Realistic NERVA engines?

[Spyritdragon]

Thanks for responding and i respect your opinions regex. But I wonder, don't you find it frustrating to have to do 20+ minute burns to get larger sized ships from kerbin to a Jool transfer orbit? I sure do! Now, if this would match reality I wouldnt be bothered, but real nuclear engines are a lot better in space then the KSP counterparts (as described). So why should that element of frustration exist? Also, I'm not editing KSP files because i consider it a game and not an exercise in computer programming .

Regarding game balance, an engine can be balanced in different ways then just the thrust and ISP. My example of making it overheat faster, and making it require heavy cooling equipment is one way. Another way would be to just increase the mass of the engine itself.

Also, what do you think of the other propositions that i made, like varying thrust based on atmospheric density and engine overheating?

And what do you think about adding a cooling unit and / or a LA-NTR based rocket engine to the game?

I like tgem as they are, but it could work. Sounds lime something youd find in a mod more than stock to me, but it could work, in a future version. Because theres a major problem :KSPs current heat and aerodynamics system is severely flawed compared to real life, which make implementing what you are suggesting hard in current versions.

And, editing the engine isnt an exercise in computer programming at all. Its litterally as simple as opening up a file in notepad and changing a number or two, then saving it.

[BrickedKeyboard]

Only one person mentioned the obvious - instead of saying "that NASA prototype made x kN in thrust", you need to mention the thrust/weight ratio. I would not be surprised if the thrust/weight ratio of the nuclear engine in Kerbal was excellent, even better than any humans have ever built. Another factor - think of how much waste heat is going to get conducted to the engine's outer casing. A real NERVA engine is going to need some massive radiator panels, which you do not have to install in this game. You also can ignore the radiation - even if Kerbals are radiation immune, we're talking radiation fluxes enough to destroy plastics and make metal brittle.

[hobbsyoyo]

They would likely use advanced ceramics today if they made a NERVA engine that weren't available in the 60's. That would help with heat for sure and possibly with mass and radiation, dependent on how much you had to use and how opaque to radiation it is. Point being that materials science has progressed lightyears from the 60's which open up lots of new possibilities and capabilities.

[LameLefty]

Someone mentioned Nova Punch for different NERVA options in the game. Let me toss out another suggestion - these are better-balanced (IMHO) in terms of thrust, mass and ISP for a "realistic" space program while still scaled to a Kerbol-sized solar system. I like 'em, a lot.

http://forum.kerbalspaceprogram.com/threads/26286-Nucleonics-Ltd-Rocketry-Division

[hobbsyoyo]

I don't find the big NERVA engine in NovaPunch to be badly unbalanced. It has good thrust and the standard 800s ISP, but weighs a lot and doesn't generate electricity. It's also physically large so it's harder to integrate it into existing designs and requires a lot of working-around to accomodate it. I don't use the other 2 nuclear engines, I think they are supposed to be fusion engines IIRC but look dumb to be honest and I don't know, they just stretch believability for me. I also haven't found a use for them yet either that couldn't be met by either the standard NERVA or the big one in NP but that's all probably just me.

[Thorbane]

In an attempt to bring "real life" nuclear engines to the game, I made some configs for the Timberwind Project from the 1990s. Using the stats from the project, they were totally game-breaking. We're talking single-stage-to-Eeloo levels of overpowered.

Huh, so I wasn't the only one.

It's past single-stage-to-Eeloo OP, it's SSTO on Eve overpowered. It's hilariously gamebreaking.

Edited November 10, 2013 by Thorbane

[Savage117]

I find it interesting that people keep saying the solar system is 1/10th the size but aren't taking into account that everything has been scaled down. In order to make Kerbol system a Sol system proxy and still make the game fun, Squad scaled down everything, not just size. In the real world the only difference, scale wise, the nuclear engine has to the Kerbal one is the changing thrust at higher altitudes. In the real world the 330 kn of thrust the NERVA does would still take a long time to get you anywhere outside Earths "SOI" and would probably require several orbits and burns to get you on a efficient escape. Just like the Kerbal one.

You need to remember our solar system is 10 times bigger than Kerbol, that means more Delta V, more thrust, more ISP, and more TWR to get anywhere. It requires , I think, around 10k Delta V to get into Earth orbit, give or take 1k Delta V, that’s a little more than double what it takes to reach orbit in KSP. Squad messed with the numbers a little to balance it to their idea of the Kerbol system, but I'm pretty sure its closer to the real thing than you might think.

I like some of your guys ideas on the upgrading of the games engines through R&D or parts that improve other parts. But I disagree with injecting real world numbers into this game unless you inject them into the entire thing, like planet distances and sizes. Which one modder is doing BTW, Nathan Kell I think his user name is.

Edited November 10, 2013 by Specialist290
Edited to remove off-topic discussion.

