Thruster Test Research Articles

Fully discrete model of kinetic ion-induced electron emission from metal surfaces

Ion-induced electron emission (IIEE) is an important process whereby ions impinging on a material surface lead to net emission of electrons into the vacuum. While relevant for multiple applications, IIEE is a critical process of electric thruster (ET) operation and testing for space propulsion, and, as such, it must be carefully quantified for safe and reliable ET performance. IIEE is a complex physical phenomenon, which involves a number of ion-material and ion-electron processes, and is a complex function of ion mass, energy, and angle, as well as host material properties, such as mass and electronic structure. In this paper, we develop a discrete model of kinetic IIEE to gain a more accurate picture of the electric thruster chamber and facility material degradation processes. The model is based on three main developments: (i) the use of modern electronic and nuclear stopping databases, (ii) the use of the stopping and range of ions in matter to track all ion and recoil trajectories inside the target material, and (iii) the use of a scattering Monte Carlo approach to track the trajectories of all mobilized electrons from the point of first energy transfer until full thermalization or escape. This represents a substantial advantage in terms of physical accuracy over existing semi-analytical models commonly used to calculate kinetic IIEE. We apply the model to Ar, Kr, and Xe irradiation of W and Fe surfaces and calculate excitation spectra as a function of ion depth, energy, and angle of incidence. We also obtain minimum threshold ion energies for net nonzero yield for each ion species in both Fe and W and calculate full IIEE yields as a function of ion energy and incidence angle. Our results can be used to assess the effect of kinetic electron emission in models of full ET facility testing and operation.

Development of a modular hollow cathode for ground testing of plasma thrusters

A hollow cathode with a modular design has been developed to assist with laboratory testing of plasma-based thrusters for satellite applications. This novel modular design includes interchangeable components for varying the geometry and tailoring the configuration to specific applications, as well as easing the replacement of individual components in the case of damage. The modular hollow cathode also presents unconventional design features aimed at improving the heating efficiency: the heater is in direct contact with the emitter and the keeper is not in physical contact with the cathode base. The modular hollow cathode development has been based on a combination of theoretical modelling and experimental testing. The influence of the novel mechanical assembly has been investigated by characterising the operational envelope at different propellant mass flow rates for xenon and krypton. The modular hollow cathode has demonstrated stable operation by sustaining discharge currents between 0.5 and 4 A at different conditions. Finally, the cathode has been coupled with a Hall-type plasma thruster operating in the 0.3–2.5 A anode current range. This paper outlines development, experimental validation of this peculiar mechanical cathode configuration, covering plasma and thermal modelling, standalone testing, and coupled Hall-type thruster operation.

Comparing torsional and lateral vibration data for deep learning-based drive train gear diagnosis

Deep learning-based fault diagnosis models have been demonstrated to recognise machine health conditions from vibration data. However, most related studies have focused on lateral vibration data, and mostly neglected torsional vibration data. Yet, torsional vibration data can provide an advantage in diagnosing gear faults. Torsional vibration is typically less noisy than lateral vibration data as it can be measured directly from the rotating components. To this end, this study presents a large gear fault dataset with artificial faults of varying severity acquired from a downscaled thruster test rig operated at a vast range of rotating speeds. The test rig was equipped with multiple torque transducers, rotary encoders and piezoelectric accelerometers. The lateral and torsional vibration data acquired with these sensors were evaluated with three popular convolutional neural networks in extensive ablation studies. An interpretability analysis was conducted based on amplitude spectra and Grad-CAM visualisations. The results demonstrate that torsional vibration can be an effective source of data for gear fault diagnosis. For example, the models diagnose the most difficult gear conditions using only one torque transducer more accurately than using three accelerometers mounted on the gear box. Furthermore, the highest accuracy in each ablation study related to experiments with combined lateral and torsional vibration data. In addition, the interpretability analysis showed that the lower frequencies had relatively higher amplitudes in torsional vibration than in lateral vibration. The interpretability analysis also indicates that the models reached higher classification accuracies with torsional vibration data due to the lower dominating frequencies. Overall, this study highlights the potential benefits of using torsional vibration data for deep learning-based fault diagnosis of gears.

International Space Station Bipropellant Plume Contamination Model update for short thruster pulse widths

The International Space Station (ISS) Bipropellant Plume Contamination Model has been a vital tool for characterizing the thruster plume-induced contamination environment at the ISS but was not intended to be used for very short thruster pulse widths. This paper presents an updated model that ensures full start-up and shut-down phases are modeled for each thruster firing, when the majority of liquid phase contaminant mass is released. The updated ISS Bipropellant Plume Contamination Model prevents potential under-prediction of thruster plume-induced contamination due to visiting vehicle proximity operations and provides a way to take advantage of thruster start-up and shut-down performance data gathered during thruster test programs, if available.

