Electrospray Emission out of a Laser Ablated Sheet of Polytetrafluoroethylene

Abstract

In recent years the use of small satellites has been becoming increasingly prevalent. The 21st century has seen governmental agencies, research organisations and private industries all regularly utilise satellites with a mass of less than 10kg for a variety of missions, due to their low cost and ease of use. With this increase in use comes a desire to increase the scope of missions for which these satellites can be used, which has spurred the development of a variety of new technologies. One of these areas that is currently being explored is the integration of on-board propulsion systems. These would allow the satellites to be used for a wide range of new missions, greatly increasing their versatility. However, in order for a propulsion system to be deemed suitable, it would need to be constrained by the low size and weight of the satellite. The presented work is an exploration of one possible option that meets these size and weight constraints: a type of thruster which relies on a process known as electrospray propulsion. Electrospray propulsion is a form of electrostatic propulsion, in which a stream of charged particles are emitted from an electrolytic liquid. This is achieved by the gen- eration of an electric field by a potential difference applied across the liquid, provided by a suitable power supply. The stream of particles originates from an emitter, which is typically less that 1mm in size, and generates a minuscule amount of thrust. As such, in order to maximise the thrust electrospray thrusters are typically comprised of an array of emitters, consisting of a large number of these emitters. These arrays are typically manufactured using techniques such as photolithography or deep reaction ion etching. The generation of these emitters is known for being complex and time consuming, requiring various pieces of equipment and different materials. This thesis details an examination of whether this process could be significantly simplified by using different manufacturing techniques and materials. More specifically, it details an investigation into whether an electrospray emitter could be created by laser ablating a flat sheet of dielectric material. This would allow for the process to require a lower cost and time investment, and would allow for the emitters to be manufactured out of a single sheet of an affordable material. This thesis describes the work done in order to manufacture, test, and characterise these emitters, which includes an examination of the effects of various geometric parameters, materials, and manufacturing techniques. The work described here consists of three main areas of investigation, namely practical work done with laser systems in order to manufacture the emitter, experimental work done with electrospray rigs in order to test the emitter, and computational modelling and simulation done in order to characterise the emitter. This investigation yielded a number of notable results. Through the use of laser ab- lation, a number of emitters with a size and shape suitable for electrospray emission were manufactured. It was found that the ideal manufacturing method was using the laser for a type of drilling known as trepanning drilling, as this yielded consistent suitable results which is necessary when manufacturing arrays of multiple emitters. A combination of experimental and computational work confirmed that these emitters could be used with a suitable power supply to generate electrospray emission, with a new method for esti- mating the power requirements devised. Furthermore, this examination revealed that polytetrafluoroethylene presented the ideal material, as it resulted in superior power requirements, and certain geometric parameters having less on a negative effect on the performance of the emitter. Finally, an experimental test of one of these emitters con- firmed that it is indeed possible to achieve electrospray emission out of an emitter that was manufactured by laser ablating a flat plate

Date of Award	1 Aug 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Olivier Allegre (Supervisor) & Katharine Smith (Supervisor)