Vacuum Space Research Articles

Lumped Parameter Analysis of Autogenous Propellant Pressurization System for Nuclear Thermal Rocket

This work proposes a new propellant management configuration for an ammonia-fueled nuclear thermal propulsion system. The suggested configuration maximizes the advantage deriving from the autogenous pressurization of ammonia by exploiting the thermal power lost by the nuclear reactor toward the vacuum space due to leaking radiation. In this layout, a tank containing ammonia in saturated conditions is placed near the nuclear reactor and receives an input thermal power proportional to the dose of gamma rays and neutrons absorbed by the tank walls and the ammonia itself. Such a thermal power accelerates the vaporization process of the saturated ammonia, thus increasing the pressure in the tank. A pressure regulator valve exploits this overpressure to pressurize the ammonia propellant contained in a run tank to the level required by the mission by connecting the two ammonia volumes. The pressure achieved inside the run tank pushes the propellant with an adequate mass flow rate inside the nuclear reactor. The developed lumped parameter analysis shows how this propellant management system can provide a constant mass flow to the nuclear reactor without using a turbopump assembly. Moreover, it is shown how the proposed concept allows for a reduction in the radiation shield mass.

Multi-Criteria Calibration of a Thermo-Mechanical Model of Steel Plate Welding in Vacuum

This paper proposes a procedurefor multi-criteria calibration of a thermo-mechanical model for numerical simulation of welding in the space vacuum. A finite-element model of a steel plate is created. Experimental and computational data are obtained. An inverse problem is formulated for the vector identification of five calibration parameters from the heat-flow model. They are evaluated for adequacy with controlled accuracy according to four criteria. An optimization problem is solved using a two-step interactive procedure. The parameter space studying method (PSI) has been applied to the study of multidimensional regions by means of quasi-uniform sounding. A Pareto-optimal set is defined. It is used to determine reduced ranked Pareto subsets by μ-selection. Salukvadze optimum is also determined.

Volatile capacitance of resistor with differential resistance

The differential current dV/dR in a resistor forms a volatile capacitance across itself. When the differential current is less than the Ohm current, V/R, the volatile capacitance is positive. Conversely, when it exceeds the Ohm current, the volatile capacitance becomes negative. If the differential current equals the Ohm current, the volatile capacitance is zero. The transition of this volatile capacitance from positive to negative has been observed in a combination of multi-walled carbon nanotube material and vacuum space. Additionally, we have fabricated a two-dimensional planar inductor without a coil using this negative capacitor.

Analysis of unstable combustion caused by the Gas–Liquid two-phase flow in small hypergolic propellant engines

Hypergolic bipropellant engines are extensively used in spacecraft operations. In these engines, the combustion reaction is initiated by the impinging jets of the oxidizer and fuel in the liquid phase. The most commonly used hypergolic fuels, hydrazine and monomethylhydrazine, as well as the oxidizer, nitrogen tetroxide, are all in liquid state under room temperature and atmospheric pressure conditions. However, as these engines are operated in a space vacuum, a portion of the propellant inevitably evaporates because of low-pressure boiling immediately after engine start-up. The mixing of gas with liquid propellant results in unstable combustion, and minimizing this effect is critical for the engine design. Particularly, preventing high-frequency combustion instability is essential as it can be detrimental to the engine. This paper presents a mechanism that activates high-frequency combustion instability, realized by analyzing the pressure within the combustion chamber during artificially induced unstable combustion. Furthermore, the methodology for establishing operational constraints based on the proposed mechanism is clarified, along with the method for collecting test data. The study findings provide important indicators for the design criteria of bipropellant engines, contributing to the diversification and complexity of space development programs.

The effect of strain effect on WS2 monolayer as a potential delivery carrier for anti-myocardial infarction drug: First-principles study.

