Thruster Model Research Articles

Better Prediction of the Performance of a Radio-frequency Ion Thruster

A zero-dimensional analytical model for an RF discharge ion thruster has been improved to predict the thruster performance better. Improvements were made by incorporating most physical phenomena expected in an RF ion thruster, such as secondary electron emission, double ionization, a variable Clausing factor, grid optical transparency, and an ion confinement factor affected by the electromagnetic field. Clausing factors were calculated for each flow rate by using a Monte-Carlo technique. The grid optical transparency was calculated using an ion optics simulation. The ion confinement factor was also calculated for each flow rate by using the calculated magnetic field strength obtained from magnetic field simulations. The ion confinement factor turned out to have the greatest effect on the results while minor corrections were achieved by other processes. Comparison with previously reported analytical solutions and experimental data showed improved prediction of the thruster performance for various size and power ranges.

Scaling Model for SPT and TAL Thrusters

Scaling methods are a straightforward way to design new thrusters at different power levels. Based on the general equations, this work derives the scaling rules from those equations and presents a model for thruster with anode layer (TAL) and stationary plasma thrusters (SPTs) that encompass the scaling methods described until now. With the exception of the magnetic field, the scaling rules derived can be used for both TAL and SPT. In addition, this model is used to study the impact of the different scaling methods in the performance of the thruster. In particular, how the total thruster efficiency is affected through the current efficiency and the influence of this efficiency loss in the thrust. Accordingly, using the rules derived from the general equations for the magnetic field, the possible conflicts with the electron confinement given by the Larmor Radius for both SPT and TAL thrusters are studied. Finally, it is shown how the selected scaling method strongly affects the expected lifetime of the thruster. In this aspect, the strict scaling results to be the most rigorous method, whereas the length extension method allows for further improvement of the lifetime.

Исследование режимов горения разряда "спица" и "колокол" на холловском двигателе мощностью 1.5 kW

Two stable operating modes, which were called “jet” and “bell” mode, were investigated for Hall thruster with power 1.5 kW. Performances (thrust, thrust specific impulse) in two modes were investigated. The study were conducted for discharge voltage 300-800 V and gas flow rate from 1.5 to 3.0 mg/s. This result is compared with the previous study, which carried out on geometrically similar but bigger Hall thruster model.

Global model of a radio-frequency ion thruster based on a holistic treatment of electron and ion density profiles

We present a global model of a radio-frequency ion thruster. The model takes into account radial and axial density distributions for electrons and ions of the plasma inside the ionization vessel. These spatial distributions are based on analytical equations and heuristic assumptions and are used self-consistently in all conservation equations. They are considered in the 3D computation of electromagnetic fields and used to calculate the induced power generated by the coil current. We also consider the spatial ionization and excitation inside the plasma volume in the context of energy and charge conservation. Furthermore, the model includes effects of local charge and power losses on the walls. The extraction grid system is modeled in detail describing each extraction channel separately. The spatial dependence of the electron and ion density profile also leads to a radially varying ion beam current and ion focus across the grid system. Therefore, the parameters of each beamlet differ and need to be described individually by the 3D ion extraction code. An extension of the extraction code also simulates the neutral gas transmission coefficient of the aperture system. This approach enables us to determine the neutral gas density inside the ionization vessel as well as the neutral gas losses. The peripheral electric losses in the coil, the RF cables and the radio-frequency generator are derived by a circuit model.