Lab-scale ballistic and safety property investigations of LMP-103S

LMP-103S is a storable, green, ammonium dinitramide (ADN)-based liquid monopropellant with significant potential owing to its improved specific impulse (≥ 6%) and density (∼24%) in comparison to hydrazine, and its superior safety and handling characteristics. LMP-103S already has a significant history of thruster testing and flight heritage. However, its baseline combustion behavior is a surprisingly understudied topic. Constant-volume strand burner experiments with LMP-103S are reported herein for pressures between 0.69 and 34.5 MPa (100 – 5,000 psia). Linear burning rates were measured from transient pressure data and high-speed video. Visible and near-IR emission spectra were recorded as well. Phenomenological combustion behaviors are reported for the entire pressure range as deduced from these diagnostics, and two clear pressure regimes are observed. Hydrodynamic instabilities and supercritical combustion processes dominate the combustion behavior in the low- and high-pressure regimes, respectively. Supporting experiments include thermal cook-off of LMP-103S and impact sensitivity testing of ADN crystals extracted from LMP-103S solution. The data presented herein significantly expand upon those available in the literature for LMP-103S, and the phenomenological combustion behavior deduced from transient, high-speed video data improve upon the state-of-the-art knowledge regarding ADN-based liquid monopropellants.

무인 수상선의 수중 추진기 고장 진단 연구를 위한 고장 특성 인자 선정 및 실험

As interest in unmanned vessel research has increased, emphasis on autonomous navigation capability and the sustainability of normal operation has been highlighted. However, research on fault detection and diagnosis (FDD) for unmanned surface vehicles (USVs) is insufficient compared with research on land machinery or unmanned aerial vehicles. Among prior studies on USV FDD, intensive analysis or diagnostics for individual elements with high failure probability were barely conducted. This study focus on fault detecting features of a USV thruster, one of the most failure-prone elements other than internal causes or software malfunctions. A hypothesis for thruster fault detecting features was made based on general thruster-related equations; the features were tested on a stand-alone thruster test to assess the feature’s acceptability. However, a stand-alone thruster test lacks important effects such as structural vibratory influence of an actual USV, thruster load difference due to inflow velocity and wave-induced vibrations as the USV slides on the water’s surface. Hence, USV capable of acquiring fine quality real-time data for FDD practice was developed, and a surface driving test in a water basin was conducted to confirm the eligibility of the selected features.

Design, Construction and Performance Evaluation of a Cold Gas Thruster Test Stand

The cold gas thruster is one of the significant components of a satellite and its application possesses a marked impact on the entire system performance. The nonlinear function and order of magnitude, lead to increasing the importance of thruster function. Therefore, pre-mission performance assessment has a considerable effect on the risk reduction of space missions. In this article, an uncomplicated and efficient pendulum scheme for development and implementation of a Thruster Test Stand (TTS), to measure the thrust produced at the end of the nozzle is proposed. The TTS is capable of measuring thrust levels in the range of 0.1Newtons to 3N with operating frequencies up to 50 Hz which is used by various satellite ranges. The experimental results demonstrate that although the designed device is less sophisticated than other test devices, it is capable of measuring the produced thrust very precisely and with less than 15mN.

In situ erosion measurement tools for electric propulsion thrusters: triangular laser head and telemicroscope

The lifetime of electric propulsion (EP) thrusters depends particularly on the erosion characteristics of operation relevant components, for instance, the grid hole erosion of gridded ion thrusters or the channel wall erosion of Hall effect thrusters. Here two tools for in situ erosion measurements are presented, a triangular laser head for surface profiling and a telemicroscope for high-resolution optical imaging. Both can give access to radial and axial erosion parameters. The measurements can be done in situ without the need for breaking the vacuum and dismounting the thruster, which reduces thruster testing time considerably. In situ measurements can also help to ensure reproducibility of thruster performance conditions and can improve statistics of thruster characterization. The present work describes the fundamentals of both techniques in detail, selected experimental setups are presented, their performance is characterized and critically evaluated. The capabilities and limitations related to erosion measurements of EP thrusters are, exemplary, demonstrated for a gridded ion thruster RIT-22 and a Hall effect thruster SPT-100D.

