Vacuum Plume Research Articles

Development of convolutional neural network-based surrogate model for three-dimensional vacuum plume prediction via direct simulation Monte Carlo method

The vacuum plume phenomenon encountered during lunar exploration missions poses significant challenges, such as impingement forces, heat fluxes, and spacecraft contamination. Numerical simulation represents the predominant method for evaluating the impacts of vacuum plumes. However, the conventional direct simulation Monte Carlo (DSMC) method, despite being the standard, is notably time-consuming and impractical for real-time analysis. Addressing this limitation, our research explores deep learning, specifically convolutional neural networks (CNN), for the efficient prediction of vacuum plume dynamics. We introduce a novel CNN-based DSMC method (CNN-DSMC-3D), leveraging a dataset obtained from three-dimensional DSMC simulations. This approach translates the spacecraft's shape and boundary conditions into a signed distance function and an identifier matrix. The CNN-DSMC-3D method effectively predicts the vacuum plume field, aligning closely with DSMC results across various lunar surface conditions. Crucially, the CNN-DSMC-3D method achieves a speed increase in four to six orders of magnitude over the conventional DSMC method, demonstrating substantial potential for real-time aerospace applications and offering a paradigm shift in the simulation of lunar landing scenarios.

Real-time vacuum plume flow field reconstruction during lunar landings based on deep learning

In space missions, the vacuum plume generated by rocket engines can negatively impact spacecraft. Therefore, researching the vacuum plume is crucial to guarantee the regular operation of spacecraft. The conventional numerical simulation methodology, the direct simulation Monte Carlo (DSMC) method, is time-consuming and lacks real-time calculation capabilities. Recently, deep learning (DL) methods have emerged in the field of fluid dynamics. In this study, a DL model trained by a convolutional neural network with multiple decoders is introduced to predict the vacuum plume flow field during lunar landings. The network processes shape topology information and boundary conditions as inputs, yielding flow field data including velocity and pressure fields as outputs. Meanwhile, the flow field prediction results under different conditions and training methods are discussed. The results show that the predicted flow field under different lunar surface conditions is in accord with the DSMC results. The maximum mean and standard deviation errors of the data distribution of each flow field do not exceed 9.72% and 9.07%, respectively. Different training methods with flat and inclined lunar surfaces also have an impact on the prediction results. Compared with the DSMC method, the DL method exhibits higher efficiency with a speedup of about four orders of magnitude, indicating that the DL-based flow field reconstruction method has strong application prospects in the real-time computation of vacuum plume flow fields.

ADRC-based compound control strategy for spacecraft multi-body separation

This paper proposes a compound control method for spacecraft multi-body separation which is based on active disturbance rejection control (ADRC), aiming to address the problems of decreased control accuracy and collisions caused by model uncertainty and vacuum plume disturbance. By comprehensively analyzing the positional relationship and attitude between each separator, the compound flight controller reconstructs the desired attitude of each separator based on artificial potential field method and realizes the tracking of the desired attitudes through ADRC. The closed-loop stability of the system is analyzed, and it is proved that the algorithm is stable in the sense of Lyapunov. The simulation results showed that the multi-body separation compound control strategy based ADRC has more advantages in robustness and security. This method is simple to implement, and it has value of reference and application in spacecraft multi-body separation.

A Review of Research on the Vacuum Plume

Chemical and electrical thrusters are generally utilized to control the attitude and orbit of spacecraft in aerospace. When they are firing, the exhaust expands into the vacuum environment, known as the vacuum plume. The plume flow can collide with spacecraft surfaces due to sufficient expansion, exerting adverse effects on the spacecraft, such as heating load, force/torque, contamination, and sputtering. Therefore, it is vital to investigate the vacuum plume to ensure the function and safety of the spacecraft. This review introduces the ground test and numerical simulation methods of the vacuum plume for chemical and electrical thrusters. The vacuum environment, invasive, and non-invasive (optical) measurements of the ground test are concluded. Numerical simulation of plume flow and its effects is exampled. The hybrid CFD-DSMC (computational fluid dynamics and direct simulation Monte Carlo) algorithm is employed to simulate the gas plume flow spanning continuum and transitional and free molecular flow regimes for chemical thrusters. By contrast, the PIC-DSMC (particle-in-cell plus direct simulation Monte Carlo) algorithm is used for the plasma plume flow containing charged particles exhausted by electrical thrusters. Moreover, the topics of fast prediction of the vacuum plume, plume–surface interaction, and plume–Lunar/Mars regolith interaction are proposed for future research.