МАТЕМАТИЧЕСКОЕ МОДЕЛИРОВАНИЕ ЭЛЕКТРОНАГРЕВНОГО ДВИГАТЕЛЯ НА ЭТАПЕ ЗАПУСКА

The subject of research in the article is the process of accelerating the working fluid in an electric heating thruster, which is part of the onboard propulsion system used in space tug. The goal is to obtain the characteristics of starting an electric heating thruster, which is part of an onboard propulsion system used in space tug, as a function of time, to further evaluate the preparation time of an onboard propulsion system for operation and approximating its temporal characteristics to chemical rocket engines. Tasks: the formation of the pneumohydraulic diagram of the onboard propulsion system, the structure of the onboard propulsion system, the creation of a mathematical model of the electric heating thruster, the determination of the functioning area of the electric heating thruster, which is part of the onboard propulsion system and the launch characteristics. The method used is: simulation of processes occurring at start-up in an electric heating thruster, which is part of an onboard propulsion system used in space tug. The following results were obtained: the range of limitations of the static dependence of the thrust of the electric heating thruster, which is part of the onboard propulsion system, on the flow rate of the working fluid in the heater power range was determined; dependences on the thrust time of the electric heating thruster, the flow rate of the working fluid of the electric heating thruster, and the power consumed by the electric heating thruster during the start-up process are obtained; as a result of the optimization of the coefficients of the controller of the electric heating thruster, the transfer function was obtained. The scientific novelty of the results consists in assessing the dynamic properties of an electric heating thruster, which is part of an onboard propulsion system mounted on a space tug, obtained in the field of limiting the thrust of an electric heating thruster, the flow rate of the working fluid of an electric heating thruster, the power of an electric heater of an engine, and the transfer function of a regulator of an electric heating thruster, which is part of onboard propulsion system.

Electron Motion in a Stationary Plasma Thruster

Electron motion in a classical three-block model of the stationary plasma thruster (SPT) invented by A.I. Morozov is analyzed. It is demonstrated that the motion of electrons produced with a zero initial velocity due to working gas ionization critically depends on the position of the starting point along the accelerating channel axis. While the electron trajectories in the cathode region are regular, they become ergodic closer to the anode, which is accompanied by enhanced particle transport along the thruster channel. This transition is associated with the presence of a boundary at which erosion of the discharge chamber wall takes place in the experiment. The discovered ergodization of electron trajectories can be responsible for the anomalous electron conductivity in the near-anode region of the SPT.

Development of an SPT-100VT Stationary Plasma Thruster with Increased Thrust

The paper presents the results of the investigation of the possibility to develop a stationary plasma thruster with increased thrust. This research was carried out by the Research Institute of Applied Mechanics and Electrodynamics, Moscow Aviation Institute (RIAME MAI) jointly with Fakel Design Bureau as an industrial partner. During research, we developed and investigated a laboratory model, prototype, and experimental model of the SPT-100VT thruster, whose main dimensions are close to those of the well-known SPT-100 serial thruster, which is produced by the Fakel Design Bureau and is successfully operating in space. As a result, it has been shown that the SPT-100VT thruster can effectively and for a long time operate with a discharge voltage of 300 V and power of up to 3 kW producing thrust more than twice that of the SPT-100 with a thrust efficiency above 60% and specific impulse over 1800 s. The increased thrust is achieved by an increase in the xenon flow rate; the efficiency of the thruster is increased due to the modernization of the thruster magnetic system and geometry of the accelerating channel.

Parametric Study of Two Stable Forms of Discharge Burning in a Hall-Effect Thruster

In this paper, we experimentally studied the behavior of the integral operation parameters of a Hall-effect thruster (thrust and specific thrust impulse) in two stable discharge glow modes significantly different from each other in anodic efficiency. The studies were conducted using a laboratory model of a Hall-effect thruster with an extended layer with an average discharge channel diameter of 77 mm in the discharge voltage range of 500–900 V and in the gas-flow rate range from 2 to 5 mg/s. The most striking distinguishing features of the observed glow regimes are the plasma jet shape and the discharge current value at almost identical input parameters (gas flow, discharge voltage, and magnetic field). In the entire studied range of input parameters when changing from the optimal mode (in terms of efficiency) to suboptimal, the main integral characteristics of the engine are shown to undergo a stepwise change: the discharge current increases by 10‒30% with a simultaneous relative drop in thrust by 5–15% and in efficiency by 20–40%. A detailed study of the anodic efficiency structure showed that, at abrupt rebuilding, the efficiency of using the electron current (the ratio of the ion current to the discharge current) changes, i.e., the electron conductivity in the engine discharge channel.