[Specialist290]

Friendly reminder from the moderation team: Discussing real-world nuclear disasters, or other's preferences of stock vs. modded installations, are a bit outside the scope of whether or not a realistic NERVA rocket would be feasible or desirable within the game. Let's try to keep this topic on the rails, please

Edited November 10, 2013 by Specialist290

[Dooz]

Well the Kerbal universe is beyond smaller the. Ours if say that Nasa Nerva were to be in the Kerbal one it would say have the thrust of a skipper so no i highly doubt it would be happening

[Borogove]

The 330kN NERVA was spec'd to weigh about 17.5 tons (TWR = 2g) (vs. the 2.25 for the LV-N, TWR = 2.72g). Even with the discounted ISP, the LV-N is more efficient.

Also, it's about 3m in diameter -- bigger than a Mainsail.

Edited November 11, 2013 by Borogove

[SSSPutnik]

[*]Holy guacamole, why arent these things in use today? they can realisticly reach 800-1100 seconds of specific impulse. I guess its because of the "N word", but the risk seems limited seeing as these engines are wrapped in carbonfibre and heat resistant composites. Land based nuclear applications seem a lot more risky to me, considering earthquakes and tsunami's and all that (COUGHfukushimaCOUGH).

Basically not used IRL because of: http://www.oosa.unvienna.org/oosa/en/SpaceLaw/gares/html/gares_47_0068.html

Boils down to no country wants to risk dropping one in someone's backyard, (including their own).

[celem]

Yeah its NIMBY all over (NotInMyBackYard).

If I recall correctly the first concept nuclear engines were shelved because the US had just signed a resolution avowing not to deploy nuclear weaponry in space. The majority of the world's nations signed this resolution and it kinda encompasses nuclear propulsions, though if i remember right this first treaty/agreement predates the spacerace.

I like the NERVA as it's currently balanced by Squad. It's a niche engine that excells at certain tasks, without being the 'goto' engine for all tasks. (I do see a lot of screenshots indicating that it is infact many people's GoTo, with NERVA-spam landers etc. This is often their lack of understanding rather than engine OP).

[Swoop]

Can I ask a silly question?

Why don't you edit the parts file of a NERVA and change the thrust / ISP to whatever you want it to be? If you want a NERVA to be 330kN then make it 330kN. Just be aware that any changes you make will be overwritten the next time you update KSP.

[magnemoe]

Basically not used IRL because of: http://www.oosa.unvienna.org/oosa/en/SpaceLaw/gares/html/gares_47_0068.html

Boils down to no country wants to risk dropping one in someone's backyard, (including their own).

More an lack of missions, NERVA is not very cost effective unless you want to do an manned mars mission or similar.

The LV-N is not the best choice for sending an probe in KSP either, neither an probe lander outside of Eeloo and Moho.

An RTG also contains radioactive materials and launching them is not an issue, yes it's less materials but that has no affect on legality.

[Skyler4856]

I think an interesting idea would be the capability to skim a gas giant for hydrogen gas. This would allow you to enter a star system and refuel.

[architeuthis]

[*]In comparisson to reality, the 60kN thrust of the LV-N atomic rocket motor in KSP is severely underpowered. I understand this from a game balance standpoint, but cant the game be balanced in a more realistic way? I mean, the last prototype NERVA engine produced 334 kN of thrust at 380 S isp (atmosphere) and with 850 S isp in vacuum.

So the KSP LV-N has 0.18 times the thrust of the planned NERVA 2 cf. the Mainsail's assumed real-life analog, the mighty Rocketdyne F-1. The Mainsail has 0.22 the thrust of the F-1. I think this is a trend for regular rocket motors in KSP, though don't get me started about the PB-Ion. Not to beat a dead horse but the thing has 1.3 times the specific impulse and 5556! times the thrust as its most powerful RL analogs... But personally, I like the overall current balance.

[*]Make the thrust of the LV-N rely on its level of overheating. So, at 0% overheating it produces no thrust. At 80% overheating it would produce 80% of its maximum thrust.

Real NTR systems were designed for a specific operating temperature, some factor of safety below the melting points of the reactor elements, so thrust is not just a simple function of temperature. However, specific impulse is. If you lowered the chamber temperature, or increased the mass flow rate, your specific impulse would drop. As you mention below in reality this would be necessary for a NTR anyway because reactors don't turn on instantly like light switch, they take time to warm up or cool down, so the beginning and end of the burn would be cold flow hydrogen with poor specific impulse. KSP's model is more simple than reality, but there is nothing wrong with that I think.

Um, no. I used to agree with your point, but some digging a while ago showed me that NERVA wasn't nearly as "solved" a problem as I thought. The killer, in a literal sense, flaw is the radiation containment; full shielding would've been too massive, so designs just used a "shadow" shield that only worked to protect the craft above the engine. Anything outside of a roughly 60° cone of dead-on front would be exposed to the reactor.

