Are Nuclear Rockets "Cheating"?

[Red Iron Crown]

Yeah the aerospike pre-nerf was the solution to almost every problem that a nuke couldn't solve. The 48-7S needs a similar treatment, IMO.

Also note that tavert's charts haven't been updated for 0.24, which changed the specs of a few engines.

[Renegrade]

And you are right about twr close to 1, in this setting the LV-N is hopeless, you will not want it for an Tylo lander as an example. An exception might be an hybrid engine on a large lander where the LV-N is used alone for the deorbit and circulate burn

Yeah, sometimes you should use them, sometimes not. My main point is basically 'a time and a place for everything'. My main beef is that people tend to spam them all over just because of the 800 isp, not noticing that they've added 50 tons of engine to a 30 ton vessel...

Hybrid engines also have other uses, my best example is the Kethane miner who mine Minmus then return to LKO, it has to have enough trust to take off from minmus, fully loaded, then burn back to LKO, and go back then the fuel is delivered. two LV-N and a skipper works nice here, Skipper is used for Minmus takeoff and perhaps the burn to LKO if you don't want to wait, on return and landing on Minmus the ship is light and can run on nuclear alone.

Mmm that's a nice idea. I haven't done enough play with Kethane or Karbonite, I should do moar and try out some designs like that later in the tree. Also, the updated Skipper is extremely good

Tavert's mass optimal engine charts. I have this in my bookmarks and refer to it regularly, it's a great resource if you're trying to maximize efficiency.

Yeah, that's a great resource, it's in my bookmarks too. I need to use it moar. I was going to write my own back in the day, but I found that instead... (when I post an ascii-formatted TWR chart, that's actually a test module for my version of that hehe)

Yeah the aerospike pre-nerf was the solution to almost every problem that a nuke couldn't solve. The 48-7S needs a similar treatment, IMO.

Yes, it does. My Horrible Nerf patch reduces it to 15 thrust, putting it slightly below a T30 (15-ish), with another nerf aimed at it's atmospheric isp just in case~. That's in contrast to Stupid_chris' rebalance, which increases the mass instead with a slight hit to vac isp. My version is still very worthy on probes and light landers in terms of dv, but isn't a replacement for the mainsail when mounted on huge arrays of cubic struts heh.

[Overfloater]

Man, I hope they don't nerf them to 550 Isp or something because of all this rant... ;-D

[Renegrade]

Man, I hope they don't nerf them to 550 Isp or something because of all this rant... ;-D

Ugh. They'd have to be made a lot lighter then. In terms of gameplay, it's actually an acceptable engine as is.

My ranting is mostly about players going "WHEE 800 ISP" and "I NEED NUKES TO GO TO X" while they blithely ignore the fact that the 800 ISP is nicely offset by the really crappy TWR and mass, and that no, chemical engines can send a reasonable craft anywhere...

[Jouni]

Basically, there are only 4 engines you should use in the game if part count and cost are not an issue:

Turbojets: for use in the atmosphere of Kerbin/Laythe

48-7s: for use when high thrust is needed

LV-Ns: for when a high TWR is not needed, but you do need decent amounts of thrust

Ions: for when a very low TWR is acceptable.

The 48-7S engine has its niche in small Tylo landers and in the upper stages of Eve landers. Otherwise it's not that efficient anymore. Nukes and ions are almost always better lander engines, unless you want to make your life easier by trading efficiency for high TWR.

I'm not sure about the lower stages of Eve landers anymore. In 0.23.5, the SLS engines were really good, but the rebalancing in 0.24 probably changed that.

[Frozen_Heart]

Basically, there are only 4 engines you should use in the game if part count and cost are not an issue:

Turbojets: for use in the atmosphere of Kerbin/Laythe

48-7s: for use when high thrust is needed

LV-Ns: for when a high TWR is not needed, but you do need decent amounts of thrust

Ions: for when a very low TWR is acceptable.

All the other engines have very marginal uses if part count is not an issue

Or you know, you could play the game for fun and just use what engines you feel like?

[davidpsummers]

A decent approximation of this in KSP could be done by changing the LV-N to use Liquid Fuel only, without oxidizer.

Of course then you would need tanks that hold only fuel and not oxidizer. Simpler to assume that if you have a LV-N, then both tanks are filled with fuel?

[Motokid600]

I'd rather build more expensive, less efficient rockets if it means shorter burn times. I don't go for anything less then a .6 twr

[juanml82]

Of course then you would need tanks that hold only fuel and not oxidizer. Simpler to assume that if you have a LV-N, then both tanks are filled with fuel?

Well, that's what the jet fuselages are. Of course, we then move to the issue of what kind of jet engine uses LH2

[Sky_walker]

I'd rather build more expensive, less efficient rockets if it means shorter burn times. I don't go for anything less then a .6 twr

We get it, we get it, no Ion drives for you.

