Thruster Performance Research Articles

초소형 위성의 랑데부/도킹 기술 검증을 위한 시나리오 설계

This paper illustrates the trajectory design of drift distance recovery after initial launch and proximity operation when verifying rendezvous/docking technology using nanosatellites. The rendezvous/docking is a technology that is the basis of on-orbit servicing technology and is a preemptive process essential for approaching a target object. In particular, since it is difficult to verify in space, nanosatellites have recently been used to reduce the risk and cost of the development stage. Therefore, this paper not only introduces the configuration and specifications of thrusters for nanosatellites but also designs relative trajectories that can take into account the thrust limitations which come from the small size and low power of nanosatellites. In addition, we intend to be helpful in later designing scenarios according to the improvement of available thruster performance through comparison of trajectories and thrust usage with cases without thrust limitations.

Hall-Effect Thrusters for Deep-Space Missions: A Review

For several decades, Hall-effect thrusters (HETs) are being used in several applications, such as orbiting satellites, deep space missions, etc. This article studies the effect of several parameters, namely, thruster geometry, magnetic field, wall material, and different propellants that significantly influence thruster performance. It was reported that annular thrusters are preferred for deep space missions, whereas, cylindrical thrusters are widely used in low power applications, such as station keeping of satellites. The lifespan of HET is a crucial parameter that is decided by the erosion of the thruster wall. Magnetically shielded thrusters are preferred not only to reduce the erosion but also the secondary emission of electrons. The overall effect of magnetic shielding is the improvement in thruster performance and its lifespan. Boron nitride and mixture of boron nitride and silica (borosil) were found to be the most appropriate thruster wall materials due to their lowest electron emission and reduced ion–wall interaction. Over the years, Xenon has been the best choice among several propellants for the HET operation. Other potential propellants include Krypton, Bismuth, Iodine, etc.

The external characteristics and inner flow research of rim-driven thruster

In order to have a more comprehensive grasp of the performance of the rim-driven thruster, the external characteristics are studied by experiment and carry out numerical simulation to study inner flow characteristics. The test results for the rim-driven thruster find that the head curve had a hump shape. The head is the largest while the flow rate Q = 600 m3/h. The numerical simulation is carried out to reveal the cause of the hump of head. The results show that large-scale backflows gradually appear near the wall in front of the impeller inlet, the central area of the impeller outlet, and the two sides of the central low-pressure zone with the reducing of the flow rate, which can cause a large flow loss and result in a drop in head. The discrepancy between the pressure surface and the suction surface of blade decreases rapidly in the range of r/ R = 0.2–0.5, which is another major factor leading to the drop in head under small-flow conditions. Structurally, there is no blade in the impeller center and there are the large backflows in the middle of impeller, which causes much volume loss and is a main cause of the decreasing of head under small flow rate.

Weibull Analysis Applications in Unexpected Electrical Breakdown of Ion Thruster

The unexpected electrical breakdown (UEBD) of ion thruster is a critical problem. It directly affects the reliability and performance of the ion thruster. The basic UEBD characteristics and Weibull theory are introduced. The self-consistency and applicability of Weibull analysis for UEBD study are discussed. The UEBD period is a proper characteristic variable for Weibull analysis. The approaches to study the factors affecting the UEBD period are presented: (i) distinguishing the effect of coupled factors with the shape parameter of a mixed Weibull distribution, and (ii) studying the effect of a single factor with its respective parameters of the Weibull distribution. The factors discussed include electric field strength, grid material, and ion density. Further aspects to investigate involving the coupling of these factors and mechanisms are prospected.

Equivalent Aerodynamic Design of Blade for Offshore Floating Wind Turbine Model

The Froude-scaled offshore floating wind turbine model is inevitably affected by the Reynolds number effect, making the model unable to correctly reproduce the thrust performance of the reference wind turbine (RWT). To solve this problem, an Xfoil-AirfoilPrep-Matlab (XAM) system and a wide tip speed ratio search method (WTSM) are proposed to design a wide tip speed ratio (TSR) thrust-match model blade. The XAM system is utilized to select the best airfoil for WTSM by calculating the lift and drag coefficients of several airfoils. The WTSM is utilized to optimize the blade chord and twist. It formalizes the blade chord and twist by polynomials and then optimizes the polynomial coefficients. The thrust coefficients construct the optimization object at different TSRs. For validating the effect of the redesigned blade, the thrust performance is compared to that of the RWT blade. In addition, the thrust performance of redesigned blade at different pitch angles is also calculated and compared to those of the RWT blade. Results show that the thrust performance of redesigned blade matches well with that of the RWT blade at 0 pitch angle, and it can also match the variations of that of the RWT blade at the other pitch angles well.

