Cusped Field Thruster Research Articles

The Reliability Modeling and Evaluation of a Cusped Field Thruster When Undertaking a Gravitational Wave Detection Mission

The propulsion system, particularly electric propulsion, holds immense significance in the context of gravitational wave detection missions. One of the key factors of a deep space exploration mission is the lifetime of the electric propulsion. Ensuring the high reliability of the propulsion system is of paramount importance; however, achieving this is challenging in the absence of adequate failure data. Conducting ground tests for a thruster tends to encounter two limitations: a lack of failure data and time constraints. To address these challenges, we propose a semi-physics sputtering method that combines a physical erosion model with empirical processes. In this study, we focus on evaluating the lifespan of a cusped field thruster (CFT) for potential application in gravitational wave detection missions. Our analysis revolves around modeling non-conservative forces in a space environment and examining their impact on a thruster’s longevity. The results indicate that, in gravitational wave missions, the survival rate of a thruster’s lifespan at 8000 h is 0.75. At a constant voltage of 500 V, the maximum corrosion depth after 5000 h is 3.1 mm, while the minimum is 0.49 mm.

Study on the ionization and acceleration of a microwave discharge cusped field thruster

The microwave discharge cusped field thruster is a novel concept electric micro propulsion device, also a candidate thruster for the gravitational detection mission. A coaxial transmission line resonator is utilized to feed the microwave into the thruster to generate Xe plasma steadily with a mass flow rate as low as 0.1 sccm. Due to the separation of ionization and acceleration, the thruster performs high operation mode stability over a wide range of voltage in low mass flow conditions. Experimental and simulation methods are carried out to study the ionization and ion acceleration of the thruster. The results show that in operating conditions with a mass flow rate of 0.1 sccm, an anode voltage of 0 V to 1000 V, and a microwave power of 2 W, the right-hand circularly polarized wave (R wave) and the ordinary wave (O wave) play the most important role in the ionization process. The ion acceleration region locates around the exit magnetic separatrix, and the acceleration region tends to converge toward the separatrix as the anode voltage increases, resulting in an increased focus of the thruster plume and concentration of the ion energy distribution. Due to the separation of the ionization and acceleration regions, the thruster performs a divergence efficiency of 0.5–0.8, and an acceleration efficiency of 0.9.

Cathode position effects on microwave discharge cusped field thruster

The microwave discharge cusped field thruster is a novel concept of electric micropropulsion device, which operates μN level thrust in low mass flow rate conditions, making use of a coaxial transmission line resonator. With its advantages of low thrust noise and high thrust resolution over a wide range of thrust, the thruster has emerged as a candidate thruster for the space-borne gravitational wave detection mission. The cathode effects commonly exist in many kinds of electric propulsion, and they are typically significant in micropropulsions. In order to find out the cathode position effects on a microwave discharge cusped field thruster, a thermionic cathode is mounted on a cross-slider for coupling. Under different cathode positions, the plume is analyzed by a Faraday probe and a retarding potential analyzer to analyze the performance and discharge characteristics. The results show that the magnetic mirror effect leads to significant degradation of anode current and an increase in low-energy ion ratio as the cathode moves away from the thruster exit. The electron conduction route also significantly impacts anode current efficiency, related to the cathode-exit distance and the thruster magnetic topology.

Experimental Investigation of the CFHT-27 Cusped-Field Hall Thruster Performance

Cusped-field Hall thrusters (CFHT) have significant potential for use in many space missions due to their simplicity, long life and high efficiency. CFHT-27, designed and developed at the Bogazici University Space Technologies Laboratory (BUSTLab), is a prototype CFHT with a 27-mm diameter discharge channel. CFHT-27 utilizes samarium-cobalt (SmCo) permanent magnets. The thrust and efficiency of a cusped-field thruster is closely related to its size and design parameters. In this study, in order to understand the relationships between the design parameters and the thruster performance, the performance tests of the CFHT-27 are carried out for a given magnetic field topology. The thruster was operated at discharge voltages ranging from 250 to 500V with argon propellant with up to 3,000 s of specific impulse. The measurements show that CFHT-27 can achieve thrust values from 1 to 46 mN. Thus, this thruster can be used for a wide range of thrust values allowing throttle capabilities for different missions.