But... that doesn't have anything to deal with the topic.

[NathanKell]

Streetwind:

Heh.

Going off memory, I *think* the Russians reported testing their NTR (RD-0410).

aaaand Astronautix says it was tested in the 80s and was considered operational. 1.8 TWR, 910s vacuum, 35.3kN thrust (so 2 tons).

Alas I don't have more data on NERVA; actually your best bet would be Starwaster, who knows a good bit more about NTRs than I do.

Also, to the people mentioning Timberwind: you understand that that was only for use once there were missiles in flight, right? It was for an environment so saturated with radiation (and so desperate) that using it would make things better (maybe some of us survive!) not worse.

[zxczxczbfg]

Of course then you would need tanks that hold only fuel and not oxidizer. Simpler to assume that if you have a LV-N, then both tanks are filled with fuel?

The liquid hydrogen fuel is the reaction mass, the loxy is used to cool the reactor's "waste" heat.

Edited September 3, 2014 by zxczxczbfg

[Motokid600]

We get it, we get it, no Ion drives for you.

But... that doesn't have anything to deal with the topic.

Nor do half of the other comments.. I was just chiming in on the what engines to use and when statement. It's already established that cheating in this game is purely subjective. At this point it's the fact that some think the LNV is the only engine worth using in vac. Which is where my previous comment comes into play. All in all you gotta use what ever engines you feel is appropriate for your payload.

Now... You can stack LNVs to get better TWR, but at what point would you get diminishing returns?

[Red Iron Crown]

Of course then you would need tanks that hold only fuel and not oxidizer. Simpler to assume that if you have a LV-N, then both tanks are filled with fuel?

Maybe, especially since liquid fuel and oxidizer are the same density.

The liquid hydrogen fuel is the reaction mass, the loxy is used to cool the reactor.

You use the reaction mass to cool the reactor on the way out, it is the addition of heat to the propellant that makes the whole thing work.

[GreeningGalaxy]

Speaking as someone who plays and loves KSP Interstellar, the LV-N might be a little overpowered- not because it has too high an ISP or thrust (the engines added by KSPI have much much higher thrusts AND ISPs), but because you don't have to worry about anything related to nuclear fuel usage, nuclear waste buildup, heat dissipation, or any of the other variables that normally go along with running a nuclear reactor. In the stock game I think using the LV-N is fine (although everyone can decide that for their own game IMO), but with KSPI installed I've shied away from it a bit because it's a bit too easy to use compared to similar KSPI engines.

[Sky_walker]

Speaking as someone who plays and loves KSP Interstellar, the LV-N might be a little overpowered- not because it has too high an ISP or thrust (the engines added by KSPI have much much higher thrusts AND ISPs), but because you don't have to worry about anything related to nuclear fuel usage, nuclear waste buildup, heat dissipation, or any of the other variables that normally go along with running a nuclear reactor. In the stock game I think using the LV-N is fine (although everyone can decide that for their own game IMO), but with KSPI installed I've shied away from it a bit because it's a bit too easy to use compared to similar KSPI engines.

Yep. There was plenty of suggestions how to improve the situation.

Probably the easiest one would be to have a reputation penalty each time you launch LV-N and another, this time a huge one, if you'll dare to crash LV-N anywhere but into the sun or gas gigant (contamination).

Though even that barely scratches the issues with nuclear engines.

Current implementation of LV-N is one of these things that "KSP teaches people wrong thing that's then horribly difficult to unlearn" - that Nukes are borderline the best thing under the sun for space flight.

[Red Iron Crown]

Current implementation of LV-N is one of these things that "KSP teaches people wrong thing that's then horribly difficult to unlearn" - that Nukes are borderline the best thing under the sun for space flight.

Almost all of the problems with NTRs in real life are political. Measured on their merits as a rocket engine, they offer a lot of advantages over chemical rockets, some of them very substantial.

[cantab]

Regarding simplicity, maybe see that as precisely the advantage of the LV-N in some modded settings - it's a simple sealed unit but with less performance than a custom setup.

Regarding nukes being the best thing for space travel, well they kind of are! Though I'd say ions and similar give them nice competition.

[kStrout]

As for heat dissipation if we assume it is a nuclear thermal rocket you are heating up propellent in the reactor and then throwing it out the back. That's how you get rid of heat as well as remember that nuclear engines do tend to overheat. If you were to shield a nuclear rocket so that it would not affect the crew I bet you would get similar TWR so there adequate balance.

