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thequestion

the thermoelectric generator is too heavy, why?

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Hello everyone, I wanted to know why the thermoelectric generator is so heavy, it weighs about 160 pounds, for me it's a lot, can you reduce that weight? :P

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12 hours ago, thequestion said:

why the thermoelectric generator is so heavy, it weighs about 160 pounds, for me it's a lot

Because Plutonium is really heavy :)

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They are full of very dense Plutonium ( bunch of different designs out there, but Ill run with this one for now).  That stuff is very dense. 

But looking at real world counterparts, if your 160 lbs is right, it's a bit less than twice the mass of comparable RTG's.   But given the rockets in KSP are somewhat over powered when compared to their real world counterparts, I think it's balanced just about right.   

As for price, the materials are expensive.  PU 238 costs around $8 million per kilo.  The Mars curiosity rover's RTG contains about 4 kilos of PU238, so that's about 32 million for just the fuel source alone, not even counting the rest of the generator or the development/production costs.  So if you look at the cost of a RTG vs the rest of a mission, KSP has the costs just about right, if not discounted. 

If we look at what the design is based from, the SNAP-19 RTG used on pioneer 10 & 11, then it's about 4 times the mass of that one.  Those contained 1 kilo of fuel each.  But I think they based the visual design off the SNAP-19, but made the electrical output more inline with the bigger RTGs, and they had very similar design looks to them. 

https://ne.oregonstate.edu/rebuilding-supply-pu-238

Edited by Gargamel

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Weight being the only limiting factor when using them; don't you think that'd be a bit overpowered compared to the other forms of electrical production?

Edited by Rocket In My Pocket

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2 minutes ago, Rocket In My Pocket said:

Weight being the only limiting factor when using them; don't you think that'd be a bit overpowered compared to the other forms of electrical production?

I think so, but I wanted to build different probes with this type of energy, only solar panels get boring...

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33 minutes ago, thequestion said:

Hello everyone, I wanted to know why the thermoelectric generator is so heavy, it weighs about 160 pounds, for me it's a lot, can you reduce that weight? :P

They're made that way on purpose, just like they're given their super-expensive price tag on purpose.  The idea is that what they provide (free electricity forever, without needing any fuel or solar input) is extraordinarily valuable, so for game-balance benefits they're made a bit awkward to use.

If you want to be able to have a "smaller RTG", here's a handy little ModuleManager snippet that can do that for you:

https://github.com/KSPSnark/SnarkTweaks/blob/master/stock/RTGAlternateSizes.cfg

...if you copy that .cfg file to anywhere in your GameData folder, it will add scaled-up and scaled-down versions of the RTG to your game.  The scaled-down version is only 13% the mass, size, cost, and power output of the original, i.e. it's only 0.011 tons, and puts out 0.1 EC/second of power.

 

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20 minutes ago, Snark said:

They're made that way on purpose, just like they're given their super-expensive price tag on purpose.  The idea is that what they provide (free electricity forever, without needing any fuel or solar input) is extraordinarily valuable, so for game-balance benefits they're made a bit awkward to use.

If you want to be able to have a "smaller RTG", here's a handy little ModuleManager snippet that can do that for you:

https://github.com/KSPSnark/SnarkTweaks/blob/master/stock/RTGAlternateSizes.cfg

...if you copy that .cfg file to anywhere in your GameData folder, it will add scaled-up and scaled-down versions of the RTG to your game.  The scaled-down version is only 13% the mass, size, cost, and power output of the original, i.e. it's only 0.011 tons, and puts out 0.1 EC/second of power.

 

I'm going to do this procedure but only after, it's that I'm busy now, but when I do this file I'll tell you :)

Edited by thequestion

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4 hours ago, Snark said:

They're made that way on purpose, just like they're given their super-expensive price tag on purpose.  The idea is that what they provide (free electricity forever, without needing any fuel or solar input) is extraordinarily valuable, so for game-balance benefits they're made a bit awkward to use.

If you want to be able to have a "smaller RTG", here's a handy little ModuleManager snippet that can do that for you:

https://github.com/KSPSnark/SnarkTweaks/blob/master/stock/RTGAlternateSizes.cfg

...if you copy that .cfg file to anywhere in your GameData folder, it will add scaled-up and scaled-down versions of the RTG to your game.  The scaled-down version is only 13% the mass, size, cost, and power output of the original, i.e. it's only 0.011 tons, and puts out 0.1 EC/second of power.

 

thank you, it worked here, I even made a copy to save ;)

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Did you really convert metric tons to pounds? That is only something us Americans would do. But 0.08 t is pretty light for free juice. Seems too light and I actually feel like I'm cheating when I put too many of these.

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Head canon: because despite their fearless attitude to crashing and exploding, Kerbals are very, very careful with nuclear stuff, and use lots of lead shielding.  Did you know that inside the covers, the actual reactor core of the LV-N is only 2cm cubed? :sticktongue:

Reality: it's a game balance thing.  You work through the tech tree to get it, then decide according to cost and mass against simplicity and convenience.  Also the nuke generator is more useful in the outer parts of the star system, whereas close to the Sun you get better returns from your solar panels.  Some mods (Planetary Bases, if I remember right, for one) have larger thermo-electric generators that are way more expensive and massive, but are really good for fit-and-forget so you don't find the scientists at the base lost power and gave up processing science because it's night, or you forgot to open the panels.

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18 hours ago, Gargamel said:

They are full of very dense Plutonium ( bunch of different designs out there, but Ill run with this one for now).  That stuff is very dense.

On 8/6/2018 at 1:33 AM, Marschig said:

Because Plutonium is really heavy :)

Well, there's the reason why the RTG is heavy in the game, and then the reason why they're heavy IRL.  Different beasties entirely.

This is a gameplay thread, so "why is it heavy in-game" is probably more on-topic, and I think that's already been addressed here.  ;)  The IRL reason why RTGs are heavy, though, has nothing to do with the fact that plutonium happens to be dense.  It's a red herring.  Explanation below, in spoiler because this is getting kind of off-topic and I don't want to derail the thread with discussion that would better live in the Science & Spaceflight thread.

Spoiler

The way to design an RTG is,

  1. How many watts of heat output do we need?
  2. Okay, well, we've got this stuff that produces heat.  How many watts per kilogram does it make?
  3. Divide #1 by #2 to figure out how many kilograms of the stuff we need.
  4. Now surround it with radiation shielding, thermocouples, radiator fins, and whatever other paraphernalia is needed to ensure that it, 1. produces electricity, and 2. won't kill you.
  5. That determines how heavy the RTG is.

The density of the radioactive material is fairly irrelevant, at least in terms of determining how much of the radioisotope you need.  It's not as if they're going by volume-- "Okay, we need a gallon of plutonium... how much does that weigh?"  (If anything, an extra-dense material makes the RTG slightly lighter, because it means the volume of the radioisotope itself is smaller and therefore all the rest of the RTG doesn't have to be built as large in order to contain it.)

If, for example, plutonium happened to produce 100 times the watts per kilogram... then you'd only need 1% as many kilograms of it, regardless of whether it's the same density as water, or 20 times heavier, or 1000 times heavier.  The fact that it's dense just means that the RTG gets smaller, not heavier.

Or, to paraphrase:  "Which weighs more, a kilogram of Styrofoam or a kilogram of plutonium?"  Answer:  The same.  A kilogram;) 

In short:  the reason RTGs are heavy isn't because the radioactive material is dense.  It's because the radioactive material produces a certain amount of power per kilogram, and therefore you need enough kilograms to meet your power requirements.

 

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