Effects of magnetic field strength on the microwave discharge cusped field thruster

The microwave discharge cusped field thruster is a novel electric propulsion concept developed for the space-borne Gravitational Wave detection mission. It is an effective combination of the cusped magnetic field and the ECR microwave plasma source, which provide the thruster strong confinement for the plasma and the ability to operate on low mass flow rate conditions. To meet the requirements on the high accuracy, low noise thrust over a wide range, a series of studies are carried out on the microwave discharge cusped field thruster. Since the magnetic field strength is one of the critical factors with a significant impact on the thruster, a plume plasma diagnosis is performed to analyze the discharge performance and plasma characteristics with different magnetic field strength conditions. A Faraday probe, a retarding potential analyzer, and an emissive probe are employed to characterize the plume. The results show that the variation of the magnetic field strength performs strong effects on the plume structure, the ion acceleration, and the electron conduction process. As the magnetic field strength weakens, the single-peaked plume profile transforms to a hollow cone structure, which is attributed to the conversion of acceleration mechanism. The thruster prototype performs a continuous thrust of 2–26.9 μN and a highest specific impulse of 248s with superior reproducibility in a low mass flow rate of 0.1sccm.

Multi-Objective Design Optimization of Cusped Field Thruster via Surrogate-Assisted Evolutionary Algorithms

Cusped field thrusters are an efficient cost-effective electric propulsion technology that offer promise for small spacecraft platforms. They offer various advantages, including simple design and low wall erosion, and hence long-life operation owing to high plasma confinement using permanent magnets over other electrostatic alternatives. Accurate physical modeling and performance characterization are crucial to achieve successful downscaling of cusped field thrusters while maintaining high performance. Multiobjective design optimization is performed by incorporating magnetic simulation coupled with an improved power balance model into evolutionary algorithms assisted by surrogate modeling, aiming to simultaneously maximize thrust, total efficiency, and specific impulse. Physical insights have been gained into key design factors to maximize thruster performance by probing into the plasma behavior inside the channel and the plume region. It has been found that altering the magnetic field distribution using an additional magnet can effectively enhance thruster performance by suppressing the plume divergence loss. Global sensitivity analysis has identified the anode current as the most influential design parameter on the performance parameters due to the active role it plays in the ionization process. Uncertainty analysis has found the considerable influence of the variations of anode potential and mass flow rate on those of thrust and specific impulse.

Multi-source information fusion for space gravitational waves detection thrust estimation on orbit

Space Gravitational Wave (GW) detection task puts forward super-low thrust noise for micro-newton propulsion system. Study shows thrust noise can be reduced by thrust closed loop feedback control structure. The effect is determined by thrust estimation accuracy. Traditionally, thrust estimation is realized by electric parameters and thrust estimation equation. However, this way is faced with high thrust estimation error in the low frequency band. Besides, the displacement sensor information of the drag-free control system can also be used for thrust estimation via disturbance observer. However, this way is only effective for low-frequency thrust due to the measurement noise of displacement sensor. A data fusion method is proposed in this paper to enhance thrust estimation accuracy. In this method, the high frequency thrust noise is estimated by electric parameters and thrust estimation equation. Meantime, the low frequency thrust noise is estimated by displacement sensor information and disturbance observer. In this paper, the cusped field thruster is used as the actuator of drag-free control system to simulate. Simulation results show thrust estimation by data fusion can effectively reduce thrust noise in the middle frequency band and enhance stability of satellites compared with that by electric parameters.

Numerical simulation of magnetic field and channel configuration effect on cusped field thruster with electron cyclotron resonance discharge enhancement

Cusped field thrusters with electron cyclotron resonance discharge enhancement have great potential in micro-Newton propulsion field. According to the magnetic field and channel configuration, the thruster can be divided into 1-stage thruster, 2-stage thruster and 3-stage thruster. The ionization region and acceleration region of the 1-stage thruster are located at the channel upstream, which causes a large amount of wall power deposition, resulting in poor performance. Due to the shorter channel of the 2-stage thruster, it is easier for electrons to reach the ECR layer on the near-antenna region to obtain energy to promote ionization, compared with 3-stage thruster. In addition, the magnetic cusp number of the 2-stage thruster wall is lower than that of the 3-stage thruster, reducing the total wall power deposition. It is necessary to use 2-stage short channel configuration to design the thruster.

Improved modeling for design optimization of cusped field thrusters with support of kinetic analysis

Electric propulsion draws increasing attention in space missions as an alternative to chemical propulsion due to its high efficiency. The cusped field thruster, a class of electrostatic propulsion, is able to operate at different anode voltages and operation points, thereby generating different levels of thrust stably and efficiently. Optimal design points have been selected via multi-objective design optimization with respect to performance measures such as thrust and specific impulse. Particle-in-cell simulation is employed for the selected design points in the present study so as to probe into the physical properties via full kinetic simulation. The influence of the magnet geometry and the resultant magnetic field distribution has been investigated, with particular focus on the effects of the inner/outer magnetic radii and neutralizer current on the plume divergence. The plume divergence has significant impact on the thruster performance. New insights have been gained into the key design factors such as the major influence of the magnet geometry and operating conditions as well as the underlying physical mechanism that crucially accounts for the thruster performance.

