Rethinking the Nuke -- for real this time

[Laie]

Hello,

It seems obvious that Squad wants to nerf the engine in some way or another. It has the best ISP, but -apparently- there has to be some downside or other. IMO, the overheating thing is just silly; I'd like to toss out a few suggestions for other ways to make the engine less of an automatic choice. Tell me what you think. Suggestions welcome.

• make it a lot heavier and more powerful (like, 20t and 400kN) to dramatically raise the threshold for when Nervas even start to become interesting. Mixed interest.
  
• make it a game mode: the player may either have nuclear engines (the future of the sixties) or ISRU (the future of today), but not both in the same game. No interest.
  
• spooling: like jets, the engines may take a while to come to full thrust, and will also take a while to shut down. Appears to be very popular.
  
• no throttle: it's either 100 percent thrust or none. Again, this is mostly aimed at landers. Noone wants this.
  

Edit: later suggestions by thread participants; I'll try to update this post as ideas come in (also my idea of what the prevailing mood is towards a given suggestion).

• make it even more expensive. Few want this, but noone has seriously objected.
  
• also give it a reputation cost. Opinions on this have been *very* divided, that point has flamewar potential.
  
• radiation effects
  
• limit it's operating time to N hours before it has to be discarded.
  
• dedicated nuclear propellant, possibly less dense than even the current half-empty tanks.
  

Edited May 18, 2015 by Laie

[Kelderek]

I agree that the overheating is lame - especially when you consider the abysmal TWR that leads to extra long burn times anyway. I can think of a couple more options for balancing:

1. Adjust the funds cost. Make it 10x more than any other engine.

2. I don't know enough about how the engine is meant to work, but to me the word "nuclear" implies radioactive which leads me to think of Uranium as a possible resource. This is a whole different can of worms, but I think it would be cool if resources could be used as building materials. If that were possible then you could have uranium required to construct the engine and the usual LF to fuel it.

Apart from that, I also like your idea to just make it much more massive.

[KrazyKrl]

Hello,

It seems obvious that Squad wants to nerf the engine in some way or another. It has the best ISP, but -apparently- there has to be some downside or other. IMO, the overheating thing is just silly; I'd like to toss out a few suggestions for other ways to make the engine less of an automatic choice. Tell me what you think. Suggestions welcome.

• make it a lot heavier and more powerful (like, 20t and 400kN) to dramatically raise the threshold for when Nervas even start to become interesting.
  
• make it a game mode: the player may either have nuclear engines (the future of the sixties) or ISRU (the future of today), but not both in the same game.
  
• spooling: like jets, the engines may take a while to come to full thrust, and will also take a while to shut down. Should make landers more difficult, requires an alternate propulsion system for fine-tuning your trajectory.
  
• no throttle: it's either 100 percent thrust or none. Again, this is mostly aimed at landers.
  

The heavy nukes would be my favorite. I recently toyed around a little and 20t/400kN means that a heavy tug can be as simple as a single large tank plus one engine. For huge missions or large motherships, this would actually be a perk. Then again, the nuke would only ever be worthwhile for huge missions... it would no longer be the go-to engine for almost everything.

• Making it a lot heavier doesn't really solve anything, as the NERVA is pretty bad with TWR anyhow.
  
• Locking out the NERVA wouldn't solve any problems, just lock gameplay for no real benefit.
  
• Spooling on the NERVA sounds good. It's gotta take at least some time to get that nuclear reactor up to temperature.
  
• No throttle makes no sense, as you can throttle the propellant flow in a real NERVA.
  

Another thing the NERVA needs; is reputation loss when destroyed without recovery. Doubly so lost reputation if a used NERVA is destroyed without recovery. (Them fission products bad mmmmkay.)

Fuel tanks need a tweakable for fuel load anyhow. LFO tanks for NERVAs is horribly inefficent, and is actually worse than using lightweight airplane fuel tanks.

[Barking Sands]

I feel that the nuclear engine already has its drawbacks: It's long and unwieldy, and its thrust to weight ratio limit its usefulness at planet surfaces.

Spooling up/down (stiction) sounds like a great touch. Might even be true-to-life if NERVA NRX actually had a design that caused stiction issues.

