Cooling LV-N "Nervas" - it's not rocket science

[xtoro]

No, it's Thermodynamics!

No, it's thermal conduction, basically what arkie87 said. Calling it thermodynamics would be the same as just calling it another generic name like "science".

[Ival70]

Nuclear engines would also need shielding and spew a lot of neutron and gamma radiation, why is that people are so vocal about their unrealistic overheating but quiet about their unrealistic lack of radiation?

Probably because nuclear engines aren't the only things currently in the game that spew radiation, and nobody wants Kerbals to worry about long drawn out painful deaths from radiation sickness.. or Kerbals are immune to the effects. Also, in a vacuum, the engine would only require a shield to prevent back-scattered radiation through the ships structure (as well as line of sight). Atmospheres add another layer of complexity because the radiation can scatter off of it and back into the ship, potentially bypassing the shield. But this is getting rather off topic..

I agree that the nerva's generate too much heat, and for both realism and game-play reasons, I would like to see it fixed.

[Dispatcher]

Nuclear engines would also need shielding and spew a lot of neutron and gamma radiation, why is that people are so vocal about their unrealistic overheating but quiet about their unrealistic lack of radiation?

I think we should have radiators and shadow shields as stock parts to complement the LV-N.

[Brotoro]

Nuclear engines would also need shielding and spew a lot of neutron and gamma radiation, why is that people are so vocal about their unrealistic overheating but quiet about their unrealistic lack of radiation?

I use my LV-Ns in a manner that accounts for their gamma and neutron flux when operating. Anyone interested in realism can do that. Putting radiation in the game would be interesting...but I don't expect Squad to do it, since they don't include other basic things that could also kill kerbals, such as starvation, high-G forces, and temperature extremes.

Squad glosses over and simplifies a lot of things about rocket engines to make things easier for players. Real rocket engines can't be restarted an infinite number of times, but KSP engines can. Real rocket engines can't be throttled from 0% to 100%, but KSP engines can. Real rocket engines can't have the weight of the rocket sitting on their nozzles, but KSP engines can. Real rocket engines have operating failures, but KSP engines don't. Real nuclear rocket engines have radiation hazards and require a cool-down thrust, but the KSP NERV doesn't. Squad glosses over all those real-world things (and more) to make things easier so that we can play the game (without needing engineers to plan our burns in detail months ahead of time, and without needing computers to control the engine systems, etc., that are required in the real world...but aren't required in KSP).

But what Squad should NOT do is MAKE UP SOMETHING UNREALISTIC, like overheating NTRs, just to make things harder for the player. If they want to nerf the NERV, there are numerous physically realistic ways to do it. They don't have to implement Faulty Rocket Science to nerf the NERV.

[SciMan]

Nuclear engines would also need shielding and spew a lot of neutron and gamma radiation, why is that people are so vocal about their unrealistic overheating but quiet about their unrealistic lack of radiation?

Sliding scale of realism vs fun. Same reason they use high-density Liquid Fuel instead of extremely low density Liquid Hydrogen.

And again, the LV-N requiring wing parts as radiators is STUPID.

I'm not saying it's unrealistic (even tho it is), I'm saying it's a bad game mechanic. Once the player has learned how to prevent the LV-N from overheating, the only thing it does to that player's ships is drive part counts higher without a good reason.

Edited May 18, 2015 by SciMan

[SkyRender]

Hopefully experiments like this will be rendered moot eventually with the introduction of a dedicated heat radiator part at some point. Until then, this is quite helpful; thank you!

[Ival70]

But what Squad should NOT do is MAKE UP SOMETHING UNREALISTIC, like overheating NTRs, just to make things harder for the player. If they want to nerf the NERV, there are numerous physically realistic ways to do it. They don't have to implement Faulty Rocket Science to nerf the NERV.

This just about sums my feelings on the matter. Also, regardless of what happens to the nerva, I would like to see a radiator part added to the game.

[Kuu Lightwing]

You don't always need wings to cool the NERVA. I used a craft with six NERVAs for the last Reddit challenge and even though I had burn times of 5 minutes, nothing exploded. I barely saw any overheat gauges.

Here's the craft (with upper stage still attached, but you got the idea): http://imgur.com/a/kVHJj#7

[SkyRender]

I suspect the justification for the LV-N heating came from this bit from Wikipedia on nuclear thermal rockets in regards to the KIWI project (precursor to the NERVA):

On the initial firings immense reactor heat and vibration cracked the fuel bundles. Likewise, while the graphite materials used in the reactor's construction were indeed resistant to high temperatures, they eroded under the heat and pressure of the enormous stream of superheated hydrogen. The fuel bundle problem was largely (but not completely) solved by the end of the program, and related materials work at Argonne National Laboratory looked promising. Fuel and engine coatings never wholly solved this problem before the program ended.

