Whats wrong with my nukes?

[colin_in_space]

My nuke engines no longer seem efficient. Mechjb doesn't give different delta-V for atmo and vacum, and this seems to be how they are behaving. So instead of an ISP of 800 it seems more like 150.

Anyone else have this sort of issue?

[Lime]

In 1.0 the nuclear engine only uses liquid fuel. So oxidizer is just extra weight.

[selfish_meme]

My nuke engines no longer seem efficient. Mechjb doesn't give different delta-V for atmo and vacum, and this seems to be how they are behaving. So instead of an ISP of 800 it seems more like 150.

Anyone else have this sort of issue?

This is how they work in the new update, they also only use liquid fuel and not oxidizer to compensate a bit. You can look up the many discussion threads about it.

[JacobT11]

In 1.0 the nuclear engine only uses liquid fuel. So oxidizer is just extra weight.

You know, the moment I discovered that was just a wonderful realization that I could cut the weight of my nuke ships.

[DBowman]

You can try my Be Cool Stock Nuke, it's got some variants on the Orange tank with only Liquid fuel, no need to carry empty Oxidizer tankage around.

[FancyMouse]

You know, the moment I discovered that was just a wonderful realization that I could cut the weight of my nuke ships.

Does it really save? Isp and thrust are the same, meaning the fuel consumption rate is the same. LFO->LF means the new LF rate is the old LF+O (mass) rate. But we don't have many LF-only tanks, and using LFO tanks will just increase the dry mass, albeit just a little - am I missing anything?

[tarkhil]

LV-N is dead. Just dead.

[KerikBalm]

Nope, you're not missing anything.

I've already seen someone else on the forums that thought it would consume LF at the same rate as before, and provide the same thrust as before, except now one doesn't need to carry oxidizer.

It doesn't work like that. As it doesn't use oxidizer, it consumes more LF per second (same total propellant mass per second, just all LF now instead of LF+O).

The tanks for it aren't quite as good anymore

[soulsource]

Let's see, what Scott Manley has to say about the LV-Ns in 1.x...

[Xannari Ferrows]

The benefits of the Nuclear Engine get better as you go bigger. Are you going massive, or staying compact?

[KroShan]

LV-N is dead. Just dead.

nope definitly not...

its only a problem for old save crafts in Orbit where you cant get rid of the oxidizer.

the major advantage of LV-N is that your last stage can be much lighter and so your launch stage is smaller. the downside is that the fuel density in the tank is lower. so you need a large tank.

-ninjad-

please watch scott manleys explanation...

[magnemoe]

The benefits of the Nuclear Engine get better as you go bigger. Are you going massive, or staying compact?

This, so use MK3 tanks.

Note that if you make an tug and send it to Duna or other places it might be smart to have some oxidizer capacity on your tug so you can use it to refuel landers or probes.

[Col_Jessep]

The LV-N is now great for large vessels that need lots of delta-v like a Jool Mothership. Why not build a tug with lots of reaction wheels, a couple of LV-Ns, Mk3 Lf tanks and leave it in LKO?

[DunaRocketeer]

I haven't yet gotten to the point where I've unlocked the LV-N's in 1.0, but how are they dead? If you empty the tanks of oxidizer then surely your vessels have a better thrust to weight ratio than in pre-1.0? What am I missing here? Do you now go through fuel twice as quick? Also, I plan on using tweakscale on some aviation tanks to make the TWR even better.

[Snark]

I haven't yet gotten to the point where I've unlocked the LV-N's in 1.0, but how are they dead? If you empty the tanks of oxidizer then surely your vessels have a better thrust to weight ratio than in pre-1.0? What am I missing here? Do you now go through fuel twice as quick? Also, I plan on using tweakscale on some aviation tanks to make the TWR even better.

They're not dead, they're just nerfed.

They still have the same Isp... but you have to remember that the Isp applies per unit of total reaction mass. It used to be that if you were building a nuke ship that needed 4 tons of reaction mass, you could use an LFO tank like the FL-T800, which gets you 4 tons of fuel (1.8 of LF plus 2.2 of oxidizer) at a cost of 0.5 tons of dry mass. Now that you can't use oxidizer, you have to use TWO of those FL-T800 tanks (with oxidizer removed)... so now you have wasted a full ton of dry mass, plus you only get 3.6 tons of reaction mass.

So the numbers are simply worse, even without taking the engine's greatly increased mass and heat into consideration.

[Sharpy]

MK3 provides some pretty big Liquid Fuel only tanks.

The savings due to LF aren't very great but they are there. Say, you need 20t of LF for the dV you need.

The tank to hold 200 units of LF weighs 1t dry mass + 20t fuel. So, 21t.

If you use LF+OX tanks, they come with 8t LF, 12t Ox, 1t dry mass. You need two and a half-sized one, 8+8+4t = 20t of fuel with 2.5t tank dry mass total. Plus struts, plus air drag, plus part count, stress and all the headaches of using too many or too big parts.

AFAIK Nerv has a pathetic efficiency on ground level, both thrust and ISp. With absolute minimum setup I got like 0.44 TWR. This changes with altitude and fast. Some 4000m is a break-even point of TWR=1. At 6-8km it actually pays to switch them on. I made an experiment with combining them with jet engines; the basic jets brought my contraption to some 6km, then I switched to the atomic, and reached 10km on some 150 units of liquid fuel, still carrying the jet engines and like 90% of their fuel.