@Kelderek: Most people agree that the Nerva should have its own fuel; hydrogen propellant. All I know about the NERVA NRX is what I can find on wiki; and I don't think there's a substantial amount of information there as nuclear engines have always been highly unpopular for obvious reasons.

Also, what KrazyKrl said.

Edited May 17, 2015 by Barking Sands

[Armchair Rocket Scientist]

• Making it a lot heavier doesn't really solve anything, as the NERVA is pretty bad with TWR anyhow.
  
• Locking out the NERVA wouldn't solve any problems, just lock gameplay for no real benefit.
  
• Spooling on the NERVA sounds good. It's gotta take at least some time to get that nuclear reactor up to temperature.
  
• No throttle makes no sense, as you can throttle the propellant flow in a real NERVA.
  

Another thing the NERVA needs; is reputation loss when destroyed without recovery. Doubly so lost reputation if a used NERVA is destroyed without recovery. (Them fission products bad mmmmkay.)

Fuel tanks need a tweakable for fuel load anyhow. LFO tanks for NERVAs is horribly inefficent, and is actually worse than using lightweight airplane fuel tanks.

Another thing the NERVA needs; is reputation loss when destroyed without recovery. Doubly so lost reputation if a used NERVA is destroyed without recovery. (Them fission products bad mmmmkay.)

I would like to add that this should ONLY be the case if the destruction occurs in Kerbin's SOI (Mun and Minmus don't count) and possibly Laythe where there's a potential biosphere to effect. Nobody cares if nuclear waste gets scattered on Moho's surface or in Jool's atmosphere. Also, LV-Ns deleted by the "abort flight" button when in stable orbits around Kerbin (simulating the spacecraft being in a safe graveyard orbit) should not affect reputation.

[Laie]

• Making it a lot heavier doesn't really solve anything, as the NERVA is pretty bad with TWR anyhow.
  
• Locking out the NERVA wouldn't solve any problems, just lock gameplay for no real benefit.
  
• Spooling on the NERVA sounds good. It's gotta take at least some time to get that nuclear reactor up to temperature.
  
• No throttle makes no sense, as you can throttle the propellant flow in a real NERVA.
  

The question of what's realistic has derailed many a thread already, I'd prefer if for once we could avoid this discussion. I'm under the impression that Squad wants there to be some unique disadvantage to the Nerva, and tried to think of things that might a) work to that effect would be more palatable than the overheating thing, but c) still a serious limitation. Between spooling and no throttle at all, I think no throttle would even be the better choice.

And I didn't propose to just make it heavier, but more powerful as well. TWR would remain the same. But today's small LV-Ns are worthwhile if you want to push as little as six tons to Duna and back; I'd like to raise the threshold considerably. It may be that a heavy Nerva's TWR could also be better than today's without imbalancing the game, but that would be something for the math geeks to figure out.

Incidentally, I'd very much prefer if the heavy Nerva would maintain it's current size. Huge tank with small nerva looks very familiar... and with my proposed stats it would even have a workable TWR.

reputation loss when destroyed

Between quicksave and revert, this will only affect those players that want to be affected. I'm afraid Squad wants something more severe.

[thereaverofdarkness]

I think making it actually cost a significant amount and maybe making it larger are the only things that should be done to nerf it. High heat generation is fine, as long as a single can run fine at full thrust, and there are ways to mitigate heat overload. After that, what should happen is that there should be more engines added with higher Isp values. If there was a ~600 Isp engine with a TWR of about 5 or so, then that would often be a popular choice for those who are making a simpler rocket.

If the LV-N were a 3.75m engine and there was a 600 Isp engine that was 2.5m, a lot of people would just use the 600 because it's a lot smaller and (should be) much cheaper.

[Kuu Lightwing]

for spooling, if it is to be implemented, it should be handled differently from jets. fuel flow should be constant, but ISP raise while NERVA is heating up and drop as it cools down. However, I don't think that would be a good mechanic because that might be a bit too annoying to use for new players.

[Renegrade]

for spooling, if it is to be implemented, it should be handled differently from jets. fuel flow should be constant, but ISP raise while NERVA is heating up and drop as it cools down.

