Vacuum Test Research Articles

The 3Cat-4 Spacecraft Thermal Analysis and Thermal Vacuum Test Campaign Results

3Cat-4 is the fourth member of the CubeSat series of UPC’s NanoSat Lab, and it was selected by the ESA Academy’s Fly Your Satellite! program in 2017. This mission aims at demonstrating the capabilities of nano-satellites, and in particular those based in the 1-Unit CubeSat standard, for challenging Earth Observation (EO) using Global Navigation Satellite System-Reflectometry (GNSS-R) and L-band microwave radiometry, as well as for Automatic Identification Systems (AIS). The following study presents the results of the thermal analysis carried out for this mission, evaluating different scenarios, including the most critical cases at both high and low temperatures. The results consider different albedos and orbital parameters in order to establish the optimal temperatures to achieve the best mission performance within the nominal temperatures, and in all operational modes of the satellite. Simulation results are included considering the thermal performance of other materials, such as Kapton, as well as the redesign of the optical properties of the satellite’s solar panels. The correlation with the thermal model and the TVAC test campaign was conducted at the ESA ESEC-GALAXIA facilities in Belgium.

Enhancing commercial check valves in downhole pump applications through laboratory testing system development

In this study, we aim to enhance the performance and longevity of downhole pumps employed in crude oil extraction in the oil industry. Downhole pumps play a pivotal role in the rod-pump system, comprising traveling and standing valves that function similarly to ball check valves. However, these valves often experience premature wear and tear. To address this concern, we embarked on experiments involving various check valve alternatives to conventional ball valves within downhole pumps. The testing conditions were controlled precisely. Furthermore, we evaluated four distinct check valve types, the original (representing the incumbent ball valves), spring-poppet (C), spring-ball (CB), and spring-poppet with soft-seated (S6C) check valves, within a controlled laboratory environment. We employed a TEXAPON N70 solution to replicate the properties and temperature conditions of crude oil. A portable ultrasonic flow meter was used to quantify the pump flow rate and assess its volumetric efficiency. In addition, we recorded data on the polished-rod load and plunger displacement to generate dynamometer cards, thereby enabling a comprehensive evaluation of the operational performance of the pump. Furthermore, we conducted a vacuum test to scrutinize valve leakage, which is a crucial indicator of the operational lifespan of a downhole pump. Our findings show that incorporating the CB check valve with the RHB pump in oil wells operated by the PTT Exploration and Production Public Company Limited (PTTEP) could result in a 15 % increase in volumetric efficiency and a remarkable 160 % improvement in durability compared to the original ball check valve.

Experimental and Numerical Investigation on Attitude Adjustment Characteristics of Spacecraft with Impulse Thruster

AbstractThe spacecraft serves as an effective tool for the space exploration. The present study is devoted to investigate the yaw attitude adjustment motion of the spacecraft influenced by the reaction-jet control system. A novel spacecraft device with impulse thrusters is designed for the vacuum test. And a synchronous test system, equipped with high-speed cameras, is established to record the motion process of the spacecraft under the various initial setting conditions. Subsequently, a six degrees of the freedom exterior ballistic model is calculated considering the interior ballistic process in the impulse thruster. The experimental results confirm that the position change of the designed device’s center of mass aligns with expectation, and the prediction error of final attitude angle remains below 2%. Based on this foundation, the change rule of the impulse thrust under different main charge loads is explored. The non-linear impulse thrust needs to be coupled with the rotation motion to enhance calculation accuracy. And the position of the center of mass is investigated to illustrate the advantage of the designed spacecraft structure. Finally, the calculation of the ignition interval time required for each target attitude angle is conducted, providing the essential data for further optimization design research. The outcomes from this paper can offer valuable technical means for advancing studies on the spacecraft attitude control.

