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Pulsed Plasma Thrusters (PPTs) were the first Electric Propulsion devices ever to be employed in an actual space mission, and continue to be used today when simplicity, robustness and scalability to different power levels are dominant requirements. Therefore, they find a natural niche of application in small-spacecraft missions, where mass, volume and onboard power are at a premium, in spite of their low overall efficiency and not fully understood physical operating principles. While PPTs have drawn renewed attention from the international space community after a long hiatus, this has been generally limited, until now, to low Delta-V, low total impulse missions. In this paper, we investigate the possibility of performing high Delta-v, high total impulse missions, such as orbit raising or even deep-space missions, using PPTs onboard small spacecraft.

An electrostatically driven pressure valve has been successfully developed based on the electrostrictive force, delivering propellant to the discharge chamber via an open-end conduit, free of any moving parts. The proof-of-concept unit has been built and demonstrated stable operation. It was shown that the conventional theory of electrostriction in liquid dielectrics is applicable for the device. The electrostatic pump has been designed for a coaxial liquid-fed micro pulsed plasma thruster prototype operating in the 1 - 2 J energy range. Active mass dosage capability is proven as a function of applied voltage and pump operational time, introducing a new class of electronically controlled feeding systems. Experimental measurements demonstrate a minimum achievable mass bit ranging from 77 to 164 ug using the voltage-controlled operation. Moreover, the pump is able to deliver up to 1 mg of propellant for a single shot. In addition to the active control, the mass flow rate can be passively adjusted by changing the capillary dimensions (radius and length), conduit material and the propellant dielectric properties.

A novel high-current heaterless hollow cathode (HHC) has been designed, constructed, and tested, with the developed system successfully demonstrating operation up to 30 A. This system overcomes the need for excessive ignition voltages or propellant pulsing, by utilising a reduced keeper orifice that enables ignition with

Xenon is the preferred propellant for electric propulsion thrusters, providinghigh thruster efficiency and long life. However, xenon is very expensive and has limited availability, which could impose serious constraints on the use of electric propulsion in some future missions. This report investigates the effect on mission cost of operating a gridded ion engine on either xenon, krypton or a 1:4 Xe/Kr mixture. Calculations of payload fraction, propellant mass, thrusting time, propellant cost, and propellant-related mission cost have been performed over a range of mission Δvs (1-5 km/s) using two different approaches: fixing the thrust, which leads to increase required power over xenon, and fixing the power available for the electric propulsion system, which leads to loss in thrust.The former approach results in significant improvements for propellant cost, but either no substantial advantages can be obtained on the overall mission cost or the cost reduction can be achieved only at higher velocity increments, which are not relevant for typical mission Δvs. The latter approach produces a relatively small (within 10% over xenon) cost reduction but at a cost of increased thrusting times. If the "New Space" approach (mega constellations) is considered, which implies a sensible reduction in the hardware cost, the outcome of the analysis is completely different and alternative propellants become advantageous over xenon for the considered Δv range (1-5 km/s).

In this work electrical resistance measurements were utilized as a mean to assess the dispersion of Graphene Oxide nanoinclusions into CFRP laminates. This approach involves resistance measurements in the through-thickness and transverse directions of the laminates. Measurements were conducted in CFRP laminates containing Graphene Oxide dispersed into the epoxy matrix with filler contents of 1wt% and 5wt%. The morphology of the samples was examined by means of optical microscopy and scanning electron microscopy. The obtained results suggest that at low filler contents, 1wt%, the dispersion is uniform into the bulk of the sample, while at higher filler loadings, 5wt%, there are indications of non-uniformity due to the formation of areas with higher filler concentration.

Within the European GIESEPP project framework, a comparative overview of the properties of propellants suitable for electric propulsion and an assessment on the impact of substituting Xenon as operating medium will be presented in this paper.A preliminary qualitative and quantitative analysis will be performed to assess the effects on the existing systems and to ensure their functionality with alternative propellants.Based on a trade-off between performance and compatibility, Krypton was selected as main alternative and Iodine as secondary (due to possible compatibility problems). However, more extensive investigations will be required to address all the possible aspects of the propellant change.

Prediction of hollow cathode orifice is one of the most important goals of a well performed design; engineers need simple design tools for a quantitative prediction of the orifice erosion. A recent work suggests the use of an analytical solution in contrast to two-dimensional numerical models, generally very hard to develop. In this work, a global model is coupled with an analytical orifice model. The orifice model solves a simplified quasi-one dimensional flow with the use of mass balance for each species, diffusion drift equation in the radial direction and convection drift equation for ions in axial direction. The use of Dirichlet boundary conditions for plasma and neutral densities, extracted current and plasma potential allows for a full characterization of quantities involved in the erosion sputtering of the orifice wall. Comparison are given with experimental data and existing literature for neutralizer NSTAR at full power with extracted 3.26𝐴 and mass flow of 3.7×10^−7 𝑘𝑔/𝑠.

Solid-fed Pulsed Plasma Thrusters (PPTs) are the only mission employed devices to-date, although they suffer from low-efficiency and lifetime limiting post-ablation effects; oppositely, gas-fed PPTs offer high efficiency (~15 – 50 %) and no contamination; however, they are subject to propellant leakage issues, difficult ignition synchronisation and higher implementation costs. Liquid-fed PPTs require the sub-systems to be revisited to adapt the device to the intrinsic benefits of fluid propellants; it is suggested to use electrowetting to initiate Perfluoropolyether (PFPE) motion under the influence of electric fields. Employing a combination of dielectric materials, locally enhanced electric fields may be manipulated to decrease the ignition voltage and consequently increase efficiency. Preliminary measurements of PFPE bulk breakdown and the electrowetting-tip ignition at the liquid surface leading to reliable ignition voltages of 8.98 ± 0.86 kV are reported. The significance of PFPE motion at the cathode/vacuum interface is discussed and a vacuum breakdown mechanism relevant to the system is hypothesized, based on the MDV vacuum breakdown model.

