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Physics, Astronomy & Cosmology / How would steam-powered ion thrusters work?
« on: 29/10/2013 17:09:39 »
Like any young man in those tender years just before turning 60 I'm fascinated with space-ships, particularly their engines and, very particularly, ion engines.
I've been following the NEXT thruster development at NASA (http://www.space.com/22916-nasa-ion-thruster-world-record-test.html) and made some observations (at least I hope that they're not assumptions!).
An ion thruster has a degree of "power to weight" about it in as far as the heavier the isotope then the more thrust it will deliver for a given exhaust velocity. A nice heavy ion like Xenon (Atomic Weight ~131) provides a nice reactive kick at velocity x while a little Oxygen ion (Atomic Weight ~16) provides little more than a tenth of that force for the same velocity. However, it takes a lot more energy to achieve that velocity with a Xenon ion. I do not know if the relationship between exhaust velocity and input power is linear and would welcome some feedback here. Would it only take a tenth of the power to accelerate an Oxygen ion to this velocity? Of course one would then only get a tenth of the thrust too.
Another observation was the relative absence of easily available Xenon.
Would it be possible to use Hydrogen and Oxygen created from electrolysis instead of Xenon? If the two gasses were ionised separately to remove all electrons before the resulting ions were accelerated then they would, effectively, be inert so there would be little risk of explosion. The Hydrogen ions would be travelling 16 times faster than the Oxygen ions but, eventually, they would grab a few electrons from the ether (lovely word!) and leave a very diffuse trail of steam in their wake.
The engines would be more complicated in as far as there would be two ionisation chambers and the thrust would be less. However, the power requirements would also be less. Furthermore water is plentiful.
I imagine it would be possible to ionise water vapour directly, in which case it would break down into separate Hydrogen and Oxygen ions anyway as there wouldn't be any electrons to form a bond. In this case the energy efficiency of first electrolysing water and then ionising the resultant elemental gasses versus simply ionising water molecules comes into play. Again, I do not know how these compare. Is it easier to ionise two elemental gasses than the compound such gasses constitute?
From the side-issues it's easy to see that I'm a dabbler, not a scientist, but I would be very interested to know if such an idea holds water (sorry, couldn't resist that). Is a steam-powered ion-thruster viable?
I've been following the NEXT thruster development at NASA (http://www.space.com/22916-nasa-ion-thruster-world-record-test.html) and made some observations (at least I hope that they're not assumptions!).
An ion thruster has a degree of "power to weight" about it in as far as the heavier the isotope then the more thrust it will deliver for a given exhaust velocity. A nice heavy ion like Xenon (Atomic Weight ~131) provides a nice reactive kick at velocity x while a little Oxygen ion (Atomic Weight ~16) provides little more than a tenth of that force for the same velocity. However, it takes a lot more energy to achieve that velocity with a Xenon ion. I do not know if the relationship between exhaust velocity and input power is linear and would welcome some feedback here. Would it only take a tenth of the power to accelerate an Oxygen ion to this velocity? Of course one would then only get a tenth of the thrust too.
Another observation was the relative absence of easily available Xenon.
Would it be possible to use Hydrogen and Oxygen created from electrolysis instead of Xenon? If the two gasses were ionised separately to remove all electrons before the resulting ions were accelerated then they would, effectively, be inert so there would be little risk of explosion. The Hydrogen ions would be travelling 16 times faster than the Oxygen ions but, eventually, they would grab a few electrons from the ether (lovely word!) and leave a very diffuse trail of steam in their wake.
The engines would be more complicated in as far as there would be two ionisation chambers and the thrust would be less. However, the power requirements would also be less. Furthermore water is plentiful.
I imagine it would be possible to ionise water vapour directly, in which case it would break down into separate Hydrogen and Oxygen ions anyway as there wouldn't be any electrons to form a bond. In this case the energy efficiency of first electrolysing water and then ionising the resultant elemental gasses versus simply ionising water molecules comes into play. Again, I do not know how these compare. Is it easier to ionise two elemental gasses than the compound such gasses constitute?
From the side-issues it's easy to see that I'm a dabbler, not a scientist, but I would be very interested to know if such an idea holds water (sorry, couldn't resist that). Is a steam-powered ion-thruster viable?