[1.0.5] Atomic Age - Nuclear Propulsion - Red Hot Radiators

[Starwaster]

That was very interesting to read, but he might have wondered how they want to deal with the boiloff. Or in any case, I wonder that

Refrigeration and LOTS of insulation is how they plan to deal with boiloff.

To achieve zero boiloff (ZBO) they will wrap the tank in 60-80 layers of MLI. ~75-78 watts of heat will penetrate and has to be dealt with. The cost in electrical power is 114 We per watt of heat.

page 23 - http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030014643.pdf

page 12 - http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120003776.pdf

MLI and boiloff in general - http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19710012082.pdf

Yeah, these documents have basically been sitting open in my browser for a few months which is how I can reply back with this so soon.

There's a formula for calculating how much heat penetrates x number of layers of insulation and I've tried stuff like altering the skin - internal conduction factor based on that with mixed results. I'm already at the low limits of what I thought would be acceptable values and I still have a lot more than 78 watts of heat coming in.

And if I configure my radiators to draw that much+conduction, they just don't seem to want to do it. (yeah I've been working on some radiator replacements based on an updated version of the RF heatpump code)

[Starbuckminsterfullerton]

Except that those stats are for liquid hydrogen.

You're right! I normally run Nertea's Cryo Engines and NFP, which has a fuel switch patch that includes LH2 and converts all Nuclear engines to hydrogen, so I forgot that for most people it is still burning kerosene.

That said, it's more of a stock fault for not having the proper fuel. They really needed to incorporate some for of fuel switch before converting the LV-N, but that's something for another thread.

[Tellion]

snip

Thank you very much!

You must spread some Reputation around before giving it to Starwaster again.

[Temeter]

regretful EDIT: Dammit, ninja'd!

I was exactly asking for something like this! Knew nasa would come up with some cool ideas. Do I interprete your post right and you're basically working on implementing something like this?

A real nuclear engine's reactor is kept from overheating by the propellant flowing through it. It is in no danger of overheating while it is in operation. IIRC, the ground tests would fire continuously for at least 20 minutes or until they ran out of hydrogen.

It's when you shut it off that overheating is a problem. You can't just flip a switch and shut the engine off while it's at full thrust. Instead, there is a 'cooldown' thrust stage where the engine is gradually throttled back. During this cooldown, Isp gradually drops down to (or by???) 40%. (which means that a nuclear engine burn has to be precisely calculated even more than usual)

Another method of cooldown following a burn involves a nozzle plug which descends out the bottom of the reactor core and plugs up the nozzle. Hydrogen is pumped in to cool it down and is vented. (has to be done in a manner that it doesn't cause unwanted deltaV changes. Such as venting from opposing sides perpendicular to the long axis)

Cooled down, each engine outputs 128 kW of heat which can be used to provide electrical power. (this is either a 'Bimodal' or 'Trimodal' depending on whether it also has the 'afterburner' feature. 'Bimodal' has been used flexibly to refer to an NTR that has either but not both of afterburner and electrical generation)

That was very interesting to read, but he might have wondered how they want to deal with the boiloff. Or in any case, I wonder that

Yep, it's interesting. Sounds like a true nuclear engine integration would be a lot more complex than what we have now, something I wasn't really aware off. I wonder what scary things you guys might implement in the future?

I was originally asking more about the possibilities of keeping cryogenic fuel from boiling, tho: The current capability of a cryogenic RO/RF tanks is far from being efficient. On a mars mission you could basically throw away the departure stage directly after the first departure burn. In my experiment a single year in space can empty a tank.

So I wonder if there are more advanced possibilities in reality, ofc too because I'm curious about how they might find they're way into the RF mod. Currently hydrogen driven stages, espeacially nuclear, have extremly limited use in space.

Edited July 10, 2015 by Temeter

[Starwaster]

regretful EDIT: Dammit, ninja'd!

I was exactly asking for something like this! Knew nasa would come up with some cool ideas. Do I interprete your post right and you're basically working on implementing something like this?

It's partially implemented now. It's not like the stock radiator that grabs heat from all over. Instead it's configured to look for parts on specific nodes OR parts it is attached to if it's a surface mounted part.

[Tellion]

So refrigeration is something we might ​see after all?

[Temeter]

It's partially implemented now. It's not like the stock radiator that grabs heat from all over. Instead it's configured to look for parts on specific nodes OR parts it is attached to if it's a surface mounted part.

Nice, can't wait to make use of those things! Should bring a lot of fresh air to interplanetary missions.

