ion thruster

[gary85]

HI

im playing campagin i unlocked ion engine and it is great but i didnt unlocked radioisotope generator yet , is 1 generator enugh to power ion thruster? and also im planing mission to eeloo but idk if solar panels will do so far away from sun . Normally i use 2 gigantor on my satelites but for that distance it will be better to use more smaller panels?

 

Edited January 8, 2016 by gary85

[MalfunctionM1Ke]

If I recall correctly, the RTG's only produce a fraction of the power any solar sail would.

The Wiki might be usefull.

RTG's produce everywhere
0,75 E/sec

Gigantor Solarsails around Kerbin
24,4 E/sec

The Ion drive under full throttle consumes 8,74 E/sec which means you need 12 RTG's which would weigh 0,96 tonnes and would cost 279,600 Funds

I am not sure on this, but if my calculations are correct, you would need about 16 Gigantor Solarsails to have full thrust around Eeloo.
But I might be wrong on this one.

Here is a the wiki-article about electric charge that also deals with the power output of solarsails:
http://wiki.kerbalspaceprogram.com/wiki/Electric_charge#Solar_panels

You could use only 2 gigantor solarsails, but keep in mind, that your probe would only run on a fraction of the thrust, which just means, that it would take more time to complete your maneuver.
This is where huge battery banks come in handy.

Edited January 8, 2016 by MalfunctionM1Ke

[Gaarst]

One RTG generates 45 EC/min or 0.75 EC/s. An ion thruster at full thrust uses over 8 EC/s. So, no one RTG is not enough.

And solar panels are almost useless past Dres.

Edited January 8, 2016 by Gaarst

[gary85]

so 12 will do , hmmm 600k for 1 satelite hmm

Ok thx for quick reply.

edit oh ye 300 k i saw bough price not unit.

Edited January 8, 2016 by gary85

[Stratzenblitz75]

Short answer: No. An ion engine consumes 8.74 EC/s at full throttle, while a single radioisotope generator only provides 0.75 EC/s. If you want to run the ion engine at 1/10 throttle, then yeah, one generator would be enough, but I doubt anyone has the patience for that.

Instead, the best solution for ion engines at that distance is probably just to use batteries. Z1-k batteries can provide 1000 EC each, which gives an ion engine almost 2 minutes of burn time. Adding 5 or so batteries would provide an ion engine for almost 10 minutes, which should be plenty of time to do an insertion burn (but It depends on how heavy your probe is). On top of that, the batteries are very lightweight; the previously mentioned Z1-k batteries have a mass of 0.05 tons, which is far less massive than a single gigantor solar panel. With this setup, you could probably get away with a single RTG to charge the batteries in between burns. 

If you want to see this setup in action, check my signature for my Jool-5 mission. There, I used an ion engine + batteries + a single small solar panel to power my return stage.

 

[Foxster]

My setup for a very long range craft with ion engines usually looks something like this:

 

That is 5250 Xenon,  a bit over 105 LF+O (for the fuel arrays), two large fuel arrays, four ion engines and PB-NUK as power backup. That's 5000+ dV on a small craft, with decent TWR. 

Or you could use two ions and one fuel array for more dV but a bit lower TWR. 

 

Edited January 8, 2016 by Foxster

[MalfunctionM1Ke]

3 minutes ago, Foxster said:

My setup for a very long range craft with ion engines usually looks something like this:

 

 

That is 5250 Xenon,  a bit over 105 LF+O (for the fuel arrays), two large fuel arrays, four ion engines and PB-NUK as power backup. That's 5000+ dV on a small craft, with decent TWR. 

 

Thats a really interesting Setup, I never quite thought about transforming LFO to power an Ion-drive though.
I might give that a try

[Foxster]

2 minutes ago, MalfunctionM1Ke said:

Thats a really interesting Setup, I never quite thought about transforming LFO to power an Ion-drive though.
I might give that a try

Hope you get on OK with it. It's much less fuss than solar panels, which don't work at the outer planets anyway. 

The multiplier of Xenon to LF+O is 0.02.  

Ion engines need a max of 8.74 charge per sec and fuel arrays supply 18, so a ratio of two engines to one array is OK. 

