Possible dumb question on Ion fuels :)

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mstrozier06

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I know there is no such thing as a dumb question, but hmmm. Well here goes <img src="/images/icons/smile.gif" /><br /><br />I understand Xenon is used primarly with Ion driven engines for space flight. But I was curious on something else. Is it possible to have both ion and cumbustion engines at the same time on a craft?<br /><br />Let me explain what I am asking as my question doesn't seem to read right to me.<br /><br />I know if you took a 9 volt batter, have two wires and place each on each terminal on the battery, then plan the other ends in a cup of water, you will see the one of the ends bubble up releasing oxygen and hydrogen back in gas form. If you place a match above the water you can see it affecting the flame of the match. Neat little trick.<br /><br />So, if you have a tank of water, and give it enough of a charge to release hydrogen and oxygen to flow into a chamber to be ionized, then it rapidly leaves this chamber (whicn on a normal engine would exit the craft giving it it's thrust) but now enters into a cumbustion chamber to be ignited and released.<br /><br />Would this work? Would this yeild better results than the normal ion engine process and still yield good fuel supply?<br /><br />I was primarly curious if with the added cumbustion would it generate more thrust?<br /><br /><br />Or is this a dud of an idea <img src="/images/icons/smile.gif" />
 
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strandedonearth

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Ion engines make low thrust on tiny amounts of reaction mass (propellant), for a high ISP (effiency). Combustion rocket engines produce large amounts of thrust using lots of propellant (fuel + oxidizer) for a lower ISP. So I'm thinking that "ion exhaust" probably wouldn't provide enough flow rate for decent combustion thrust.<br /><br />I've been wondering about trying it the opposite way, adding ion accelerator grids at the end of the rocket nozzle to add a little more velocity to the exhaust gas. The gas would also have to be ionized first. To power the grids, I was thinking thermocouples, with the hot side inside the engine bells and the cold side inside the tanks.<br /><br />The two problems I see are ionizing the exhaust and finding grids that would survive in a rocket blast.
 
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vogon13

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The V-2 had steering vanes in the rocket exhaust. They did erode slowly in the heat, but they also lowered the efficiency of the rocket significantly. <br /><br />So finding grids that survived the heat <b>and</b> did not cause a net drop (let alone an increase) in rocket efficiency would be a real trick.<br /><br />Also, to appreciably increase the thrust of the rocket with accelerateor grids, the power requirements would be large.<br /><br />Like really, really large.<br /><br />Big . . . . <br /><br />Enormous really.<br /><br /><br />Like bigger than large and then some.<br /><br /><br /><br /><br />(Just applying this to the Space Shuttle main engines would require a significant percentage of the total US electrical generating capacity)<br /><br /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>
 
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darkenfast

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In response to your question above, I believe that the energy required to break the water down into it's constituent hydrogen and oxygen, will always be slighty greater than the energy released by the two elements combining to form water again (silly old universe and its rules!). It's a bit like lifting oneself by one's own bootstraps.
 
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mstrozier06

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Thanks for the information. I've found something similar to what I was asking for -- VASIMR that NASA is working on. My question was rather aimed at a hybrid type motor that working on both parts.<br /><br />As someone stated, the power to break down the water alone would be too big. And from what I've read on VASIMR the power required would be massive in that area as well.<br /><br />Solar power I guess could work for these engines, however in the inner solar system. And side note, guess my question wasn't rather dumb at all haha <img src="/images/icons/smile.gif" /> I just think way to much. Sometimes it drives my wife crazy over this stuff <img src="/images/icons/smile.gif" /> but it's who I am haha.<br /><br />Thanks
 
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