That's a good point - I like that. I like that quite a bit. It's both a balancing factor (gameplay) AND realistic at the same time! I definitely support this concept. It may not solve all of the issues, but it would at least tone down on the "use LV-N anywhere there's a vacuum" issue.

However, I don't think that would be a good mechanic because that might be a bit too annoying to use for new players.

They can suck it. It's deep in the tech tree, they won't have to deal with it right away. Don't dismiss your own good idea because a handful of people might be initially confused by it. It's an advanced part, after all. There's no need for it to be simplistic.

[Wallygator]

I don't think it is "obvious" they want to nerf the LV-N.

I think they either haven't paid enough attention to the real science surrounding the technology OR they just haven't thought it through enough OR it's bugged.

LV-Ns will overheat if they run out of fuel before they are shut down (I believe that is accurate), and this could be built into the operating mechanic (out of fuel? Throttle stuck on? It's getting' hot in here... que DJ music, kaboom.)

LV-Ns should not overheat if run at 100%, but they should start to overheat if run at some threshold below that, the lower the thrust they faster they should overheat.

Spooling? could be fun - just make a timer after firing the engine before any thrust is generated - and make the thrust taper off in a similar manner once the throttle is shutdown. Totally agree ---> It could also NOT BE fun to a lot of players.

They already weigh a lot, making them heavier? what's the point...

Cost increase? OK by me.

Edited May 18, 2015 by Wallygator

[Kuu Lightwing]

No, I meant spooling in general. With jets it usually doesn't matter because you are running them constantly, but for a rocket engine you will be constantly overshooting the nodes, and that's not the best thing to deal with - it's annoying.

[Laie]

Spooling can be bypassed by just shutting down the engine: zero thrust in an instant. At least that's how it works with jets. That's what gave me the idea to go with no throttle at all: if everybody is going to use it like this anyway, why not make it official?

Either way, one will need an alternate propulsion system for fine adjustments. In most cases, RCS should do. Or a single small engine on top of everything else.

[Screeno]

I think, leave the poor thing alone its fine how it is! (though, a little more thrust could be nice, say 65 or maybe even 70 kn )

Just to add, the real nerva had 333.6 Kn of thrust, 850 isp, weighed 34 metric tons when empty, and was about 10 m wide and 40 something m long. So maybe moar thrust for our tiny scaled down nerva wouldn't be unrealistic.

Edited May 18, 2015 by Screeno

[Sky_walker]

• make it a lot heavier and more powerful (like, 20t and 400kN) to dramatically raise the threshold for when Nervas even start to become interesting.
  
• make it a game mode: the player may either have nuclear engines (the future of the sixties) or ISRU (the future of today), but not both in the same game.
  
• spooling: like jets, the engines may take a while to come to full thrust, and will also take a while to shut down. Should make landers more difficult, requires an alternate propulsion system for fine-tuning your trajectory.
  
• no throttle: it's either 100 percent thrust or none. Again, this is mostly aimed at landers.
  

• Makes sense. They could make it an XL size engine (still very forgiving comparing to the real engine) and increase weight further.
  
• Yep. Disable them by default in Hard mode. Most people never even learn how to do interplanetary flight without nukes, and unlike Rapiers (that suffer similar problem - people not having a clue how to build SSTO without them) nukes are available in a mid part of the tech tree.
  
• That would be really great
  
• No, thanks. That's not realistic, NEVRA engines did have throttle.
  

What I would suggest adding:

• Radioactive effects.
  
  • I wrote a bit about it here, TL;DR: add green glow to the radioactive area or parts that suffered radioactive exposure, make Kerbals turn permanently brown or make their heads glow green when in longer (30s?) contact with radioactive areas, in EVA mode you can give them Geiger meter similar to the one from Fallout games warning about radioactivity.
    
  • Destroying NEVRA should cause a radioactive cloud - lasting at least a year on a ground (if not being permanent), and in space it could existing only within physics range (for simplification).
    
  • Placing Kerbals anywhere else than above the engine for a prolonged amount of time will make them suffer radioactive effects (so no LV-Ns in pull configuration), even if engine is shielded
    
  • Possibly: add an option to remove shielding - unshielded engine should be notably lighter but much more dangerous for Kerbals and much more expensive in reputation, generally: Something that you want to use only for fully unmanned missions.
    