Magnetic field tailoring effects on ion beam properties in cylindrical Hall thrusters

The magnetic field is the most important element in designing a Hall thruster and improving thruster performance because it directly influences the behavior of electrons in the discharge channel. In this work, magnetic field tailoring, parallel magnetic fields to the thruster channel wall, has been attempted in a cylindrical Hall thruster, and the resultant ion beam properties are studied. The magnetic field tailored cylindrical Hall thruster demonstrated much higher ion current and propellant efficiencies than the conventional cylindrical Hall thruster, with an identical mass flow rate. A large fraction of multiply charged ions (>65%) was observed and reduced beam emission was demonstrated near the channel wall. Further, the channel wall is solely coated without erosion even at the end of the channel. Hence, tailoring of the magnetic field in cylindrical Hall thrusters could significantly enhance the potential of Hall thrusters in space applications owing to their higher propellant efficiency and reduced wall interaction.

Sputtering yield and nanopattern formation study of BNSiO2 (Borosil) at elevated temperature relevance to Hall Effect Thruster

Lower sputtering yield of the discharge wall material is a crucial parameter for the performance of Hall Effect Thruster (HET). In this article, we report the sputtering yield of HET wall material BNSiO2 (borosil) at elevated temperature ∼ 600 °C using quartz crystal microbalance (QCM). We observe a linear increase in the sputtering yield with temperature and it remains stable during long duration experiments using Xe ions. Two different crystallographic orientations of borosil give a slight variation in the yield. The higher yields for higher operating temperatures is proposed to be due to the thermal spike nature. Microscopic surface morphology shows only different grains of BNSiO2, however high resolution nanoscopic view reveals the formation of nanoripple like structures over different grains. The periodicity of such features increases with ion dose (sputtering time) and temperature in the range of 70–190 nm. Local curvature dependent erosion plays crucial role in such pattern formation.

A nonlinear time-domain BEM for the performance of 3D flapping-wing thrusters in directional waves

Recent studies indicate that flapping-foil biomimetic systems can significantly improve ship propulsion in waves. In most cases horizontal wing(s) are used performing vertical oscillatory motion induced by ship heaving and pitching responses in waves, while foil's rotational motion is actively controlled. Aiming to the detailed investigation of the free-surface effects, a GPU-accelerated Boundary Element Method (GPU-BEM) has been developed for the hydrodynamic analysis of 3D lifting bodies in non-linear waves with an angle of incidence and motions. The nonlinear free-surface conditions are satisfied at the exact location of the free-surface boundary. A nonlinear pressure-type Kutta condition is applied at the trailing edge and the dynamic evolution of the free vortex wake is obtained by a time-stepping method. The free-surface boundary conditions and Kutta condition are used to set up the nonlinear and nonlocal evolution equations. For the treatment of the dynamical system, the present BEM is coupled to the dynamical equations and it is integrated in time domain with an iterative scheme. Results are presented for a few subproblems of special interest, such as the wave resistance and the enforced radiation problems of smooth immersed bodies and compared with other methods for verification. Subsequently, the unsteady biomimetic thruster is examined in unbounded domain, beneath the free surface in the absence of incident waves, and in the presence of obliquely incident waves, illustrating the performance of the system. The present method can be exploited for the systematic investigation and the design of flapping-foil thrusters for augmenting ship propulsion in waves.

Thrust ripple analysis for improved modular tubular permanent magnet synchronous linear motor

Various technologies have ever been developed to minimize the detent force of linear motors. Although the traditional modular structure can effectively reduce the detent force, the width of the flux barrier and the number of units severely limit its application. To solve these, this paper proposes a new modular type of tubular permanent magnet synchronous linear motor (TPMSLM), which consists of two identical unit motors. For simplification, a subdomain analytical method of the unit motor is firstly established, and its accuracy is verified by a comparison with that of the finite element method. Using the two approaches, the important parameters of the motor are analyzed. A modified two-unit modular TPMSLM is also proposed through the star vectograms of the electromotive force, which achieves thrust performance similar to the traditional three-unit modular TPMSLM with a smaller axial size. Moreover, to make full use of the volume of the flux barrier, end teeth are added at both ends of the unit motors. The simulation results indicate that a reasonable end tooth structure can not only reduce the magnetic leakage phenomenon of the end but also effectively improve the thrust of the motor.

