Nuclear engines useless?

[Fullmetal Analyst]

i dont get the point of using nuclear engines, they seem to need huge tanks to get a reasonable amount of dV, and seem to be worse than other engines in general

here some example:

two rockets with same payload, both have almost same dV, but the hydrogen version is a lot bulkier while actually having 100 less dV

(hydrogen / terrier engine)

so whats actually the point of these nuclear engines?

they dont seem really useful compared to other fuel types

 

when i remove the truss and SAS the stats are still ridiculous

Edited March 14, 2023 by Fullmetal Analyst

[HenryBlatbugIII]

1. "Bulky" only matters if you're in an atmosphere.  If you're launching from Kerbin maybe a nuclear engine is a bad idea, but in a vacuum you only need to care about the mass rather than the volume.

2. The nuclear engine has a higher mass but also a higher Isp.  Therefore, the nuclear rocket will be heavier if you're building for a small amount of dV but lighter if you're building for a large amount of dV.  (I don't have the stats in front of me right now to calculate the changeover point.)

3. This is speculation, but once resource harvesting is added I wouldn't be surprised if Hydrogen is easier to harvest than Methalox.

It's definitely not a strict upgrade from the Terrier, but it does have its uses.

[LameLefty]

The SWERV is awesome. I have a SWERV-powered transfer stage fed from a 50 ton LH2 tank, with a probe core, reaction wheels and some minimal RCS that can push itself out of LKO  with 16,000 m/s dV available. With a 4-crew methalox lander as payload, it still has over 10K m/s dV available. Once you go nuke and figure out how to use it., you never go back.

That said, to use an architecture like this efficiently, you have to be able to rendezvous and dock in both LKO and around wherever you leave your lander, and right now our tools to assist with this are quite limited. 

[The Aziz]

Wet/dry mass difference. That tiny ship carries over 4 tons of methalox, while there's only roughly 2.5 tons of hydrogen in the nuclear craft. It's larger, but the mass barely increased. So, you can have larger, potentially heavier spacecraft using lighter fuel and an engine that's not that much different (aside of vacuum isp) from the terrier.

[Wheehaw Kerman]

10 minutes ago, HenryBlatbugIII said:

1. "Bulky" only matters if you're in an atmosphere.  If you're launching from Kerbin maybe a nuclear engine is a bad idea, but in a vacuum you only need to care about the mass rather than the volume.

Strap enough Clydesdales on and you can brute force pretty much anything into Kerbin orbit without needing a sustainer.  Until I started figuring out how to work around the newness and the bugs my basic build was three XL hydrogen tanks and a SWERV with eight Clydesdales mounted radially.  You can go places with that.

[magnemoe]

14 minutes ago, The Aziz said:

Wet/dry mass difference. That tiny ship carries over 4 tons of methalox, while there's only roughly 2.5 tons of hydrogen in the nuclear craft. It's larger, but the mass barely increased. So, you can have larger, potentially heavier spacecraft using lighter fuel and an engine that's not that much different (aside of vacuum isp) from the terrier.

I say the nuclear engines  and especially the new SWERV works better with an heavy payload, say an Duna mission with crew quarters and an dedicated lander, perhaps extra fuel for the lander so you can use it multiple times. The nuclear engines looses out if you have an light payload. If you want to maximize dV for something light its better to have an chemical upper stage. Same is true in KSP 1 but the bulkiness make it harder to build. 

38 minutes ago, HenryBlatbugIII said:

1. "Bulky" only matters if you're in an atmosphere.  If you're launching from Kerbin maybe a nuclear engine is a bad idea, but in a vacuum you only need to care about the mass rather than the volume.

2. The nuclear engine has a higher mass but also a higher Isp.  Therefore, the nuclear rocket will be heavier if you're building for a small amount of dV but lighter if you're building for a large amount of dV.  (I don't have the stats in front of me right now to calculate the changeover point.)

3. This is speculation, but once resource harvesting is added I wouldn't be surprised if Hydrogen is easier to harvest than Methalox.

It's definitely not a strict upgrade from the Terrier, but it does have its uses.

3: I thought the same, ice is common in the outer solar system. But for this we would need hydrolox engines to take full advantage of it. 

[FlazeTheDragon]

Ima just leave this here

Your problem is using the nerv. Nerv is dead content and is surpassed in literally every way by Swerv.

Edited March 14, 2023 by FlazeTheDragon

[Razor235]

I admit I've been having difficulty finding a good use case for them.  The sheer bulk to get any reasonable dV out with a suitable payload requires orbital construction (treacherous at best with current bugs), atrociously large single launch (5 fps the whole way, yaaaaaay), or nuclear SSTO, which I dislike for petty reasons.   I've been sticking to chemical rockets for interplanetary.  It's this weird place where the NERV  sucks but SWERV is too good (tank mass excepted).