Myocardial infarction is one of the major health challenges. It is of great significance to develop potential delivery carriers for new anti-myocardial infarction drugs. In this paper, based on first-principles calculations, monolayer WS2 with excellent photoelectric properties was verified as a carrier for the anti-myocardial infarction drug amiodarone (AMD). Studies have shown that the WS2-adsorbed AMD system (WS2@AMD) maintains structural stability and produces an adsorption energy of-2.12 eV. Mulliken charge analysis shows that electrons are transferred from WS2 atoms to AMD atoms. Among them, C, N and O obtained the maximum values of 0.51,0.37 and 0.56 e electrons, respectively, while H and I lost the maximum values of 0.32 and 0.24 e electrons, respectively. The optical response of WS2 adsorbed AMD system is similar to that of WS2. The light absorption coefficients of the two materials in the near ultraviolet region and the visible region can reach the order of 105 cm-1 and 104 cm-1, and the strain makes the light absorption peak red-shifted. The feasibility of temperature-controlled release mechanism of WS2 as AMD carrier was discussed. This theoretical work helps to improve the performance of two-dimensional nanomaterials and make them better as drug delivery carriers to improve the therapeutic effect of myocardial infarction. These results indicate that the WS2 monolayer has potential applications in the development of drug delivery carriers. In this study, based on first-principles calculations, the CASTEP simulation software package was used to study the structure and properties of materials. The interaction between electrons and ions is considered by using Ultrasoft pseudopotentials. In order to eliminate the spurious interaction between adjacent structures caused by periodic calculations, a vacuum space no less than 18 Å is placed in the vertical direction if necessary. Different functions may produce different density functional calculation results. Due to the low sensitivity of the crystal structure to the calculation details, the PBE functional under the generalized gradient approximation (GGA) was initially used for structural optimization, and the energy cutoff value was set to 500 eV. Grimme 's dispersion correction was used to make the results more accurate. The Brillouin zone (BZ) is sampled by a 7 × 7 × 1 K-point grid to ensure the reliability of the original lattice calculation. The lattice vector and atomic coordinates are relaxed, and the tolerance of each atom is less than 0.01 eV/Å. The energy tolerance at the atomic position is less than 10-7 eV/atom. When calculating the band gap, the HSE06 hybrid functional is used to modify the optimized structure of the PBE functional to obtain more accurate results. Spin-polarized DFT calculations were performed to calculate the electronic structure.

“We Must Participate with the Fruits of Our Faith in Building Socialism”. The Preaching Committee in the Danubian Reformed Church District in the Mid-20th Century

As a result of the communist takeover in 1948, the Bishop of the Danubian Reformed Church District, László Ravasz was deposed, and Albert Bereczky took his place. In the end of 1951, Bereczky wrote a report to the general meeting of the Reformed Church in which he requested the authorization to set up a “preaching committee” with the aim of supervising sermons. He believed it was important for the pastors to talk about issues of their time in sermons because “we don’t preach in a vacuum space but to real people”. In reality, the committee’s function was the full control over pastors and the search for the ideological/theological content (which is called “narrow-road” theology) in preachings. That is why every pastor was asked to send in one sermon that was to be delivered between 1/01/1952 and 25/02/1952. József Bodonhelyi, head teacher of practical theology at the Faculty of Theology of the Reformed Church, who was also member of this preaching committee, wrote notes about these received texts and sermons where he probably appeared in person. We could find certain qualifications in his notes that seriously affected the careers of the pastors (for example, “he doesn’t address the issues of our time”; “his teaching is dangerous”; “he must urgently retire”). Keywords: Albert Bereczky, Reformed homiletics, history of preaching, preaching, Church history

A positive metric over DGKT vacua

We study the notion of a metric over the space of AdS solution in string theory, leading to an associated distance between them. Such a distance is the idea underlying the AdS distance conjecture. We utilise the previously developed prescription for extracting such a metric: taking an off-shell quadratic variation of the string theory effective action and then evaluating it over the space of on-shell solutions. It was shown that this prescription leads to a well-defined positive metric over M-theory Freund-Rubin vacua. In this work, we use the same prescription to calculate the metric over type IIA DGKT vacua. These are much more involved, they have multiple flux parameters and exhibit scale separation. While it remains an open question whether these vacua exist as fully localised solutions of string theory, they are well-defined within the four-dimensional effective theory, which is all that is required for the calculation. We find that they also have a positive metric over them. Interestingly, this metric turns out to be independent of the many flux parameters in the solution, similarly to what happens for metrics over scalar field spaces. This non-trivial flux cancellation, as well as results from explicit vacua, lead us to propose a Swampland condition: that the metric over the space of vacua in quantum gravity, as defined by the above prescription, is always positive.

