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(a) Schematic drawing of an electrospray emitter and the test setup for its electrical characterization, including a switchable gate for time-of-flight (ToF) measurements. Note the active propellant feed system driven by a controlled nitrogen pressure in the ionic liquid storage vacuum tank on the left hand side. (b) Process flow with stacked layers made by planar photolithography for the integrated fabrication of the capillary layer and spacer (extraction electrode support) layer, and SEM micrograph of a structure made this way. (c) Single emitter prepared by stacked plasma technology. (d) Illustration of the principle of twophoton microlithography. (e) SU-8 "volcano type" microemitter structure written using two-photon microlithography with a Nanoscribe PPGT in galvo mode.
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The transition from OLD SPACE to NEW SPACE along with increasing commercialization has a major impact on space
flight in general and on electric propulsion by ion thrusters in particular. Ion thrusters are nowadays used as primary
propulsion systems in space. The article describes how these changes related to NEW SPACE affect various aspects that
a...
Citations
... Electron emission cathodes are key components of various high frequency, high power vacuum electronic devices such as traveling wave tubes and klystrons, and lower power device applications such as electron microscopes, ion thrusters for satellites, and thermionic energy converters for concentrated sunlight and industrial waste heat. [1][2][3][4] The electron emission from the cathode is largely determined by which surface terminations and orientations are present on the emitter, and their respective work function values. A stable, low work function surface is desired to provide efficient electron emission current during cathode operation, where emission may be controlled by incident photons (photoemission), high temperature (thermionic emission), electric field (field emission), or ARTICLE pubs.aip.org/aip/apm ...
Perovskite SrVO3 has recently been proposed as a novel electron emission cathode material. Density functional theory (DFT) calculations suggest multiple low work function surfaces, and recent experimental efforts have consistently demonstrated effective work functions of ∼2.7 eV for polycrystalline samples, both results suggesting, but not directly confirming, that some fraction of even lower work function surface is present. In this work, thermionic electron emission microscopy (ThEEM) and high-field ultraviolet photoemission spectroscopy (UPS) are used to study the local work function distribution and measure the work function of a partially oriented- (110)-SrVO3 perovskite oxide cathode surface. Our results show direct evidence of low work function patches of about 2.0 eV on the cathode surface, with a corresponding onset of observable thermionic emission at 750 °C. We hypothesize that, in our ThEEM and UPS experiments, the high applied electric field suppresses the patch field effect, enabling the direct measurement of local work functions. This measured work function of 2.0 eV is comparable to the previous DFT-calculated work function values of the SrVO-terminated (110) SrVO3 surface (2.3 eV) and SrO-terminated (100) surface (1.9 eV). The measured 2.0 eV value is also much lower than the work function for the (001) LaB6 single crystal cathode (∼2.7 eV) and comparable to the effective work function of B-type dispenser cathodes (∼2.1 eV). If SrVO3 thermionic emitters can be engineered to access domains of this low 2.0 eV work function, they have the potential to significantly improve thermionic emitter-based technologies.
... Electric propulsion (EP) systems have gained significant traction in both scientific and commercial sectors [3]. A key technology in this area is the radiofrequency ion thruster (RIT), an ion source also used for surface modification. ...
The research activities conducted at the Space Electronics Research Group of the University of Applied Sciences (THM) in Giessen focus on the electronic hardware required for the operation of plasma sources and specifically electric propulsion (EP) devices. The main topics include radio-frequency generator (RFG) development for inductive and capacitive loads, radiation tests of commercial off-the-shelf components (COTS) for cost reduction of flight hardware, as well as electromagnetic interference tests and qualification of RFGs and electric thrusters in vacuum. Beside these the group also works on plasma modelling, novel propulsion devices and novel plasma diagnostics. The paper is an overview on the ongoing research activities and available test facilities with their respective capabilities.
... The commercial use of space and the increasing integration of the space sector with the traditional economy, known as NewSpace, is progressing rapidly [1][2][3]. More and more companies from a wide range of industries are using satellite-based technology for a wide variety of applications [4]. ...
... By accepting a higher risk of failure, development cycles can be shortened to further reduce costs and accelerate the payback of such an investment. Despite this paradigm shift, general requirements such as reliability, robustness and efficiency remain important requirements for mission success and concern not only the propulsion system but also its interaction with other electronic components [2,3]. ...
