Please explain to me, what all the LV-N hype is about?

[Xyphos]

Cuz I just don't get it. they're small underpowered engines that don't need oxidizer but we don't have any suitable LF-only tanks outside of spaceplane parts.

I attempted to use them but I find them to be quite lacking.

[FancyMouse]

Cuz I just don't get it. they're small underpowered engines that don't need oxidizer but we don't have any suitable LF-only tanks outside of spaceplane parts.

I attempted to use them but I find them to be quite lacking.

Vaccum Isp is the magic. Suppose you have 10t payload and you need 2km/s dV for a single stage (that's your interplanetary stage usually), see how much you'll need with a nuke comparing with others.

[RyanRising]

They're really efficient, but really low-thrust, so they would be good for places when you need a lot of delta-V but not a lot of oomph. Perfect for interplanetary missions. Although, I don't know what you mean by hype. They've been around for quite a while now.

[SemiaCloud]

I love the LV-N.

[fairytalefox]

They were very unique before 1.0 when they worked on usual fuel/oxidizer blend and didn't have overheating issues. For now, well, I'd rather say the whole LV-N ecosystem is kinda broken. It doesn't mean LV-N's aren't cool. They are. They just kinda lack parts to team up with.

[Xyphos]

2km/s dV single stage is basically take-off from Kerbin.

So you're saying that LV-N is only for interplanetary transfers, say.. from Kerbin orbit to Eve?

[wfalcon]

The big advantage with the LV-N engine is it's high specific impulse. This means that it's a very efficient engine. With this engine you get a large amount of delta-v using a relatively low amount of fuel.

This advantage is offset somewhat by the fact that the engine itself is rather heavy. This means that for spacecraft with smaller payloads, you're better off sticking with the LV-909. However, if you have a larger payload and you're going on a long journey then this rocket is definitely worth it.

[FancyMouse]

2km/s dV single stage is basically take-off from Kerbin.

So you're saying that LV-N is only for interplanetary transfers, say.. from Kerbin orbit to Eve?

It doesn't do well for landing/launching activities where atm Isp and/or TWR comes to the picture. But for activities with little requirement for them (interplanetary transfer, most notably), nuke is a really good option (not always, though)

I also use nukes in other scenario, like moving stuff from one space station to another.

[Terwin]

2km/s dV single stage is basically take-off from Kerbin.

So you're saying that LV-N is only for interplanetary transfers, say.. from Kerbin orbit to Eve?

That is not their only usage, but that is where they shine.

The isp of 800 seconds is more than double the second best(poodle at 350 seconds) non-electric engine.

The only stock engine with better space ISP is the ion engine which has 1/30 the thrust of the nuke, an isp of 4200 seconds, but requires a lot of electrical power to run.

I don't have any problem running nukes with MK3 parts, and that size even allows things like drills and ISRU in the cargo bay.

[Laie]

Cuz I just don't get it. they're small underpowered engines that don't need oxidizer but we don't have any suitable LF-only tanks outside of spaceplane parts.

I attempted to use them but I find them to be quite lacking.

They *are* quite lacking, and I heartily agree about them being underpowered. Yet they're still twice as efficient as the next best engine. That's really all that it's about.

[georgTF]

There are lifting engnies, airbreathers, tiny/ion engines and then there are orbital engines. Those are usually not very powerfull but are economical and the nuke is extremly economical so it's often the engine that gets the best range. 909, aerospikes and poodles are all very good engines and are often picked over nukes when the craft is very light, or needs a high thrust engine. Landers need to burn very quickly sometimes for example. Nukes are also terrible for orbital insertion burns when there's no chance of airbraking. They're also very heavy and the craft needs heat management.

I don't think it's hype per se, it's just that it's damn hard to find a reason not to use them simply because of the glorious range they offer. Since spaceplanes use LF tanks and are usually not too heavy they are very well suited for nukes, and SSTOs are very popular so there's some hype there. Tugs or fuel tankes also also ideal craft for nukes. Basically any craft that isn't too light or too heavy, or doesn't need to be thrifty with fuel or high Dv burns done in very little time, is better off using the nuke than anything else.

The fact that is't heavy, bulky and hot is for balance and to give other engines a purpose. They're far from underpowered. They're pretty balanced with their problems, otherwise they'd be OP.

[Scotius]

They *are* quite lacking, and I heartily agree about them being underpowered. Yet they're still twice as efficient as the next best engine. That's really all that it's about.

Actually, compared to their real-life predecessors L-VN's are nerfed hard. It was a conscious choice of the developers - Nukes with nearly RL-ish stats would be THE best engines in the game. For every purpose.

[sal_vager]

Was a real, full sized Nerva ever made? All I can find are test articles.

[hellion13]

I have no use for efficiency. Its going to get there as fast as possible. If it doesn't have at least a twr of 4.00 its not good enough. I'm worse with probes. They need a twr of 8 or higher. Im trying to achieve blow it up in the atmosphere shortly after take off TWRs or at least peg the g meter. L-VNs are too slow for me.

[MaverickSawyer]

Was a real, full sized Nerva ever made? All I can find are test articles.

They were working on a flight article, but they never hit flight hardware phase. But they DID do a to-spec NERVA and hot fired it at Jackass Flats, NV. Ran it for more than 30 minutes, if memory serves.