Hydrogen permeability testing of fibre reinforced thermoplastics under cryogenic conditions – validation of a test rig concept

The need to decrease the gross weight of cryogenic hydrogen fuel systems in future zero emission mobility leads to increasing activities in the field of cryogenic lightweight engineering. Fibre reinforced thermoplastic composite materials (FRT) are considered for cryogenic applications despite their bias towards permeation. However, permeation through plastic materials is of major concern in cryogenic applications. Even tiny fluxes can very much compromise the insulating power of high vacuum spaces required for insulation of cryogenic systems such as tank structures or transfer lines. Hence, it is essential to qualify those FRT in terms of their hydrogen permeability for future usage in mobile cryogenic applications. The conventional concepts for measuring permeability in plastic materials are not sufficient for cryogenic measurements of FRT as shown in a previous paper. For that, a novel laboratory test rig concept was proposed. In this paper, we validate this concept and show its eligibility for measuring permeation of hydrogen through thermoplastic materials. Therefore, we report results of helium permeation through polytetrafluoroethylene (PTFE) at room temperature and compare those results to literature permeability data.

The effect of simulated space vacuum conditions on some biochemical and physiological responses of quinoa

The effect of simulated space vacuum conditions on some biochemical and physiological responses of quinoa

Dielectric assist accelerating structures for compact linear accelerators of low energy particles in hadrontherapy treatments

Dielectric Assist Accelerating (DAA) structures based on ultralow-loss ceramic are being studied as an alternative to conventional disk-loaded copper cavities. This accelerating structure consists of dielectric disks with irises arranged periodically in metallic structures working under the TM02-π mode. In this paper, the numerical design of an S-band DAA structure for low beta particles, such as protons or carbon ions used for Hadrontherapy treatments, is shown. Four dielectric materials with different permittivity and loss tangent are studied as well as different particle velocities. Through optimization, a design that concentrates most of the RF power in the vacuum space near the beam axis is obtained, leading to a significant reduction of power loss on the metallic walls. This allows to fabricate cavities with an extremely high quality factor, over 100,000, and shunt impedance over 300 MΩ/m at room temperature. During the numerical study, the design optimization has been improved by adjusting some of the cell parameters in order to both increase the shunt impedance and reduce the peak electric field in certain locations of the cavity, which can lead to instabilities in its normal functioning.

Analysis of the thermal effect of two external parallel printed circuit board conductors set on a metal base and operating in a space vacuum on each other

Background. The need to analyze the thermal effect of two external parallel conductors is due to an increase in the density of the conductive pattern. For printed circuit boards set on a metal base and operating in the vacuum of space, this need is aggravated by the weakness of the issue's development. 
 Aim. Analysis of the mutual influence of two external parallel printed circuit board conductors set on a metal base and operating in a space vacuum on each other to identify the dependence of their temperature on the distance between them and determine the distance at which this dependence practically disappears.
 Methods. To achieve the purpose, a finite element method calculation implemented in the ANSYS program, the Steady-State Thermal module, was used. Three multilayer printed circuit boards were calculated: 4-layer, 6-layer, 8-layer. The temperature coefficient of resistance was taken into account separately, by recalculation.
 Results. Graphs of the dependence of overheating (the difference between the temperature of the printed conductor and the metal base) on the distance between the printed conductors were constructed. The approximation of the obtained results is carried out. According to the approximated dependencies, the minimum values of the distances between printed conductors are found, at which the cross influence of printed conductors practically disappears. As the thickness of the printed circuit board increases, this distance increases.
 Conclusion. The results obtained can help to assess the influence of neighboring printed conductors in the design of the boards of the onboard equipment of spacecraft.