The 1.25 diameter hydrogen tank seems utterly worthless even if the other tanks can have some uses.

 

Hilariously it reminds me of Terra Invicta where all engines, NTRs included, are terrible until gas core fission, which are only useful for planetary defense anyway

Edited March 14, 2023 by Razor235

[The Aziz]

Admittedly currently they're not that useful (though in KSP1 a small nuclear spacecraft was what brought me to Moho and back after refueling, wouldn't have done that with conventional rocket), but once we get proper cargo to move around, they'll be a fine middle ground between methalox and orion propulsion (probably also much cheaper to manufacture).

[FlazeTheDragon]

24 minutes ago, Razor235 said:

I admit I've been having difficulty finding a good use case for them.  The sheer bulk to get any reasonable dV out with a suitable payload requires orbital construction (treacherous at best with current bugs), atrociously large single launch (5 fps the whole way, yaaaaaay), or nuclear SSTO, which I dislike for petty reasons.   I've been sticking to chemical rockets for interplanetary.  It's this weird place where the NERV  sucks but SWERV is too good (tank mass excepted).

The 1.25 diameter hydrogen tank seems utterly worthless even if the other tanks can have some uses.

 

Hilariously it reminds me of Terra Invicta where all engines, NTRs included, are terrible until gas core fission, which are only useful for planetary defense anyway

Theres actually an intermediate size nuclear engine in the games hidden assets (you can find it and use it, but i dont think its 100% finished so its parameters may change). You probs seen it in my SAS post/video lol.

It actually allows for slightly more shapely hydrogen ssto builds. Also, once cargo bays are actually usable, you can probs encase the hydrogen tanks in a cargobay to make it not look as goofy.

But, i do agree. Im a huge fan of sleek and ''fast'' looking ssto's and the whole hydrogen giga chungus vibe isnt the most appealing to me either.

[Fullmetal Analyst]

hmm true, looks like this will be able to haul quite a bit of stuff into space

[Razor235]

The triumph of thrust over aerodynamics.

[FlazeTheDragon]

7 minutes ago, Razor235 said:

The triumph of thrust over aerodynamics.

You may not like it, but this is what peak performance looks like

Spoiler

 

[Razor235]

Bosozuko rockets aren't real and cannot hurt me... 

Bosozuko rockets aren't real and cannot hurt me... 

Bosozuko rockets aren't real and cannot hurt me... 

 

[The Aziz]

3 minutes ago, FlazeTheDragon said:

You may not like it, but this is what peak performance looks like

  Hide contents

 

Your horse looks weird

[FlazeTheDragon]

Just now, Razor235 said:

Bosozuko rockets aren't real and cannot hurt me... 

Bosozuko rockets aren't real and cannot hurt me... 

Bosozuko rockets aren't real and cannot hurt me... 

 

LMAO, that is actually such a good comparison xD

1 minute ago, The Aziz said:

Your horse looks weird

[Fullmetal Analyst]

guess this covers all intermediate exploration needs
the lander can refuel 5 times for a total of ~8200 dV

[Strawberry]

1 hour ago, Razor235 said:

It's this weird place where the NERV  sucks but SWERV is too good (tank mass excepted).

Yeah this is my main issue with them as well. Ive been trying to find a case where youd use NERV over SWERV and I cant find any. With any reasonable payload, a swerv will outperform a nerv engine in both delta v and thrust, for example with a large hydrogen tank, with a payload of a strut adapter and a medium command module is roughly the break even point for when a swerv engine becomes better then a nerv engine . The only time a nerv engine will outperform a swerv engine is when you're using incredibly bare bones and small payloads with basically no structural elements. I think a few changes could help the NERV engine loads.

1. Increase the density of hydrogen.

Hydrogens low density is to promote orbital construction which is good, but it feels way too little. These two fuel tanks have the same weight. I think from a player intution standpoint this just makes things unclear how much fuel you're actually sending up as it just feels unrealistic. This would reduce how much volume is taken up by hydrogen, thus making smaller nuclear spacecraft with NERV engines viable. Currently if you want to go nuclear you need to go large, but if you increased hydrogen density then you could make medium sized nuclear spacecraft viable. This would reduce how much hydrogen promotes orbital construction  and buff already honestly pretty strong nuclear engines which is why I would suggest point two.

