater filament, it is recommended that the apparatus be redesigned to utilize a rigid heating element similar to that used during the Radioisotope Propulsion Technology Program (Project POODLE) in the 1960s.

Development and validation of an iodine plasma model for gridded ion thrusters

Iodine is emerging as an attractive alternative propellant to xenon for several electric propulsion technologies due to its significantly lower cost and its ability to be stored unpressurized as a solid. Because of the more complex reaction processes and energy-loss channels in iodine plasmas however, as well as the historical lack of reliable collision cross-section data, the development of accurate theoretical and numerical models has been hindered. Using recently calculated theoretical cross-sections, we present an iodine plasma model and perform a comparison with experimental data obtained from an iodine-fuelled gridded ion thruster. The model is in reasonable agreement with experimental measurements of the ion beam current, propellant mass utilization efficiency, and ion beam composition, and is able to quantitatively and qualitatively reproduce system behaviour as the input mass flow rate and RF power are varied. In addition, both the model and experiment show that the use of iodine can lead to a performance enhancement when compared with xenon. This occurs because of the combination of different iodine reaction processes, collision cross-section values, and inelastic energy thresholds which result in lower collisional energy losses, as well as an increased antenna-plasma power transfer efficiency for thrusters using a radio-frequency inductive coil.

Licensing Approach Applicable to Land Facilities Supporting Nuclear-Powered Submarines

The nuclear licensing process is a fundamental stage for the design and deployment of a nuclear facility. In Brazil, the licensing process of Central Nuclear Almirante Álvaro Alberto (CNAAA) nuclear power plants, in Angra dos Reis - RJ, was established mainly based on the U.S. Nuclear Regulatory Commission (U.S.NRC) guidelines. However, for each purpose specific requirements are established which promote a standardisation appropriate to the type of installation in question. Thus, not every nuclear installation can be adequately framed in the standards and requirements established for the licensing of a nuclear power plant, especially when considering nuclear facilities for strategic and defense purposes. For instance, the Specialized Maintenance Complex (CME) project that is being developed by the Brazilian Navy and aims to offer all the structure and systems for support on land to the first Brazilian nuclear-powered submarine. Therefore, when considering the interfaces between maritime/naval systems and operations, the purpose and specificity of installations such as CME extrapolate the commonly established nuclear normative framework. Due to the innovation of this type of installation in Brazil, there is no specific regulation for its licensing, constituting a unique situation for both the Brazilian Navy (applicant) and the National Nuclear Energy Commission - CNEN (Brazilian Nuclear Licensing Agency, which, in the near future, will have its function incorporated into the National Nuclear Safety Authority, ANSN). Even when researching standards and other guides in ostensible sources of nations that holds nuclear reactor technology for naval propulsion (and land support facilities), no normative guidance dealing specifically with the safety analysis and licensing of this type of installation has been identified. Thus, this paper proposes a first approach and analysis of the standards used by the U.S. Department of Defense (U.S.DOE) comparing them to the standards of the U.S. Nuclear Regulatory Commission (U.S.NRC) aiming to compose a specific normative proposition to carry out the safety analysis and licensing of a nuclear-powered submarines land support facility.

Hardware in the loop experiments on the interaction between a diesel-mechanical propulsion system and a ventilating propeller

The interaction between ship propulsion machinery, propellers and the highly dynamic environment which is the sea is a complex yet highly relevant subject. During a storm, for example, waves and ship motions may cause the propeller to draw air, or ventilate, resulting in rapid changes in propeller thrust and load torque. These fluctuations propagate through the propulsion system, potentially causing excessive loads on propulsion machinery, while also reducing the ship's manoeuvrability. A profound understanding of these complex interactions still lacks. One result of this knowledge gap is the limited acceptance of new technologies for ship propulsion, especially those technologies known to have limited transient capabilities. In this paper, hardware in the loop (HIL) is proposed as a solution to this knowledge gap. Paying specific attention to propeller ventilation, HIL is used to identify new aspects of interaction between engine and propeller, thus demonstrating the added value of HIL for ventilation studies.