The Iris CubeSat mission: Science payload description for a pathfinder geological space weathering investigation

The Iris mission is a student-led 3-U CubeSat comprised of a science payload of 20 geological samples placed in low-Earth orbit (LEO) to study the effects of space weathering (i.e., those aspects that can be investigated in LEO). This experiment is the first of its kind to take place in the vacuum of space. The science objective of the mission is to investigate how space weathering processes affect the surfaces of airless planetary bodies by monitoring the spectral reflectance properties of geological samples over time. Two three-color cameras acquire spectral reflectance data within the visible spectrum to measure any spectral and/or textural changes exhibited throughout the ∼1-year orbital mission. This mission will provide valuable data to help understand how the space environment may affect the surfaces of the Moon, Mercury, and main-belt and near-Earth asteroids. The acquired data will help constrain meteorite-asteroid links and provide insight into the spectroscopic analysis of samples returned from the Moon, and near-Earth asteroids Itokawa, Bennu, and Ryugu. The results of this mission will also complement the results of laboratory simulations of space weathering. All samples selected for flight on the CubeSat have undergone several tests to ensure suitability for launch and operations. This paper describes the payload subsystem, sample selection and preparation.

First-principles study of the electronic structure and optical properties of C-doped SnS2.

Density functional theory (DFT) was used to investigate the effects of varying carbon doping concentrations on the electronic and optical properties of SnS2-doped systems. The findings show that a doping concentration of 3.7% in SnS2 results in the highest structural stability and the lowest formation energy. A pure SnS2 monolayer is an indirect bandgap semiconductor, and the result reveals that increasing carbon doping correlates with a gradual reduction in the system's bandgap. The density of states analysis reveals that the valence band comprises C-2p, S-3p, and Sn-5p orbitals, whereas the conduction band consists of S-3p, Sn-5s, and C-2p orbitals. Furthermore, doping concentration appears to cause a redshift in both the absorption coefficient and reflection peaks, which both decrease as doping concentration increases. The calculations for this study were performed using DFT within the CASTEP module of Materials Studio Segall et al.J Phys: Condens Matter 14(11):2717, 2002. The system parameters and structures were optimized to determine the electronic structure and optical properties. Geometric optimization and calculations were carried out with the generalized gradient approximation plane-wave pseudopotential method and the Perdew-Burke-Ernzerhof functional Perdew et al.Phys Rev Lett 80(4):891-891, 1998. The parameters for structural optimization included a plane-wave expansion cutoff energy set at 500eV and a k-point mesh of 6 × 6 × 1 for Brillouin zone integration. The electronic convergence criteria were established at 1.0 × 10-5eV/atom for the unit cell energy and 1.0 × 10-6 eV/atom for self-consistency. The internal stress deviation was maintained below 0.05 GPa, the atomic force interactions were kept under 0.03eV/Å, and atomic displacements during geometric optimization were confined to less than 0.001Å. To calculate the properties of the SnS2 monolayer, a vacuum spacing of 15Å along the z-axis was introduced to prevent interactions between adjacent layers.

The socio-politics of (Re)constructing home in a post-displacement context in rural Zimbabwe

This paper contributes to and advances the sociological discourse on ‘homing’ by examining the implications of the socio-political dynamics of resettlement, with particular reference to the 2014 Tokwe-Mukorsi flood victims in rural Zimbabwe, five years after they were resettled in Chingwizi. The article highlights the intricacies encountered by displaced persons as they strive to establish what they consider an ideal home – one that guarantees, at the very least, food security, shelter, safety, property rights, identity, and a sense of belonging. Drawing on actor-network theory, the article utilizes empirical qualitative data gathered using interviews and focus groups from displaced persons and government officials. The intention was to illuminate how homing experiences are influenced by socio-ecological encounters between displaced persons and other key actors. From the adversities resulting from the floods, the victims waded not in a socio-ecological vacuum or neutral space but in a hotly contested terrain as they sought to adapt to climatic conditions at the new location, overcome past cultural fixations, and ultimately build a new homely life. The study found that these processes, inter alia, meant navigating the complex socio-political dynamics of exclusion and marginalization that rendered the quest for an ideal home untenable.

