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[url][/url] I just pledged it. Had a look at it and actually the first thought which struck my mind: "Why did no one else ever get this idea?". The concept of replacing xenon with water especially appeals to me since water is very common around the solar system. Allows for easy refueling of spacecraft. Have a look & discuss.

 I just pledged it. Had a look at it and actually the first thought which struck my mind: "Why did no one else ever get this idea?". a) Xenon is a gas and water is liquid. Meaning that the same mass of water takes more space than the same mass of xenon, because liquids cannot be compressed. b ) It's not easy to create ions from water, especially in space You need a lot of electric power, for a proccess known as "Electrolysis of Water" ([url]http://en.wikipedia.org/wiki/Electrolysis_of_water[/url] and up untill now solar collectors weren't very efficient. Besides the hardest part of space exploration, is climbing the first 200 km, in order to leave the gravity well of Earth. In fact the technology they propose is known for decades, It's called "Electrically Powered Spacecraft Propulsion" ([url]http://en.wikipedia.org/wiki/Electrically_powered_spacecraft_propulsion[/url] but it's also known as "Ion/Plasma Thruster" ([url]http://en.wikipedia.org/wiki/Ion_thruster[/url]

I am well aware of electrolysis and ion thrusters  If you want to compress xenon to a sufficiently high density to equal water, you need a considerable pressure vessel. Which also brings its own share of problems. On the other side, the power needed for electrolysis is something which likely is the main cause this hasn't been done before As you mentioned.

 If you want to compress xenon to a sufficiently high density to equal water, you need a considerable pressure vessel. You do not need to. You will compress it just enough to save some space.

I do not exactly see the advantage then in having it as a gas instead of liquid

 I do not exactly see the advantage then in having it as a gas instead of liquid  Less volume in the spaceship?

Less volume in the spaceship? Could you explain further? I think I am missing a key element you are trying to convey. It sounds contradictory to me since compressing it would require a pressure tank, which would increase mass. In space there is no friction, but there still is mass of objects.

You will not press it, to reach liquid state. Just enough to save space, without having to add mass, for pressure keeping systems. 

Hmmm, well, I still do not entirely understand, but that might also be related to me still being in semi-zombie mode due to just waking up. But for that matter, I do see a point in gas being used (instead of water), since gas like xenon is quite easy to turn into plasma. At least, with water you need to do electrolysis which adds mass and not to forget, power consumption/drain, which would require better power generation. I think that is a very big concern in this project.

 which would require better power generation. I think that is a very big concern in this project. Yes. And even if you use optimised solar collectors, the further you get away from the sun, the less power output you have. That's why for long missions they use isotope generators (which is a form of nuclear power). Hmmm, well, I still do not entirely understand, but that might also be related to me still being in semi-zombie mode due to just waking up. Try squizing a syringe. You can compress the air in it, nearly one third of the original volume.

I think I see what you are meaning