PB-NUK Radioisotope Thermoelectric Generator

[Eagleye]

Hi,

I want to make a rover that can run all day using the PB-NUK Radioisotope Thermoelectric Generator (it's this one http://wiki.kerbalspaceprogram.com/wiki/PB-NUK_Radioisotope_Thermoelectric_Generator), but I don't understand how it works. I've been searching on the internet for some time, but unfortunately, I didn't find anything useful. Can someone please explain to me how to properly use it? Thanks for your help.

[Starman4308]

How to use the PB-NUK:

Step 1: Put it on the rover

Step 2: Enjoy 0.75 EC/sec per RTG forever. In the real world, RTGs decay over time, in large part because your radioisotope, usually Pu-238, has a half-life (~90 years for Pu-238), but KSP doesn't model RTG decay.

There may also be decay of the thermoelectric elements, but there's no getting around the radioisotope decay.

Step 3: Try not to smash your RTG into a cliff wall.

Overall, for gameplay, the RTG is very expensive, and has a poor electricity production-to-mass ratio, but that electrical supply is completely independent of sunlight. As such, they're popular for night-time operations, and operations out near Jool and Eeloo, where solar panels diminish to near-uselessness because of how far from Kerbol you are.

If you're into mods, Near Future adds some full-up fission reactors, which provide electrical output (per kilogram) on par with solar panels, but require cooling, and they do use up enriched uranium.

[Eagleye]

Thanks for the help, I always thought it produced more EC and didn't understand why my rovers didn't really work as good as I expected. BTW I play sandbox , so I don't have to worry about being restricted with parts and/ or loosing all the money because I am able mess up literally anything. Also, I will check the mod because it looks interesting.

Edited June 21, 2017 by Eagleye

[nascarlaser1]

Using USI core by @RoverDude also adds in different nuclear reactors of different sizes. Not sure how they compare to near future though (I only used the USI stuff)

[Zhetaan]

@Eagleye:

For some more detailed information, the RTG works in the code by having electrical output but requiring no input; it just creates ElectricCharge from nothing.  As far as how to use it, it has nodes at the round ends and it also surface attaches, so it can go anywhere on your rover.  Just stick it on and it will work.  It is heavier than every stock solar panel but the Gigantor, and its power-to-mass ratio is the worst of any electrical part.  It's extremely expensive--though you play sandbox so that's not a problem for you--but the point is that the comparatively free power is the only advantage of an RTG over other generators.

Solar panels work with 43% of their LKO-rated output at Duna, 11% at Dres, 4% at Jool and 1% at Eeloo.  They get better as you get closer to the Sun, going to 191% at Eve and 668% at Moho, but you may want RTGs there, too, because solar panel output drops as the temperature goes up or as the atmosphere gets thicker, so you won't see anything like double output on Eve's surface.  Moho's night lasts for nearly 62 days, so for a rover there it makes a lot of sense to be less dependent on solar power.

Personally, I tend to use RTGs as supplemental power units to take the edge off of the solar power requirements.  For example, a Gigantor at Jool still produces 57 EC per minute (the RTG produces 45), but when used in combination with a solar power system, you have to consider that the RTG nullifies some of the battery requirement for the night side, not just the solar panel.  For example, let's say you're in low orbit of Jool, which has an orbital period of close enough to one hundred minutes.  If I have electrical equipment that requires, say, 100 EC per minute to operate, then I use up 10,000 EC per orbit.  Two Gigantor solar panels, at .3 tonnes each, will provide that power on the daylight side, but for the night, I need 4,000 EC of storage (the darkness time on that orbit is about forty minutes).  A Z-4K provides that at .2 tonnes, for a total electrical mass of .8 tonnes.

But wait, that's not the whole picture!  Two Gigantors produce 114 EC per minute at Jool, but my equipment uses 100 of that, so I'm only devoting 14 EC per minute to charging the battery on the day side.  That gives me 840 EC in the battery when I go to the dark side, not 4,000.  Adding another Gigantor gives me a total of 4,260 EC per daytime per orbit to charge the battery.  This means that we need another solar panel whose only job is to charge the battery, and the total needed mass is 1.1 tonnes.

If we use an RTG, we get 45 EC per minute forever.  This means that we can figure the electrical needs based on a 55 EC per minute requirement.  One Gigantor provides that at Jool (with only 2 EC left over), and the reduced load means I only need to store 2,200 EC to last the night.  Two Z-1K batteries and one Z-200 give this for .11 tonnes.  A second Gigantor (plus the 2 EC left over from the first) provides 3,540 EC every daytime per orbit; the total electrical system is now .08 for the RTG, .11 for the three batteries, and .6 for the two Gigantors, for a total of .79 tonnes.  If I use two RTGs, then I can switch the batteries with a Z-400 and get rid of one of the Gigantors, for a total mass of .48 tonnes--this is less than one half the mass of the solar-only system.