  [*]Launching NEVRA in career mode should have (high) reputation cost attached to it (eg. in Hard Mode it could be ~40 reputation), so launching missions with multiple NEVRAs would be difficult to pull off.

  [*]Make it an XL-sized engine (size 3 if I remember well? the largest one, like SLS), and increase weight further - as already mentioned before

  [*]Increase thrust significantly (eg. 4 times in vacuum) to make it more realistic and compensate for added disadvantages

No, I meant spooling in general. With jets it usually doesn't matter because you are running them constantly, but for a rocket engine you will be constantly overshooting the nodes, and that's not the best thing to deal with - it's annoying.

All it would change is how you operate thrust. With LV-Ns you'd slowly increase, take a break, increase again, take a break... untill you're happy with the speed it accelerates. Then cut it to zero (cut liquid fuel flow) in an instant when you reached the node. It will require more skill, but won't be annoying.

Edited May 18, 2015 by Sky_walker

[Murph]

Launching NEVRA in career mode should have (high) reputation cost attached to it (eg. in Hard Mode it could be ~40 reputation), so launching missions with multiple NEVRAs would be difficult to pull off.

It could be a mistake to have any form of pro/anti nuclear politics in the game, so I'm not sure that's really a good idea. For all we know, Kerbals could have a very high tolerance to radiation, so it could be entirely a non-issue for them.

[Sky_walker]

It could be a mistake to have any form of pro/anti nuclear politics in the game,

I'm not interested in discussing pro or anti-nuclear politics, I'm interested in facts. And it's a historical fact: Nuclear engines weren't used on spacecrafts because of the political costs. IMHO the closest equivalent in KSP to that is reputation.

For all we know, Kerbals could have a very high tolerance to radiation, so it could be entirely a non-issue for them.

That's a wild assumption. For all we know: radiation isn't implemented in the game. That's where story ends.

[Murph]

I'm not interested in discussing pro or anti-nuclear politics, I'm interested in facts. And it's a historical fact: Nuclear engines weren't used on spacecrafts because of the political costs, something that has a closest equivalent in KSP reputation.

NASA's NERVA was shelved because the funding was cut due to lack of willingness to proceed further with Apollo and beyond (to Mars). The history I've read says that it was a political move, but with financial motivation. It had very little to do with anti-nuclear politics, or nuclear safety concerns, and everything to do with national budgets and willingness to continue investment in space exploration.

That's a wild assumption. For all we know: radiation isn't implemented in the game. That's where story ends.

It's no more of a wild assumption than assuming that the people of Kerbin would have any problems with nuclear propulsion to justify a reputation hit.

[Sky_walker]

It had very little to do with anti-nuclear politics, or nuclear safety concerns

Safety concerns were an important reason why programme did not receive additional funding. But yes, funding for the Mars mission was a major factor for the decision, no doubt.

It's no more of a wild assumption than assuming that the people of Kerbin would have any problems with nuclear propulsion to justify a reputation hit.

Doesn't really matter. Fact is that radiation isn't implemented in the game. It's not something you can discuss with, it's a binary operation, either it is or it's not, and it's not.

Edited May 18, 2015 by Sky_walker

[Murph]

Safety concerns were an important reason why programme did not receive additional funding. But yes, funding for the Mars mission was a major factor for the decision, no doubt.

Funding is the only and primary reason given by Los Alamos themselves, safety concerns are not cited at all.

http://www.lanl.gov/science/NSS/issue1_2011/story4full.shtml

It was the Mars mission that led to NERVA's termination. Members of Congress judged the manned mission to Mars was too expensive and that funding the project would continue to foster a costly "space race" between the United States and the Soviet Union.

NASA evidently do not consider it to be blocked on safety grounds, having briefly revived the concept as Project Prometheus in 2000, which was again cancelled due to budget, and not safety concerns.

No, it's not. Fact is that radiation isn't implemented in the game. It's not something you can discuss with, it's a binary operation, either it is or it's not, and it's not.

Yes it is. You have to make a huge assumption to reach the conclusion that nuclear rockets should require a reputation hit, namely that Kerbals have a serious anti-nuclear politic to be concerned about. It's a mistake to add that, it brings real world politics into the game, it's a terrible idea to let the game stray into that territory.