Membrane distillation of saline feeds and produced water: A comparative study of an air-gap and vacuum-driven modules

Air gap membrane distillation (AGMD) and vacuum membrane distillation (VMD) are two membrane-based desalination processes that utilize temperature differences to generate water vapor for purification. This study evaluated the viability of both processes for treating different types of saline water, such as Arabian Gulf seawater and oil field-produced water. Factors such as feed temperature, feed concentration, recirculation flow rate, air gap, and vacuum space depth were investigated to understand their impact on permeate flux in AGMD and VMD configurations. The results showed that AGMD achieved higher permeate flux at lower feed concentrations, while VMD performed better at higher concentrations. Increasing the feed temperature led to increased permeate flux in both configurations, with AGMD showing a greater increase. Results also indicated that lower gaps were preferred in both configurations, and the tested membranes showcased excellent salt rejection capabilities. These findings provide valuable insights into the potential applications of AGMD and VMD in desalination, especially in regions with water scarcity or pollution.

Reviewing the Role of Virtual Particles in the Vacuum

Experimental evidence has established the existence of virtual particle pairs (VP) in the vacuum of space. The origin of these Virtual Particles is traced to the interacting waves of the Zero Point Energy (ZPE). The strength of the ZPE has been shown to increase with cosmic expansion, meaning the VP numbers would also increase simultaneously. Classical theory states that every time a charged particle undergoes an acceleration, it emits secondary radiation. The random waves of the ZPE impacting on all subatomic particles causes them to jitter (the ‘zitterbewegung’). This jitter results in extremely rapid and continuous changes in direction for all subatomic particles and thus ongoing accelerations. As a consequence, all particles will emit secondary radiation which, in turn, boosts the ZPE strength locally around massive objects (along with a corresponding increase in VP numbers). The role played by the ZPE and associated Virtual Particles in the vacuum is then explored in relationship to the speed of light as well as some other effects that were predicted by relativity. These effects can now be shown to have an actual physical cause related to the ZPE and associated Virtual Particles.

TiO2 nanotube arrays-based photoelectrocatalyst: Tri-Doping engineering and carbon coating engineering boosting visible activity, and stable hydrogen evolution

The integration of non-metallic doping and carbon coating for TiO2-based photoelectrocatalysts can be recognized as a promising strategy to enhance their hydrogen production performance. To this end, this study explored the carbon coating engineering to induce stable multi-element doping with an aim to develop high-performance TiO2 nanotube array-based photoelectrocatalysts. The resulting structures consisted of carbon–nitrogen-sulfur-tri-doped TiO2 nanotube arrays with a nitrogen-sulfur-codoped carbon coating (CNS-TNTA/NSC). The fabrication process involved a one-step, low-cost strategy of the carbon-coated tridoped reaction confined in vacuum space, utilizing polymer thiourea sealed in a controlled environment. Compared the photocurrent density of CNS-TNTA/NSC with pristine TNTA, the photocurrent enhancement of approximately 18.3-fold under simulated sunlight and a remarkable increase of 32.8-fold under simulated visible light conditions. The enhanced photocatalytic activity under visible light was ascribed to two factors: First, C, N, and S tri-doping and Ti3+ created a diverse array of impurity energy levels within the band gap, which synergistically narrowed the band gap and further enhanced response to the visible light range. Second, the presence of a carbon coating shell doped with N and S can greatly promote electron transfer and efficient electron-hole pair separation. This study could provide significant insights concerning the design of sophisticated photoanodes.