The article for the NERVA also contains this tidbit:

The most serious injury during testing was a hydrogen explosion in which two employees sustained foot and ear drum injuries. At one point in 1965, during a test at Los Alamos Scientific Laboratory, the liquid hydrogen storage at Test Cell #2 was accidentally allowed to run dry ; the core overheated and ejected on to the floor of the Nevada desert. Test Site personnel waited 3 weeks and then walked out and collected the pieces without mishap. The nuclear waste from the damaged core was spread across the desert and was collected by an Army group as a decontamination exercise.

Without further research, one might be tempted to think that nuclear propulsion and overheating were synonymous. However, that's far from true: by the end of the testing cycle, the NERVA engines were only in danger of dangerously high heat build-up if the fuel source was depleted entirely while the engine was still on.

[Wallygator]

If squad adds a dedicated radiator part for LV-N, I wonder if one could copy the relevant info from its part config and paste it into the LV-N part config.

So, if they fix the LV-N to operate properly, great. If they poop out a radiator, that's great also - just an excuse for me to learn a bit about part configs.

I could probably figure it out, but I'm too lazy at the moment and can't be bothered.

[Levelord]

I suspect the justification for the LV-N heating came from this bit from Wikipedia on nuclear thermal rockets in regards to the KIWI project (precursor to the NERVA):

On the initial firings immense reactor heat and vibration cracked the fuel bundles. Likewise, while the graphite materials used in the reactor's construction were indeed resistant to high temperatures, they eroded under the heat and pressure of the enormous stream of superheated hydrogen. The fuel bundle problem was largely (but not completely) solved by the end of the program, and related materials work at Argonne National Laboratory looked promising. Fuel and engine coatings never wholly solved this problem before the program ended.

The article for the NERVA also contains this tidbit:

The most serious injury during testing was a hydrogen explosion in which two employees sustained foot and ear drum injuries. At one point in 1965, during a test at Los Alamos Scientific Laboratory, the liquid hydrogen storage at Test Cell #2 was accidentally allowed to run dry ; the core overheated and ejected on to the floor of the Nevada desert. Test Site personnel waited 3 weeks and then walked out and collected the pieces without mishap. The nuclear waste from the damaged core was spread across the desert and was collected by an Army group as a decontamination exercise.

Without further research, one might be tempted to think that nuclear propulsion and overheating were synonymous. However, that's far from true: by the end of the testing cycle, the NERVA engines were only in danger of dangerously high heat build-up if the fuel source was depleted entirely while the engine was still on.

Pretty much this. The hydrogen is stored cryogenically (at least according to current tech and research) and running it through the engine where it picks up the heat from the reactor and gets propelled out. In essence the reactor is losing heat by transferring that heat to the cold hydrogen, expanding it and expelling it out the back.

[Xaver]

Aah heat and mass transfer, my hatelove at university. Thank you for wrighting it down in more or less easy words.

[regex]

I suspect the justification for the LV-N heating came from this bit from Wikipedia on nuclear thermal rockets in regards to the KIWI project (precursor to the NERVA):

The justification for LV-N heating is that always ran hot and that, when the parts were remade for the new system, numbers were probably just multiplied wholesale. Under the old temperature system the LV-N running hot was never a big deal, under the new thermal management system it takes some clever use of heat sinks and potentially additional parts. While undoubtedly unrealistic, I find it a fascinating gameplay mechanic.

[m4v]

Sliding scale of realism vs fun. Same reason they use high-density Liquid Fuel instead of extremely low density Liquid Hydrogen.

And again, the LV-N requiring wing parts as radiators is STUPID.

I'm not saying it's unrealistic (even tho it is), I'm saying it's a bad game mechanic. Once the player has learned how to prevent the LV-N from overheating, the only thing it does to that player's ships is drive part counts higher without a good reason.

I'm not against arguing is a bad game mechanic, I'm against using "realism" arguments.

edit:

And since I got here I might give my opinion. I don't think it that nervas overheating is a bad mechanic, there aren't other engines that makes you consider the heat management of your vessel. If you are against mechanics that increase your part count, you might want to remove ElectricCharge from the game as well, is only there for rise the part count and kill your probes when you forget to open solar panels.

Edited May 18, 2015 by m4v

[lazarus1024]

Sun shields and folding radiators that rotate away from the sun would be cool. Then maybe ramping up heat load so that Moho vicinity will cause a ship to slowly cook if you don't implement heat mitigation stuff I think would be very cool.

[Gkirmathal]

There were changes made to the engine that made it less efficient (having to carry around extra mass in radiator parts or limiting how you can attach the engine)...that's the definition of a 'nerf.'

And it's all silly, because NTR engines do not produce copious amounts of heat like this (anybody can learn how NTR's work...it's not secret information...you just need to put in a little effort). Having them overheat like this is Bad Rocket Science, Squad.