[cantab]

I was able to operate my ion ship at Jool on solars, albeit at severely reduced throttle. And I'm pretty sure that was after the solar panel curve was corrected. If you build for it you should be alright.

[Mastikator]

It's worth mentioning that around Eeloo you probably won't need high accelerations anyway, you could probably get away with thrusting at lower magnitude for everything but landing (which you might not even be able to do with just ion thrusters). So even if one RTG isn't enough to power one ion thruster you can just power at 16% with a 4x physics time warp.

[Foxster]

You can just about manage a landing and re-orbit on Eeloo with ions but the payload has to be minimal. Wouldn't be much of a mission. 

Last night I took a spin out that way and just added a little LF+O stage for the landing and partway back to orbit. 

[Fearless Son]

58 minutes ago, Foxster said:

That is 5250 Xenon,  a bit over 105 LF+O (for the fuel arrays), two large fuel arrays, four ion engines and PB-NUK as power backup. That's 5000+ dV on a small craft, with decent TWR. 

Or you could use two ions and one fuel array for more dV but a bit lower TWR. 

Your design is really cool, and using LF/O-fed fuel cells to power ions is something I have given idle consideration to, but I have to wonder, does the extra mass of the fuel really justify the ions and xenon tanks?  Like, I thought that the point of ion engines was to get great range and reduce the total mass of the craft, and that if you start putting fuel back in you defeat the purpose of having ion engines to begin with.  

But I am guessing for the payloads you build, you have gotten a pretty good handle on being on the favorable side of that balance.  

[Foxster]

1 minute ago, Fearless Son said:

Your design is really cool, and using LF/O-fed fuel cells to power ions is something I have given idle consideration to, but I have to wonder, does the extra mass of the fuel really justify the ions and xenon tanks?  Like, I thought that the point of ion engines was to get great range and reduce the total mass of the craft, and that if you start putting fuel back in you defeat the purpose of having ion engines to begin with.  

But I am guessing for the payloads you build, you have gotten a pretty good handle on being on the favorable side of that balance.  

Well, the big solar panels are pretty heavy anyway and these days their output is not good as you head away from the sun, so you need a few. You don't need much LF+O to run the fuel cells. But the biggest advantage for me is that I just know the craft will carry on working all the time i.e. no problems with eclipses and awkward orientation during burns. 

You can get creative and mix up fuel cells, batteries and solar panels to achieve some minimisation of mass but to be honest I can't be bothered. That last craft posted above is only 7t, it's not hard to get that kind of payload to Eeloo. 

[Geschosskopf]

I find the ion engine rather useless IN CAREER due to its cost and late appearance on the tech tree.  Granted, both figures are realsitic given that ion engines are pretty recent things and a lot had to be researched and all before they were possible.  However, its low thrust severely limits its usefulness, basically just small probes and minimalist landers for very low-gravity worlds.  Small probes are nice early in career games but not of much value by the time you unlock ion engines, and by then ypu've probably already been to Gilly, too.   Thus, the only real application of ions in a career game is landing on Pol or Bop if you haven't been there already, but for these you can make a chemical rocket that costs way less, and is less complicated to run (no fuel cells).  Thus, I find ion engines only useful in science or sandbox games where money isn't an issue.

[gary85]

ye i just tested sateltie with 2 ant engines , it got less delta-v but it is 2 x cheaper + i can put 1 fuel cell and send it everywhere i want i guess i reserve ion for moho.

[gogozerg]

Ion drive at full power is nice when solar power is high. (Typically good when navigating around Moho)

Otherwise, I never use it. The game is just not meant for it, when "accelerating on rails". You would need a progressive slow ion thrust for probes heading to outer planets.

[Plusck]

I've sent an ion-powered survey scanner to Eeloo, forgot to add the RTG and left it with my original design with 8x 6-panel solars.

That means I'm left with under a sixth of the thrust of the ion, but with the supreme slowness of the orbits out there it is not really a problem - it just means making more of an effort to match orbits with Eeloo before you make the encounter, otherwise the capture process would be painful. I have enough batteries for a full burn of about 250m/s (iirc) as it is.

However, even if I had added an RTG or two, it would only have improved the situation slightly and at great cost.

Edited January 10, 2016 by Plusck