Quasi-steady testing approach for high-power Hall thrusters

Hall effect thrusters operating at power levels in excess of several hundreds of kilowatts have been identified as enabling technologies for applications such as lunar tugs, large satellite orbital transfer vehicles, and solar system exploration. These large thrusters introduce significant testing challenges due to the propellant flow rate exceeding the pumping speed available in most laboratories. Even with proposed upgrades in mind, the likelihood that multiple vacuum facilities will exist in the near future to allow long duration testing of high-power Hall thrusters operating at power levels in excess of 100 kW remains extremely low. In this article, we numerically explore the feasibility of testing Hall thrusters in a quasi-steady mode defined by pulsing the mass flow rate between a nominal and a low value. Our simulations indicate that sub-second durations available before the chamber reaches critical pressure are sufficiently long to achieve the steady-state current and flow field distributions, allowing us to characterize thruster performance and the near plume region.

Design, Construction and Performance Evaluation of a Cold Gas Thruster Test Stand

The cold gas thruster is one of the significant components of a satellite and its application possesses a marked impact on the entire system performance. The nonlinear function and order of magnitude, lead to increasing the importance of thruster function. Therefore, pre-mission performance assessment has a considerable effect on the risk reduction of space missions. In this article, an uncomplicated and efficient pendulum scheme for development and implementation of a Thruster Test Stand (TTS), to measure the thrust produced at the end of the nozzle is proposed. The TTS is capable of measuring thrust levels in the range of 0.1Newtons to 3N with operating frequencies up to 50 Hz which is used by various satellite ranges. The experimental results demonstrate that although the designed device is less sophisticated than other test devices, it is capable of measuring the produced thrust very precisely and with less than 15mN.

Vacuum Challenges for Ion Thruster Testing

SummaryElectrical propulsion is the keyword for nowadays movement of space vehicles. Ionized particles, usually xenon ions, are accelerated by thrusters in an electric field. State‐of‐the‐art xenon thrusters emit a gas flow of 0.1 to 10 mg/sec. In order to maintain a high vacuum pressure at this flow in thruster test chambers, a large pumping speed is required, often in the range of 10'000 to 100'000 l/s for xenon.The advantage of a large ion mass for the propulsion system is a major challenge for vacuum pumps.Leybold has developed an optimized and simple cryogenic solution for Xe pumping. Strong single‐stage Gifford‐McMahon type cold heads carry metal discs which condense the Xe gas with a pumping speed at the edge of the theoretical limit. In this work, we will present the whole vacuum system for a thruster testing facility.

An experimental and numerical investigation on hydrodynamic characteristics of the bow thruster

While maneuvering or positioning in different situations, the hull, the angle of the inlet current, and the tunnel opening fairing onto the hull have serious impacts on the performance of the bow thruster. The co-operation of multiple bow thrusters affects each other in the hydrodynamic performance. In this study, we report a thorough investigation of the hydrodynamic performance of the bow thruster combining experimental and numerical methods. The influence of the hull, the inflow angle, and the fillet radius of the tunnel opening is considered. The interaction between multiple bow thrusters is also studied. Open water tests and single bow thruster tests with the hull at eight different inflow angles were performed. Numerical simulations under the same condition were performed using the u-RANS method, and the accuracy of numerical results is verified by comparing with experimental data. Then, the flow field details of the single bow thruster condition were extracted. By analyzing the velocity distribution in the tunnel, the coupling influence of the hull and the inflow angle can be studied. Moreover, numerical simulations were performed for four hull models with different fillet radii for the tunnel opening. The influence of the opening fairing is analyzed by comparing numerical results and detailed flow fields. Finally, the co-operation of two bow thrusters is simulated, and the interaction between three bow thrusters is investigated. The results show that the joint influence will lead to a large-scale, asymmetric reversed flow zone at the tunnel opening. The reversed flow zone changes with the inflow angle and leads to a great difference in pressure distribution for different blades of the propeller. The opening fairing of the tunnel can improve the uniformity of the flow field in the tunnel, restrain the asymmetric pressure distribution on the propeller, and raise the efficiency of bow thruster. In addition, during co-operation, the induced flow direction of the propeller has a significant influence on the performance of the bow thruster. The upstream bow thruster can slightly improve the efficiency of the downstream bow thruster.