Structural characteristics of the upstream sheath of the ion optics and its application in evaluating the beam performance of an ion thruster

To evaluate the extraction capabilities of ion optics and promote the generation of highly collimated ion beams for propulsion, the properties of the upstream sheath of the ion optics and how those properties relate to the beam divergence are investigated numerically and theoretically. The characteristics of the beam divergence at different grid parameters are studied from the behaviors of the impingement current and divergence angle obtained by simulations. Additionally, the simulations indicate the existence of an optimal structure for the upstream sheath of the ion optics, one that corresponds to a moderate focusing effect and a relatively small divergence angle. The plasma densities at the dividing points of different sheath structures are then derived with the matching model of the ion optics and the Child–Langmuir law, coupled with semi-empirical approaches based on the simulation results. According to the theoretical analyses, the range of existence of the most-desirable sheath structure depends on the strength of the penetration of the extraction field, the voltage between the grid apertures, and the distance between the upstream surfaces of the grids. Also, sensitivity analyses are performed with the numerical partial derivatives of the models to investigate how the grid parameters affect the sheath structures. The plasma densities at the dividing points generally vary synchronously with the changes of grid parameters, but the ranges of variations are different. Consequently, the desirable sheath structure and operating conditions of the ion optics can be achieved by correctly adjusting the grid parameters.

Experimental scaling laws for the discharge oscillations and performance of Hall thrusters

Low-frequency (5–30 kHz) discharge current oscillations characterize the operation of Hall thrusters and represent a valuable metric not only to monitor the thruster behavior, but also to optimize the thruster performance. Two types of low-frequency oscillation modes are commonly observed: a global “breathing” mode, associated with the propellant ionization, and a local mode, typically characterized by a lower oscillation amplitude and the appearance of azimuthal spokes. The main characteristics of discharge oscillations and the transition between the two oscillation modes vary greatly with the thruster geometry and the operating condition. In this work, we present the results of an experimental campaign carried out on a 20 kW-class thruster prototype, SITAEL’s HT20k, with an exchangeable discharge channel and a magnetic circuit. Three different channel sizes were tested over a wide range of operating conditions and magnetic fields. For each operating point, a high frequency measurement of the discharge current was performed, recording the main characteristics of the oscillations. The data collected were then processed to derive the influence coefficients of each thruster parameter on the discharge current characteristics, as well as their dispersion. Finally, this allowed us to formulate general, data-driven scaling laws for the discharge current salient features, such as oscillation amplitude and dominant frequency. The gathered insight sheds light on the physical processes involved in the thruster discharge. At the same time, the possibility to model with simple functional laws the main oscillatory mode of Hall thrusters offers a unique aid to the optimization of thruster design and the evaluation of thruster performance during life.

Numerical study of the effect of radial magnetic field on performance of Hall thruster

The Hall-effect thruster has wide applications for commercial aerospace because of the high thrust density and simple structure. In order to further improve the performance of low-power Hall thruster and to solve the problem that the performance of low-power Hall thruster for low-orbit satellites is limited by the input power and maximum magnetic field intensity, the influence of radial magnetic field distribution in the discharge channel on the performance of the thruster is studied by numerical simulation and theoretical analysis in this work through changing the radial magnetic gradient on condition that the axial magnetic profile and the magnetic strength remain unchanged. The results show that the potential of the acceleration zone decreases with the increase of radial distance when the discharge parameters, propellant flow rate and axial magnetic field are unchanged. Therefore, the greater the radial magnetic field gradient near the inner wall of the thruster discharge channel, the greater the kinetic energy of the ions drifting along the axial direction to the thruster outlet, , and the greater the thrust of thruster. The research results of this work provide theoretical support for the magnetic field design and performance optimization of hall thrusters.

Influence of acceleration grid voltage and anode flow rate on performance of ion thruster

In order to achieve the optimal performance and reliability of the ion thruster in a wide power range, the influence of acceleration grid voltage and anode flow rate on the performance of ion thruster are studied experimentally and theoretically. The results show that in a certain range the ion beam current decreases continuously with the decrease of the absolute value of the accelerating voltage, and then increases suddenly. The electron backstreaming limited voltages in large and small thrust modes are –140 and –115 V, respectively. When the anode flow rate increases, the discharge voltage and discharge loss increase monotonically, and the deceleration current decreases monotonously. Under the power of 300−4850 W, the thrust is 11−188 mN, the specific impulse is 1800−3567 s, and the efficiency ranges from 34% to 67% by adjusting the anode current, grid voltage and working fluid gas flow. The maximum efficiency of thruster reaches 67% at 3000 W. This turning point is critical for thruster design and on-orbit applications. Choosing a reasonable range of working parameters can improve the performance and life of the thruster in application.

