Are Nuclear Rockets "Cheating"?

[davidpsummers]

I've been avoiding the nuclear rocket because it seems like "cheating". A magic rocket that just solves so many of your problems? Is there any real rocket (or a "really proposed" rocket that works like it does)?

[Kasuha]

It has its basis in existing technology: NERVA engine

Edited August 23, 2014 by Kasuha

[Sirine]

Yes. And no.

Never any rockets launch with nuclear yet.

Edited August 23, 2014 by Sirine

[CaptRobau]

They're based in reality and are balanced by having a low TWR and high cost. So no.

[Cmdr. Arn1e]

This is a game we all like to play... if it's in the game, it's not cheating (Except the Dev Console...)

Some people go and edit the CFG files to make 'ordinary' engines FAR more powerful than the LV-N's 800 ISP in vacuum... now that's cheating!

Guess you also shouldn't use any of the jet engines or the Ion engines either if you decide not to use LV-N's... as they are as unrealistically OP...

[Scotius]

L-VN is one of few examples of reverse nerf in game actually. Real life NERVA had superior thrust, and so would be very overpowered in the game - there would be no point in using any other engine outside of the atmosphere.

[Tw1]

there would be no point in using any other engine outside of the atmosphere.

Some might argue that there already isn't, apart from the ion engine. Or the 24-7S.

[codepoet]

I never use NERVAs because that are the rules I have imposed on my own gameplay. It would be cheating for me to use it because that is the rule I have imposed on myself.

[Brofessional]

It's a proven technology, working prototypes have been made in real life, but never flown. In part due to the risk of dispersing radioactive material in the event of a rocket malfunction.

[Madrias]

I think the LV-N is very balanced, actually. Low thrust, absurdly heavy, but it has tons of fuel efficiency. My only "rule" in my space program is no igniting LV-N's in the atmosphere.

[Red Iron Crown]

It's cheating if it feels like cheating to you.

I agree that the engine is so good in orbit that there are very few situations where another engine is better.

[Frozen_Heart]

They are actually heavily nerfed compared to the real life version. (which was never flown) They actually produce just as much thrust as chemical rockets and are also more efficient in atmosphere than them as well!

Anyway its a single player game so your own rules are what matters. For most of my missions I rarely use them.

[KerikBalm]

All real life rockets have way better TWR than what you see in KSP.

All RL fuel tanks weigh much less (when empty, compared to full) than in KSP.

Many RL liquid fuel engines have ISPs better than 400, while KSP's top out at 390

However, RL is 10-11x "bigger".

If we were to scale things correctly, then 1 Kerbal meter = 10 Real meters. An exhaust velocity of 8000 m/s would only be an exhaust velocity of 800 Kerbal meters/second, and would have an in game ISP of 80, not 800.

1 earth gravity would only be .98 kerbal m/s^2... thrusts would have to be adjusted downwards.

In real life, we make rocket stages with a 17:1 empty:full ratio for *everything*, engines and fuel tanks, and all other systems, in KSP, its impossible to get better than 9:1 (and if you want a TWR over at least 1:1, it gets even worse)

Lets look at the shuttle external tank + space shuttle main engines, and the tsiolkovsky rocket equation, vs some KSP contraption that is a Mk1-2 command pod, 2 orange tanks, and a poodle engine getting 390 ISP.

Shuttle orbiter weight: 68.58 tons

Tank empty weight: 58.5 tons

Tank full weight: 760 tons.

So M_0 = 68.58+58.5+760 = 887 tons

M_1 = 68.58+ 58.5 = 127.08

M_0 / M_1= 6.98

ISP: 455

9.8 * 455 * ln 6.97 = 8664 m/s

KSP equivalent:

pod: 4 tons

Engine: 2 tons

Fuel tank weight: 4 tons empty, 36 tons full.

M_0= 78 tons

M_1= 14 tons

M_0/M_1= 5.57

9.8*390* ln 5.57 = 6565 m/s

RL example gets almost 32% more dV

Nerva engines are very real, and were tested in flight configuration, they are flight ready, but they haven't actually been used.

* A failed rocket launch with an obliterated nuclear reactor is feared by the public: note that until you switch such a reactor on for the first time, its not veyr radioactive, no more so than the RTGs we already send up

* Its heavy, much like the KSP nuke, this means that its not mass efficient to use one if all you want to do is go to low orbit. Planned missions to mars were all initially assuming the use of NERVA engines. However, missions to mars were never undertaken because of the cost of such a project, so NERVA engines became rather unneccesary.

They did look into using it as a 3rd stage on the saturn V, but they just stopped the saturn Vs all together

http://en.wikipedia.org/wiki/Saturn_C-5N

I'd love to see something like project prometheus with a biomodal nuclear reactor.

Nuclear thermal for an ejection purn, switching to some form of ion drive for a braichistichone followup, making the travel time shorter.

Possibly even make a trimodal one where the nuke helps provide thrust during liftoff to orbit

http://www.projectrho.com/public_html/rocket/enginelist.php#ntrsolidcore

A useful refinement is the Bimodal NTR.

Say your spacecraft has an honest-to-Johnny NERVA nuclear-thermal propulsion system. Typically it operates for a few minutes at a time, then sits idle for the rest of the entire mission. Before each use, one has to warm up the reactor, and after use the reactor has to be cooled down. Each of these thermal cycles puts stress on the engine. And the cooling process consists of wasting propellant, flushing it through the reactor just to cool it off instead of producing thrust.