Edited July 11, 2015 by Temeter

[JaffaFediration]

Oh muh gush, nuclear powered jet engines! Finally!

[autumnalequinox]

First: Love this mod. Second: Anybody made a MM file to turn all nuclear engines into generators? Would this be remotely realistic? I figure at the very least nuclear engines would have a thermocouple to generate some limited electricity (output a bit better then an RTG) instead of a full reactor type setup. Does anybody think this would be severely unbalancing?

[Overjay]

Does this mod work well with RealFuels?

[Tellion]

We have configs for the Lightbulb and the Lantern in the stockalike engine pack, I think the Turbojet should work without any modification. Best way to find out is to try

[the8cell]

I don't think the lightbulb is that OP at all, considering how heavy and expensive it is.As well as being deep enough in the community tech tree to be late game. It doesn't _fundamentally_ change the purpose of an interplanetary nuclear stage, it's just more efficient than using a bunch of NERVs to accomplish the same thing.

In my opinion, the most game balance and style affecting engine is the RTG one. It allows for nuclear level ISPs on probes and upper stages. I like it, but If there's any one thing about it I would change, I'd say the gimballing should be scaled down a bit.

[RadPig94]

I guess this is a great place to start my first post

Anyways, I'm having a bit of a problem. What is supposed to be the effectiveness of the Heatsinks? I notice that it does not change the rate of reaching overheat or speeding cooldown up. When I use the Size 1 I do notice that it does glow red, I just thought overheat was not affected because its puny size and only using 1. But the other sizes do not seem to be doing anything, not even glowing. I put 20 of the biggest heatsinks for my lightbulb but they seem to do nothing.

It might be because I am using v1.0.0 though, I'm just not sure because the engines themselves work as intended

[RadPig94]

I'm having problems. I'm here to ask about the heatsinks and their effectiveness. Using 20 size3 heatsinks seems to do nothing for keeping the engines cool.

It maybe because I'm using v1.0.0, I'm just not sure because the engines themselves work as intended

[Starwaster]

I'm having problems. I'm here to ask about the heatsinks and their effectiveness. Using 20 size3 heatsinks seems to do nothing for keeping the engines cool.

It maybe because I'm using v1.0.0, I'm just not sure because the engines themselves work as intended

1.0.0 of KSP?

Then the heat sinks will do NOTHING.

Upgrade to 1.0.4

[ThatOneBritishGuy...]

Shouldn't the nuclear turbojet have an although long, but not unlimited lifetime, considering that it contains constantly decaying radioactive material? Just asking before I make a NFP config for it to consume/contain nuclear fuel.

[Starwaster]

Shouldn't the nuclear turbojet have an although long, but not unlimited lifetime, considering that it contains constantly decaying radioactive material? Just asking before I make a NFP config for it to consume/contain nuclear fuel.

Its operational lifetime would be measured in years. Maybe decades. Unless you gave it an unnaturally short lifetime, it wouldn't likely have much impact on the game.

(Not saying don't do it, just that practically speaking I haven't found it to make much difference. That's what we did with most of the NTR configs and personally I find that I end up abandoning games that I use those engines in before the engines run out)

Edited July 15, 2015 by Starwaster

[KAO]

maybe it would make sense to have its operational lifetime decay at an increased rate when in operation? maybe then it could take on-board uranium as a fuel.

At least giving them an operational lifetime would be a real concern for those who play with Kerbal Galaxy those 200+ year trips will do it.

[TheSaint]

The core life of a nuclear reactor is defined by the amount of U235 that is present in the core. U235 has a half-life of over 700 million years. You aren't going to see any reduction in core life due to radioactive decay over any reasonable game time spans, even on an interstellar mission.

Core life is reduced by use, but not on the time scales that we see in the game. Most commercial reactor cores have a lifespan of 2-3 years at 100% reactor power. That's operating continuously, uninterrupted, at full power, for two to three years. I can't think of any space-based nuclear propulsion application that would even approach that demand. You would run out of reaction mass in minutes to hours. You wouldn't even get close to a week, never mind two years.

What you would more likely do is engineer the life of your reactor core to match the maximum burn time within the designed operational lifetime of your spacecraft, then within those constraints make it as lightweight as possible. Even within that type of design criteria it would probably be pretty easy to design in a double or triple lifetime design margin. All things considered, the game's abstraction of, "Nuclear engines have an unlimited core lifetime." is not at all unreasonable.