... The high symmetry simplifies a complete assessment of the EM characteristics of the thruster. Third, the microwave frequency of f x = 2.45 GHz used for exciting the plasma of the ECR thruster during operation is quite high compared to those, for example, used in radio frequency ion thrusters (RIT), which typically operate in the lower MHz or upper kHz range [2]. According to the standards, the radiated EMI should be measured in a frequency range from at least 30 MHz to 18 GHz [17,18]. ...
The demand for space propulsion systems is increasing due to the rising number of satellite launches. Electric thrusters gain considerable importance as highly efficient systems in space. As the thrust generation process involves electrically charged particles in motion, ion and plasma thrusters can cause electromagnetic noise, which may interfere with satellite electronics or radio communication. Our objectives are to quantify such emissions and to better understand their origin. We use two facilities to achieve this goal: a semi-anechoic chamber (SAC) with a dedicated vacuum chamber and a mode-tuned vacuum chamber, also known as a reverberation chamber (RVC). Here, we conduct measurements in both facilities on an electron-cyclotron resonance (ECR) thruster with a magnetic nozzle in order to assess its electromagnetic compatibility (EMC). This thruster emits a quasi-neutral plasma plume without requiring an additional neutralizer, thus, is especially suitable for conducting our studies. The thruster in operation acts as an electromagnetic noise source contributing to different frequency ranges. In addition to the excitation frequency band, the data reveals emissions occurring approximately one decade lower in frequency. These emissions depend on propellant mass flow, background pressure and excitation power, i.e., vary with the electron density of the plasma generated inside the ECR thruster. The thruster was characterized following primarily MIL-STD-461G and further ECSS-E-ST-20-07C.
... Ion Propulsion Systems; Ion propulsion systems operate based on the principle of electrostatic or electromagnetic acceleration of ions to generate thrust (Holste et al., 2020). These systems typically utilize a propellant, commonly xenon gas, which is ionized within a discharge chamber. ...
Electrical propulsion systems have revolutionized satellite technology by offering greater efficiency, longer mission durations, and increased maneuverability compared to traditional chemical propulsion systems. This review explores current technologies and future prospects in the field of electrical propulsion systems for satellites. The discussion begins with an overview of existing technologies, including ion propulsion systems, Hall effect thrusters, and pulsed plasma thrusters. Each technology's principles of operation, advantages, limitations, and notable applications are examined. The review delves into the future prospects of electrical propulsion systems, exploring advanced concepts such as magnetoplasmadynamic thrusters, variable specific impulse magnetoplasma rockets, and electrospray propulsion systems. Additionally, miniaturization and efficiency improvements, as well as sustainable and green propulsion alternatives, are discussed. Challenges and opportunities facing the field are addressed, including technical hurdles like power generation and management, thruster lifespan, and regulatory and economic considerations such as policy frameworks and market dynamics. In conclusion, the review underscores the critical role of continued research and development in electrical propulsion systems for satellites. As the demand for more capable and sustainable satellite missions grows, advancements in propulsion technology will be essential in meeting these evolving needs and pushing the boundaries of space exploration.
... It is an urgent task for engineers to limit the rapid growth of space debris caused by space activities to avoid potential future risks [7][8][9]. In order to boost the deorbiting process of the CubeSat, four kinds of deorbiting equipment are available: electrodynamic force tethers [10], onboard thrusters [11], solar radiation pressure sails [12], and aerodynamic drag sails [13]. ...
... A further analysis is presented to juxtapose the drag force generated by the drag sail with the thrust force of widely utilized electric thrusters, as introduced in Section 1. Given that electric thrusters represent an alternative approach to the drag sail technique, this study undertook a comparative evaluation of the drag forces derived for the two higheraltitude scenarios examined herein against the thrust forces produced by standard ion thrusters [11]. The 4 m 2 drag sail is capable of generating drag forces of 5.1 mN at an orbital altitude of 300 km and 0.4 mN at 450 km. ...