Simulation of magnetoplasmadynamic process with applied magnetic field

The magnetoplasmadynamic thruster is a typical representative of the high-power electric propulsion device, and the magnetoplasmadynamics process is its core operating mechanism. In order to understand the influence of applied magnetic field on its operating characteristics, the particle-in-cell particle simulation method combined with the scale model based on the self-similarity criterion is used to simulate the operating process of magnetoplasmadynamic thruster with applied magnetic field. The reliability of the model and method are verified by comparing with the experimental results. The plasma characteristic parameter distribution of the thruster during ignition is analyzed, and the influence of external magnetic field and cathode current on the thruster performance are discussed. The research results show that the construction of the discharge arc between the cathode and anode is a key step for thruster ignition and efficient operation. A low-intensity magnetic field is not conducive to the construction of a stable discharge arc, while the plasma beam is concentrated near the axis and the main thrust generation mechanism is the self-field acceleration. The discharge arc between cathode and anode is stable by applying a high magnetic field, and the main mechanism of thrust generation is vortex acceleration, which causes the thrust and specific impulse to increase linearly with the strength of the external magnetic field. The efficiency of the thruster increases with cathode current and the applied magnetic field intensity increasing. The discharge voltage increases with the augment of cathode current, but first decreases and then increases with applied magnetic field intensity increasing.

Performance Evaluation of a Hybrid Thruster for Spherical Underwater Robots

In this paper, a hybrid thruster for spherical underwater robots was developed and its performance was evaluated. The objective of this work was to improve the execution efficiency, multimodality and maneuverability of the autonomous underwater robot (AUV). Firstly, using meshing method, the open-water performance and flow field of individual water-jet and propeller thruster were analyzed. Numerical simulations were calculated and verified using experimental data. Then, the interaction between the hybrid thrusters were discussed, the flow field characteristics and hydrodynamic performance of the hybrid propulsion system were validated through streamline and pressure distribution. Finally, the hybrid propulsion system was designed, the thrust measurement experiments and the basic motion experiments for spherical underwater robot (SUR) using a hybrid thruster were carried out, including water-jet mode, propeller mode and the hybrid mode. The experimental results further verified the performance of the hybrid propulsion system, which meet the requirements of rapidity and flexibility, as well as the feasibility of underwater applications.

Design of input parameters and operating characteristics for multi-mode ion thruster

In view of the requirements for the application of electric propulsion system to China's asteroid deep space exploration mission, the relationship between input parameters and output characteristics of the thruster is established based on the basic plasma theory, and the input parameters such as screen grid voltage, beam current, anode current, acceleration voltage and propellent flow rate at each operating point are designed. The operating characteristics of the thruster are studied experimentally and theoretically. The test results show that under the design input parameter values, the maximum error of thrust is less than 3% and the maximum error of specific impulse is less than 4% at 23 operating points, the ion thruster can operate steadily in an input power range of 289–3106 W, thrust range of 9.7–117 mN, specific impulse range of 1220–3517 s, and efficiency range of 23.4%–67.8%. The electron backstreaming limited voltage decreases monotonically with thrust increasing and its minimum and maximum thrust value are 79.5 V and –137 V, respectively. The discharge loss decreases from 359.7 to 210 W/A as the power increases, and there is an adjusted turning at the input power 886 W, the efficiency increases with power increasing and after 1700 W the efficiency growth rate slows down and stabilizes. The optimum operating interval should be selected in practical on-orbit application. Controlling these parameters reasonably can improve thruster performance and lifetime. A 300-h wear test shows that the thruster works stably and the performance indicators meet the design requirements of ±3% uncertainty.

