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StarManta

[1.0.5] Do radiators even do anything aside from with ISRU?

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I built a large first stage booster using several of the "Twin Boar" LF boosters, as they were the most powerful engine available to me. I discovered that, when fuel crossfeeding was being used, these engines could run long enough to heat up to the point of explosion; before my last one could use up all its fuel and/or get the payload to orbital speed, it would go boom.

But I think, I have all these radiator parts! I only needed to buy another 15-20 seconds, so I slap a couple of the small radiators on that last engine - even a little bit of heat reduction would probably be enough since it'd be running from the moment the engines light up. I launch, and the little radiators almost instantly turn red, which I take as a good sign - they must be removing heat. ....except that when I get to the final stage, the last engine explodes again, with almost exactly the same amount of fuel left in the stage as before.

Alright, they're just not big enough. That's fair, it's a big boost and a little radiator. So I unlock the Large size radiator, and I cover that last booster with the things - I think about 20 large radiators overall, covering every exposed surface. Launch again... and again the thing explodes with no apparent change.

I eventually decided to use the slightly less powerful Mainsail for that last stage, which had no such overheating problem, and I got the payload into orbit. But now I'm thoroughly confused about the radiators. What do they do? What are they for? It would appear they do nothing at all.

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ISRU, NERV, and sometimes when aerobraking you need to cool down quickly between passes through the atmosphere.  That is pretty much all you really need them for.  Using them in the atmosphere (when the Twin Boar would be most useful) won't help you that much.  It's better just to discard it.  The sad thing is, we really don't need that many of them for those purposes, most of them could be removed from the game.

Edited by Alshain

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For major heat-dump, the big foldable radiators put the static ones to shame-- they pull a lot of heat out of there.  Drawback being that you can't use them while flying through atmosphere, so I suppose they wouldn't be useful in your particular use case.

The foldable radiators are useful if you're going very close to the sun-- they auto-rotate to stay edge-on to the sun, so they can radiate heat even when your ship is in full sunlight.  It's not so much of a big deal in stock, since you can visit Moho without radiators... but it becomes an issue if you get much closer than Moho.  Not a lot of reason to do that in stock KSP, but (for example) some mods (like New Horizons) add planets that are significantly closer, and then it really helps.

Also, there are some mods that add other engines and parts that generate lots of heat, and the big radiators help a lot with that.  For example, the "Nuclear Lightbulb" engine from Porkjet's Atomic Age mod is basically a super-NERV, generates ridiculous amounts of heat, blows up in under a minute if you run it full throttle without radiators.  A couple of the extra-jumbo-size folding radiators will keep it running.

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You might also want to try thrust limiting the Twin Boars slightly.  Try kicking it down to 94.5% and see if you still have the overheating problem.

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On 1/29/2016 at 2:39 PM, StarManta said:

But now I'm thoroughly confused about the radiators. What do they do? What are they for? It would appear they do nothing at all.

Radiators are good for several things:

  • Keeping drills and ISRUs happy
  • Keeping fission reactors happy (if you have a mod for them)
  • Keeping nuclear engines happy during long burns.  Stock NERVAs aren't so bad and might be able to run for a minute or 2 without them, but need about 2 medium retractables for interplanetary burns of 5-10 minutes.  Mod nukes (especially those in Atomic Age) get rather hotter so need more radiators.  That mod's Nuclear Lightbulb needs 2x large retractables.
  • Keeping the whole ship happy when operating near or especially inside of Moho.

Radiators are NOT (or SHOULD NOT be) good for dissipating reentry heat.  They conceivably might help some on ascent, up until you get fast enough to start showing flames, at which point they SHOULD do more harm than good.  But if you're overheating on ascent (and I haven't had that happen since way back in the 0.2-somethings a couple years ago), then you're doing something wrong in the rocket design department :D

 

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10 hours ago, Geschosskopf said:

 They conceivably might help some on ascent, up until you get fast enough to start showing flames, at which point they SHOULD do more harm than good.

I think you misunderstand. This isn't whole-ship-flaming heat, this is the engine part itself overheating just from thrust. (It happens in vacuum, too; in fact, that's where the real problem lies, as by the time I get to this point, I'm trying to circularize my orbit.)

On 1/29/2016 at 5:18 PM, Snark said:

For major heat-dump, the big foldable radiators put the static ones to shame-- they pull a lot of heat out of there.  Drawback being that you can't use them while flying through atmosphere, so I suppose they wouldn't be useful in your particular use case

Actually that would be. This becomes a real problem after I've left the atmosphere. I can't find any foldable radiator parts, though - where are they?

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1 hour ago, StarManta said:

I think you misunderstand. This isn't whole-ship-flaming heat, this is the engine part itself overheating just from thrust. (It happens in vacuum, too; in fact, that's where the real problem lies, as by the time I get to this point, I'm trying to circularize my orbit.)

