Rethinking the nuke engine, where can we take it from here?

[Colonel_Panic]

So yesterday I built a new lander using a nuke engine, and noticed the mechanics had changed since I last played... so much so, in fact, that it turned out to not have enough dV to complete the mission! Partly because I was carrying around dead weight in oxidizer instead of extra fuel.... Anyway, Jeb is now floating in space and rethinking his life while I plan a rescue mission. I hope I gave him enough spare life support supplies.

I also noticed heat seems to be a major problem now. Together this raises a few questions...

Are nuke engines now more practical on spaceplanes? it seems that without the need for onboard oxidizer, this would be the natural choice for planning SSTO missions with limited wet weight. Has anyone yet built a good spaceplane design with 2 turbojets and a nuke? how about 2 nukes and a turbojet?

Is there a good method for bleeding off the extra heat they generate? It seems like ship designs centered around nuke engines could now benefit from dedicated heat radiators, to keep the engines and fuel tanks cool during long burns. Thermal management is now a practical part of logitstical planning, and I consider this a win, but only if there's an actual way to manage it.

[Spartwo]

One issue I'm seeing is that the pure LF tanks don't have proportional fuel loads so things built have twice the space used up for their fuel....which is annoying if you adore capital ships.

[HoloYolo]

Coming straight from the wiki page, "It will overheat when run at full throttle, but it will usually stabilize before completely filling the overheat bar. " You don't need to worry about it exploding, it stabilizes.

[FonVegen]

Well, for weight-limited SSTOs, nukes may not be the best option. You know, the amount of mass you can leave out due to oxidiser being unnecessary is replaced my the mass of the NERVs. At least that's what I think. Very large designs would probably be less of an issue.

So far wings work well as radiators. Although it's a little bit weird that we have to use plane parts on interplanetary spaceships just to keep the engines from exploding...

[diegzumillo]

I'm also thinking about that now, things are much more complex. They nerfed the nuke engines a little, but they also made it not needing ox. So it's still a powerful engine but it's more complicated. It used to be "is it in space? nukes" now not so much.

[KerikBalm]

So far, I haven't had a problem with them overheating in 1.02 (1.0 was a different story).

However, at the moment, only the space plane parts are good fuel tanks for them... so that isn't so great

[panzer1b]

One issue I'm seeing is that the pure LF tanks don't have proportional fuel loads so things built have twice the space used up for their fuel....which is annoying if you adore capital ships.

I just edit the .craft file to make them have equivalent volume but ONLY LF. While some might argue otherwise, i do not consider this a cheat, since you should be able to decide your fuel ratio. There is also a mod i used to use (but dont anymore as it modulemanager is now unable to be removed without breaking stuff and i dont like mods i cant remove when im not actively using them), i beleiev it was called modular fuel tansk or something, and i consider it 100% fair and balanced (and imo features like picking your fuel ratios should be stock).

Aside from that capital ships didnt change too much. And well, aside from being unable to make super long burns on a few ships, its still more or less teh exact same gameplay. Then again, ive started messing with ion poiwered capital ships, since ions are tiny, very hard to actually hit, and work period regardless of location, so you can have engines inside your hull spread around nicely.

I'm also thinking about that now, things are much more complex. They nerfed the nuke engines a little, but they also made it not needing ox. So it's still a powerful engine but it's more complicated. It used to be "is it in space? nukes" now not so much.

it still pretty much devolves to nuke or ions depending on mass. yes you still CAN make conventional LFO engine rockets, but they never did before and still dont make any sense as they get even worse ISPs now, so forget excessive ranges from those.

The game (career aside) is basically nuke or ion for long distance space engine, and LFO for landing/takeoff (and even nukes can do landing/takeoff on some bodies fine). Even with overheating the ISP difference is so absurdly high that it more then compensates for heating issues, extra mass of engine, ect.

Edited May 7, 2015 by panzer1b

[Aerindel]

Yep. The heat issue was fixed in 1.02, but the fuel tank issue is disappointing. All squad would have had to do is make bright yellow (or whatever) version of existing tanks and fill them with only LF but like a lot of 1.0, they didn't seem to think things through.

