Ions

[Colt]

In astronomy last week we were reading a chapter on light, and to understand light, we have to understand the atom. I read the section on how ions are created and realized that the ion cannons in Star Trek/ Star Wars would never work. You would have to force the ionized material (say hydrogen) toward the target using something like magnetics. I also realized that this would affectively amount to an ion engine. If anyone has any input on this please post.

Sorry if I do not post in reply or am around much in the following weeks, something bad has happend tonight and I am not sure what time I will have to come here. Farewell for now. -Colt

[sacrelicious]

I still don't understand how that means they wouldn't work (although I have no doubt they are another poorly thought out sci-fi crutch).

what you describe as having to "force the ionized material (say hydrogen) toward the target using something like magnetics" is already a proven (albeit impractical) technology called the rail gun, the only difference being that the projectile(s) is(are) of a very small size.

as for that amounting to an ion engine, I am lost since I don't really know what an ion engine is, or how a rail gun that uses ions would effectively be one. if by that you are suggesting that the recoil of the ion cannon would amount to propulsion in the opposite direction, well there are alays means of dampening recoil, and while in a vacum none of them are 100%, with a little calculated thrust from you primary propulsion system (or even a secondary one dedicated to that purpose) you should be able to totally negate the effects.

but again, this is not a subject I am very knowledgable on, so please correct me where I am wrong /phpBB/images/smiles/icon_smile.gif

[darkhunter]

As far as I know, ion engines are around/under developement. Basically all they do is use an electrified grid to accelrate charged ions out the back of the ship to provide thrust.

Even thought the exhaust has a high velocity, it only imparts a small amount of thrust due to the small amount of material ejected, although it will provied a constant,low acceleration for a very long time which will result in a rather large velocity after a time.

Unfortunatly, TIE fighters as depicted are not possible.... /phpBB/images/smiles/icon_smile.gif

[David Hall]

The experimental probe Deep Space 1 (http://nmp.jpl.nasa.gov/ds1/) used an ion propulsion system. It was a resounding success.

In essence, an ion engine sends a stream of ionized particles out, causing a reaction in the opposite direction. It's a very efficient, but also a very, very weak, form of propulsion. The acceleration is very slight, maybe about as strong as the force of a piece of paper resting on your hand, but you can keep it up indefinitely, so over time you can achieve great velocities.

[sacrelicious]

I wonder how that compares (efficiency-wise) with a solar sail.

[darkhunter]

On 2003-02-09 08:29, sacrelicious wrote:
I wonder how that compares (efficiency-wise) with a solar sail.


Once the sail is built, the thrust is free--it just falls off with the sunlight hitting it (I think with the inverse square law...)

Ion drive would maintain the same thrust for as long as it's running.

Bottom line: close to a star,on a vector close to directly away from it, a solar sail would be the way to go. Away from the star, or on a vector tangent to the star, I'd use the ion drive.

Best of both worlds: Use the sail to brake and for initial acceleration away, and when the push of the sunlight falls off, furl the sail and use the ion drive for interstellar thrust and manuvering. Use a small magnetic scoop (like a Bussard ramjet without the fusion) to gather more fuel. Instead of trying to fuse it, just condense it into a usable form for the ion drive...

edit: spelling
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<font size=-1>[ This Message was edited by: darkhunter on 2003-02-09 10:15 ]</font>

[sacrelicious]

On 2003-02-09 10:13, darkhunter wrote:

Best of both worlds: Use the sail to brake and for initial acceleration away, and when the push of the sunlight falls off, furl the sail and use the ion drive for interstellar thrust and manuvering. Use a small magnetic scoop (like a Bussard ramjet without the fusion) to gather more fuel. Instead of trying to fuse it, just condense it into a usable form for the ion drive...

edit: spelling
_________________
Words define reality, but they can't alter it.

<font size=-1>[ This Message was edited by: darkhunter on 2003-02-09 10:15 ]</font>


I may be thinking of something else, but as I understand it that megnetic scoop thing would have to be extremely massive, whereas one would want to keep mass to a minimum in a solar sail powered vehicle, especially if that sail is being used to get you up to speed. true?