Fluid simulation of ionization process in iodine cusped field thruster

In this paper, a one dimensional fluid model of iodine cusped field thruster is built along two typical electron paths. Simulation results show typical low frequency oscillations of plasma parameters. Density of I2+ is similar to that of I+, while density of I− is smaller than those of I+ by two orders of magnitude. Simulation results show that ionization rate and thrust of iodine cusped field thruster are a little higher than that of xenon cusped field thruster. However, electron density of main ionization region in iodine cusped field thruster is much higher than that in xenon cusped field thruster, which may be due to diversity of plasma components and complexity of ionization process. Compared with xenon cusped field thruster, ionization intensity is enhanced and main ionization region moves towards downstream of channel in iodine cusped field thruster, which is related to dissociation process of I2. With decrease of leak electron proportion, ionization strength of secondary ionization region located in the middle magnetic cusp is enhanced and ionization strength of main ionization region is weakened. The main ionization region moves towards upstream of channel. These phenomena are mainly because confinement of electrons by middle magnetic cusp is enhanced, which causes excessive consumption of I2 and decrease of I2 dissociation intensity.

Latest progress in Hall thrusters plasma modelling

In the last 30 years, numerical models have revealed different physical mechanisms involved in the Hall thruster functioning leading to a bridge between analytical prediction/empirical intuition and experiments. For this reason, the need for a model to study Hall thruster operation continues to increase. Two basic approaches exist: one based on fluid/hybrid simulation where the velocity distribution of electrons is prescribed and the plasma inside the thruster, considered as quasineutral, is described with macroscopic quantities (density, velocity and energy), with unmagnetized ions being considered as collisionless; the second approach is based on a kinetic description for charged particles where no approximations are made regarding their velocity distributions. Fluid or hybrid approaches offer the advantages of computational efficiency with modest hardware requirements. They are very useful to perform parametric studies but actually the anomalous phenomena believed to be responsible for electron transport across the magnetic field barrier have not been self-consistently modeled using a fluid approach. A kinetic approach is able to better capture phenomena originating on the Debye scale length like the lateral sheaths, E × B electron drift instability, and it is important to explain the anomalous electron transport, but kinetic simulations require very long run times. For the latter, the advances in computer hardware over the past years have allowed researchers to perform simulations under conditions closer and closer to the actual thruster operation. In this review, we will present two approaches, with emphasis on numerical schemes used with assumptions and approximations and the main results obtained. Future directions in the Hall thruster modeling will finally be outlined.

Numerical modeling of high efficiency multistage plasma thrusters for space applications

The high efficiency multistage plasma-thruster (HEMP-T) represents an ion thruster technology that was developed by Thales Deutschland GmbH beginning in the early 2000s. It features a dielectric-coated discharge channel with an anode at the channel bottom. A magnetic field is applied by periodic permanent magnets (PPMs) that is mostly axially oriented in most channel regions, with radial orientation only at spatially confined magnetic cusps resulting in low particle fluxes towards the dielectric wall. The typical length scales in the description of the HEMP-T plasma range from microscopic over mesoscopic to macroscopic. Microscopic effects are introduced, e.g., by atomic interactions and surface interactions. Mesoscopic scales appear by the gyro radius of particles in the magnetic field and the formation of a transition zone between plasmas and walls on the length scale of some Debye lengths, respectively. Large-scale macroscopic length scales are introduced, e.g., by the plume expansion and interaction with test vessel walls. For a correct description of both thruster and plume plasma, one has to solve a kinetic problem for the whole region of interest, including all significant physical processes. This review offers an overview of modeling strategies and their results for the HEMP thruster. The axisymmetric 2D3v Particle-in-Cell (PIC) simulation method is used to identify the basic physics of the acceleration channel and the near-field plume region. Direct comparison with the observed plasma radiation and angular ion energy distributions, both for stationary and dynamic modes, is also presented. While good qualitative agreement with experimental data is achieved, even better agreement with experiments is necessary to predict thruster performance via numerical models in the future. The limited size of the simulation domain restricts the study of the coupled thruster-plume dynamics, which is an important aspect for the interaction of ion thruster and carrier spacecraft. Improvements in computer technology, the use of hierarchical models and the multigrid method discussed in this review can help overcome these limits and improve the quality of predictive thruster modeling.