[panzer1b]

Yep. The heat issue was fixed in 1.02, but the fuel tank issue is disappointing. All squad would have had to do is make bright yellow (or whatever) version of existing tanks and fill them with only LF but like a lot of 1.0, they didn't seem to think things through.

id prefer modular fuel loadouts for tanks. That way we can get the right shape we want with teh right fuel types or fraction we want. ofc it should be limited so LFO tanks cant bring xenon or whatnot, but within limits i think it should be allowed to change fuel ratio.

Then again, ive already been doing this for a while by editing the .craft file.

[Aerindel]

id prefer modular fuel loadouts for tanks. That way we can get the right shape we want with teh right fuel types or fraction we want. ofc it should be limited so LFO tanks cant bring xenon or whatnot, but within limits i think it should be allowed to change fuel ratio.

Then again, ive already been doing this for a while by editing the .craft file.

I would prefer that too but I was trying to think of the laziest possible way for the devs to give us LV-N tanks.

[BDelacroix]

With heat being a thing, we really need dedicated radiators.

[-Velocity-]

One issue I'm seeing is that the pure LF tanks don't have proportional fuel loads so things built have twice the space used up for their fuel....which is annoying if you adore capital ships.

This is not an issue. This is realistic- in fact, it may even be GENEROUS. IRL, NERVA-style engines use liquid hydrogen. Liquid hydrogen has a density of 0.07 g/cm^3. That's right, one cubic meter of liquid hydrogen only weighs 70 kg (a cubic meter of water weighs 1000 kg).

[diegzumillo]

The fuel amounts should work like this: there's three sliders, one for lf, one for ox and one for total fuel. The sliders are dynamic and obey the equation lf+ox=total (with coefficients to handle different densities, if desired by the devs). Then the player can adjust at will how much of what goes in each tank.

Edited May 7, 2015 by diegzumillo

[Renegrade]

Yep. The heat issue was fixed in 1.02, but the fuel tank issue is disappointing. All squad would have had to do is make bright yellow (or whatever) version of existing tanks and fill them with only LF but like a lot of 1.0, they didn't seem to think things through.

Or did they? Real life NTRs really only get the high Isps with hydrogen - and hydrogen is a copper plated bee with an itch to store even for short duration flights (like Saturn V's S-II and S-IVB stages or the Space Shuttle's main tank). It requires a lot more tank to store (low density, therefore more tank per ton, therefore poorer tank mass ratio), and is VERY cryogenic. Hydrogen leaks out of cryo tanks at a rate of about 1% per day - by the time an actual NTR craft reached Duna (~66 days for the first available window on a delta-v optimal transfer), half of the tank would have leaked away. A Jool or Eeloo transfer would leave you with about a percent of fuel left.

Actually, on second thought, yeah, maybe they didn't think things through. We need a set of tanks for 'Nerv fuel' with REALLY bad mass ratios that boils off rapidly...

[regex]

Actually, on second thought, yeah, maybe they didn't think things through. We need a set of tanks for 'Nerv fuel' with REALLY bad mass ratios that boils off rapidly...

Eh... I prefer to think that we're getting massive overheating because we're running kerosene through the engine and getting LHyd isps out of it. Unrealistic, but this is #LOLSOKERBAL-land to begin with and there might as well be a trade-off and interesting mechanic for the heating system aside from reentry.

Although it would be hilarious to read all the outrage if a nuclear-engine spaceplane had to look something like this due to the required tankage:

[Laie]

Yep. The heat issue was fixed in 1.02, but the fuel tank issue is disappointing. All squad would have had to do is make bright yellow (or whatever) version of existing tanks and fill them with only LF but like a lot of 1.0, they didn't seem to think things through.

The heat issue isn't fixed. At best, it's now halfways manageable where 1.0.0 was way beyond good or evil.

The problem I see is that we already have enough part clutter. I think some degree of proceduralising will become inevitable: same basic shape in different sizes for the x-to-y adapters, four lengths for the cylinders. Color-coded by content. And if you want an orange tank full of xenon, so be it. That will be 2 million funds, please.

Hydrogen leaks out of cryo tanks at a rate of about 1% per day

For gameplay purposes, I'm strictly against boiloff. Like life support or RemoteTech, it shouldn't be tossed at everyone.