Research on the influence of gas types on the pumping performance of dry Roots vacuum pump

With the advancement of technology, dry vacuum pumps are widely used in aerospace, semiconductor, chemical and pharmaceutical and scientific equipment due to their clean and oil-free advantages. Usually the pumped medium contains different types of gases, dry Roots vacuum pumps are prone to unstable performance, which can adversely affect process efficiency. To investigate the influence of gas types on the pumping performance of Roots vacuum pump, experimental research was conducted on self-designed dry vacuum pump theoretical verification platform and test pump. The gas mixture of 70 % nitrogen and 30 % helium was tested using 2-lobe, 3-lobe and 5-lobe Roots while numerical simulations were conducted on air, nitrogen, helium and hydrogen. The experimental results indicate that the gas type affects the pumping speed of the Roots pump. In addition, the numerical simulation results show that hydrogen has the greatest influence on the pumping performance of the Roots; the pumping speed shows ‘W’ type fluctuation in one cycle when the 3-lobe Roots pumps hydrogen. The pumping speed of the 5-lobe Roots is most affected by changes in gas types. This study is of guiding significance for the application and design of dry Roots vacuum pumps in different process environments.

Enabling High-Power Conditioning and High-Voltage Bus Integration Using Series-Connected DC Transformers in Spacecrafts

This article proposes a photovoltaic power processor for high-voltage and high-power distribution bus, between 300 V and 900 V, to be used in future space platforms like large space stations or lunar bases. Solar arrays with voltages higher than 100 V are not available for space application, being necessary to apply power conversion techniques. The idea behind this is to use series-connected zero-voltage and zero-current unregulated and isolated DC converters to achieve high bus voltage from the existing solar arrays. Bus regulation is then achieved through low-frequency hysteretic control. Topology description, semiconductor selection, design procedure, simulation and experimental validation, including tests in vacuum and partial pressures, are presented.

Numerical study on the influence of cell gas on the compression behavior of expanded polypropylene

AbstractExpanded polypropylene (EPP) bead foam mainly consists of entrapped gas within closed polymer cells. This numerical study presents a method to account for the influence of this entrapped gas on the compression behavior of EPP foam. The method developed combines a finite element (FE) model of the foam structure with a smoothed particle hydrodynamics model to simulate the effect of the cell gas. The foam structure is modeled using the open‐source software neper, the FE simulations are conducted using the explicit FE solver of LS‐Dyna. Numerically obtained stress–strain curves for the investigated foam materials, both with and without considering the cell gas, are compared with experimental data from tests using a specially designed vacuum test chamber. The comparison shows a good agreement between numerical and experimental results, indicating that entrapped cell gas increases the structural stiffness under compression. However, in load‐hold‐unload tests, the numerical model fails to accurately capture the stress relaxation behavior observed during the hold phase of the experiment. This study highlights the significant impact of cell gas on the compression behavior of EPP foam and the need for further refinement in simulation strategy to capture effects like the stress relaxation and multiaxial loading.

Design and manufacturing of Welded Vacuum Testing (WVT) tool

To ensure the quality of welded joints in the hull area, welding testing is very important and must be carried out. But unfortunately, currently the quality testing process of welded joints was still limited to penetrant tests and lime tests. The purpose of this study was to obtain a portable welding testing machine that was able to obtain fairly accurate test results on hull welding defects using a vacuum system. The research method is experimental by involving data collection through field experiments, testing is carried out with the resulting weld defect research subjects and the length of testing time on 1G and 3G position welding. The results of the study by compared tests among Welded Vacuum Testing (WVT) machines, Magnetic Particle tests (MP), and Penetrant Tests (PT). The three experiments detected leaking weld defects, spark sparks, pinholes, overlaps, and undercuts. For test results with machines made, welding defects that were successfully detected were leaks in the 1G position welding workpiece and undercut in the 3G position welding workpiece. Air bubbles at a vacuum pressure of 0.2 bar are detected, meaning that there is a defect in the welded joint. This tool can be used in bilge testing.

Thermomechanical Collaborative Design and Experimental Verification of a Sandwich Structure with a Polyimide Foam Core

This paper introduces the technology and performance of a new sandwich structure consisting of carbon fiber composite face sheets, a polyimide foam core, and an aluminum honeycomb panel with both heat insulation and load-bearing functions. The heat-resistant performance of the sandwich structure was evaluated. The vacuum thermal conductivity of the sandwich structure in the vertical direction ranges from 0.54 to 0.92 (W/[m⋅K]) with increasing temperature from −170 to 135°C. A multilayer finite element model of carbon fiber cloth, polyimide foam, and aluminum honeycomb was established. Finally, a comprehensive evaluation of the mechanical and thermal insulation performance of the sandwich structure was conducted through random vibration testing and thermal vacuum testing. The results showed that the sandwich structure had good stiffness and thermal insulation performance, successfully verifying the effectiveness of the collaborative design.