Distributed finite-time fault-tolerant containment control for multiple ocean bottom flying nodes

The Ocean Bottom Flying Node (OBFN) is a kind of small Autonomous Underwater Vehicle (AUV) used in detection of seabed resources. Based on directed commination topology, this paper investigates the problem of distributed finite-time fault-tolerant containment control for multiple OBFN systems in presence of model uncertainties, external disturbances, and thruster faults. By choosing the nonsingular fast terminal sliding surface and defining the containment error variables, a distributed finite-time containment control method is designed, so as to make the states of the multiple OBFN systems converge to the sliding surface in finite time. The thruster faults, model uncertainties, and external disturbances are considered together and estimated by utilizing Neural Networks (NNs). An adaptive law is designed to compensate the upper bounds of estimation error. Based on the graph theory and matrix theory, it is demonstrated that the follower OBFNs could enter the convex hull formed by the leader OBFNs in finite time through using the Lyapunov approach. Numerical simulation is presented to show the effectiveness of the proposed algorithm.

Development of a helium collisional radiative model for a helicon thruster

A helicon thruster was developed to research a diagnostic technique for determining plasma parameters using emission spectroscopy and helium line ratios. Conventional plasma diagnostics consisting of conductive components which contact the plasma directly can have measurement errors in the presence of radio frequency, electric, or magnetic fields. A non-invasive diagnostic technique is sought to eliminate these problems. A collisional radiative model is needed to determine the electron density and temperature that result in the measured emission line ratios. This research describes a quasi-steady state collisional radiative model used to determine the electron temperature and density in a helium helicon thruster.

Fully 3-D Numerical Investigation of Phenomena Occurring in Marine Magnetohydrodynamic Thrusters

A magnetohydrodynamic (MHD) thruster is a type of electric motor which does not have mechanical moving parts and directly converts electrical energy into mechanical energy. In this paper, a multiphysics numerical simulation has been performed to investigate the phenomena occurred in the channel of marine MHD thrusters. In this simulation, all electric, magnetic, and fluid flow fields have been considered 3-D. For this purpose, a marine MHD thruster model with saddle-shaped coils is selected, and its dimensions are determined. Then, this thruster is simulated numerically, and its electromagnetic and fluid flow parameters are studied. In this simulation, the effects of seawater electrolysis and end loss are taken into account. An experimental setup is established to validate the results obtained from the numerical simulation. The results reveal that the nonuniformities of the electric and magnetic fields along the channel have a great impact on the performance of the thruster. Unlike the results obtained in the previous studies, it is shown that the velocity near the electrodes is higher than that near the sidewalls arisen from the higher electromagnetic force close to the electrodes.

Hydrodynamic Analysis-Based Modeling and Experimental Verification of a New Water-Jet Thruster for an Amphibious Spherical Robot.

Thrusters are the bottom actuators of the amphibious spherical robot, and play an important role in the motion control of these robots. To realize accurate motion control, a thrust model for a new water-jet thruster based on hydrodynamic analyses is proposed in this paper. First, the hydrodynamic characteristics of the new thruster were numerically analyzed using computational fluid dynamics (CFD) commercial software CFX. The moving reference frame (MRF) technique was utilized to simulate propeller rotation. In particular, the hydrodynamics of the thruster were studied not only in the axial flow but also in oblique flow. Then, the basic framework of the thrust model was built according to hydromechanics theory. Parameters in the basic framework were identified through the results of the hydrodynamic simulation. Finally, a series of relevant experiments were conducted to verify the accuracy of the thrust model. These proved that the thrust model-based simulation results agreed well with the experimental results. The maximum error between the experimental results and simulation results was only 7%, which indicates that the thrust model is precise enough to be utilized in the motion control of amphibious spherical robots.

A Low-Cost Test Bench for Underwater Thruster Identification

Underwater vehicles are increasingly being used for the inspection of marine structures, bathymetry and underwater intervention applications. The manoeuvring performance of these vehicles is critically dependant on the quality of the thruster model which must faithfully represent the relationship between the thruster inputs and corresponding outputs. Thruster manufacturers typically provide only the essential electrical, mechanical and thrust performance characteristics, for this reason the identification of the thruster’s parameters is especially important for constructing a reliable control system for the underwater vehicle. Physical testing using some form of test bench is normally used for identifying the thruster parameters. These test benches usually consist of a water tank and the thruster which is clamped to some form of instrumented reaction frame for measuring the model parameters. The cost of a test bench varies according to two major factors which are the size and the instrumentation which strongly depends on the physical quantities that we are trying to measure. In this article we will make a state of the art survey of existing test benches in order to provide a technical basis that will allow us to build a low-cost test bench. A thruster will be modelled using the resulting test bench and the outcomes will be presented at the end of this paper.