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The incorporation of composite CFRP in wind turbine blades while to allows for longer and lighter blades challenges the efficiencyectiveness of their lightning protection system. The electrical anisotropy of these CFRP materials is a key factor and affects their performance. The present study investigates the influence of adding Graphene Oxide (GO) nanoparticles in to CFRP as a means to improve their electrical conductivity in the transverse and through thicknessthrough-thickness directions. Epoxy resin containing GO in filler contents of 5wt% and 6wt% was prepared and infused in unidirectional (UD) laminates. The GO nanofiller was dispersed in the epoxy resin prior to the infusion by means of speed mixing. The sample morphology was examined by means of optical microscopy. DC electrical resistance measurements were conducted in the transverse and through thicknessthrough-thickness directions to quantify the influence of the nanofiller. In For both filler volume contents loadings an increase was observed for both the transverse and through thicknessthrough-thickness directions compared to the neat CFRP.

The through-thickness thermal conductivity of unidirectional CFRP laminates was examined by means of a steady-state technique based on the Guarded Hot Plate (GHP) method. By establishing the one-dimensional heat flow through the sample and measuring the heat flux the thermal conductivity was determined. To validate the technique, measurements were conducted in two different materials with well-defined values. PTFE and Fused Silica samples were employed as reference materials. Calibration runs showed good correlation with the expected literature values for both of the reference materials. Unidirectional CFRP laminates with a fibre volume content of 57% were manufactured using Vacuum Assisted Liquid Resin Infusion in three different thicknesses to assess the measuring capabilities of the apparatus. Consistent results were obtained for all three laminate thicknesses thus validation the efficiency and accuracy of the technique.

The motion of an arc plasma in a quenching chamber has a significant influence on the interruption performance of low-voltage switching devices (LVSDs). It is necessary to build an arc modelling tool, which can predict an arc behavior during an interruption process, to save development cost and time. This paper presents a numerical model of an arc plasma in LVSDs, which can reduce complexity and calculation load of an arc simulation by avoiding fully coupled modelling between fluid dynamics, and electromagnetism. There are two steps in the proposed arc modelling; the first is the finite element analysis of Lorentz force generated by nonlinear ferromagnetic material and current path in a quenching chamber, the second is the finite volume analysis of arc motion with consideration for fluid dynamics and heat transfer. This arc modelling also takes into account a contact motion, potential drops in the sheath layers of splitter plates and plasma radiation. It is shown that the simulated result has a similar trend with experimental data in terms of the arc motion as well as current and voltage waveforms.

Arc modelling is an efficient tool for predicting the switching performance of low-voltage switching devices (LVSDs) prior to testing real products. Moreover, it offers a valuable design aid in the improvement and optimization of LVSDs. This paper focuses on the investigation of evaluators that predict re-ignition phenomena and the numerical simulation of arc characteristics in LVSDs. It is found that the probability of re-ignition depends strongly on the ratio of the system voltage to the exit-voltage. The implemented 3-D arc model is based on conventional magnetohydrodynamics theory and takes into account the properties of air that vary with temperature and pressure, motion of the contact, arc root formation and plasma radiation. The simulated results are compared with experimental data to validate the proposed arc model and the voltage trends show agreement.

The impact of a lightning strike causes a short high electrical current burst through Carbon Fibre Composites (CFC). Due to the electrical properties of CFC the large current leads to a rapid heating of the surrounding impact area which degrades and damages the CFC. It is therefore necessary to study in detail the thermal response and possible degradation processes caused to CFC. The degradation takes place in two ways, firstly via direct mechanical fracture due to the thermal expansion of the CFC and secondly via thermo-chemical processes (phase change and pyrolysis) at high temperatures. The main objective of this work is to construct a numerical model of the major physical processes involved, and to understand the correlation between the damage mechanisms and the damage witnessed in modern CFC. For this work we are only considering the thermo-chemical degradation of CFC. Bespoke numerical models have been constructed to predict the extent of the damage caused by the two thermo-chemical processes separately (e.g. a model for phase change and a model for pyrolysis). The numerical model predictions have then been verified experimental by decoupling of the damage mechanisms, e.g. the real Joule heating from a lightning strike is replaced by a high power laser beam acting on composite surface. This was done to simplify the physical processes which occur when a sample is damaged. The experimentally damaged samples were then investigated using X-ray tomography to determine the physical extent of the damage. The experimental results are then compared with the numerical predictions by considering the physical extent of the polymer removal. The extent of polymer removal predicted by the numerical model, solving for pyrolysis, gave a reasonable agreement with the damage seen in the experimental sample. Furthermore the numerical model predicts that the damage caused by polymer phase change has a minimal contribution to the overall extent of the damage.

Various numerical techniques have been applied to multidimensional field diffusion problems with front-type behaviour, moving boundaries and non-linear material properties. Advantages and implementation challenges of the methods are discussed with special attention paid to conservation properties of the algorithm and achieving accurate solutions close to the moving boundaries. The techniques are evaluated using analytical solutions of diffusion problems with cylindrical symmetry.

A finite element model has been used to study potential distribution and current flow paths in highly anisotropic composite materials. Unexpected results are obtained, which are found consistent with minimising of Joule heat release in the material.