So, generally, don't bother switching them on below 6km and you're good.

[DunaRocketeer]

They're not dead, they're just nerfed.

They still have the same Isp... but you have to remember that the Isp applies per unit of total reaction mass. It used to be that if you were building a nuke ship that needed 4 tons of reaction mass, you could use an LFO tank like the FL-T800, which gets you 4 tons of fuel (1.8 of LF plus 2.2 of oxidizer) at a cost of 0.5 tons of dry mass. Now that you can't use oxidizer, you have to use TWO of those FL-T800 tanks (with oxidizer removed)... so now you have wasted a full ton of dry mass, plus you only get 3.6 tons of reaction mass.

So the numbers are simply worse, even without taking the engine's greatly increased mass and heat into consideration.

Got it, thankyou.

[Xannari Ferrows]

They haven't been nerfed at all. Quite frankly, they needed a push in the right direction. If anything, I'd say they were improved, but not because they are easier to use, oh no.

The only reason for that line of thinking is because of the game balancing. In real life, this'd be perfect [disregard the lack of liquid hydrogen].

[Rickenbacker]

We really, really need the option to go 100% fuel / 100% oxidizer or anything in between for ALL tanks in stock. Perhaps with a button to restore the proper ratio, if we screw it up, as we inevitably will .

[maltesh]

I ultimately wound up doing three things:

I installed Modular Fuels, so I could fill the stock fuel tanks with liquid fuel alone.

I lowered the heat production so that they produced as much heat as a skipper. While I've seen posts that the heat production of LV-Ns is overstated in stock,I'm hard-pressed to find more reputable confirmation, and my biggest objection is that spacecraft don't cool down while unloaded, and the stock heat management capabilities leave a lot to be desired. I may wind up lowering the heat production even more.

I'm also experimenting with Near Future's Heat Control parts.

The LF-only tanks are Kerbpainted reddish so that I can easily tell them from LF/O tanks.Probably going to have to upgrade to the folding radiators on most of my designs, though.

[Red Iron Crown]

They haven't been nerfed at all.

Increasing the mass of them from 2.25t to 3t without an increase in thrust or Isp is pretty clearly a nerf.

That said, they are still very useful. For single use they're only really good if going beyond Duna/Eve, but if you are doing ISRU + reusable tugs they really shine.

[storm6436]

Yeah, I can't help but roll my eyes a bit Manley's "Nothing to see here, move along."

Sure you don't carry the oxidizer with you any more, but as he points out, you have to stack quite a few tanks to get to the cream filling.

If the performance of version 2 is less than version 1 under identical conditions, it's a nerf by definition. Sure one may try to make the case it's a lateral nerf / repurposing... But that doesn't handwave away the fact that certain use cases were definitely nerfed.

[storm6436]

I'd also like to point out there's nothing wrong with repurposing stuff... But playing sophistry games with word definitions got old for me back when I beta tested UO and EQ.

Personally, the tech tree needs some love. Would like to see either more engines or tech blocks that, when researched, altered base stats a small amount (1-5%)... Give me something to do with the massive gobs of science I have laying around that helps me feel like I'm accomplishing something. Past a certain point I don't need cash.

I'd happily snap up tech upgrades... Alternate versions of modules for example, like DMagic's not-huge material science node. A tech step that adds +5 vac ISP to transfer motors like the terrier? Sure! Even a sliding scale, where smaller motors get more out of it, like +5 ASL ISP for the reliant, its brother (and any similar size class, so probably the little mammoth too), +4 for the mainsail/skipper, and +3 for the huge guy? Sure.

Heck, make it where the trade off is cost. Exotic material upgrade, -5% engine/tank/structural mass for +10% cost? I'd buy that. I'd even go for gating some stuff behind material science upgrades, things that could only be done big prior to the new material can be researched into smaller versions, provided it's not volume dependant.

Then again if I was calling the research shots, some folks would cringe. There'd be multiple types of science to done... And all that heliodynamic science you just did will not solve a material science problem when you're trying to come up with a better ceramic ablator. Just like all the material science in world might make a stronger/lighter wing, but it won't give you a better wing shape.

[Sharpy]

Yeah, I can't help but roll my eyes a bit Manley's "Nothing to see here, move along."

Sure you don't carry the oxidizer with you any more, but as he points out, you have to stack quite a few tanks to get to the cream filling.

Seriously? Mk3 Liquid Fuel Fuselage Long takes 10 000 liquid fuel units, with dry mass of 7.14 (57.14 full)

Compare that to Kerbodyne S3-14400 Tank with 14400 units of LF+Ox, 10 tons of dry mass (82 full).

That's 2.8% increase in dry mass if you take 3 MK3 instead of 2 Kerbodyne.

How many of these do you need to fly from Kerbin to Jool on the nuke engine?

[Feradose]

I quite like not being able to change tanks to pure LF now. It is a Nerva, it should be using hydrogen and hydrogen isnt that dense. Giving less fuel per tank. Just like a tank with removed LOx, it just feels like a low density tank. But the dry weight.. I personally wouldnt mind low density LF tanks that arent atmosphere optimized, but, are space optimized girders with insulator sheet layer for minimum dry weight. What iwould really suck is boiloff. It would be really annoying.