Radiators suck heat out of other parts and literally "radiate" it into the surrounding environment.  Therefore, they keep individual parts from overheating, provided they're within 2 part (for fixed radiators) or open (for retractables).

Running engines overheat if they produce heat faster than they can get rid of it.  Except for NERVAs, attaching the engine to a fuel tank is sufficient to solve this problem because the fuel tank acts as a heat sink for the engine.  The LFB is a special case of a combined engine + fuel tank.  This means that any heat produced by the engine will stay in the same part if you don't stick another fuel tank on top of the LFB unit.

So I can see this being a potential problem with the LFB.  Now, in real life, the LFB should NOT heat up as fast as other engines because of its integral fuel tank (at the part level, it should have a much higher specific heat than a regular engine).  So if the game uses the same general specific heat value for the LFB as for normal engines, then you could overheat them.  It would be the same as attaching a normal engine at the end of a girder, despite the integral fuel tank.  This might be worth posting as a bug report, but I'd look at the part file first to be sure.  I've never seen any variable labeled "specific heat" in the KSP heat stuff so I'm not sure how the system actually works.

1 hour ago, StarManta said:

Actually that would be. This becomes a real problem after I've left the atmosphere. I can't find any foldable radiator parts, though - where are they?

They're in the Utilities section, usually on the page after the fixed radiators.  

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On 1/29/2016 at 4:18 PM, Snark said:

Also, there are some mods that add other engines and parts that generate lots of heat, and the big radiators help a lot with that.  For example, the "Nuclear Lightbulb" engine from Porkjet's Atomic Age mod is basically a super-NERV, generates ridiculous amounts of heat, blows up in under a minute if you run it full throttle without radiators.  A couple of the extra-jumbo-size folding radiators will keep it running.

Now that you mentioned Atomic Age, is there any difference (i.e. radiating ability) between the three sizes of wrap-around radiators in that mod and the corresponding three sizes of stock folding radiators?  I first thought the wrap-around ones were better, but maybe they're just the same, just different form factor.  Sure, it's cool to have your whole ship glow red when it's wrapped in those things, but I'd like to get some hull real eastate back for other purposes. :)

 

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5 minutes ago, Laguna said:

Now that you mentioned Atomic Age, is there any difference (i.e. radiating ability) between the three sizes of wrap-around radiators in that mod and the corresponding three sizes of stock folding radiators?  I first thought the wrap-around ones were better, but maybe they're just the same, just different form factor.  Sure, it's cool to have your whole ship glow red when it's wrapped in those things, but I'd like to get some hull real eastate back for other purposes. :)

I see little if any difference between Atomic Age's radiators and stock fixed radiators.  Because I don't use fixed radiators except on a very few planes with nuke turbojets, I find them essentially useless, like all fixed radiators.  Use the retractables if you need any.

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25 minutes ago, Laguna said:

Now that you mentioned Atomic Age, is there any difference (i.e. radiating ability) between the three sizes of wrap-around radiators in that mod and the corresponding three sizes of stock folding radiators?  I first thought the wrap-around ones were better, but maybe they're just the same, just different form factor.  Sure, it's cool to have your whole ship glow red when it's wrapped in those things, but I'd like to get some hull real eastate back for other purposes. :)

The wrap-around radiators are better than the old, pre-1.0.5 static panels, but not as good as the folding radiator panels.  If you rummage through the Atomic Age forum thread, somewhere in there is a post where Porkjet mentions the relative amounts, i.e. how many of this-size Atomic Age radiator are equivalent to how many of that-size folding radiator.

Porkjet created those radiators before 1.0.5, when the stock static panels were much less effective than they are now, and AFAIK he hasn't updated them since.  So the Atomic Age radiators still work, but are kinda obsolete these days; I haven't used them since 1.0.5.

 

1 hour ago, Geschosskopf said:

Radiators suck heat out of other parts and literally "radiate" it into the surrounding environment.  Therefore, they keep individual parts from overheating, provided they're within 2 part (for fixed radiators) or open (for retractables).

Actually, even the static panels cool down the whole ship.  They're supposed to only cool two parts away, but there's a bug and that designed limitation doesn't actually apply.  I was asking about it in another thread, a couple of months back, and one of the devs chimed in that yes, they're aware of the issue.  So my guess is that that'll be fixed in 1.1 and your above statement will become correct soon.

 

3 hours ago, StarManta said:

can't find any foldable radiator parts, though - where are they?

One reason you may be having trouble seeing them is that they don't actually have "radiator" in their name-- they're called "Thermal Control System" (which is why they're not listed next to the static panels-- the list is sorted alphabetically, so they end up on a different page, as Geschosskopf points out).  They look like white rectangles in the thumbnail view.  Here's a list of all the radiator parts, so you can see what they look like.