Modeling and Adaptive Control for Multirotor Subject to Thruster Dynamics

Research on high-speed flight dynamics of multirotors is in increasing demand for “quick-reach” missions such as short-distance delivery and disaster assessment. The conventional works have integrated a linear thruster model in the dynamics modeling stage and developed a corresponding control algorithm; however, the linear thruster assumption has been shown to be accurate only in a near-hover state through wind tunnel tests. This paper proposes a novel multirotor dynamics model incorporating blade element momentum theory (BEM), which can precisely predict transient thruster output in various flight states (e.g., no flow, oblique flow, and pure side flow). With the proposed dynamics model, degradation of control performance caused by disturbances and variations is noticed under typical flight state (e.g., high-speed forward flight and drastic vertical rising). Finally, an adaptive robust backstepping control algorithm is proposed to achieve guaranteed performance under the aforementioned variations and disturbances. The simulations are carried out on a small quadrotor to verify the proposed approach.

Development of a Novel Launch System Microwave Rocket Powered by Millimeter-Wave Discharge

This paper presents the state of art of Microwave Rocket development and related researches on atmospheric discharge in a high-power millimeter-wave beam. Its operational mechanisms, thruster design, history of development, and flight path and cost analyses are introduced along with millimeter-wave discharge observations and numerical simulations. A thruster model of 126 g weight with no on-board propellant was launched to 1.2 m altitude using a 1 MW class gyrotron. A flight analysis that shows 77% cost reduction is possible using Microwave Rocket as the first stage of H-IIB heavy. A millimeter-wave discharge with unique plasma structure such as a quarter-wavelength microstructure and a comb-shaped filamentary structure was observed and reproduced by a two-dimensional numerical model.

Radio-Frequency Ion Thruster with Additional Magnetic Field: Experimental Investigation

Performances of a radio-frequency ion thruster with an additional external magnetic field in the area of the high-frequency discharge are experimentally investigated and the results of the investigation are presented. The calculated distribution of a magnetic field generated by an additional magnetic system for the current in the winding 1 A is given. How an additional external magnetic field influences on the ion current is examined. Performances of a laboratory model of a radio-frequency ion thruster with and without a constant external magnetic field are compared. Modes of thruster operation and current values in a magnetic system’s windings under which the increment of ion current is minimal are determined.

Adaptive Backstepping Terminal Sliding Mode Control Method Based on Recurrent Neural Networks for Autonomous Underwater Vehicle

The trajectory tracking control problem is addressed for autonomous underwater vehicle (AUV) in marine environment, with presence of the influence of the uncertain factors including ocean current disturbance, dynamic modeling uncertainty, and thrust model errors. To improve the trajectory tracking accuracy of AUV, an adaptive backstepping terminal sliding mode control based on recurrent neural networks (RNN) is proposed. Firstly, considering the inaccurate of thrust model of thruster, a Taylor’s polynomial is used to obtain the thrust model errors. And then, the dynamic modeling uncertainty and thrust model errors are combined into the system model uncertainty (SMU) of AUV; through the RNN, the SMU and ocean current disturbance are classified, approximated online. Finally, the weights of RNN and other control parameters are adjusted online based on the backstepping terminal sliding mode controller. In addition, a chattering-reduction method is proposed based on sigmoid function. In chattering-reduction method, the sigmoid function is used to realize the continuity of the sliding mode switching function, and the sliding mode switching gain is adjusted online based on the exponential form of the sliding mode function. Based on the Lyapunov theory and Barbalat’s lemma, it is theoretically proved that the AUV trajectory tracking error can quickly converge to zero in the finite time. This research proposes a trajectory tracking control method of AUV, which can effectively achieve high-precision trajectory tracking control of AUV under the influence of the uncertain factors. The feasibility and effectiveness of the proposed method is demonstrated with trajectory tracking simulations and pool-experiments of AUV.