Reducing space debris is a critical challenge in current space exploration. This study focuses on designing a drag sail for CubeSat models and examining their aerodynamic properties using the direct simulation Monte Carlo (DSMC) method. The analysis encompasses the aerodynamic performance of intricate three-dimensional shapes with varying sail dimensions at orbital altitudes of 125 km, 185 km, 300 km, and 450 km. Additionally, free molecular flow (FMF) theory is applied and compared with the DSMC findings for both a flat-plate model and the CubeSat. The results reveal that FMF accurately predicts the drag coefficient at altitudes of 185 km and above, while significant discrepancies occur at lower altitudes due to increased inter-molecular collisions. This study also suggests that the drag sail substantially enhances the CubeSat's drag force, which effectively reduces its deorbiting time.
... Broad beam ion source technology has been existed for a long time, but there are still ongoing technical issues that need to be dealt with. One such challenge is scaling of ion sources for space applications, particularly in the context of small electrical thrusters designed for CubeSat applications, which continue to suffer from low discharge efficiency [35,51,52]. The discharge efficiency of the broad beam ion source may be improved by increasing the grid transparency and reducing the plasma loss area. ...
Multicusp gridded ion sources have applications in space propulsion, surface modification studies, and neutral beam injectors for fusion research. The majority of applications for low power ion sources include mass spectrometers, surface modification, ion implantation, and electric thrusters. The main
parts of these ion source systems are the multicusp plasma chamber, extraction system, neutralizer, and beam transport systems. The electrical efficiency of these ion sources depends on the confinement of primary electrons in the plasma chamber with a suitable magnetic multicusp configuration and performance of ion extraction system consisting of a set of thin multi-aperture grids. Additionally, adequate space charge neutralisation of the ion beam needs to be provided to confirm proper extraction and transport of the ion beam. In this thesis, a ring cusp ion source has been designed and developed to produce ion beam of heavy ions (e.g. Ar+) within the energy range of 1-2 keV and the beam currents up to 100 mA. In this ion source, a hot filament is utilised as a cathodes to produce the plasma discharge. The positive ions in the plasma are extracted out and accelerated using an electric field applied between two extraction grids having multiple apertures. The magnetic cusp configuration of the plasma chamber has been optimised to maximise the confinement of primary electrons by using a simulation tools, CSTStudio. The extraction system, also known as ion optics, was designed and developed using OPERA3D trajectory simulations for minimising the ion beam divergence. Thermo-structural analysis has been
carried out to avoid the deformation in the extraction grids resulting from the thermal loads from the plasma and beam ions. Experimental investigations have been carried out to study the extraction and transport behaviour of ion beams with and without space charge neutralisation. The characterisation of the extracted ion beam is carried out by measuring the beam profiles and estimating ion beam divergence and total beam currents at different locations along the beam path using an eleven-channel
Faraday Cup Array (FCA) and a nine-channel Fixed Wire Array (FWA). The FCA is designed with multiple electrodes for filtering out the primary electrons and slow-moving charge exchange ions, while suppressing the secondary electrons from the ion collector. Using a mathematical model that considers the beam as a superposition of multiple Gaussian beam-lets directed towards a focal point, measured radial profiles of ion current density have been utilised to determine the beam divergence and focal
length. The beam attenuation due to charge exchange processes, radial transport of slow-moving charge exchange ions, space potential and fluxes of neutralizing electrons in the ion beam are also investigated to understand the beam transport and neutralization processes in the ion beam.
... Ion thrusters are great & efficient for orbit maneuvering and transferring orbits. [1] Use of ion thrusters enables low latency communication, military surveillance, and other applications. This research paper focuses on the development and implementation of a hybrid airbreathing ion propulsion system designed to lower the satellite orbit altitude specifically at altitudes of around 150-200 km, where there is still a trace of oxygen that can be utilized for air intake. ...
... The second grid (acceleration grid), which is typically at a negative potential, accelerates ions emerging from the plasma thus creating thrust. [1] connecting the fuel system with multiple fuel nozzles to the combustion chamber for high thrust requirements when needed, and ensuring alignment and compatibility. Since the entire model is composed of PLA material, multiple layers of aluminium foil are applied to the inner surface of the combustion chamber and nozzle to prevent melting. ...
... The mass of 2 molecule is derived using the molar mass of 2 as well as Avogadro's number to get us the following mass of a 2 molecule: Therefore, the impulse of the ion thruster by each stage is 69.06 Newton second [1] ...