Electron cyclotron resonance discharge enhancement in a cusped field thruster

Electron cyclotron resonance (ECR) is induced to enhance the discharging performance of a cusped field thruster, by feeding microwave into the channel. Due to a critical combination of ECR discharge and DC discharge, propellant utilization is significantly improved, with varying degrees of impact on other parameters. The DC mode, the ECR mode and the combined mode are achieved and analyzed respectively. A Faraday probe and a retarding potential analyzer are employed to diagnose the plume plasma, and approximate calculated thrust is given. Moreover, high frequency electric field simulation is carried out to indicate the microwave feeding process in different mass flow rate conditions, making use of a particle-in-cell simulation result. The result shows that the ECR enhancement is particularly effectual in low mass flow conditions, and the special plasma distribution in the cusped magnetic field leads to the propellant utilization trend in the combined mode.

Preliminary Experimental Characterization of a Microwave Discharge Cusped Field Thruster

The cusped field thruster has become a candidate thruster in next-generation space science missions due to its low complexity and potential long life over a wide range of thrust conditions. However, the reduction of propellant utilization and, as a result, the total performance degradation has emerged in works on cusped field thruster downscaling. In this work, a coaxial resonator is utilized to feed the microwave (MW) into the near-anode region of the cusped field thruster, which contributes to ionization at a relatively low mass flow rate. With a LaB6 thermionic emission cathode, the thruster can operate in two modes: MW excited mode and the MW-DC mixed mode. The results show that the thruster can operate with a minimum mass flow rate minimum of 0.004 mg/s and achieves a continuously adjustable thrust from 1.9 μN to 30.8 μN. The performance variation characteristics over the three control parameters (anode voltage, mass flow rate, and MW power) are considered. Additionally, a plume plasma diagnosis is performed with a Faraday probe and a retarding potential analyzer to analyze the discharge performance and plasma characteristics with different operating conditions.

Low Power Cusped Field Thruster Developed for the Space-Borne Gravitational Wave Detection Mission in China

The microthruster is the crucial device of the drag-free attitude control system, essential for the space-borne gravitational wave detection mission. The cusped field thruster (also called the High Efficiency Multistage Plasma Thruster) becomes one of the candidate thrusters for the mission due to its low complexity and potential long life over a wide range of thrust. However, the prescribed minimum of thrust and thrust noise are considerable obstacles to downscaling works on cusped field thrusters. This article reviews the development of the low power cusped field thruster at the Harbin Institute of Technology since 2012, including the design of prototypes, experimental investigations and simulation studies. Progress has been made on the downscaling of cusped field thrusters, and a new concept of microwave discharge cusped field thruster has been introduced.

Thrust noise cause analysis and suppression of a cusped field thruster

The drag-free control technology is a critical technology to guarantee the ultra-low disturbance satellite platform. Thrust noise is the primary disturbance of the drag-free control system because the thruster acts as the actuator of this system, so it would seriously affect the performance of the control system. To study and suppress thrust noise, a cusped field thruster, which has the feasibility of being applied to the drag-free control tasks, is used in this research. According to the experimental results of thrust noise, it can be seen that the thrust noise spectrum under different working conditions is different slightly, but the trend is similar. The amplitude spectrum densities of thrust in the high-frequency region present white noise characteristics, while the amplitude spectrum densities increase with the decrease of frequency in the low-frequency region. Based on the input-output thrust model and the experimental data of the anode voltage and flow rate, the effects of the anode voltage fluctuation and flow rate fluctuation on the thrust noise are analyzed. The high-frequency part (above 0.05Hz) of thrust noise is mainly caused by the flow rate noise, while the drift of thruster operation states leads to low-frequency (10−3Hz–0.05Hz) fluctuation of thrust. Finally, based on the feedback control theory, a noise suppression method is designed by controlling the anode voltage. Closed-loop simulation results of the thruster verify that the method is effective.

Simulation study of influence of exit magnetic separatrix angle on plume divergence control

Cusped field thruster is a novel electrostatic thruster suitable for space exploration, but with high plume divergence angle. In this article, a 2D Particle-in-cell plus Monte Carlo (PIC-MCC) model is built to study the influence of exit magnetic separatrix angle on controlling plume divergence of cusped field thruster. The electric potential contour line distribution characteristics near exit magnetic separatrix with different angle are obtained and their formation mechanism is explained by magnetic mirror effect and electron pressure term. Simulation results show laying additional magnetic ring at the exit of channel can transfer exit magnetic separatrix towards inward of channel, which can decrease angle between electric potential contour line and central axis and increase ion axial speed. It is mainly due to change of magnetic field line direction and enhancement of magnetic mirror effect. However, simulation results show that ionization intensity in the channel decreases after adopting the plume control method. The plume divergence control method increases the channel length and causes the exit magnetic cusp inside the channel. Therefore the influence of exit magnetic separatrix angle on the characteristics of electron and ion energy deposition distribution on wall is further investigated.