[Brotoro]

No, I meant spooling in general. With jets it usually doesn't matter because you are running them constantly, but for a rocket engine you will be constantly overshooting the nodes, and that's not the best thing to deal with - it's annoying.

It's true that having a spooldown time on the NERV would be annoying from a gameplay aspect. KSP makes a lot of simplifications about how engines work to account for the fact that KSP is a game wherein we are doing rocket engine burns by the seat of our pants instead of calculating them out in detail ahead of time as would be done in reality.

An alternate way to model the NTR's cooldown thrust phase would be to subtract a certain amount of fuel everytime the NERV's thrust is cut to zero. The amount subtracted would depend on the integrated throttle setting from the previous n seconds...So if the player does a proper tailoff of the burn, the hit would be small. And if the cutoff is sudden, the hit would be larger. But this method would not cause players to overshoot their maneuver nodes.

Or, an alternate way of modeling this would be to simply decrease the Isp by a bit to represent the efficiency loss during the cooldown phase.

[nholzric]

This thread won me over. If you want to tweak the LV-N to encourage other engines, you've thought of some interesting ideas. I'm a big fan of increasing the cost of using the engine using various mechanisms. The monetary cost is an obvious place to start. I also like the idea of making the LV-N bigger and heavier that way it's still useful for large interplanetary ships - their "proper" domain?? - but not so good an option to slap on any old inter-munar transport or lander.

Until reading this thread I was miffed at their cowling - how if you clustered several together they could knock each other off when they were activated - but really that's just another cost to using a powerful engine, I get it.

An alternate way to model the NTR's cooldown thrust phase would be to subtract a certain amount of fuel everytime the NERV's thrust is cut to zero. The amount subtracted would depend on the integrated throttle setting from the previous n seconds...So if the player does a proper tailoff of the burn, the hit would be small. And if the cutoff is sudden, the hit would be larger. But this method would not cause players to overshoot their maneuver nodes.

Or, an alternate way of modeling this would be to simply decrease the Isp by a bit to represent the efficiency loss during the cooldown phase.

If you were trying to be stingy couldn't you deactivate all your fuel tanks to prevent the LV-N from stealing fuel at spool-down? I prefer the idea of a variable ISP depending on throttle. In Manley's Interstellar videos there was an engine where the ISP dropped the higher the throttle. Generally speaking the LV-N is using an energy source to heat fuel so maybe it works the same way - this seems like a reasonable mechanic to complicate the LV-N's use without making them incomprehensible. (Chime in if you know how they work and this is completely wrong)

[Tankman101]

So I decided to finally create an account here to share my thoughts (Well, technically mine and parts of an acquaintance of mines) of LV-N balancing.

All numbers are brainstorming only and can be changed as needed.

• LV-N will use nuclear fuel, let's call it "Fissle" for now.
  
• LV-N will only use Fissle when reactor is on, which is when the throttle is up or when activated manually.
  
• Reactor will have 6 months of combined on time fissile material.
  
• Reactor will have a, let's say, 2 minute warm up time before the engine is able to produce ANY thrust. This allows it to stay a precision interplanetary engine but require some foresight
  

Optional will be to have the reactor create heat during the no thrust period and then cool down the ship when the thrust is applied. Should encourage some smart designs.

NOTE: The only thing worse than overheating is a space engine that spools. I get that smaller precision engines are supposed to be used, but in reality we will overshoot the target by 200 m/s and then waste 1k m/s of tug fuel correcting.

[rcp27]

What I would suggest adding:

• Radioactive effects.
  

This rather overlooks the fact that the combination of solar wind and cosmic rays means that outside of the magnetosphere and atmosphere of Earth (and, presumably, Kerbin), space is pretty seriously radioactive already. One of the big concerns about real Mars missions is preventing the astronauts from suffering very severely from the effects of radiation on the long transfer flight.

[arkie87]

I'm a bit confused by this thread. The LVN is already well balanced. If you compare deltaV ratios between optimized LV-N and LV909, you need a pretty big payload to make the LVN worthwhile... no?

[Laie]

They already weigh a lot, making them heavier? what's the point...