Astrodynamical middle-frequency interferometric gravitational wave observatory AMIGO: Mission concept and orbit design

AMIGO is a first-generation Astrodynamical Middle-frequency Interferometric Gravitational Wave (GW) Observatory. The scientific goals of AMIGO are to bridge the spectra gap between first-generation high-frequency and low-frequency GW sensitivities: to detect intermediate mass BH coalescence; to detect inspiral phase and predict time of binary black hole coalescences together with binary neutron star & black hole-neutron star coalescences for ground interferometers; to detect compact binary inspirals for studying stellar evolution and galactic population. The mission concept is to use time delay interferometry (TDI) for a nearly triangular formation of three drag-free spacecraft with nominal arm length 10,000 km, emitting laser power 2–10 W and telescope diameter 300–500 mm. The design GW sensitivity in the middle frequency band is [Formula: see text] Hz[Formula: see text]. Both geocentric and heliocentric orbit formations are considered. All options have LISA-like formations, that is, the triangular formation is [Formula: see text] inclined to the orbit plane. For all solar orbit options of AMIGO, the first-generation TDI satisfies the laser frequency-noise suppression requirement. We also investigate for each option of orbits under study, whether constant equal-arm implementation is feasible. For the solar-orbit options, the acceleration to maintain the formation can be designed to be less than 15 nm/s2with the thruster requirement in the 15 [Formula: see text]N range. AMIGO would be a good place to test the feasibility of the constant equal-arm option. Fuel requirement, thruster noise requirement and test mass acceleration actuation requirement are briefly considered. From the orbit study, the solar orbit option is the mission orbit preference. We study the deployment for this orbit option. After a last-stage launch from 300 km Low Earth Orbit (LEO), each S/C’s maneuver to an appropriate 2-degree-behind-the-Earth AMIGO formation in 95 days requires only a [Formula: see text]v of about 80 m/s.

선수 스러스터를 이용한 실선스케일 조종시험에 관한 연구

This study aims to investigate the bow thruster performance of the research vessel “NARA” by full-scale maneuvering trials. The thruster test method refers to ITTC’s recommended procedures and guidelines. Turning tests with the bow thruster are performed at speed conditions of 0, 2, and 4 knots. The test results indicate that the Rate of Turn (ROT) increased when the ship is in a higher speed condition. Due to the position of the propeller and the housing of the bow thruster, there is difference in the efficiency of the bow thruster according to the turning direction. Zigzag tests with the bow thruster were conducted at speed conditions of 2 and 4 knots. At speeds above 4 knots, it seems difficult to change the course only with the bow thruster.

A 100 KW Class Applied-field Magnetoplasmadynamic Thruster.

Applied-field magnetoplasmadynamic thrusters (AF-MPD thrusters) are hybrid accelerators in which electromagnetic and gas dynamic processes accelerate plasma to high speed; they have considerable potential for future space applications with the significant advantages of high specific impulse and thrust density. In this paper, we present a series of protocols for designing and manufacturing a 100 kW class of AF-MPD thruster with water-cooling structures, a 130 V maximum discharge voltage, a 800 A maximum discharge current, and a 0.25 T maximum strength of magnetic field. A hollow tantalum tungsten cathode acts as the only propellant inlet to inhibit the radial discharge, and it is positioned axially at the rear of the anode in order to relieve anode starvation. A cylindrical divergent copper anode is employed to decrease anode power deposition, where the length has been reduced to decrease the wall-plasma connecting area. Experiments utilized a vacuum system that can achieve a working vacuum of 0.01 Pa for a total propellant mass flow rate lower than 40 mg/s and a target thrust stand. The thruster tests were carried out to measure the effects of the working parameters such as propellant flow rates, the discharge current, and the strength of applied magnetic field on the performance and to allow appropriate analysis. The thruster could be operated continuously for significant periods of time with little erosion on the hollow cathode surface. The maximum power of the thruster is 100 kW, and the performance of this water-cooled configuration is comparable with that of thrusters reported in the literature.

STG-ET: DLR Electric Propulsion Test Facility

Abstract: DLR operates the High Vacuum Plume Test Facility Göttingen – Electric Thrusters (STG-ET). This electric propulsion test facility has now accumulated several years of EP-thruster testing experience. Special features tailored to electric space propulsion testing like a large vacuum chamber mounted on a low vibration foundation, a beam dump target made of low sputtering material, and a performant pumping system characterize this facility. The vacuum chamber is 12.2m long and has a diameter of 5m. With respect to accurate thruster testing, the design focus is on accurate thrust measurement, plume diagnostics, and plume interaction with spacecraft components. Electric propulsion thrusters have to run for thousands of hours, and with this the facility is prepared for long-term experiments. This paper gives an overview of the facility, and shows some details of the vacuum chamber, pumping system, diagnostics, and experiences with these components.