[magnemoe]

Speaking as someone who plays and loves KSP Interstellar, the LV-N might be a little overpowered- not because it has too high an ISP or thrust (the engines added by KSPI have much much higher thrusts AND ISPs), but because you don't have to worry about anything related to nuclear fuel usage, nuclear waste buildup, heat dissipation, or any of the other variables that normally go along with running a nuclear reactor. In the stock game I think using the LV-N is fine (although everyone can decide that for their own game IMO), but with KSPI installed I've shied away from it a bit because it's a bit too easy to use compared to similar KSPI engines.

Nerva is cooled by the LH2 before you send it into the reactor, it might be an issue if you run it on methane who is not cryogenic but would probably just require that you use more of the reaction mass for cooling before sending it into the core.

Using the reaction mass for cooling should work for an 800 m/s ISP engine but not something far more efficient as you would use to little reaction mass.

I also think the nuclear reactor would last the mission, you don't have to swap fuel rods often and the reactor would just be active while burning.

[Renegrade]

The 48-7S engine has its niche in small Tylo landers and in the upper stages of Eve landers. Otherwise it's not that efficient anymore. Nukes and ions are almost always better lander engines, unless you want to make your life easier by trading efficiency for high TWR.

What? The LV-N is almost two times heavier than my typical munar lander's payload (ie after taking all engines and fuel tanks off - it's about 1.41t without LS). Can an ion-based Mun lander even work? I know it has about 5-ish local TWR, but that's just for lifting the drive itself. To get a 2.0 local TWR, you'd need 14 drives on a 1.41t lander.. and they'd have to be mass zero in that case, and they'd have no xenon or solar power (unless you abused the massless oxstat nonsense #lolsolar).

Ion drives are still 2.0 kn thrust and 0.25t right?

(Also since I think stock progression is hideously broken, I'd like to point out that 40% of the science in the game is on the Mun, and 60% is on Minmus, and +inf% is in the contracts...)

[magnemoe]

Almost all of the problems with NTRs in real life are political. Measured on their merits as a rocket engine, they offer a lot of advantages over chemical rockets, some of them very substantial.

Think the main issue is lack of missions, you don't need it much for small probes (you don't need it in KSP for small probes either)

Some missions like the Pluto flyby might benefit from it however not worth the cost of developing it for this.

For a manned mars mission it would be very useful, you would need it or some other engine types like vasmir, who also require an real nuclear reactor for power.

Two other arguments against the political problems, no real problem using RTG on probes and no problem for Russia to develop it, NASA and ESA might even have sponsored this development.

[magnemoe]

The 48-7S engine has its niche in small Tylo landers and in the upper stages of Eve landers. Otherwise it's not that efficient anymore. Nukes and ions are almost always better lander engines, unless you want to make your life easier by trading efficiency for high TWR.

I'm not sure about the lower stages of Eve landers anymore. In 0.23.5, the SLS engines were really good, but the rebalancing in 0.24 probably changed that.

The 48-7S is default probe engine, so much better ISP than the ant it win if you need 4 or more oscar tanks. It continue to be the best up too a ton payload and the 707 takes over.

You can land with LV-N however because of the length you pretty much need two of them and you need an pretty huge lander for the 5 ton engine weight will carry itself, more like a mobile base than an lander.

Most landers also just have to go from low orbit to surface and back to mothership

[Red Iron Crown]

Think the main issue is lack of missions, you don't need it much for small probes (you don't need it in KSP for small probes either)

Some missions like the Pluto flyby might benefit from it however not worth the cost of developing it for this.

For a manned mars mission it would be very useful, you would need it or some other engine types like vasmir, who also require an real nuclear reactor for power.

Agreed. For sending probes around the system it's not necessary. If we want to take the next step and do manned missions, something like the NTR will basically have to be developed.

Two other arguments against the political problems, no real problem using RTG on probes and no problem for Russia to develop it, NASA and ESA might even have sponsored this development.

There are protests against RTG launches (though generally minor ones), but an NTR seems to be scarier because it exhausts irradiated propellant. As for Russia, they've always had a very practical approach to spaceflight.

[NathanKell]

The only time I've heard LOX talked about for NTR is for LANTR, LOX-Augmented NTR. Because LH2 in an NTR is very efficient but low-thrust, there was a proposal (for Lunox, if anyone remembers Fusty's Munox command pod it was a real thing...) to augment the NTR by pumping LOX into the exhaust, which would react with the LH2 and basically make a hybrid hydrolox/nuclear thermal engine with lower (500-600s IIRC) Isp but much, much higher thrust.

There's another problem beyond political with NTR: LH2 is nasty stuff to use, both for its lack of density and its strongly cryogenic nature (high boiloff problems).

See this series of posts by Bob Braeunig. Details there, summary a few posts later, Methane gets added a few posts down, and summary at the bottom of the page. tl;dr Liquid Methane NTR is probably the best compromise between stage dry mass, Isp, thrust, and boiloff.

Also, Renegade: do *not* look into the abyss of unreality that is ion-powered crewed landers. It hurts too much.