Passive thermal control design and flight operation results of nano moon lander OMOTENASHI

OMOTENASHI is a 6U CubeSat launched by the first NASA SLS rocket. Its mission was to demonstrate that a CubeSat can make a semi-hard landing on the Moon. Tight resource constraints make it difficult to mount a heater and a radiator in a CubeSat, so passive thermal control is a prominent design feature of OMOTENASHI that resolves the technical difficulty. In November 2019, a thermal vacuum test was conducted. This paper discusses the thermal design and the test results. OMOTENASHI was launched by SLS rocket on November 16, 2022. After the SLS rocket separation, OMOTENASHI's attitude control malfunctioned so it could not generate power from its solar cells. Eventually, communications were lost and have not been restored. Brief telemetry data confirmed that the temperature monitor functioned correctly for 30 min. This paper reports the flight results of the thermal status during the first ground station pass. Also, a comparison between the analysis model and telemetry data is shown. Finally, based on its estimated trajectory, the future thermal profile of the spacecraft and the result of the search operation are discussed.

Application of vacuum-laser therapy in complex treatment of chronic gingivitis

The high prevalence of chronic forms of gingivitis among young individuals is an urgent problem of modern dentistry, the solution of which requires new approaches and methods. Thus, this study aimed to investigate the clinical and functional state of the periodontium at the initial inflammatory processes in the tissues and its correction using physical methods of treatment. Clinical examination, index assessment, laser Doppler flowmetry, and video registration of vacuum test in a patient with chronic gingivitis revealed an increase in gingival capillary resistance and improvement of microcirculation in the periodontium at the end of vacuum therapy combined with exposure to laser radiation of red wavelength on periodontal tissues in the complex of standard treatment measures. The results of the functional methods of research after the end of physical influence on periodontal tissues are confirmed by the decrease of bleeding and increase of oral hygiene level according to the clinical instrumental examination and by the absence of patient complaints. Thus, the clinical case demonstrates the promising application of vacuum-laser therapy in the complex treatment of chronic gingivitis.

Loss of insulation vacuum tests on an EuXFEL cryomodule

Many Free Electron Lasers (FEL) are nowadays based on linear superconducting accelerators (linacs). The typical layout of such a linac consists of a number of cryomodules (CMs) arranged in strings. Each cryogenic circuit in a string is protected by safety valves (SVs) in case of failure of the system or a catastrophic event. A typical worst-case scenario considers the venting of the insulation vacuum, causing a fast and uncontrolled warm up of the cryogenic circuits. Such venting can for example take place across a pump port belonging to a string. The amount of heat deposited on each circuit is a very important parameter to correctly size the safety devices.This paper describes the tests performed at DESY on an EuXFEL cryomodule to evaluate the heat input to the three cryogenic circuits of the CM while venting the insulation vacuum. Test results are given with a particular focus of their application to long strings.

First results of non-evaporable getter pump studies for the application in the EAST tokamak

Enhanced particle exhaust is pivotal in optimizing fuel recycling and bolstering plasma performance within fusion reactors. Non-Evaporable Getter (NEG) pumps, renowned for their robust high-temperature tolerance, high pumping speeds and large adsorption capabilities, emerge as highly promising candidates for augmenting the particle exhaust efficiency of tokamaks. Rigorous evaluations have been undertaken to ascertain their pumping efficacy within a vacuum testing setup and the EAST tokamak environment. Experimental data have consistently demonstrated that NEG pumps maintain stable operation across a broad temperature range, from ambient conditions to 200 °C, with a notable direct correlation observed between the pumping speed and the ambient temperature. Their performance surpasses that of conventional cryopumps, especially at D2 gas pressures exceeding 0.1 Pa. Additionally, the application of nitrogen passivation has been validated as an effective method to modulate the pumping speed and to mitigate the risk of hydrogen embrittlement and oxygen and carbon contaminations. Despite exposure to the extreme operational demands, including 30 h of plasma exposure, and lithium processing, atmospheric conditions, and water leaks, the NEG pumps preserved approximately 70 % of their initial pumping capacity. These results underscore the compatibility of NEG pumps with the challenging environments of plasma operations, positioning them as a viable and promising solution for particle exhaust in the next-generation fusion reactors.

