Is Nitrogen adequate as fuel for an ion-drive?

[keermalec]

One usually reads about Xenon or Mercury being used as fuel in ion-drives. What makes them adequate? I would prefer Nitrogen, as it is easilly found in the atmospheres of several planets. Can it be considered an adequate fuel? <div class="Discussion_UserSignature"> <p><em>“An error does not become a mistake until you refuse to correct it.” John F. Kennedy</em></p> </div>

 

[MeteorWayne]

F=ma.<br /><br />Is it adequate? It depends on how much power you have available. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[bdewoody]

As I recall nitrogen is very stable and would be difficult to ionize. <div class="Discussion_UserSignature"> <em><font size="2">Bob DeWoody</font></em> </div>

 

[heyscottie]

Even though Xenon is a noble gas, it is many periods further down, making it harder to ionize than nitrogen:<br /><br />Nitrogen first ionization energy: 1402.3 kJ/mol<br />Xenon first ionization energy: 1170.4 kJ/mol<br />Mercury first ionization energy: 1007.1 kJ/mol<br /><br />I don't know what other factors besides ionization energy make an ideal ion fuel. Gold, for example has an ionization energy of only 890.1 kJ/mol. Lithium and Sodium are among the easiest to ionize, at 520.2 and 495.8 kJ/mol, respectively.<br /><br />I expect something that is too reactive would be detrimental to engine design and fuel integrity, so noble gasses are likely to be favored over elements like Lithium and Sodium.

 

[heyscottie]

Correction:<br /><br />I meant to say<br /><br />........., making it EASIER to ionize than nitrogen.<br /><br />And yes, we are just talking about elemental nitrogen here, so there would be an extra step to break the strong triple bonds....

 

[keermalec]

OK, but does ionization use up an important part of the ion-drive's energy? Atomic weight of Xenon is 131 g/mol so ionization energy per kg is 8'900 J. In the case of Nitrogen this would be (1402+945/2)/0.014=134'000 J/kg.<br /><br />It seems like much much more but if one takes an ion-drive like the NSTAR, it provides 2.288 kW of energy for 0.00000302 kg of ejected Xenon per second. ie: 760'000'000 J/kg of Xenon (energy is used mainly for accelerating the atoms). Using up an extra 125'000 J/kg to ionize nitrogen shouldn't make a big difference or should it? <div class="Discussion_UserSignature"> <p><em>“An error does not become a mistake until you refuse to correct it.” John F. Kennedy</em></p> </div>

 

[ceetee]

Unless it's an elaborate hoax there's no need for ion drives http://emdrive.com/dynamictests.html

 

[docm]

It <b>is</b> bogus. Discussed ad nauseum several months ago, so please read this Wikipedia article first <i>then</i> if you have any questions use "search" and review what's already been posted before making people repeat themselves <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>

 

[ceetee]

I had read the Wikipedia article. I also viewed the dynamic tests, which if I recall rightly weren't there when the New Scientist article and responses came out - hence my reference to 'elaborate hoax'. <br />

 

[gunsandrockets]

Interesting question.<br /><br />But the proper forum for this question is probably Business & Technology rather than the Space Science & Astronomy forum.

 

[keermalec]

Ceetee that em drive produces 18.8 mN of thrust per kW. The NSTAR ion drive propduces 40.5 nM of thrust per kW, so it is still better.<br /><br />To verify the added benefit if having no reaction mass we need to know the weight of the experimental em thruster, which is not given. <div class="Discussion_UserSignature"> <p><em>“An error does not become a mistake until you refuse to correct it.” John F. Kennedy</em></p> </div>

 

[keermalec]

Anyone know what is the relationship between molecular mass of the propellant and drive thrust/isp in an ion drive?<br /><br />I would assume that, regardless of the nature of the propellant, the same number of particles goes through the perforated plate, with an energy equivalent to their electrical charge. Using the E = (1/2)mv^2 equation we should be able to calculate their velocity.<br /><br />isp will be velocity / 9.81<br /><br />thrust will be velocity * expelled propellant mass / second<br /><br />Xenon:<br />Atomic weight: 131 g/mol<br />ionic charge: +3<br /><br />Nitrogen:<br />Atmic weight: 14 g/mol<br />Ionic charge: +3<br /><br />Therefore a Nitrogen ion-drive should have an isp 3x higher than Xenon but a thrust 10x lesser.<br /><br />Anything wrong with this reasoning? <div class="Discussion_UserSignature"> <p><em>“An error does not become a mistake until you refuse to correct it.” John F. Kennedy</em></p> </div>

 

[CalliArcale]

Keermalec has requested that this thread be moved to Space Business & Technology, which I think is a very good idea. So I'm moving it now. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[kelvinzero]

I cant help you with the science, but this link mentions MPD thrusters using hydrogen and nitrogen, and has a table that mentions hydrogen.<br /><br />ion thrusters<br /><br />More on the <br /> mpd thruster

 

[spacester]

Hi Keermalec . . . in the FWIW category . . . <br /><br /> space storable propellants thread<br /> <div class="Discussion_UserSignature"> </div>

 

[keermalec]

spacester, there is no info on nitrogen as fuel for ion or electrical drives on the thread you linked to. I searched the whole 6 pages...<br /><br />Kelvin, thanks for the links, they are most interesting.<br /><br />There is nothing on using Nitrogen as propellant for ion drives. However, one does find that nitrogen can be used as propellant for magnetoplasmadynamic drives. Unfortunately, this is only theoretical. No MPD drives have been used yet.<br /><br /> <div class="Discussion_UserSignature"> <p><em>“An error does not become a mistake until you refuse to correct it.” John F. Kennedy</em></p> </div>

 

[docm]

One factor I haven't seen listed above is the liquid->gas expansion ratio of argon vs. nitrogen;<br /><br />Argon: 1:840<br />Nitrogen: 1:694<br /><br />which should translate into a higher volume of gas per volume of stored liquid. <div class="Discussion_UserSignature"> </div>