I'm fairly familiar with the design and operation of an ion engine, although I do have a two questions in regard to its operation. 1) Normally, an ion engine would be used in space (which is naturally a vacuum) and would output its given thrust. Prior to space flight, is there a need to maintain the vaccum within the chamber where the ionization occurs? 2) When looking at the ion optics, we see that there is 2 perferated sheets, with holes .1 mm range (if i remember correctly) on each sheet. I'm assuming that this would be enough to cause a 'leak' in the chamber, if it was a vacuum to begin with. Does the chamber need to be a vacuum in order for the ionization to occur? If yes, what is the highest pressure density that the chamber can be in order for ionization to occur? I guess more specifically my question is, can an ion engine function in a non vacuum environment? (obviously there would be a problem with weight to thrust, but i'm not concerened with that) I'm aware that NASA (it could of been the ESA) uses a vacuum chamber to test the ion engine. I'm just curious if it would function in a normal atmospheric pressure environment, and if not, could you balance it out by maintaining a certain vacuum within the chamber. Just thought of a 3rd question: Would an ion drive work under water?