Also on the subject of Jool, remember that every one of Jool's moons is tidally locked, so the nights get quite long on Bop and Pol.  Any surface rover will need you to think about the means of power generation if you want to use it at night.

When we go to Eeloo, note that a Gigantor still provides 33 EC per minute, so it does have some use there, but Eeloo is past the point where the stock RTG outperforms the stock solar panels.

At Dres, on the other hand, a single Gigantor provides over 162 EC per minute.  At a 12 km orbit, you have an orbital period of approximately 45 minutes.  The darkness time here will be in the order of 15 minutes.  This requires 1,500 EC of battery if we're using the same 100 EC per minute rocket we sent to Jool, which we can get for .075 tonnes.  RTGs mass at .08 and you're already down to one solar panel, so there's no way to improve on the solar-only system with a hybrid as far as orbiting craft are concerned--but three RTGs will power the craft on their own at a mass of .24 tonnes, rather than the solar system's .375 tonnes.  It will also cost sixteen times more to save 135 kg, but that's not a problem for you.

[Starman4308]

8 hours ago, nascarlaser1 said:

Using USI core by @RoverDude also adds in different nuclear reactors of different sizes. Not sure how they compare to near future though (I only used the USI stuff)

In my experience, roughly on par with each other, though I prefer the aesthetics of the NF reactors. Don't forget the NF reactors have an optional top node that can be activated from the part menu.

[Vanamonde]

Thread moved to Gameplay Questions, since it's seeking help rather than offering it. 

[Snark]

On 6/21/2017 at 4:54 AM, Eagleye said:

I always thought it produced more EC and didn't understand why my rovers didn't really work as good as I expected.

Yeah, they have a fairly tiny output.  It's great for applications that don't actually need much sustained electrical power, such as running a probe by keeping the probe core alive and running the reaction wheels.  But it's a very poor choice for things that need high, sustained electrical power, such as mining drills, ISRU refineries, science labs, and continuous rover driving.

You can run an RTG-powered rover if you put a bunch of batteries on it... just not indefinitely.  You can just run it until it gets tired, then you have to stop and wait for the RTG to charge it up again.  (Good news is that you can park the rover to do that, so you can timewarp as fast as you need to.)

If you want high sustained power without solar, then your only stock option is basically fuel cells.  They work great, and they produce lots of power... the unfortunate drawback being that they do consume fuel, so a fuel-cell-powered rover won't run forever.

Or if you want to go with a mod, there are mods out there that have compact nuclear reactors that can put out lots of power pretty much indefinitely.  USI, for example, has a nice selection of them, including a cute little 0.625m model that's only around 0.12 tons IIRC, and has plenty enough power to run a rover.

[Starman4308]

1 hour ago, Snark said:

If you want high sustained power without solar, then your only stock option is basically fuel cells.  They work great, and they produce lots of power... the unfortunate drawback being that they do consume fuel, so a fuel-cell-powered rover won't run forever.

Or if you want to go with a mod, there are mods out there that have compact nuclear reactors that can put out lots of power pretty much indefinitely.  USI, for example, has a nice selection of them, including a cute little 0.625m model that's only around 0.12 tons IIRC, and has plenty enough power to run a rover.

If you have a high level engineer aboard and are careful not to stray too far from ore concentrations, you can also use ISRU to generate more fuel than it takes to power the drills and ISRU unit. Completely unrealistic, but it's hardly the only absurdity.

What is surprisingly realistic is that 0.625m nuclear reactor from USI; it's not that much lighter than actual reactors sent to space. I still prefer the Near Future aesthetics, but the lightest NF reactor is about 0.33 tons.

[Snark]

19 minutes ago, Starman4308 said:

What is surprisingly realistic is that 0.625m nuclear reactor from USI; it's not that much lighter than actual reactors sent to space.

Yah, the USI reactors are fun.  Main thing is that it's hard to tell if they're on or off (have to check the right-click menu).  I should really add an  IndicatorLights patch for them so they light up when turned on.  Either that, or hornswoggle someone else into doing it for me. 

[Azimech]

Yep, for most rovers a few fuel cells and a single short 1.25m tank is sufficient to circumnavigate the Mün or sometimes even Duna. Unless you're in a hurry. Then you'll need more cells and more fuel.