The aim of this project is to develop an innovative propulsion system that combines the principles of air-breathing engine and ion propulsion to reduce the orbit of satellites to a range of 150 to 200 kilometers above the Earth's surface. The propulsion system uses two technologies, namely the ion thruster and jet engine, to create a hybrid ion propulsion system. The research involves the design and development of a three-stage ion grid system and a fuel system to achieve an exhaust velocity of 7+ meters per second. The results of the project demonstrate that the proposed hybrid airbreathing ion propulsion system can be used as propulsion system in satellites at very low Earth orbit, which is particularly useful for applications such as weather forecasting, military surveillance, and high-speed communication and for aircraft & missile propulsion system etc. In comparison to conventional propulsion systems, the hybrid airbreathing ion propulsion system offers several advantages such as higher fuel efficiency, lower operating costs and reduced environmental impact. These benefits make the hybrid airbreathing ion propulsion system a promising technology for future space missions, including satellite deployment in very low Earth orbit and for aircraft & missile propulsion system.
... At the University of Giessen, inductively coupled ion sources were adapted as a thruster for spacecraft propulsion systems [1]. Radio-frequency ion thrusters (RIT) generate the thrust by ejecting ions with a high velocity of up to 30 km/s [2,3]. ...
Ion propulsion systems with a small thrust can be used in space missions for highly accurate controllability while possessing low power and propellant consumption. At the University of Giessen, radio-frequency ion thrusters are miniaturized with thrusts in the order of micro-Newtons ( $$\mu$$ μ N-RIT). As the size of the thruster becomes smaller the plasma properties can not be measured inside a closed plasma chamber. The simulations are needed to investigate plasma properties like temperature, density profile which would aid further opimization. In this work, we discuss kinetic simulations of plasma inside the RIT-1.0 thruster using in-house developed PlasmaPIC code that incorporates Monte-Carlo collisions (MCC) and Direct Simulation Monte Carlo (DSMC) for neutral gas distribution. We briefly present the features of PlasmaPIC and simulation of stable plasma generation. We also show the influence of neutral gas and extraction properties for the RIT-1.0 thruster under consideration.
... A gridded ion thruster (GIT) is an electric propulsion device commonly used due to its high-specific impulse (> 3000 s) [1]. GIT generates thrust by selectively extracting only ions using ion optics (grids). ...
In this paper, we discuss various aspects of the plasma plume that forms when testing a Gridded Ion Thruster (GIT) inside a vacuum chamber. We use fully kinetic simulations of an ion engine using the hybrid MPI-CUDA code CHAOS which uses the PIC-DSMC method. The GIT is modeled as a separated source ion engine, with the neutralizer placed outside the ion source. The vacuum chamber is modeled as a symmetric rectangular domain, and the ion and electron sources are considered as being circular. We consider the plume to be made up of neutral Xenon atoms, singly charged Xenon ions, and electrons. The charge distributions in the plasma plume are calculated and analyzed at steady state. Comparisons are made to GIT plumes in space environments as well.
... They are a promising option for micro propulsion applications, such as on CubeSats. Their scalability is a key factor driving the interest in these thrusters for micro and nano satellites [2][3][4]. Electrospray thrusters can be easily downscaled and even benefit from it, which sets them apart from more traditional electric propulsion systems like Hall thrusters [5]. Another reason is that depending on the system configuration a neutraliser can be omitted from the propulsion system, thus reducing the already low power requirements further [2]. ...
An internally wetted capillary-type electrospray thruster design is presented. The capillary emitters are optimized for fabrication using 3D micro lithography and can achieve sub 10-micrometer capillary diameters with an aspect ratio of over 20. Also provided is a design for a completely modular integrated extraction electrode that comprises an electrode carrier produced by 3D micro lithography and a thin metal film. The electrode orifices, distance to emitters, and size are all customizable thanks to the modularity of the design, which is compatible with any electrospray thruster type. The design provides alignment precision within 5 micrometers of the emitter tip and electrode orifice. While our new electrode achieved reproducible extraction, instability is still present. The data on emission from these emitter-electrode stacks is presented, as well as in situ microscopic optical observation of individual emitters. The images demonstrate emission in multiple extraction modes, microfluidic behaviour of the capillaries in space-like conditions, and interactions of the emission modes with the integrated electrode.