Unlocking stray light mysteries in the CoRot baffle with the time-of-flight method

Stray light (SL) has emerged as a primary limiting factor for space telescopes. Pre-launch testing is essential for validating performance and identifying potential issues. However, traditional methods do not enable the decomposition and identification of individual SL contributors. Consequently, when problems arise, resolving them often involves a cumbersome and risky trial-and-error approach. The time-of-flight (ToF) method was recently introduced, employing a pulsed laser source and ultrafast sensor to characterize individual SL contributors. A proof of concept was achieved using a simple three-lens system. In this paper, we apply the ToF method to a real space optical system: the spare model of the CoRoT baffle. We successfully measured individual SL contributors over a dynamic range of 10−11, identifying direct scattering on vane edges and two-step scattering paths. Our results provide a performance breakdown, differentiating intrinsic baffle SL from contributions arising from experimental conditions. Notably, the ToF method allowed us to discriminate air scattering, eliminating the need for expensive vacuum testing. The ToF provides unparallel insights, including defects identification. For instance, we identified the presence of localized dust particles causing significant SL. These results confirm the utility of the ToF method even for the most challenging space systems.

Thomson scattering measurements in the krypton plume of a lanthanum hexaboride hollow cathode in a large vacuum test facility

Laser Thomson scattering is a minimally intrusive diagnostic technique for determining electron temperature, density, and bulk velocity in plasma systems. Advances in technology have made possible the application of Thomson scattering to electric propulsion-relevant plasma systems, with reported electron number-density detection limits as low as 1×1016 m−3, and electron temperatures from one-to-tens eV. However, the implementation of laser Thomson scattering in large vacuum testing facilities, wherein electric propulsion devices are tested, remains a challenge. This work presents the implementation of a laser Thomson scattering system in a large vacuum test facility at the Georgia Tech High Power Electric Propulsion Laboratory. The diagnostic was optimized for maximum light-collection efficiency and ease of re-alignment while the facility is at vacuum. The high light-collection efficiency allowed reduced accumulation times to achieve the target detection limit of 1×1017 m−3. The diagnostic is used to measure axial electron property profiles in the near-field plume of a lanthanum hexaboride hollow cathode operating at 25 A on krypton at a background pressure of 1.3×10−6 Torr—Kr. The diagnostic is quantitatively compared to similar systems in the literature. The resulting axial points, collected from 2 to 8 mm downstream of the cathode keeper orifice, are qualitatively and quantitatively compared with simulations and experimental measurements made with electrostatic probes and laser-induced fluorescence. The main quantitative difference between measured values and results is the one to two order of magnitude difference in the peak electron density, being attributed to the relative size and location of the external anode with respect to the cathode keeper.

Grouping Neural Network-Based Smith PID Temperature Controller for Multi-Channel Interaction System

The thermal vacuum test (TVT) is an important verification process in the development of spacecraft and load. There are often multiple temperature points on the device under test (DUT) that require control. The interaction among multiple channels poses a challenge for temperature control in the TVT. To solve this problem, a multi-channel Smith proportional–integral–derivative (PID) controller based on a grouping neural network (Grouping-NN) is proposed. Firstly, the mathematical derivation for a typical multi-channel temperature control model of the TVT is carried out. Then, the multi-channel interaction system is identified using a Grouping-NN to predict the output temperature of each channel by grouping the hidden layer neurons according to the number of channels. Finally, two Grouping-NNs are utilized to update the Smith predictor, and the time-delay error is fed back to the PID controller, which is used to optimize the control effect of the multi-channel interaction system under high time delay. The proposal is compared with the traditional PID controller and Smith predictor-based PID controller through simulation. The simulation results show that the proposed method has better suppression of overshooting. In addition, the algorithm is verified by controlling the temperature of six channels in a practical thermal vacuum test.