Black holes and non-perturbative gravitational waves in f(R) gravity

Exact solutions of spherically symmetric black hole and gravitational wave are explored in f(R) gravity in arbitrary dimension. We find two exact solutions for the radiation and absorption of null dust. In the framework of general relativity, the Birkhoff theorem strictly forbids the existence of spherical gravitational waves in vacuum space. We find spherical non-perturbative gravitational waves, which are shear-free, twist-free, but expanding.

Development of an accelerator-based neutron source to prototype Mo-99 production, Part II: A liquid LBE loop under a high vacuum

To provide US domestic supply of Mo-99 without using high-enriched uranium (HEU), a subcritical uranium target assembly (UTA) is irradiated by an accelerator-based neutron source to create Mo-99 through fission. Part I of this work discusses the design of a liquid lead–bismuth eutectic (LBE) windowless target for an accelerator-based neutron source development. Part II discusses how to couple this windowless target to an accelerator operating at an ultra-high vacuum and the subcritical UTA cooled by water at room temperature.Due to the windowless design of the target, the liquid LBE flow shares an ultra-high vacuum (<1.3 × 10−7 Pa or 10−9 Torr) space with the accelerator. As a result of this shared vacuum space, the LBE system must operate at a high vacuum (10−3 ∼ 10−6 Pa or 10−5 ∼ 10−8 Torr). A magnetic rotary motion feedthrough unit utilizes magnetic fluid to allow rotation of the pump while maintaining a high vacuum environment. Prior to testing the LBE system under vacuum, a pump curve measurement is performed to estimate flowrate in the system. This measurement also generates data on orifice loss coefficients, which are compared to correlations in literature. The second experiment investigates vacuum level in the LBE system during operation. High vacuum is maintained (10−3 ∼ 10−5 Pa or 10−5 ∼ 10−7 Torr) during system operation, and a residual gas analyzer (RGA) scan shows that partial pressures of residual gases in the LBE system lower over the duration of LBE system operations. The third experiment investigates the gravity driven liquid LBE flowing out of the target chamber in the return line, which is partially full. If the liquid LBE is not drained quickly enough, flooding in the target chamber could occur. The coefficient n in the Manning equation is found to be around 0.008 s/m1/3. The last experiment performed is a demonstration that a vacuum jacket could provide sufficient thermal insulation to allow coupling between 300 °C LBE loop and a water tank at room temperature. The results from these experiments have influenced the development of the neutron source for the future commercial scale Mo-99 production system.

Experimental and numerical investigations of an open-cell copper foam (OCCF)/phase change material (PCM) composite-based module for satellite avionics thermal management in a thermal vacuum chamber (TVC)

Small satellites' thermal control in the space environment is crucial. Phase change materials (PCM) are promising options for satellite thermal management in space thermal conditions. The current work provides an experimental and numerical investigation of a thermal control module (TCM) using an open-cell copper foam (OCCF)/PCM combination. The experimental tests were carried out in a thermal vacuum chamber (TVC), which simulated the vacuum space environment. The PCM thermal conductivity was boosted using OCCF and aluminium fins. The metallic parallel fins divided the heat sink into six cuboid cavities and were filled with PCM. Two samples with different pores per inch (PPI) of OCCF were adopted, one with 10 PPI and the other with 20 PPI. For the experimental work, the adopted PCM was SP 31. Two levels of heating loads were applied to the TCM: 10 W and 7 W. The numerical model was verified using the experimental work findings. The experimental work concluded that the PCM capsulation sealing is a dominant factor for successful capsule design under vacuum operation. The thermal conductivity enhancers (TCEs) remarkably improved the thermal management performance of the PCM. The case with PCM reported a reduction in the maximum temperature by about 43.67 % and 41.4 % at 7 W and 10 W, respectively, relative to the case without PCM. The PCM/fins combination could improve the PCM performance and mitigate the maximum temperature from 41.7 °C to 39.6 °C with a reduction percentage of 5 %. The OCCF reported better thermal performance than the metallic fins. The OCCF with 10 PPI decreased the PCM maximum temperature by 10.3 %. The OCCF with 20 PPI reported a reduction in the PCM maximum temperature by 13.8 % at 10 W heating power.