Very low thrust station-keeping for low Earth orbiting satellites

Traditional station-keeping for Earth observation satellites with chemical thrusters generally involves maneuvers every couple months that are able to change significantly the semi-major axis and the inclination. These strategies do not scale down to very low thrust level (a few hundreds of μN) electrical thrusters. This paper presents both in-plane and out-of-plane strategies that spread corrections over very long arcs and discretize them to tiny maneuvers every couple orbits, taking into account mission-constraints on maneuvers locations. These strategies scale up to medium thrust strategies, filling the gap between propulsion technologies. The out-of-plane strategy although features a new no-deadband property and controls the full orbital momentum. All strategies allow control very close to the reference (a few hundreds meters in osculating parameters) and very low cost.

Preliminary Sizing of Electric-Propulsion Powertrains for Concept Aircraft Designs

The drive towards a greener and more sustainable future is encouraging the aviation industry to move towards increasing electrification of its fleet. The development of electric propulsion technologies also requires new approaches to assess their viability in novel configurations. A methodology is proposed which consists of four sub-procedures; powertrain modelling, performance analysis, aerodynamic modelling, and sizing. This approach initially considers powertrain modelling using AIAA symbol representations, and a review of the available literature establishes state-of-the-art component values of efficiency, specific power, specific energy, and specific fuel consumption. The sizing procedure includes a mission and aerodynamic analysis to determine the energy and power requirements, and it relies on a mass regression model based on full-electric, hybrid, VTOL and fixed-wing aircraft found in the literature. The methodology has been applied to five case studies which are representative of a wide range of missions and configurations. Their predicted masses from the sizing procedure have been validated against their actual masses. The predicted total mass shows generally good agreement with the actual values, and in addition, accurate values for active mass have been predicted. A sensitivity analysis of the sizing procedure suggests that future work may include a more accurate analysis of aerodynamics and mission if the methodology were to be applied for selecting aircraft concepts.

Deep-learning prediction and uncertainty quantification for scramjet intake flowfields

Scramjet is a promising propulsion technology that provides efficient and flexible access-to-space and high-speed point-to-point transportation. Since the design process of scramjet (supersonic combustion ramjet) engines requires numerous flowfield evaluations, fast and accurate flow predictions play a key role in promoting the development of knowledge and technologies. Deep learning techniques are increasingly used for flow prediction, and the present study applies them to viscous supersonic flowfields inside scramjet intakes. The capability and limitations of deep learning prediction for such flowfields have been investigated from the viewpoints of both physics and machine learning by means of uncertainty quantification and principal component analysis. The results indicate that the flowfields with complex aerodynamic phenomena such as boundary layer separation and Mach disks are difficult to predict. It has been attributed to lack of similar flowfields as well as the sensitivity of the fluid phenomena to the geometries. Uncertainty quantification effectively allows for the detection of such difficult cases without model verification prior to utilization. It has been further employed to address the issues in the prediction of flowfields with boundary-layer separations by increasing the number of training data effectively.

(Invited) Analytical Solutions for Quality Assurance across the Battery Manufacturing Process

Battery performance degradation and potentially dangerous incidents such as thermal runaway and fire can originate from defects in lithium battery components or during cell assembly. Therefore, quality assurance is extremely important aspect of the manufacturing process to identify and eliminate defects that may give rise to cell failure and dangerous incidents. From validating raw material purity and monitoring electrode thickness, to inspection of component alignment and integrity during assembly, different analytical capabilities are used to ensure quality is maintained through battery manufacturing workflow. In this presentation examples of using in-line and off-line analytical characterization techniques, such as in-line basis weight and thickness measurement systems and electron microscopes, to monitor the quality during battery manufacturing process will be discussed. Advances in in-line and off-line metrology and quality control tools are an important enabler for solving the current challenges and facilitating future growth in electric propulsion and energy storage technologies.

Nuclear thermal coupling optimization of baffled NTP reactor

Nuclear thermal propulsion (NTP) technology has characteristics of high power and high specific impulse. In particular, CERMET fuel reactors have received a lot of research due to simple form and structure. A general CERMET fuel reactor model is established by using three-dimensional Monte Carlo code and commercial CFD program. After nuclear thermal coupling optimization, three partition schemes of baffled reactor were proposed to reduce the temperature difference between the wall and the coolant and lower the relative spike factor in the inner region. A feasible design of redundant control system was then proposed, with a cold clean excess reactivity greater than $4.59 and a minimum dry shutdown reactivity lower than -$7.94, where there was a high control accuracy of 6.7 pcm/mm. The reactor finally realized safety of the core temperature lower than 3000 K under the conditions of total exit temperature of 2650 K and thrust of 25000 lb.