High performance field emission cathode based on the diamond nanowires prepared by nanocrystalline diamond films annealed in air

This paper reports the field emission (FE) characteristics of a diamond nanowires (DNWs) array. The nanocrystalline diamond (NCD) film was deposited on silicon by microwave plasma chemical vapor deposition (MPCVD) and then annealed in air forming DNWs and hydrogenated at last. A high-field flat-plate emission test structure with a 1.03 μm gap between anode and cathode was prepared and the electrical properties proved it feasible. The FE performance of DNWs array was measured in a vacuum test system and that of NCDs film as a comparison. Finally, their FE parameters were analyzed and extracted based on the Fowler–Nordheim (F-N) theory. The results show that transforming NCDs film into DNWs array can improve the FE characteristics greatly. The turn-on field is as low as 1.36 V μm−1 dropping by one order of magnitude, while the field enhancement factor and FE current density are up to 156.68 and 484.75 mA cm−2 respectively rising both by two orders of magnitude. This excellent FE performance stems from the characteristics of large aspect ratio, very small tip radius and high density of DNWs.

Artificial neural network-based temperature prediction of a lunar orbiter in thermal vacuum test: Data-driven reduced-order models

This study presents data-driven reduced-order models (ROMs) of a lunar orbiter based on principal component analysis (PCA) and artificial neural networks (ANNs) for a ground thermal vacuum test to simulate space thermal environments. We employed a radial basis function network (RBFN) and deep neural network (DNN) from among the various types of ANNs. PCA extracts features from high-dimensional data, such as thermal analysis data. It is utilized in machine learning algorithms as a preprocessing step before inputting the data into neural networks. This process improves the convergence speed and training performances compared to using neural networks alone. The coefficients of the extracted principal component modes were regressed using the RBFN and DNN. Twenty thermal design parameters comprising infrared emissivity, effective thermal conductivity, thermal contact conductance coefficients, and thermal conductance were used to train the ROMs. We conducted training and test of the proposed models during the cold and hot balance phases of the ground test. Consequently, the temperature map can be estimated in seconds for the new design parameters, and the model results are consistent with thermal analysis and measurement data.

Preventing Alloy Electrocatalyst Segregation in Air Using Sacrificial Passivating Overlayers.

Many alloy electrocatalysts, including intermetallics, are exceptionally sensitive to segregation in air due to the electronic dissimilarity of the constituent metals. We demonstrate that even alloys with strong cohesive energies rapidly segregate upon air exposure, completely burying the less reactive constituent metal beneath the surface. To circumvent this issue, we develop and validate a new experimental approach for bridging the pressure gap between electronic structure characterization performed under ultrahigh vacuum and electrocatalytic activity testing performed under ambient conditions. This method is based on encapsulation of the alloy surface with a sacrificial passivating overlayer of aluminum oxide. These passivating overlayers protect the underlying material from segregation in the air and can be completely and rapidly removed in an alkaline electrochemical environment under potential control. We demonstrate that alloy surfaces prepared, protected, and introduced into the electrolyte in this manner exhibit near-surface compositions consistent with those of the bulk material despite prior air exposure. We also demonstrate that this protection scheme does not alter the electrocatalytic activity of benchmark electrocatalysts. Implementation of this approach will enable reliable correlations between the electrocatalytic activity measured under ambient conditions and the near-surface electronic structure measured under ultrahigh vacuum.

Radio Frequency System, Power Converters and Cryomodule installation and tests as a Polish in-kind contribution to the European Spallation Source (ESS)

The European Spallation Source (ESS) project currently enters the final stage of installation. Since 2017, a group of engineers and technicians from The Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Science (IFJ PAN) are involved in the project. The contribution to the project can be divided into three main tasks: Radio Frequency Distribution System (RFDS), RF (Radio Frequency) Power Stations and Cryomodules.The RFDS in ESS project is one of the largest installations of this type consisting of 155 RF high power systems. Engineers and technicians from IFJ PAN were responsible for preparation, installation and RF measurements of the above-mentioned system. The team is also involved in preparation and conducting low and high power tests of the RF stations.The IFJ PAN team is also responsible for the preparation as well as vacuum and cryogenic tests for 9 Medium and 21 High Beta Cryomodules, before they are installed in the tunnel.The advanced quality control and quality assurance were mandatory for this work because the costs of failures, as well as potential delays, would have a huge impact in the project realisation. Therefore dedicated methods and approaches have been adapted to this work using experience gained by the IFJ PAN team on previous projects like LHC, XFEL and W7X.

Residual Error Integral Predictor-Based Smith Fuzzy PID Temperature Controller for Thermal Vacuum Test

Residual Error Integral Predictor-Based Smith Fuzzy PID Temperature Controller for Thermal Vacuum Test