[Starwaster]

Something else of interest: IRL, one of the touted advantages of a nuclear engine is its reusability. But actual plans call for dumping them in heliocentric space at the end of a mission. (So.... we send that sucker to Mars, it returns a few years later and then we get rid of it instead of refueling it and sending it on another mission? Huh?)

[Temeter]

Something else of interest: IRL, one of the touted advantages of a nuclear engine is its reusability. But actual plans call for dumping them in heliocentric space at the end of a mission. (So.... we send that sucker to Mars, it returns a few years later and then we get rid of it instead of refueling it and sending it on another mission? Huh?)

Probably it's a matter of comeplexity: The idea is to first build a working one, fly it to the mars, find out all problems, and then try building an improved one. We didn't even do interplanetary manned missions until now, last time humans left LEO was in the sixties, there was never a hydrogen driven interplanetary stage, let alone nuclear engines, etc, lots of new technologies. Logical first step would be to do it correctly, reusability is probably a thing of the future. I mean, look at the least time we tried reusability.

We don't have more than some vague ideas of a concept of a plan to mars missions, so finding an application for reusable interplanetary tugs itself would be quite hard.

I always thought the main advantage of a nuclear crafts was the lower payload due to their efficiency, tho. Never heard much about nuclear reusability in my limited experience.

Edited July 16, 2015 by Temeter

[billkerbinsky]

Something else of interest: IRL, one of the touted advantages of a nuclear engine is its reusability. But actual plans call for dumping them in heliocentric space at the end of a mission. (So.... we send that sucker to Mars, it returns a few years later and then we get rid of it instead of refueling it and sending it on another mission? Huh?)

The problem (for solid-fuel reactors at least) is the medium-half-life fission products. Half-life is long enough that they don't decay right away, short enough that they produce enough radiation (either directly or from shorter-half-life decay products) that they're annoying to handle.

Ground-based reactors generally have large pools of water to shield spent fuel assemblies.

To refuel, you'd have to either build on-orbit handling facilities, or deorbit them safely (without scattering nuclear waste across a continent) and refuel on the ground. Until there are enough nuclear engines flying around to make it cost-effective to build the orbital refueling facility it's probably cheaper to park them in heliocentric orbits.

[Starwaster]

The problem (for solid-fuel reactors at least) is the medium-half-life fission products. Half-life is long enough that they don't decay right away, short enough that they produce enough radiation (either directly or from shorter-half-life decay products) that they're annoying to handle.

Ground-based reactors generally have large pools of water to shield spent fuel assemblies.

To refuel, you'd have to either build on-orbit handling facilities, or deorbit them safely (without scattering nuclear waste across a continent) and refuel on the ground. Until there are enough nuclear engines flying around to make it cost-effective to build the orbital refueling facility it's probably cheaper to park them in heliocentric orbits.

Except that they wouldn't be beyond their useful lifetime. We just don't want to keep them around and we're stuck in the mentality of throwing away 90% of our rockets.

[ThatOneBritishGuy...]

Except that they wouldn't be beyond their useful lifetime. We just don't want to keep them around and we're stuck in the mentality of throwing away 90% of our rockets.

Perhaps if SpaceX can get their Falcon 9 to work we wouldn't have that problem . Honestly though, as billkerbinsky mentioned, it isn't a very cost effective prospect to reuse the nuclear engines and until it becomes one, there won't be any reuse of them. Simple as that. Not only is it bad PR to use anything which even remotely sounds "Nukulaar", but then going ahead and using an old engine again is sure to send people into a panic. The general public doesn't tend to enjoy using old things with explosive potential over long periods of time. It builds a sort of misconception that a nuclear engine is a ticking time bomb. On the other hand bringing one back to Earth would be all but impossible, as that leaves quite a more genuine fear to be had. The only two remaining practical solutions would be dumping them in orbit around the sun, or not using them at all. Considering how expensive these engines are, how experimental they are, and how horrifying they are to the public, I don't see them being used AT ALL in the foreseeable future. If they are of course, I would imagine they would go for the more publicly appealing option of dumping them somewhere and forgetting about them, and I belive that to be the most logical option.

Edited July 16, 2015 by ThatOneBritishGuy...

[Temeriki]

Anyone else getting a NaaN error when trying to launch the nuclear plane example. I can load it fine into the hanger, but once I launch my background goes black, I can still see the character icons, and i have the normal game icons but their unclickable. I can escape out, but I have to exit the game completely to clear it. Ive repeated this 3 times, I do have a few mods installed, KJR is one of the physics mods, along with far. Anyone else notice this?