The folding panels can't stand up to airflow, but are otherwise quite a bit nicer than the static panels.  They have a bigger heat-draining capacity.  They rotate to stay edge-on to the sun, so you can use them for solar heating problems.  And you can turn them off.  Radiators draw electricity continuously while they're running, regardless of whether there's actually any work for them to do (i.e. heat available to drain).  The folding panels turn off when you retract them (stop cooling, and stop drawing electricity).  The static panels, on the other hand, are always on and there's no way to turn them off, so a ship loaded up with them will always be leaking electricity with no way to stop it.  Unless you install this little mod that *cough* I wrote to make them turn-offable... ;)

 

Edited by Snark

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On 29/1/2016 at 9:39 PM, StarManta said:

... So I unlock the Large size radiator, and I cover that last booster with the things - I think about 20 large radiators overall, covering every exposed surface. Launch again... and again the thing explodes with no apparent change.

I eventually decided to use the slightly less powerful Mainsail for that last stage, which had no such overheating problem, and I got the payload into orbit. But now I'm thoroughly confused about the radiators. What do they do? What are they for? It would appear they do nothing at all.

tbh, I'm not entirely sure how well radiators in KSP model radiated energy.

However, in real life there is no point having more than 4x symmetry for edge-mounted radiators. In fact, anything more than 2x symmetry will be inefficient because the heat radiated from the radiators (bearing in mind that they work purely by radiation in space, so they are never optimised for convection) is in turn radiated back into the other radiators. A radiator arrangement that looks like the fins on a motorbike engine would be utterly inefficient in space: most of the heat would be radiated straight back into the next radiator.

Assuming that KSP does model radiated heat from engines properly, your problem is probably that while all of your Twin Boars are running they are heating each other up significantly. By the time you get to your last Twin Boar, it is already at the limit of its suvivable temperature and there is too little fuel left to soak up the excess heat. The amount of heat is simply far too much for fixed radiators to cope with (especially since they too have been heated by the atmosphere and each other). So it goes boom.

Of course, if a similarly-powered engine works where the Twin Boar doesn't, that indicates a bug of sorts. The obvious difference is that the fuel and engine are combined in one part, so (like SRBs) the whole part heats more explosively than when the heat-shifting mechanic functions between an engine and an attached fuel tank. This would suggest that as it uses up its fuel, it loses its ability to absorb more heat.

So when it comes down to it, the radiators and Twin Boar end up being relatively realistic. If anything, it is the Mainsail that is OP by not exploding in the same situation ; )

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The great thing about the foldable radiators is that you can start using them from 30000 meters on up in Kerbal's atmosphere.  30000-70000 meters is where any heating problem will probably occur, from either taxing the engine or reentry.  I haven't tested them in the atmosphere at interplanetary intercept speeds yet though, so any panels extended is an unknown to me past 2500 m/s.  [I also did the test during 1.0.4, so it's possible they changed it since then]

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I've used the static panels to reduce atmospheric heating for high-speed aircraft.  This may seem an odd choice, but there is a logic to it.  If you look in the .cfg file for a part, you will see a value called "emissiveConstant".  This is a value less than 1.0 which tells how quickly a part gets rid of heat.  Parts that have good values (.9 to .95) include: engines, wings, the pre-cooler, and radiators.

So why choose a radiator when a wing will provide the same function and provide lift as well?  The panels tend to have less mass than the other parts mentioned, which keeps the thrust-to-weight ratio high and allows for high speed travel in atmospheric flight.  I've managed sustained flight over long distances at a speeds of mach 4.5+.  The other bonus is that the radiator panels don't impact lift, so you can attach them to the specific part that is in danger of overheating.  For example, cockpits don't naturally radiate heat and can have a low maximum internal temperature.  If that part overheats, you lose everything.  You could attach wings to the part, but that might throw off the center of lift.  You might attach a pre-cooler, but that might throw off the center of mass.  Since the radiator doesn't impact lift and has a smaller mass than other parts, it has little impact on the balance between center of mass and center of lift.

They do slightly increase drag, but I've found it a worthwhile trade-off.

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47 minutes ago, PPR said:

The other bonus is that the radiator panels don't impact lift, so you can attach them to the specific part that is in danger of overheating.

Note that as of 1.0.5, it doesn't matter where you attach the radiator, since they pull heat from anywhere on the craft.  Supposedly the static panels are supposed to work only up to 2 parts away from the radiator, but my experience has been that they actually pull heat from the whole craft.  I assume this is a bug, we'll see whether they fix that in 1.1. :)

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My non expandable panels do not pull heat out of my ISRU which is 6 parts away. I suspect they cool the entire ship by cooling the part they are attached to which will cool the ship. I thought they cold reach 4 parts too. Heat transfer is core temp from part to part and I believe radiators can only pull out core temp as well so skin temp failures are not helped much by radiators

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Is there any way to actively or passively cool a parts skin temperature?

As to the non folding radiators, I've flown an SSTO and had the cockpit explode, then added small nonfolding radiators on the side and flown the same ascent path and had it not explode.  I had built a large mk3 SSTO spacesplane if that matters

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