This and only this. Nerva's and the 1.0 heat system in KSP makes the LV-N function flawed.

In a Nuclear Thermal Rocketengine the propellant functions as the coolant in thrust mode.

The propellant draws the heat away from the reactor, reactor J output = fuel flow, and thus the propellant becomes superheated and used as thrust.

The need for Radiators in KSP to use an NTR, if you like somewhat of a degree of realism, is in my opinion ridiculous.

[Maddmatts]

You guys, there's a seriously easy solution to this if it's really that much of a problem for you:

1) Find liquidengineLV-N.cfg, open it with your text-editor of choice (usually notepad)

2) Find "Heat Production = 432"

3) Change the number to whatever you want.

4) Save file

[Scourge013]

I spent many years as a coach of a collegiate Debate Team. I mention this because I call things as I see them. So here's how I see this:

Thoughts on the OP: I did not read all of your post. Not because it was "sciencey" but because after your direct and helpful tl;dr, I found your tone to be dismissive and rude. I heartily suggest that the next time you want to write a persuasive argument about something controversial, you put the air quotes and sarcastic references to rocket science and magic away and use the good ol' fashioned three step Refuation Model: State the claim you disagree with, state your position (and NOT how you feel emotionally), present your observations or other evidence, explain--with reasoning--why your observations or evidence supports your point of view. People will be more likely to take your point of view seriously.

Side notes that I think all of us should keep in mind: Opinions on a topic are subjective--they rely more on personal experience and frames of reference for their formation and validation than reality or truth. This is why scientists insist on reproducible experiments that can transfer from culture to culture and person to person--people need to have the same personal experience with reality, usually, in order to agree on what reality or the truth is.

However, the controversial nature of a topic is objective. Ironically enough, the fact that people use facts to support their respective positions is what makes two sides of an issue controversial--and that controversy isn't going to go away just because you have facts to back you up because again...everyone has facts to back them up. It's like an academic Mexican Standoff if you will. Everybody has the rhetorical equivalent of loaded guns pointed at each other and the situation is not likely to get any better just because you personally have a loaded gun. Being dismissive in that climate is only going to provoke someone to pull a trigger. And that's going to make things very messy.

Until consensus is reached, this topic will be controversial and needs to be treated with care by all parties so that there is less shooting and more experimentation and common experience being shared.

Summation of the issue: Clearly, the OP thinks that LV-N heating is not a big issue because wing parts circumvent the mechanic--obviously the OP has done research to demonstrate how subjectively easy the OP feels this is. While others feel a mechanic that, in practice anyway, requires aerodynamic parts designed for lift in atmospheres to be used on a craft that will only ever be in the vacuum of space to be laughable regardless of how easy it is--this is also a fact. Except for their apparent heat radiating qualities, wings are just extra dead-weight mass on a deep space craft. This is especially troubling considering how many deep space craft designed by the community are "min-maxed" to get the most delta-v and adding wings will interfere with that.

My thoughts on the controversy: I think what we need now is some experimentation that attempts to compare the relative efficiency of a craft with an LV-N and wings for radiation versus a reasonably similar craft with an LV-N and no wings, but thrusted down such that the engine won't explode if left on unattended.

But first we have to agree on what "efficiency" is. Is it total delta-v? Is it ease in playability? Is it something else?

In order to form a consensus about efficiency we are going to have to do whole lot of writing and thinking about--okay, you know what?

[Cynicism]This whole scholarly attitude on controversial issues thing is too hard. The last time I had to put wings on a vacuum-only craft to get it working was when I had to put wings on my Mun lander because there weren't landing legs yet. This ain't no 1.0.x release, this be Beta .91. Derp derp, Squad, derp derp.[/Cynicism]

[serious Mode] Though for what is is worth, I did find radiators an interesting design challenge and mechanic on the Interstellar mod. I would not be upset if Squad added radiator part(s) in a subsequent title update. Even if requiring them for a LV-N is apparently unrealistic, I feel it'd lead to more interesting design decisions. Quite frankly, I could go either way on this because I also feel LV-Ns should also work out of the box without support parts given the gamey nature of...uh...the game.[/serious Mode]

Edited May 18, 2015 by Scourge013

[Hanuman]

My opinion is a pretty simple one. It should just be assumed that the LV-N has whatever radiators it needs to function as part of the basic model. Just like every other engine is assumed to include all the pieces and parts they need to function. No, it doesn't need remodeled. No, we don't need extra radiator parts (for this issue specifically). It should be assumed that like every other engine, if you stick it on, and you have the resources it requires, then it will work to spec. To do otherwise isn't adding gameplay elements, it's just breaking the messaging.

