Question: Hi Charlie, Do you believe that the technology peope like you are working on now will ever be used on domestic vehicles, to propell us furthur, faster and more effeciently? Do you think that through the use of thrusters such as yours to be able to (eventually) enable us to have domestic flying machines / transport? Also, with the ion power that you use, how are you able to control the rate at which the thruster uses the fuel, or is is simply just a guesstimates as to the quantities? How are you able to keep the grid, through which the ions pass, negative, and stop it becoming neutral, by gaining other protons? Is there a chance that one of the (very) few particles in space could collide with it and make this happen? Thanks, Andrew

Charlie Ryan answered on 23 Mar 2011:

@08wooda thanks for your detailed (and long!) question! It really is great that you are so interested in my research and what i am doing!
Sadly the mini ion thrusters i am working on will never have enough power to propel a human-carrying vehicle within the earth atmosphere – the thrust produced from these mini ion engines is so small it would have no effect against air resistance, or the friction involved with turning the vehicles wheels.

Your question on how the flow rate is controlled though is excellent! To understand it i think i need to explain a little more about the thruster….
The thruster consists of a needle through which the liquid propellant is injected. Opposite the needle is a flat ring of metal to which a really high voltage (about 1000 volts!) is connected. This creates a really strong electric field between the needle and the metal ring, which makes the droplets ejected from the needle break down into ions. These ions are the pulled through the hole of the metal ring (as they are oppositely charged to the voltage on the ring). This accelerates the ions to really high speeds – about 10 km per second!!!
So – how do you control the flowrate? There are two basic ways:1. You push the liquid propellant through the needle using a pump: 2. the electric field itself will pull the liquid out. But the actual control is really, really difficult, and is something we are working on at the moment. Currently we find that the electric field pulls the liquid from the emitter too fast, and the whole thruster just gets covered with propellant. Not good!!

There is a problem also with the ions rather than going through the metal ring (the grid) they can get misdirected and hit it. We hope to solce this problem by making the metal ring hole a little larger so that they can’t whack into it!

Thankfully the amount particles in space is very small and shouldn’t affect the thruster or the metal ring (we call this the extractor electrode – because it extracts the ions, and is an electrode!).

One thing i didn’t mention was the size of the needle – its tiny! About 10 millionth of a metre, do impossible to see with the eye (i have to use various microscopes). Also, we hope to have hundreds of these tiny emitters firing at once, to increase the thrust force a little.

I hope that helps – and that i haven’t rambled too much! Any further question please ask!