Making it a lot heavier doesn't really solve anything, as the NERVA is pretty bad with TWR anyhow.

I think, leave the poor thing alone its fine how it is! (though, a little more thrust could be nice, say 65 or maybe even 70 kn )

Because the Nerva isn't so heavy after all. Please consider the following wallpaper (all tanks are 100% fuel). I've put the stats into each picture, but just to be sure: except for the first, each of the following designs carries the equivalent of six nukes, including 300kg of extra weight per engine as stand-in for structural parts and heatsinks. I've come up with that 6x number mostly because it suits my own needs, but I've done some browsing of Jool-5 and Eve Rocks submissions and a lot of vessels have either six or twelve nukes; there's also a few that have four, eight, or ten, but the six-or-twelves are a clear majority. So maybe that number isn't that bad after all.

One might argue that I'm going over the top, that a Nerva that only ever makes sense in the company of the biggest tanks in the game is too much. You may even be right. But the current Nerva is just too damn small: the first vessel just doesn't warrant the use of nukes (IMO, all IMO -- can't stress this enough). Making the Nerva more powerful at the same TWR would rule out the small stuff, and would greatly improve the part count on the vessels that really need it.

Please also note how even the totally overpowered, 5m/s² tug still has a better fuel economy than a Skipper or Rhino. So much for the Nerva being "too heavy already" or forcing you to a crawling speed. The TWR isn't that bad in the context of the other engines we're having.

@SkyWalker: I'd actually quite happy if the high-powered, heavy Nerva remained a small diameter part. It reminds me of this:

Just to add, the real nerva had 333.6 Kn of thrust, 850 isp, weighed 34 metric tons when empty, and was about 10 m wide and 40 something m long. So maybe moar thrust for our tiny scaled down nerva wouldn't be unrealistic.

Common mistake: you're quoting the numbers for an entire Nerva-driven rocket stage, including a hydrogen tank the size of the space shuttle's. The bare-bone engine would have been more like 7t.

Spooling? could be fun [...] Totally agree ---> It could also NOT BE fun to a lot of players.

I think it would be quite palatable. One can easily learn how to deal with it, even mittengrabbers like myself will get "good enough" results. While mildly annoying, it makes a lot more sense than the current heat thing, and is easier to cope with, too.

- - - Updated - - -

So I decided to finally create an account here to share my thoughts [...]

• LV-N will use nuclear fuel, let's call it "Fissle" for now.
  
• LV-N will only use Fissle when reactor is on, which is when the throttle is up or when activated manually.
  
• Reactor will have 6 months of combined on time fissile material.
  
• Reactor will have a, let's say, 2 minute warm up time before the engine is able to produce ANY thrust. This allows it to stay a precision interplanetary engine but require some foresight
  

Welcome to the forum!

I'd also prefer if there was a dedicated nuclear propellant, and the ability to tweak a tanks' contents as needed. One might even call it "Hydrogen" and make it a lot less dense than fuel... I think that, too, would be a lot easier to sell than the half-empty tanks we have now, even if it was objectively just as bad or even worse. I'll add that to the OP if you don't mind.

NOTE: The only thing worse than overheating is a space engine that spools. I get that smaller precision engines are supposed to be used, but in reality we will overshoot the target by 200 m/s and then waste 1k m/s of tug fuel correcting.

If your vessels makes 5m/s² (that's TWR 0.5, which would be a lot for a nuclear vessel) and takes ten seconds to spool down, you will overshoot by ~25m/s. Even with very little skill, you should be able to bring this to within 5m/s. The remainder can be coped with using smaller engines, like a single LV-909 / 48-7S, or maybe even RCS and monopropellant.

- - - Updated - - -

Radioactive effects.

[...] add green glow to the radioactive area or parts that suffered radioactive exposure, make Kerbals turn permanently brown or make their heads glow green when in longer (30s?) contact with radioactive areas,[...]

This would be quite an addition to the game... and while it sounds quite interesting at first, it would probably be an even worse gameplay mechanic than heat.

- - - Updated - - -

@ALL:

Thanks for the good discussion so far, and for not derailing the thread over politics. I'll update the OP to give a crude idea of what has been said so far, I'll also add the new suggestions.