If Squad feels that this extraordinary engine needs an extraordinary nerf, I'd like to repeat Brotoro's idea of making nukes spool, much like jets do. Let them take a few moments to come to full thrust, and again some time to throttle down. That would even be kinda-sorta realistic, while overheating definitely is not.

[Brotoro]

If you want to consider real fuels that could be used in KSP, I prefer the idea of going with methane/LOX. You can use methane in rocket engines and jet engines, and you can use it in a NERVA with an Isp of 644 seconds. You can make these propellants and find them in space (from water ice, CO₂, and methane deposits). Both liquids are moderately cryogenic (compared to LH₂), and the overly massive tanks we have in KSP could be because of the insulation and refrigeration systems needed to prevent boil off (engineers say they can make an LH₂ tank system for Mars missions that include refrigeration systems that won't have significant boil off).

But I don't expect Squad will do this.

- - - Updated - - -

The heat issue isn't fixed. At best, it's now hallways manageable...

Lale is correct.

[regex]

The heat issue isn't fixed.

Lale is correct.

Unfortunately that's a pretty subjective balancing point; I completely disagree with these statements.

[Aerindel]

Well, I'll put it this way, I don't have any problem with nuke heat in 1.02 My ship runs out of fuel after a 40 minute burn without blowing up.

It could be completely removed for all I care because with no way to manage heat it either builds up and destroys your ship or its balanced so it doesn't, in which case why have it at all? They completely removed the heat mechanic from ISRU and drills because it wasn't working, they should just do the same for nukes....and while there at it re-entry since heat doesn't really matter their either.

[Colonel_Panic]

To clarify, my ship didn't blow up from overheating, just watching the heat accumulate and spread from tank to tank was a little unnerving, and I wanted to know if there were a particular design method to managing heat.

overheating is a fairly realistic issue with some propulsion systems like that (have you tried radiating heat in a vacuum?), so I don't see it as a "problem" per-se. Not as long as there's a solution for it, anyway. Gameplay wise I'm fine with it. As said before, this is kerbal physics... not every theoretical technology need be perfectly realistically balanced.

I could just use plane tanks, but what's this I hear about fuel flow issues? I want to stage drop tanks and leave them behind with the heavier part of the lander before making the return trip... fuel flow management is kinda important.

I agree that stock KSP should let you tweak your fuel tank ratios within reason (some tanks may only be suitable to some types of fuel), but what about in terms of a short term solution in 1.0.2?

Edited May 7, 2015 by Colonel_Panic

[regex]

To clarify, my ship didn't blow up from overheating, just watching the heat accumulate and spread from tank to tank was a little unnerving, and I wanted to know if there were a particular design method to managing heat.

Large parts and tanks with lots of fuel soak up heat. I generally use a few wings to help radiate heat (my tug lost a bunch of radiative wings with 1.0.2), and you can also use the Gigantors to help. In KSP you're probably never going to face a burn larger than, say, 4km/s (braking at Moho) if you're not doing anything strange so if you can recover from that you're doing just fine. Less engines will also help; building a vehicle with multiple nukes will make heat management a lot harder.

I could just use plane tanks, but what's this I hear about fuel flow issues? I want to stage drop tanks and leave them behind with the heavier part of the lander before making the return trip... fuel flow management is kinda important.

Uh, IIRC the nuke engines draw from the furthest tanks first, even if they're, say, Mk3 (which comprise a tug of mine). Jet engines and rapiers draw from tanks evenly.

[Brotoro]

...IIRC the nuke engines draw from the furthest tanks first, even if they're, say, Mk3 (which comprise a tug of mine). Jet engines and rapiers draw from tanks evenly.

Regex is correct here.

[Laie]

Uh, IIRC the nuke engines draw from the furthest tanks first, even if they're, say, Mk3 (which comprise a tug of mine). Jet engines and rapiers draw from tanks evenly.

The drawing evenly is a property of the (jet) engines, not the tanks.

[Aerindel]

overheating is a fairly realistic issue with some propulsion systems like that (have you tried radiating heat in a vacuum?), so I don't see it as a "problem" per-se. Not as long as there's a solution for it, anyway.

That is the issue, with no radiator parts there is no solution.

[regex]

with no radiator parts there is no solution.

Your statement is false. Every part is a radiator, some better than others, and every part is a heat sink, for better or worse.