Fast vacuum plume prediction using a convolutional neural networks-based direct simulation Monte Carlo method

The vacuum plume, which can incur impingement forces, heat fluxes, and contaminations on the spacecraft, has been a vital issue in space missions such as lunar landings. The direct simulation Monte Carlo (DSMC) method is generally used to simulate the vacuum plume. However, DSMC is a particle simulation, and thus, it is very time-consuming, making it impossible to achieve real-time analysis during lunar landings. Motivated by this tricky issue, we explore the feasibility of deep learning to predict the vacuum plume using convolutional neural networks (CNN). In the study, a CNN-based DSMC method (CNN-DSMC) is proposed. The dataset is obtained by the DSMC simulation. The inputs of CNN-DSMC are the shape information and the boundary conditions, which are transformed into the signed distance function (SDF) and identifier matrix (IM), respectively. In particular, a shock-based partitioned method is developed to construct IM to suit the complex flow field with the shock wave. Finally, a vacuum plume velocity field is predicted using the proposed CNN-DSMC, and the prediction of CNN-DSMC is well consistent with DSMC results. Most importantly, compared with the traditional DSMC, the speedup of CNN-DSMC can be up to 4 orders of magnitude, suggesting that CNN-DSMC is a promising method for real-time analysis during lunar landings.

The Investigation of Plume-Regolith Interaction and Dust Dispersal during Chang’E-5 Descent Stage

The plume-surface interaction that occurs as a result of a variable-thrust engine exhaust plume impinging on soil during landings is critical for future lunar mission design. Unique lunar environmental properties, such as low gravity, high vacuum, and the regolith layer, make this study complex and challenging. In this paper, we build a reliable simulation model, with constraints based on landing photos, to characterize the erosion properties induced by a low-thrust engine plume. We focus on the low-thrust plume-surface erosion process and erosion properties during the Chang’E-5 mission, aiming to determine the erosion difference between high- and low-thrust conditions; this is a major concern, as the erosion process for a low-thrust lunar mission is rarely studied. First, to identify the entire erosion process and its relative effect on the flat lunar surface, a one-to-one rocket nozzle simulation model is built; ground experimental results are utilized to verify the simulated inlet parameters of the vacuum plume flow field. Following that, plume flow is considered using the finite volume method, and the Roberts erosion model, based on excess shear stress, is adopted to describe plume-surface interaction properties. Finally, a Lagrangian framework using the discrete phase model is selected to investigate the dynamic properties of lunar dust particles. Results show that erosion depth, total ejected mass, and the maximum particle incline angle during the Chang’E-5 landing period are approximately 0.2 cm, 335.95 kg, and 4.16°, respectively. These results are not only useful for the Chang’E-5 lunar sample analysis, but also for future lunar mission design.

Adsorption Isotherms of Low-Pressure H2O on a Low-Temperature Surface Measured by a Quartz Crystal Microbalance.

The low-pressure gas in the vacuum plume produced by the chemical thrusters contaminates the spacecraft when adsorbed on the low-temperature surface. To provide theoretical support for further research on gaseous plume pollutants, the adsorption isotherms of low-pressure H2O were measured by a quartz crystal microbalance (QCM) at temperatures ranging from 233 to 273 K. The measured isotherms are similar to the type-I and type-II isotherms and have been correlated by various models (e.g., the Langmuir, Dubinin–Radushkevich, Brunauer–Emmett–Teller (BET), and universal models). It shows that the universal model has a great advantage in predicting the adsorption at a specific temperature point in our study. To estimate the adsorption at the continuous temperature range, the critical parameters of the multi-Langmuir model were expressed in semiempirical formulas. Since the normalized isotherms of H2O at different temperatures converge well, a simplified multi-Langmuir (SML) model was proposed. The experimental results at the temperature and pressure ranges we explored are consistent with the results predicted by the SML model, suggesting that the SML model is more suitable and convenient to predict the low-pressure adsorption of H2O for a continuous low-temperature range. Moreover, the low-pressure adsorption behaviors of H2O and CO2 on the low-temperature surface are compared and discussed.

Research on ignition process of micro solid rocket motor in vacuum

Aiming at the ignition process of micro solid rocket motor in space, the effects of different structure on the ignition gas filling process were investigated by means of experiment and numerical simulation. By establishing numerical simulation model and the mass flow rate model of ignition chamber for black powder, pressure establishment process was researched under different parameters (the igniter quantity is 0.2g and 0.5g, outlet size of ignition chamber is Φ4mm and Φ7mm respectively). Meanwhile, the ignition experiment was conducted in vacuum (the ambient pressure is 16Pa) that pressure curve and vacuum plume phenomenon were obtained. The results indicate that simulation value of pressure establishing process relatively consistent with experimental one, so the mass flow rate model of ignition chamber for the black powder is evidently efficient. Therefore, the numerical method proposed in this paper can provide a theoretical basis for further research on the ignition process of micro solid rocket motor.