Longitudinal Motion Due to Action of Tunnel Thrusters

Abstract Tunnel thrusters are propulsion and active control devises that provide a side force, or transverse thrust, to support mooring operations or position keeping. They shorten the time of manoeuvring, reduce the cost of towage and since inception, manoeuvrability specifically in ports has become a lot easier. Tunnel thrusters can either be operated manually or with the help of Dynamic Positioning systems which makes it even more efficient. Theoretically, the transverse force due to tunnel thruster action should generate only lateral and rotational motion. Therefore, it is typical and a common practice during manoeuvring simulations that the longitudinal motion due to the action of tunnel thrusters is neglected. Nevertheless, the experience of masters and pilots shows that some longitudinal motion due to the action of tunnel thrusters appears. This paper shows some examples of turning manoeuvres carried out with bow thrusters only, i.e. no additional control devices or tug assistance have been used. The manoeuvres have been carried with minimal possible initial longitudinal nor lateral speed. Model tests have been done with the use of large manned models of VLCS, PCTC and LNG carrier, which differ in hull shape, dimensions and shape coefficients. Results obtained from the tests confirm that the motion caused by bow thruster besides rotational and lateral motion consists additionally of longitudinal motion. Analysis of the combination of motions due to the action of tunnel thrusters have been done and some rationale for this phenomenon has been presented. Additionally a short analysis of position of pivot point during tunnel thruster test has been carried out.

5 N Scale Preliminary Thruster Test with an ADN-based Monopropellant

5 N Scale Preliminary Thruster Test with an ADN-based Monopropellant

ЗОНДОВІ ТА СПЕКТРАЛЬНІ ДОСЛІДЖЕННЯ МАЛОПОТУЖНОГО ЕЛЕКТРОРЕАКТИВНОГО ХОЛЛОВСЬКОГО ДВИГУНА

The work is devoted to the study of a low-power Hall Effect Thruster. The currency of developing and increasing of integral characteristics of Hall Effect Thruster with power consumption less 0,3 kW is substantiated. The main directions of low-power Hall Effect Thruster investigation are considered. The analysis of latest investigations and studies of low-power Hall Effect Thruster showed the existence of three main directions - development of fundamentally new schemes, improvement of existing models, as well as works on study of physical processes features in Hall Effect Thruster with power consumption up to 0,3 kW.Using developed Hall Effect Thruster ITM-31, distribution of plasma parameters in the discharge channel has been studied by probe diagnostic, and the wear of the discharge chamber walls has been studied by optical spectroscopy. Thruster characteristics are given. Investigations were carried out in a vacuum chamber 0,5 m in diameter and 0,8 m in length. The pumping was carried out by a diffusion pumps. At a maximum xenon consumption rate 1,5 mg/s, the working pressure in the vacuum chamber did not exceed 2∙10-3 Torr. Probe measurements were performed using a single probe; probe was inserted into the discharge channel from the anode side. Calculation of plasma parameters was carried out graphically. The temperature and concentration of charged particles are calculated, and the electric potential distribution is obtained. Conclusions are made about the properties of the accelerating layer.It is shown that one of the non-intrusive methods of diagnostics is the method of optical emission spectroscopy (OES). With the help of this method it is possible to provide plasma parameters investigation and characteristics of the construction wear during the thruster testing at different regimes of operation and on each stage of thruster lifetime. For the spectroscopic investigation of the Hall Effect Thruster discharge chamber walls wear the scheme of the experiment and the equipment description is presented. For the estimation of the discharge chamber insulators erosion rate the spectral lines criteria and method of wavelengths selection is presented. Mathematical model of the thruster plasma plume experimental emission spectral data processing is described that was developed on the basis of actinometry hypothesis and corona model. Results of the spectroscopic investigation of the discharge chamber erosion rate at different thruster operational regimes are presented. From experimental and theoretical model the dependence of the discharge chamber insulators erosion rate from the discharge voltage was processed.

STG-ET: DLR electric propulsion test facility

DLR operates the High Vacuum Plume Test Facility Göttingen – Electric Thrusters (STG-ET). This electric propulsion test facility has now accumulated several years of EP-thruster testing experience. Special features tailored to electric space propulsion testing like a large vacuum chamber mounted on a low vibration foundation, a beam dump target with low sputtering, and a performant pumping system characterize this facility. The vacuum chamber is 12.2m long and has a diameter of 5m. With respect to accurate thruster testing, the design focus is on accurate thrust measurement, plume diagnostics, and plume interaction with spacecraft components. Electric propulsion thrusters have to run for thousands of hours, and with this the facility is prepared for long-term experiments. This paper gives an overview of the facility, and shows some details of the vacuum chamber, pumping system, diagnostics, and experiences with these components. New version available: DLR Institute of Aerodynamics and Technology. (2018). STG-ET: DLR Electric Propulsion Test Facility. Journal of large-scale research facilities, 4, A134. http://dx.doi.org/10.17815/jlsrf-3-156-1