Development of Ignition Unit for Liquid-fed Pulsed Plasma Thrusters

Lead Research Organisation: University of Southampton
Department Name: Electronics and Computer Science


The Liquid-fed Pulsed Plasma Thrusters (LPPTs) suffer from various disadvantages, such as low operational efficiency, propellant mass losses due to post ablative effects and failure of the system due to short circuiting of the traditional ignitor plug. The approach to solve these issues is to revisit the sub-systems for LPPTs, investigating favourable liquid discharge conditions under high vacuum at the fundamental level. The aim is to redesign the traditionally employed semiconductor spark plug, specifically for liquid-fed PPTs. However, the redesigned device may have a wider applicability.
The reduction in ignition voltage, among other advantages, has been preliminary tested; showing the advantages of using electrowetting in to enhance the electric field locally and ultimately induce discharge at lower applied voltages, as desired.
The second part of the project is to implement a new feeding system which, in conjunction with the ignition unit, would raise the operational efficiency of LPPTs; consequently making them more competitive with other electric propulsion systems.


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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509747/1 01/10/2016 30/09/2021
1807891 Studentship EP/N509747/1 10/10/2016 09/04/2021 Cristian Dobranszki
Description A suggested ignition method for liquid-fed pulsed plasma thrusters - surface flashover for the selected PFPE propellant. The ignition method investigated increases reliability of the discharge from a statistical perspective, decreases the electric field (amd hence the power) required for the ignition process itself and potentially increases the ablated material by the triggering system.
Exploitation Route The ignition unit developed will benefit the further research on liquid-fed pulsed plasma thrusters, as the ignition method investigated decreases the power requirements and hence increases the efficiency of the entire system. In turn liquid-fed pulsed plasma thrusters become more attractive for industry as their profitability increases monotonically with the overall system efficiency.
Sectors Aerospace, Defence and Marine

Description Research collaboration within H2020 PATH project 
Organisation University of Padova
Country Italy 
Sector Academic/University 
PI Contribution DC hollow cathode electron source is used for plasma generation
Collaborator Contribution University of Padova provided EM signal coupler
Impact A thermionic plasma source apparatus that has been developed for high-density gaseous plasma antenna applications. The plasma in the apparatus has been characterised for a range of operational conditions. It was found that a plasma source apparatus utilizing a thermionic hollow cathode can provide high-density enhanced plasma enhancing Gaseous Plasma Antenna (GPA) operational performance. This apparatus has demonstrated higher electron densities at low pressures than has been experimentally achieved before for such applications. Potentially this can allow GPA's to reach gain levels comparable to a metallic antenna. The system was successfully operated with xenon, argon, and krypton, with xenon providing the highest electron densities at low pressures.
Start Year 2017
Description 36th International Electric Propulsion Conference, Vienna, Austria, 15-20 September 2019 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Development of Electrostrictive Force-Feeding Sub-system for Liquid Pulsed Plasma Thrusters
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 µg 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.
Year(s) Of Engagement Activity 2019
Description Space Propulsion Conference 2018, Seville, Spain, 14 - 18 MAY 2018 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
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 increasing 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 vacuum breakdown model.
Year(s) Of Engagement Activity 2018