[Streetwind]

The NERVA-XE was the closest thing to flight hardware they had... it was a test article built "as if" it was meant to be flight hardware. Still, it was not a complete engine, but rather just the parts required for the test.

They tested that successfully, went back to the drawing board, produced the design for the second-generation NERVA-2 that incorporated all the many lessons learned from the NERVA program and far exceeded the performance of what was previously tested, and presented it to the government... and promptly got a big fat "CANCELLED" stamped on their foreheads for their efforts.

Later-on, at the height of the cold war, there was a program called Project Timberwind which studied nuclear engines in an "end of times" scenario. Basically, high performance open-cycle nuclear engines for atmospheric and space use when nobody cares about radiation anymore because the nukes are already flying. Thank god that project remained a paper design study that lost all reason to exist with the fall of the Soviet Union...

The performance of the LV-N ingame, TWR and Isp wise, was actually pretty much a carbon copy of the NERVA-XE test article before 1.0. But then it was nerfed some because in KSP's tiny solar system with its tiny dV costs, the advantage it offered over chemical engines was so large that it made everything else pointless. And that doesn't make for interesting gameplay.

[Xyphos]

I have no use for efficiency. Its going to get there as fast as possible. If it doesn't have at least a twr of 4.00 its not good enough. I'm worse with probes. They need a twr of 8 or higher. Im trying to achieve blow it up in the atmosphere shortly after take off TWRs or at least peg the g meter. L-VNs are too slow for me.

you only need a twr of 1.2 for takeoff. 4 is overkill.

but, now that I know LV-N's real purpose, I may use them more often. thanks peeps.

[Teilnehmer]

…in KSP's tiny solar system with its tiny dV costs, the advantage it offered over chemical engines was so large that it made everything else pointless.

I didn’t get that.

The less ÃŽâ€v needed the less preferable LV-Ns are. Isn’t that right?

[KerikBalm]

I didn’t get that.

The less ÃŽâ€v needed the less preferable LV-Ns are. Isn’t that right?

Yes, but if the LV-N had a better TWR, it would be preferable in every case.

Now, with its TWR nerfed, for low dV needs, its not so preferable, and thus the KSP system with its smaller dV requirements, actually has a place for non-Nuke engines.

Nuke engines are great for either high dV single stages, or high payload fractions that don't need high TWR.

If I have a 100 ton payload, engine mass doesn't matter so much if I'm pushing it with 4 LV-909s or 4 LV-Ns.

The TWR will be nearly the same, but the propellant mass required will be much less.

Of course now with ISRU, I don't worry about fuel efficiency as much as I used to.

When I had to send fuel tankers to Duna/Mun/the Jool system from Kerbin, I wanted my landers to use as little fuel per trip as possible, so I could get as many trips to the surface as possible without having to send a fuel tanker to resupply a fuel depot.

Now I can make my own fuel on site... so...

Also when I was biome harvesting, I'd like to carry 2x goo, 2x mat bays - now that scientists can reset them, I can transmit, reset, take data and store it in the pod, reset, take data and leave it in the instrument.

So my lander dry mass decreased... and the LV-N mass increased...

So... all that combined means I stopped using the LV-N as my lander engine... which is also good because now I use shorter engines and my landers are less prone to tipping over.

[Sharpy]

They were very unique before 1.0 when they worked on usual fuel/oxidizer blend and didn't have overheating issues. For now, well, I'd rather say the whole LV-N ecosystem is kinda broken. It doesn't mean LV-N's aren't cool. They are. They just kinda lack parts to team up with.

That's because you people just don't invest into the heavy airplane lines. There's a plenty of MK3 parts and they synergize with LV-N very well.

[annallia]

I still find them useful... On my tugs. That is about it really, the odd interplanetary craft as well but it has to be a specific build now not just anything going interplanetary.

And honestly the only reason I find them useful on my tugs is I hate docking them to refuel so being able to do that far, far less (and using a mod that gives large LF tanks) they are preferable still to me.

[Kurld]

Sort of off topic, IRL, didn't they use superheated water as the propellant? Or am I mis-remembering?

[Rhomphaia]

Sort of off topic, IRL, didn't they use superheated water as the propellant? Or am I mis-remembering?

You are thinking of the Nuclear Salt Water Rocket.

https://en.wikipedia.org/wiki/Nuclear_salt-water_rocket

Crazier than NERVA, not quite as Crazy as Project Orion

https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)

[Red Iron Crown]

I must refer to UmbralRaptor's entirely accurate "Stages of Rocket Design":

0. I don't know what any of these numbers mean.

1. More thrust!

2. More TWR! (engines per tank, boosters)

3. More Isp!

4. I want more ÃŽâ€V?

5. Oh, so that's how mass ratios work...

6. Fun with payload fractions!

Sounds like the OP is at step 1 or 2. When you get to steps 3 and 4, suddenly the LV-N becomes awesome.

[Orbital Vagabond]

[h=2]Please explain to me, what all the LV-N hype is about?

[/h]

Sure: Pre-1.0, LV-Ns handily beat basically every other other engine for efficiency.

This changed in 1.0, and now some players are disappointed that "Use nukes" isn't the answer to maximize dV in every case.

The game state now is better for the change, and people will get over it in time. 1.0 also nerfed some other engines like the 48-7S that ruined similar "use this for everything" situations.