Meanwhile, during the rest of the mission, your spacecraft needs electricity to run life support, radio, radar, computers, and other incidental things.

So make that reactor do double duty (that's where the "Bimodal" comes in) and kill two birds with one stone. Refer to above diagram. Basically you take a NERVA and attach a power generation unit to the side. The NERVA section is the "cryogenic H2 propellant tank", the turbopump, and the thermal propulsion unit. The power generation section is the generator, the radiator, the heat exchanger, and the compressor.

Warm up your reactor once, do a thrust burn, stop the propellant flow and use the heat exchanger and radiator to partially cool the reactor to power generation levels, and keep the reactor warm for the rest of the mission while generating electricity for the ship.

This allows you to get away with only one full warm/cool thermal cycle in the entire mission instead of one per burn. No propellant is wasted as coolant since the radiator cools down the reactor. The reactor supplies needed electricity. And as an added bonus, the reactor is in a constant pre-heated state. This means that in case of emergency one can power up and do a burn in a fraction of the time required by a cold reactor.

Pretty ingenious, eh?

And the Pratt & Whitney company went one step better. They took the Bimodal NTR concept and merged it with the LANTR concept to make a Trimodal NTR. Called the Triton, it can be used in LANTR mode when thrust is more important than specific impulse, NTR mode when specific impulse is more important than thrust, and in power generation mode while coasting.

[magnemoe]

It's a proven technology, working prototypes have been made in real life, but never flown. In part due to the risk of dispersing radioactive material in the event of a rocket malfunction.

And because you only need it for larger ships, manned missions to Mars or similar. It's not cost effective for sending a small probe to Eve or Duna in KSP either.

[zarakon]

If you're talking about the stock LV-N, I'd say it's pretty well balanced

If you're talking about a mod that gives you something like nuclear pulse propulsion, then it's probably pretty cheaty

[Torham234]

For a long time I didn't use LV-N, precisely because I thought it cheating. But I think they are viable engine, especially in career, since they require quite a investment in research. I still observe some self imposed rules, like never using them inside the atmosphere, and not leaving them as a space debris in free orbit. They have uses, balanced out by bulky size, high costs and they are quite heavy.

[Torham234]

For a long time I didn't use LV-N, precisely because I thought it cheating. But I think they are viable engine, especially in career, since they require quite a investment in research. I still observe some self imposed rules, like never using them inside the atmosphere, and not leaving them as a space debris in free orbit. They have uses, balanced out by bulky size, high costs and they are quite heavy.

Edit: Also, radiation fallout is not such a big issue as people might think.

.

[RabidMonkey]

Out of curiosity, I made an engine that matched the stated capabilities of second-generation NERVA-type engines (Look up the Timberwind series - stupidly efficient and powerful). Past 5% thrust, it made a surprisingly effective bid for freedom, tearing through the rest of the rocket.

[Wanderfound]

I prefer not to use LV-N's, not because I think it's "cheating" but because they make it a bit too easy for me (and just me; y'all have fun however you like). I'd probably change on that if they gave the LV-N its own fuel type and attendant hassles.

[Overfloater]

I can understand if someone calls part-clipping, intake-spamming/stacking, infiniglide cheating. But this? . _ .

This is called using a legitimate game component which has it's downsides.

So what's next... "is using an engine other than a Mainsail cheating?"?

[tater]

Scotius is right about them being nerfed in game. The reason NERVA wasn't used was more to do with politics (safety concerns) than anything else. In a less politically regulated, danger averse space program, we'd have flown them for sure.

[cantab]

The LV-N's often the best engine but not always, other engines can be competitive, so no it's not cheaty.

48-7S spam is worse in terms of exploiting parts in "unnatural" ways, but even that's not really cheating - I'd fault the game for having wonky part balance, not the player for taking advantage of that.

[r_rolo1]

I'd probably change on that if they gave the LV-N its own fuel type and attendant hassles.

This. The idea of a NERVA engine that uses oxidizer is ... stupid, to say the least. Even using monoprop would be more sensible :/

On topic: claiming that using a legit vanilla part is cheating is really a misuse of the word cheating. Claiming that it badly fits the game balance would make sense ( if appliable, OFC ), and SQUAD already tuned down parts for that exact same complaint ( RIP sky-high thrust 0.15 aerospike ... ) ... but TBH I think the current Nuke actually fits relatively well in terms of game balance ( if you dismiss the whole oxidizer thing , that is ... ). There are worse fits, like the 48-7S ...

[No one]

If any stock part is cheating due to being unrealistic it would be jets. Real jets have similar Isps but don't classify intakeair as reaction mass. KSP jets do, and thus are much more efficient.

That said, I'm going to have to agree with what everyone else said that using a stock part for its intended purpose is never cheating.

Some might argue that there already isn't, apart from the ion engine. Or the 24-7S.

The 505 can be better depending on the mass of the ship.

[Scotius]

Out of curiosity, I made an engine that matched the stated capabilities of second-generation NERVA-type engines (Look up the Timberwind series - stupidly efficient and powerful). Past 5% thrust, it made a surprisingly effective bid for freedom, tearing through the rest of the rocket.

After reading about those engines i want one in the game Awesome pieces of machinery indeed - too bad no one built them.