Experimental investigation of dielectric wall material effects on low-power HEMP thruster

The high efficiency multi-staged plasma (HEMP) thruster, also known as the cusped field thruster, becomes a candidate microthruster of new generation space observation missions for its low complexity and potential long life over a wide range of thrust. Since there is a lack of relevant research of the wall material effects on the HEMP thruster, a low-power HEMP thruster with three different dielectric wall materials is tested to discover the effects on performance and discharge characteristics. A Faraday probe, a retarding potential analyzer, and a Langmuir probe are employed to diagnose the plume, and the plasma behavior differences in ionization and acceleration processes are indicated. The result shows that the secondary electron emission coefficient of the wall material has definite effects under a low mass flow rate, which is similar to the effects on the Hall thrusters, but no distinct difference is found in high flow rate conditions.

Multiobjective Optimization and Particle-In-Cell Simulation of Cusped Field Thrusters for Microsatellite Platforms

A multiobjective design optimization (MDO) study has been conducted to characterize and maximize the performance of the downscaled cusped field thruster with respect to thrust, total efficiency, and specific impulse characterized by common design parameters: anode voltage, anode current, mass flow rate, and geometric configuration. Particle-in-cell (PIC) simulations have been performed for the selected design points identified in MDO study for verification by accurately accounting for phenomena and performance losses that originate from uncertainties and complexities associated with the thruster design and physics. The fidelity of the models employed in MDO has been enhanced owing to the new physical insights gained from the detailed analysis of the PIC results. The prediction errors associated with uncertainties such as the beam current and divergence angle have been reduced to within 5%.

Effects of Thrust Noise and Measurement Noise on Drag-Free and Attitude Control System

In order to reduce the interference of space environment in space microgravity experiments, one drag-free and attitude control system could be used in space science experiments to compensate non-conservative forces and to minimize residual disturbances of the satellite. As the main parts of the drag-free control system, noises of thrusters and GPS receivers have significant impacts on the performance of the control system. To accurately analyze these effects, a cusped field thruster is used in this paper and its noise characteristics are measured first. Second, a drag-free and attitude control system with both thrust noise and measurement noise considered is designed. Then, the effects of these noises on the whole control system are analyzed thoroughly. Finally, two noise reduction methods for those two noises are used in this study and the effectiveness of noise suppression methods is verified.

Particle‐in‐cell simulation of an optimized high‐efficiency multistage plasma thruster

AbstractElectric propulsion attracts increasing attention in contemporary space missions as an interesting alternative to chemical propulsion because of the high efficiency it offers. The High‐Efficiency Multistage Plasma thruster, a class of cusped field thruster, is able to operate at different anode voltages and operation points and thereby generate different levels of thrust in a stable and efficient way. Since experiments of such thrusters are inherently expensive, multi‐objective design optimization (MDO) is of great interest. Several optimized thruster designs have resulted from a MDO model based on a zero‐dimensional (0D) power balance model. However, the MDO solutions do not warrant self‐consistency due to their dependency on estimation from empirical modelling based on former experimental studies. In this study, one of the optimized thruster designs is investigated by means of particle‐in‐cell (PIC) analysis to examine the predicted performance characteristics with self‐consistent simulations. The 0D power balance model is used to develop additional diagnostics for the PIC simulations to improve the physics analysis. Using input parameters for the 0D power balance model from the PIC simulations allows further improvement for the design optimization.

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.

Study of channel length effect on low power HEMP Thruster

The HEMP Thruster, also known as “cusped field thruster”, becomes a candidate micro thruster of new generation space observation missions for its low complexity, potential long life over a wide range of thrust. As one of the main parameters of thruster, channel length selection is required in the downscaling of cusped field thruster. Three low power thrusters with different channel length are designed to discover the effect on performance and discharge characteristics. Due to the complexity of the ionization and acceleration process of the special cusped magnetic field, the plume is diagnosed by a Faraday probe and a retarding potential analyzer, and a Partial-In-Cell simulation is carried out to analyze the discharge mechanism. The result shows that lengthen of channel length has a diminishing positive effect on propellant utilization, but a negative effect on the total efficiency and kinetic performance at the same time. Decisive factors are discovered through the study on four internal efficiencies, with crucial physics process analyzed in the numerical simulation, which provides an important reference for the downscaling of the electric propulsion devices and similar low-temperature plasma discharge conditions.