Experimental investigation on vacuum plume interaction of hydrogen/oxygen engines

Experimental investigation on vacuum plume interaction of hydrogen/oxygen engines

Investigation on the Interface Smoothing of Coupled N–S/DSMC Method Using Image Processing Filters

Gas flow problems involving both continuum and rarefied regimes are common in many scientific and engineering applications. Coupled N–S/DSMC method is a major solution to simulate the continuum–rarefied transitional flow. Interface determination is one of the key aspects in developing coupled N–S/DSMC solver, which is often implemented using continuum breakdown parameters to indicate the rarefication level. Due to the statistics characteristic of DSMC method, distribution of the continuum breakdown parameters usually fluctuates, resulting in difficulty in locating the interface. Considering the similarity between continuum breakdown parameter smoothing and noise reduction in image processing, a general smoothing method is proposed in this paper, which employs the image filters to smoothen the distribution of continuum breakdown parameters. Two commonly used image filters, the mean filter and the median filter, are investigated. Several comparison studies are implemented by simulating a typical vacuum plume impingement flow problem. The median filter with 5 × 5 mask provides the best performance. The flow problem of flow over a 2D cylinder is used to validate the coupled N–S/DSMC solver using median filter to smoothen continuum breakdown parameter, which proves the accuracy of the coupled solver and validity of the smoothing method.

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.

Three-dimensional particle simulation of ion thruster plume impingement

The interaction between the high-energy particles in the plume and the spacecraft surfaces will produce interference torque that affects the operating state of the spacecraft in orbit. The thrust of an electric propulsion system is quite small, so it is difficult to be measured directly. The Vacuum Plume Laboratory (VPL) measured the LIPS-200 type ion thruster plume force in an order of 10−3N using a fully elastic micro thrust measuring device. In this paper, the particle in cell (PIC) method and the direct simulation Monte Carlo (DSMC) method are employed to analyze the three-dimensional plasma environments under specified experimental conditions. The Maxwell model is used to calculate the plume force on a 300 mm diameter plate. Simulation results of the plume force give good agreements with the experimental data. Moreover, the effects of the 300 mm diameter aluminium plate on the flow field in vacuum conditions are analyzed. The results show that the number density of atoms is greatly increased before the plate, which has a further impact on the distribution of charge exchange ions (CEX). The enhanced CEX ions moving towards the solar battery panels or sensitive optical components may cause possible damage or interference, which should be avoided by the designers.

Investigation on aerodynamic force effect of vacuum plumes using pressure-sensitive paint technique and CFD-DSMC solution

Pressure-sensitive paint (PSP) technique was employed to experimentally investigate the aerodynamic force effect of vacuum plume in this study. The characterization and comparison for two types of PSP were firstly conducted in an air pressure range from 0.05 to 5000 Pa. The PSPs were prepared using PtTFPP as the active dye and different binders, i.e., polymer-ceramic (PC) and poly(1-trimethylsilyl-1-propyne) [poly(TMSP)]. The static calibrations showed that PtTFPP/poly(TMSP) had a higher pressure sensitivity and a lower temperature dependency compared to PtTFPP/PC in this pressure range. The pressure distributions of a single and two interacting plumes impinging onto a flat plate model were measured using PSP technique. The experimental data were compared to numerical solutions that combined both the computed fluid dynamics (CFD) and direct simulation Monte Carlo (DSMC) methods. Remarkable agreements were achieved, demonstrating the feasibility and accuracy of the numerical approach. Finally, the aerodynamic force effect of interacting plumes at different separation distances was investigated numerically.

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

Update on Diagnostics for DLR‘s Electric Propulsion Test Facility

DLR has operated since the end of 2011 a dedicated electric propulsion (EP) test facility, the High Vacuum Plume Test Facility Göttingen – Electric Thrusters (STG-ET). This EP test facility has now accumulated several years of thruster testing experience. Special features characterize this facility tailored to electric space propulsion testing. In the first place, a large vacuum chamber mounted on a low vibration foundation characterizes the facility. A performant pumping system ensures a good vacuum, and a target with low sputtering coating dumps the beam power. The vacuum chamber is 12m long and has a diameter of 5m. With respect to thruster tests, 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. The present paper gives an overview of the facility, and describes the vacuum chamber, pumping system, diagnostics, and experiences with these components. After commissioning of STG-ET, the main focus was put on the testing of Hall-effect and gridded ion thrusters.