Low-Thrust, Multiple-Near-Earth-Asteroid Mission Design with Sample Return to Earth Using Machine Learning

Sample return missions to near-Earth asteroids (NEAs) are invaluable for the scientific community to learn more about the initial stages of the solar system formation and life evolution. Low-thrust propulsion technology enables missions with multiple-asteroid rendezvouses to collect samples and eventually return to Earth, thanks to its high specific impulse. To identify the best asteroid sequences with return to Earth, this work proposes to employ machine learning techniques and, specifically, artificial neural networks (ANNs), to quickly estimate the cost of each transfer between asteroids. The ANN is integrated within a sequence search algorithm based on a tree search, which identifies the asteroid sequences and selects the best ones in terms of propellant mass required and interest value. This algorithm can design NEA sequences so that specific asteroids of interest, for which a sample return would be more valuable, can be targeted. A pseudospectral optimal control solver is then used to find the optimal trajectory and control history. The performance of the proposed methodology is assessed by analyzing three distinctive NEA sequences ending with return to Earth and rendezvous. Near-term low-thrust propulsion enables to rendezvous five asteroids, and return samples to Earth in about 10 years from launch. It is demonstrated that visiting more scientifically interesting asteroids increases the appeal of the sequence at the cost of more propellant mass required.

Matching and performance analysis of a solid oxide fuel cell turbine-less hybrid electric propulsion system on aircraft

Advanced low-carbon propulsion technology is one of the major initiatives to address aviation environmental challenges. In this paper, a solid oxide fuel cell turbine-less hybrid electric propulsion system is developed. It is a new engine, in which the power consumed by the compressor comes from a fuel cell, not a turbine. The aircraft's propulsion comes from the high-velocity exhaust discharged from the nozzles. To make the key fuel cell work properly and determine the system operating parameters, it is necessary to study the matching and performance of the hybrid electric propulsion system. In this study, a performance analysis model of the hybrid electric propulsion system is established. In particular, a one-dimensional fuel cell is simulated to obtain its localized thermal gradient. The results show that the hybrid electric propulsion system has a satisfactory performance under the design conditions. It is superior to the gas turbine-based engine in performance, and they have different performance trends. The operating range of compressor pressure ratio is determined. The sensitivity analysis shows that in addition to compressor pressure ratio, Mach number, reforming temperature, and fuel utilization have a great influence on the performance, which is worthy of further study.

Full-Core Coupled Neutronic, Thermal-Hydraulic, and Thermo-Mechanical Analysis of Low-Enriched Uranium Nuclear Thermal Propulsion Reactors

Nuclear thermal propulsion is an enabling technology for future space missions, such as crew-operated Mars missions. Nuclear thermal propulsion technology provides a performance benefit over chemical propulsion systems by operating with light propellants (e.g., hydrogen) at elevated engine chamber conditions. Therefore, nuclear thermal propulsion reactor cores exhibit high propellant velocities and elevated propellant and fuel temperatures, subsequently leading to relatively high thermal stresses and geometrical deformation. This paper details the numerical approach to solve the thermo-elastic equations, which was implemented into the recently developed ntpThermo code. In addition, this paper demonstrates the extension of the Basilisk multiphysics framework to perform full-core coupled neutronic, thermal-hydraulic, and thermo-mechanical analysis of nuclear thermal propulsion reactors. The analyses demonstrate and quantify thermo-mechanical feedback, which for the investigated cases, acted to reduce maximum fuel temperatures and pressure drop across the fuel element channels. Thermo-mechanical feedback had a significant impact on the mass flow distribution within the reactor core and, thus, a substantial impact on solid-material temperatures and stresses, but only a minor impact on reactivity and local power distributions. Sensitivity studies revealed that the friction factor correlation applied to perform the analysis has a significant impact on the pressure drop across the fuel element channels. The most important observation of this research is the importance of incorporating the thermo-mechanical feedback within an integrated multiphysics solution sequence to enable the consistent design of future nuclear thermal propulsion systems.