2. Introduce radiation and thermal heating to nuclear engines.

Nuclear engines should produce both heat and radiation, with NERV producing a more manageable amount compared to SWERV engines. Heat would lead to a simple dry mass and volume penalty to nuclear engines, since SWERV would presumably produce much more heat this would hit them more. Finally, add radiation to nuclear spacecraft. This radiation can be reduced by two ways, shadow shields/radiation blocking, and distance. NERV engines would have minimal radiation meaning that they could be blocked by hydrogen tanks and a shadowshield easily, but SWERV engines would be radioactive to the point you need to use lots of struts for it to be viable. This would mean that for SWERV engines a large chunk of the spacecraft must be constructed by orbital construction, whereas for NERV engines you can easily send it up in one piece. 

[jimmymcgoochie]

Nuclear engines aren’t directly comparable to conventional rockets: they’re much heavier, use a propellant that’s very un-dense (weird that there isn’t a word for that…) and so need disproportionately large fuel tanks, but their trade off is extremely high ISP and so much greater maximum delta-V than a chemical rocket can achieve. The Terrier is a perfectly good engine for the upper stages of launch rockets and for landers, but nuclear engines are meant for throwing large vessels between planets and the IRL Nerva was intended for use on interplanetary spaceships where its high ISP and long burn time made it the ideal choice for throwing several hundred tons between Earth and Mars.

Hydrogen is also much more abundant than methane- it can be electrolysed from water or skimmed from a gas giant, whereas making methane from scratch would require hydrogen production as well as getting hold of carbon, most likely from CO2, and then you need the oxygen to burn it with.

The balance between chemical and nuclear rockets is a lot more clear-cut in reality than the 1/10 scale Kerbal version, but you can’t get five-figure delta-V from a chemical engine in KSP or KSP2 but you can easily do so with the NERV in either case, never mind the considerably more efficient SWERV.

TL;DR, chemical rockets are for spacecraft, nuclear rockets are for spaceships. NTRs scale much better as vessels and distances get larger and should be used accordingly.

[magnemoe]

1 hour ago, FlazeTheDragon said:

Theres actually an intermediate size nuclear engine in the games hidden assets (you can find it and use it, but i dont think its 100% finished so its parameters may change). You probs seen it in my SAS post/video lol.

It actually allows for slightly more shapely hydrogen ssto builds. Also, once cargo bays are actually usable, you can probs encase the hydrogen tanks in a cargobay to make it not look as goofy.

But, i do agree. Im a huge fan of sleek and ''fast'' looking ssto's and the whole hydrogen giga chungus vibe isnt the most appealing to me either.

Is that the engine with an retractable vacuum nozzle and option for an oxygen afterburner? 

[jimmymcgoochie]

10 minutes ago, Strawberry said:

1. Increase the density of hydrogen.

Liquid hydrogen is not dense. It’s an extremely small, extremely light molecule that has a really low density and so you need a much larger volume of hydrogen to contain the same mass of hydrogen compared to methane. It doesn’t matter if it’s “unintuitive” because it’s completely realistic.

The problem isn’t that the NERV is bad, but that the new SWERV is OP in comparison with its significantly higher ISP blowing the NERV out of the water. If the SWERV was just a bigger engine with more thrust and similar ISP and mass:thrust ratio a la Restock+ Cherenkov then there wouldn’t be an issue.

[FlazeTheDragon]

5 minutes ago, magnemoe said:

Is that the engine with an retractable vacuum nozzle and option for an oxygen afterburner? 

Probably, it has an alternate mode which retracts the nozzle, but the afterburning mode currently does not work.

[LameLefty]

Just now, jimmymcgoochie said:

The problem isn’t that the NERV is bad, but that the new SWERV is OP in comparison with its significantly higher ISP blowing the NERV out of the water. If the SWERV was just a bigger engine with more thrust and similar ISP and mass:thrust ratio a la Restock+ Cherenkov then there wouldn’t be an issue.

SWERV is great! It’s only OP in the case of a pure sandbox, with all parts unlocked and usable from the get-go. In a true career-based campaign with an actual technology tree, you can be sure it’s going to be waaaay up there past the basic NERV, and require a lot of Science!(tm) to unlock for your late-game in-system bases, colonies and stations. 

[regex]

Nuclear engines matter when you go big. For smaller stuff like your example craft, normal chemical engines are better.

[Tapeta]

I think nobody is reading parts descriptions. SWERV is suppose to be a "GASCORE" nuclear engine. Solid core nuclear thermal engines were tested in RL, but nobody knows how the heck will gascore reactor work without spewing its intrails all over current orbit.

SWERV is completely different league than NERV.

Edited March 14, 2023 by Tapeta