Design and optimization of aerospike nozzle for rotating detonation engine

Rotating detonation engine (RDE) is increasingly viewed as a viable technology to improve the performance of propulsion devices. At now, the design of RDE faces challenges when integrated with aerospike nozzle due to the large pressure fluctuations of rotating detonation waves. To optimize the nozzle configuration for thrust generation, the current work investigates the performance of RDE combined with various types of aerospike nozzles. The method of designing optimal aerospike nozzle for RDE with annulus combustion chamber is proposed. A series of three-dimensional numerical simulations are conducted to obtain the thrust performance of nozzles based on open-source software OpenFOAM. The flow-field structure, pressure gain in combustor and thrust performance of RDE are investigated. The results suggest that although the instantaneous flow-field in RDE is time-varying, the averaged plume field can be viewed as axisymmetric under-expanded supersonic jets. It's reasonable to use the time-averaged value of physical quantities for nozzle design. For nozzle with inward-bend cowl lip and isentropic ramp surface, the supersonic flow in nozzle undergoes approximate isentropic expansion with minimum loss. The flow at nozzle exit is basically parallel to chamber axis, generating the optimal thrust. This indicates that the aerospike nozzle is a good match for efficient expansion of rotating detonation products for propulsion. Moreover, the stagnation pressure gain in combustor has been greatly improved with the constriction nozzle throat. This suggests that in order to elevate the chamber pressure, the convergence section with nozzle throat should be adopted in RDE just as in traditional rocket engines.

Combined electrostatic analyzer—Wien filter probe for characterization of species distributions in Hall thrusters

We present a combined electrostatic and magnetostatic plasma diagnostic tool used to measure current fractions of ion species in a Hall-effect thruster plume. Hall thrusters produce thrust by accelerating singly and multiply charged ions to high velocity. Singly charged ions fall through potential differences from their point of creation to the location of measurement, which varies as a function of time and position resulting in a relatively wide distribution of energy. This process is further complicated by both direct and multi-step creation of multiply charged ions and by ion-neutral collisions. The result is that Wien velocity filter (ExB) spectra typically have overlapping peaks. Analysis of these spectra requires assumptions about the velocity distribution function (VDF) that are hard to verify and can result in the incorrect species current distribution used to calculate thruster performance efficiencies. We present how adding an energy filter in line with an ExB probe can result in a more accurate measurement of the species current fraction while also providing information about the ion energy distribution of each species. The combined diagnostic was used to measure the species current distribution in a 1.5 kW Hall thruster operating on krypton. The diagnostic setup and data analysis of the probe measurements are presented and compared against results utilizing established VDF-fit and integration techniques applied to standard spectra measured by a standalone ExB probe.

Porosity Effect of the Silver Catalyst in Hydrogen Peroxide Monopropellant Thruster

In monopropellant system, hydrogen peroxide is used with catalyst to create an exothermic reaction. Catalyst made of silver among the popular choice for this application. Since the catalyst used is in porous state, the effect of its porosity in the hydrogen peroxide monopropellant thruster performances is yet unknown. The porosity changes depending on factors including catalyst pact compaction pressure, bed dimension, and type of catalyst used. As researches on this topic is relatively small, the optimum porosity value is usually left out. The performance of the thruster indicated by the pressure drop across the catalyst bed. Porosity of the catalyst bed adds additional momentum sink to the momentum equation that contributes to the pressure gradient which lead to pressure loss inside thruster. The effect of porosity influences the performance and precision of the thruster. Study of the pressure drop by the catalyst bed requires a lengthy period and expensive experiments, however, numerical simulation by mean of Computational Fluid Dynamics (CFD) can be an alternative. In this paper, 90 wt% hydrogen peroxide solution with silver catalyst is studied in order to investigate the influence of porosity to the performances of the thruster, and to find the optimum porosity of the thruster. Species transport model is applied in the single-phase reaction simulation using the EDM for turbulence-chemistry interaction. Through this study, the effect of porosity towards the thruster performances represented in term of pressure drop, exit velocity, bed temperature, and thrust, and porosity of 0.4 found to be as an optimal value.

UUV Platform Optimal Design for Overcoming Strong Current

This paper proposes an optimal design method for an unmanned underwater vehicle (UUV) platform to overcome strong current. First, to minimize the hydrodynamic drag components in water, the vehicle is designed to have a streamlined disc shape, which help maintaining horizontal motion (zero roll and pitch angles posture) while overcoming external current. To this end, four vertical thrusters are symmetrically mounted outside of the platform to stabilize the vehicle’s horizontal motion. In the horizontal plane, four horizontal thrusters are symmetrically mounted outside of the disc, and each of them has the same forward and reverse thrust performances. With these four thrusters, a specific thrust vector control (TVC) method is proposed, and for external current in any direction, four horizontal thrusters are controlled to generate a vectored thrust force to encounter the current while minimizing the vehicle’s rotation and maintaining its heading. However, for the numerical simulations, the vehicle’s hydrodynamic coefficients related to the horizontal plane are derived based on both theoretical and empirically derived formulas. In addition to the simulation, experimental studies in both the water tank and circulating water channel are performed to verify the vehicle’s various final performances, including its ability to overcome strong current.