[darkhunter]

On 2003-02-09 10:24, sacrelicious wrote:


On 2003-02-09 10:13, darkhunter wrote:


<font size=-1>[ This Message was edited by: darkhunter on 2003-02-09 10:15 ]</font>


I may be thinking of something else, but as I understand it that megnetic scoop thing would have to be extremely massive, whereas one would want to keep mass to a minimum in a solar sail powered vehicle, especially if that sail is being used to get you up to speed. true?


I'm talking about something nice and small--don't know how big it would need to be, but since all we want to do it top up fuel I don't think it would have to be as big as if we were trying for fusion.

[sacrelicious]

well if I understand the principals correctly, you're basically just collecting stray atoms and particles from space. if that is the case, then couldn't the solar sail collect them much better being that it has a larger surface area? then all you need to do is to "scrape" them off the sail and shove em into the ion engine, correct?

this would make any megnetic scoop wholey unecesary.

<font size=-1>[ This Message was edited by: sacrelicious on 2003-02-09 10:59 ]</font>

[cable]

The acceleration is very slight, maybe about as strong as the force of a piece of paper resting on your hand, but you can keep it up indefinitely, so over time you can achieve great velocities.

looks like an ante pulling a jumbo jet .... /phpBB/images/smiles/icon_smile.gif

[darkhunter]

On 2003-02-09 10:58, sacrelicious wrote:
well if I understand the principals correctly, you're basically just collecting stray atoms and particles from space. if that is the case, then couldn't the solar sail collect them much better being that it has a larger surface area? then all you need to do is to "scrape" them off the sail and shove em into the ion engine, correct?

this would make any megnetic scoop wholey unecesary.

<font size=-1>[ This Message was edited by: sacrelicious on 2003-02-09 10:59 ]</font>


Don't see why it wouldn't work--if we've got the material strong enough to pull a spacecraft around, with porper care scraping wouldn't be a problem. We'll just have to see which works out lighter a strong sail with sracper or a weaker sail with a magnetic scoop....

[Kizarvexis]

I wonder. Would it be possible to combine a solar cell for making electicity with a solar sail for riding the solar wind?

Of course, then you would have a solar cell sail. Say that five times fast. /phpBB/images/smiles/icon_smile.gif

Kizarvexis

[nebularain]

On 2003-02-09 17:52, Kizarvexis wrote:
Say that five times fast. /phpBB/images/smiles/icon_smile.gif


That, that, that, that, that

(Sorry , couldn't resist. /phpBB/images/smiles/icon_biggrin.gif )

[Colt]

I think that some of you might have misunderstood me. I was making the point that in S-F the ion cannons are always depicted as basically a laser that does different things (i.e. short out electronics). I have heard of two methods for ion propulsion. One is to strip the ions and accelerate the ionized material out the back or to electricity through some sort of grating which uses the ions as propulsion and not any material (meaning it would have an indefinite fuel supply). -Colt

[Kizarvexis]

On 2003-02-09 18:34, Colt wrote:
One is to strip the ions and accelerate the ionized material out the back or to electricity through some sort of grating which uses the ions as propulsion and not any material (meaning it would have an indefinite fuel supply). -Colt



As I understand it (which admittedly isn't much /phpBB/images/smiles/icon_smile.gif) the fuel is ionized and then spit out at high velocities. (10% of light or so) Since you are spitting out a small quantity of ions at very high speeds, you get a steady small thrust that can be kept going for a long time to get the spacecraft to high velocities. The biggest advanage is the small fuel load, measured in pounds IIRC, but the biggest disadvantage is the small impulse, i.e. tiny amount of thrust (the aforementioned weight of a piece of paper). High velocities for the spacecraft are only reached after many, many hours/days of thrust.

I can't help you much on the Ion cannon issue from Star Wars though. Here is a page that describes Ion cannons from a fan perspective. It might help.

Turbolaser Commentaries (http://www.stardestroyer.net/tlc/Ion/index.html)

Kizarvexis


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<font size=-1>[ This Message was edited by: Kizarvexis on 2003-02-09 18:55 ]</font>