Experimental and numerical investigations of vacuum plume interaction for dual hydrogen/oxygen thrusters

In spacecrafts such as high-altitude rockets and lunar landers, multiple thrusters or engines operate simultaneously with a small separation distance. Thus, the plume interaction may cause a different three-dimensional flow field with a single plume or plumes separated by a large distance. To study the flow field of the plume interaction, a hydrogen/oxygen sample thruster with a thrust of 60 N with the same propellant, mixing ratio, and shrunken bell-nozzle profile as an actual engine was first designed and tested in the Vacuum Plume Effects Experimental System (PES). The pressure field of the plume was determined using a pitot-tube array. The experimental data were compared with the results from a numerical solution that combined both computational fluid dynamics (CFD) and direct simulation Monte Carlo (DSMC) analyses, and a favorable agreement was obtained, demonstrating the application ability of the CFD-DSMC method to predict the plume flow field. Subsequently, two identical sample thrusters were modeled with a separation distance ranging from 1.0 to 3.0 times the diameter of the nozzle exit and a deflection angle ranging from 0° to 20°, and the plume interactions were numerically investigated.

An introduction to the novel vacuum plume effects experimental system

This paper introduces a newly developed vacuum Plume effects Experimental System (PES) used for plume effect tests of rocket engines and vacuum heat tests of satellites. The design level, manufacturing technique, and testing capabilities of the PES have reached a highly advanced level at home and abroad. The PES mainly consists of a vacuum chamber, vacuum acquisition system, nitrogen system, helium system, and parameter measurement system. A breakthrough was obtained on the Large Scale Cryo-Pumping System, which was based on a combined liquid nitrogen and liquid helium heat sink. An internal cryopump with a limiting temperature of 4.2 K and an efficient absorption area of 305 m2 was developed. The absorption capability of the cryopump was above 7×107 L/s. Vacuum plume tests were performed in the temperature ranges of ambient temperature, liquid nitrogen, and liquid helium. The experimental results showed that the plume test capability of PES is higher than that of similar foreign equipment STG and CHAFF-4. For 2 g/s and 117 N rocket engines, the dynamic vacuum degree of environment was 8.0×10-4 Pa (approximately 137 km height) and 1.1×10-2 Pa (approximately 106 km height), respectively.

Research on vacuum plume and its effects

In vacuum environment, the exhaust flow of attitude control thrusters would expand freely and produce the plume, which possibly causes undesirable contamination, aerodynamic force and heating effects to the spacecraft. Plume work station (PWS) is developed by Beihang University (BUAA) for numerically simulating the vacuum plume and its effects. An approach which combines the direct simulation Monte Carlo (DSMC) method and difference solution of Navier–Stokes (N–S) equations is applied. The internal flows in nozzles are simulated by solving the NS equations. The flow parameters at nozzle exit are used as the inlet boundary condition for the DSMC calculation. Experimental studies are carried out in a supersonic low density wind tunnel which could simulate the 60–80km altitude environment to investigate the plume and its effects. To demonstrate the capability of PWS, numerical simulations are performed for the vacuum plume of several typical attitude control thrusters. The research results are of great help for the engineering design.

Large-scale Vacuum Vessel Design and Finite Element Analysis

The vacuum plume effects experimental system (PES) is the first experimental system designed to study the effects of vacuum plume in China. The main equipment, a vacuum chamber of 5.5 m in diameter and 12.8 m in length, and structure design of hinged door are described. The finite element method (FEM) is adopted to analyze the static strength and stability of the PES vacuum chamber. It is demonstrated that the static strength and stability are qualified. For the 5.5 m diameter vacuum chamber door, three design schemes are put forward. After comparisons are made, the single-axis-double-pin hinged door is selected. The FEM is applied to checking its static strength as well as distortions. The results show that the door's distortion and displacement change mainly due to the gravity of the door which leads to its sinking. The calculated displacement is less than 7.8 mm, while the actual measurement is 5 mm. The single-axis-double-pin hinged door mechanism completely satisfies the design requirements. This innovative structure can be introduced as a reference for the design of large-scale hinged doors.

1155 REMPI およびイオン TOF 法による超低密度流の流速計測

In the DLR-high vacuum plume test facility STG, experiments have been performed to study the expansion of supersonic plumes into vacuum with N_2 as a test gas. So far, the molecule number flux, the rotational temperature and the density were measured by the 2+2 REMPI technique with a stimulation wavelength of 283-284mm. This method is also suitable to measure the absolute flow velocity by the ion-time-of-flight (ion-TOF) method. This study is focused on the experimental methods of measure the flow velocity of rarefied plumes. The results of measurements in highly rarefied plumes taken on-axis for several stagnation temperatures are presented, and the measured angular velocity profiles (off-axis) are discussed and compared to the theory. The effect of the suction voltage on the flow velocity measurement by the ion-TOF method is also clarified.