So every time in KSP that you turn your LV-N craft retrograde to another craft within, say, ~500m in real life you'd be scrambling that craft's electronics and giving its crew (if any) cancer.

I'd love to see a "tamer" version of NERVA someday, but I certainly understand the opposition to its use.

-- Steve

This is quite true, but it's not a flaw it's just optimization. For a ship designed to operate in deep space only a tiny tiny percent of the time would it be in close proximity to other spaceships. Lugging around literally tons of useless mass just leads us to getting screwed by the rocket equation, so instead we just use a shadow shield and develop good safety protocols. The engines are at their most dangerous when they are in active operation because nuclear fission blasts neutron radiation all over the place, but once the motor is off this rate of neutron radiation flux exponentially decays. After about 24 hours of your last burn the neutron radiation become negligible. However there is still gamma radiation from fission products in the reactor core, and these are more or less constantly in the background for a reactor that has been turned on at least once. So your nuclear powered space tug will have maintain a constant aspect with respect to its rendezvous target (say a propellant depot for refueling, or a surface to orbit space shuttle for payload transfer) and only use RCS for close by maneuvering, to avoid irradiating anyone. If you were visiting a space station robotic tender tugs could attach a non-integral sideshield to the NERVA motor (space stations can have many high mass luxuries like this because they don't have big delta-v requirements). I actually roleplay this in KSP because it makes it more fun for me, though manually tedious. Maybe I'll try to write a kOS script to maintain attitude automatically:) He is a diagram for illustration:

Edited November 11, 2013 by architeuthis

[architeuthis]

There is radiation, but adding lots more exposure means astronauts will roast even faster than expected on their interplanetary trip. Also, the reactor is constant exposure, whereas deep-space radiation comes largely in events (CMEs).

There is plenty of constant background charged particle radiation in space (van Allen belt radiaion, cosmic rays, etc.). If if was just solar flares, designing spacecraft with storm cellars would solve the problem. With regards to a plain-old thermal NERVA it is mostly dangerous only when it is actively running (if it is bi-modal, then I guess that's another story). Ironically, using NTR may mean less radiation for astronauts if it means their overall trip times are shorter then with chemical or electric alternative propulsion methods.

And unless you build the reactor in space, there's the minor issue of how to get it up to space. The safest real-life rockets still have a roughly 1% failure rate.

This is the main reason against using nuclear engines. The proposed nuclear replacement for the S-IVB would require the power output of a large nuclear power station. Imagine what would happen if there was a launch failure: we're talking about a nuclear disaster that makes Chernobyl look small time.

Actually in many ways proper nuclear reactors are safer to launch than the RTGs used on many planetary missions. The NERVA engine would have used Uranium-235 in the reactor. It has a long half-life of roughly 700 million years, thus it is naturally only lowly radioactive. I'm not saying you should wash your face with it in the morning, Uranium is a heavy metal and is chemically toxic (though much less so than mercury or arsenic), but the radioactivity is not dangerous. By contrast, the Plutonium used in RTGs has a half-life of only 88 years. If the reactor has never been activated there will be no dangerous stored fission products. If the rocket were to fail on lift off it is likely that the environmental impact of nasty chemicals in the rocket itself would be far more severe than that of the uranium in the reactor.

More dangerous would be having an old used reactor, with lots of built up fission products, reentering the atmosphere. Simple solution to that: don't put them in low orbits where that might eventually be a problem, or have an reliable infrastructure for disposing them into a safe orbit (using space tugs, or a built in disposal rocket).

[FreeThinker]

Intresting ideas, I will look if I can incorperate some into my Kerbalised Interstellar Mod

[Bill Phil]

Well, to be fair, the original NERVA had a bad TWR. Like just over 1.

[dryer_lint]

I don't really get what the problem with launch failures would be - just build the launch pad in some deserted area that goes over the ocean. Earth survived a few nuclear bomb tests anyways, right?

[Bill Phil]

I don't really get what the problem with launch failures would be - just build the launch pad in some deserted area that goes over the ocean. Earth survived a few nuclear bomb tests anyways, right?

People are just scared of the N word.

[Iskierka]

Not especially - the reason nuclear tests stopped was more than "people are scared of the N-word", and a running NTR is looking at levels of radiation comparable to the grounds around Chernobyl mid-meltdown. It's not exactly insignificant.

[Dkmdlb]

Earth survived a few nuclear bomb tests anyways, right?

Just a few thousand.

[Bill Phil]

Not especially - the reason nuclear tests stopped was more than "people are scared of the N-word", and a running NTR is looking at levels of radiation comparable to the grounds around Chernobyl mid-meltdown. It's not exactly insignificant.

It's not like a NERVA is a multi pile reactor complex. Plus it could eject/vaporize the fuel, although that's a complicated system.

[sal_vager]

There's other nuclear rocket engine types that don't seem to get the attention they deserve, anyone else here heard of the nuclear lightbulb?

It could give between 1500 and 3000 Isp.