That does not include having to only use it on huge ships for heat transfer, nor having to glue on extra parts. How or whether the LV-N is used or "overused" is inconsequential. Personally, I dislike having to manage and worry about heating effects, beyond that of re-entry. Yeah, I know it's a real thing, but it's not something I enjoy.

[Soda Popinski]

One could justify the added heat by the fact they don't actually use hydrogen as a propellant. Liquid hydrogen is very very cold (boils at 20 kelvin at 1 atm), and would draw off a lot of heat from an NTR.

"Liquid fuel" may be a lot warmer than that, so may not draw off as much heat.

[Archgeek]

I think we should have radiators and shadow shields as stock parts to complement the LV-N.

Actually, there's a rather visible shadow shield in the LV-N model already. You can see it right above the reactor bit.

You don't always need wings to cool the NERVA. I used a craft with six NERVAs for the last Reddit challenge and even though I had burn times of 5 minutes, nothing exploded. I barely saw any overheat gauges.

Indeed! Additional testing is needed to ensure the central tank and KR-L2 aren't key to the design, but an old hybrid drive stage with 6 LV-Ns on radial mk2 LF tanks has proven to work a treat, to the point that it asymptoically cannot overheat under infinite fuel, due to the conduction and rad fluxes approaching one another with hundreds of Kelvin to spare.

In fact the trick may largely be to just put a larger tank on each, since radiation is affected by the pre-calculated surface area of a part's mesh. If your craft needs solar panels anyway, I've also found that even the mk1 LF tanks are impervious under infinite fuel with the help of either 2 gigantors or 8 mid-size panels.

[nholzric]

[Cynicism]This whole scholarly attitude on controversial issues thing is too hard. The last time I had to put wings on a vacuum-only craft to get it working was when I had to put wings on my Mun lander because there weren't landing legs yet. This ain't no 1.0.x release, this be Beta .91. Derp derp, Squad, derp derp.[/Cynicism]

Hey, great point! KSP has a long and glorious history of using wing-parts to do non-wingy things. Like you said, back in version ye'old-ksp when the Mun was added, wings were the go-to landing-legs. They were much less fragile than engine nozzles.

[regex]

One could justify the added heat by the fact they don't actually use hydrogen as a propellant. Liquid hydrogen is very very cold (boils at 20 kelvin at 1 atm), and would draw off a lot of heat from an NTR.

"Liquid fuel" may be a lot warmer than that, so may not draw off as much heat.

I've already made the argument, several times, that the NTR is essentially pushing Aerozine 50 (not Kerosene, as I earlier claimed) out the back-end and getting cryogenic hydrogen isps with literally no worries about fuel boil-off, fuel density, fouling, or other strange effects, but that doesn't seem to matter to those claiming "realism". I certainly don't think the NTR is realistic right now but the mechanics are interesting and building a good, low-part count tug with NTRs should be considered a design challenge on the order of SSTOs.

Indeed! Additional testing is needed to ensure the central tank and KR-L2 aren't key to the design, but an old hybrid drive stage with 6 LV-Ns on radial mk2 LF tanks has proven to work a treat, to the point that it asymptoically cannot overheat under infinite fuel, due to the conduction and rad fluxes approaching one another with hundreds of Kelvin to spare.

In fact the trick may largely be to just put a larger tank on each, since radiation is affected by the pre-calculated surface area of a part's mesh. If your craft needs solar panels anyway, I've also found that even the mk1 LF tanks are impervious under infinite fuel with the help of either 2 gigantors or 8 mid-size panels.

I can confirm that a good, large heat sink works quite well to manage the heat, especially if you're doing the normal stock-ish burns of 3km/s or less. Honestly, you really shouldn't need to be running for longer than that and, if you are, you probably have a special craft anyway.

E: It's also important to note that testing with infinite fuel is inaccurate since the fuel itself has thermal mass and the reduction in that mass must be accounted for.

[Archgeek]

I can confirm that a good, large heat sink works quite well to manage the heat, especially if you're doing the normal stock-ish burns of 3km/s or less. Honestly, you really shouldn't need to be running for longer than that and, if you are, you probably have a special craft anyway.

E: It's also important to note that testing with infinite fuel is inaccurate since the fuel itself has thermal mass and the reduction in that mass must be accounted for.

Indeed, and considering how easily something can be made asymptotically thermo-stable, that makes it all the safer to forego radatiative fins and friends and just let heatsinking do the work for most reasonable burn times.

HEH , by infinite fuel, I mean running the tank from full to empty, then turning on infinite fuel, in order to test worst-case heating. I have several "nuke test" craft on various terrifying and/or very​ hyperbolic trajectories in my sandbox save from this Thomas Foolery.

Edited May 18, 2015 by Archgeek
missing space implying some sort of onion-based propellant.

[The Lone Wolfling]

The best radiator I've found, mass for mass, is the structural intake, of all things. Beats everything else I've tried, hands down. Lot of parts, though.