PSA: Nuclear engine overheating

[Brotoro]

But is that good? If the nukes can't transfer their heat elsewhere, won't they just explode all the faster?

And, the ablator is getting used up, so this is not a solution if you want to make reusable nuclear Tugs.

[Frozen_Heart]

As I thought. Heat shields protect the rest of the craft from LV-N heat remarkably well. I had to run some fuel lines though but that's cool.

Docking ports also do this just as well and don't require fuel lines. Also they don't run out of ablator either.

However the LV-N itself overheats above 20% throttle if the part above is a good insulator.

Does anyone one which parts are the worst insulators? some of these in between a docking port and a LV-N should both radiate heat and prevent it getting to the fuel above.

[Redshift OTF]

But is that good? If the nukes can't transfer their heat elsewhere, won't they just explode all the faster?

And, the ablator is getting used up, so this is not a solution if you want to make reusable nuclear Tugs.

I haven't tried it in space but the Nukes didn't over heat significantly before I ran out of fuel. Ablation takes place over a temp of 500 but it is non linear. Between 500-600 I had to run it at 10x time acceleration to see the ablation take effect. As long as the heat shield isn't run too hot it shouldn't ablate significantly.

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Docking ports also do this just as well and don't require fuel lines. Also they don't run out of ablator either.

However the LV-N itself overheats above 20% throttle if the part above is a good insulator.

Does anyone one which parts are the worst insulators? some of these in between a docking port and a LV-N should both radiate heat and prevent it getting to the fuel above.

Interesting about docking ports. I haven't tried any other parts. Just getting the latest Hyperedit so I will see how this performs in space.

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OK so I tested these in space and yeah, they get really hot really fast. I didn't realise they were that bad. The heat shields did protect the quad coupler really well but ablation was significant and the Nukes still overheated.

[Temeter]

Hey, i've go an idea:

You can stop ressource usage (cklicking the tick beneath the tanks fuel gauge), so shouldn't you be able to do do that same with an ablator below the engine? Meaning you only activate ablating when your craft reaches a critical heat, using it as an emergency cooling?

edit: Nvm, you can't manually switch ablation. Too bad.

Edited April 29, 2015 by Temeter

[Redshift OTF]

Hey, i've go an idea:

You can stop ressource usage (cklicking the tick beneath the tanks fuel gauge), so shouldn't you be able to do do that same with an ablator below the engine? Meaning you only activate ablating when your craft reaches a critical heat, using it as an emergency cooling?

It doesn't let you do that sadly. Ablation is automatic above temps of 500.

[Whirligig Girl]

There's also the fact that you're getting liquid hydrogen isp out of what is essentially kerosene with the thermal properties of Aerozine 50. Plus, you don't have to worry about liquid hydrogen boil-off. We gloss over a lot of things in stock KSP for interesting gameplay, so having the engines heat the craft when thrusting instead of dealing with radiation and shadow shields isn't so terrible.

Plus, Atomic Rockets says that Spaceships Got Wings.

You know what? All they guys at Squad should have a read of Atomic Rockets.

[spaceBrezel]

Nuclear engines tend to overheat yes, but its not a big problem imho. One can always stop a burn and split burn times.

Currently in my career game (normal) i did start exploring Jool and its planets.

Made this little tug to carry a small science satellite to Jool. It explored Jool (no aerobreak) and is currently in orbit around Tylo with fuel left.

burn time was like ~10min nonstop

My first tugs looked more like this:

Notice the "Rockomax Brand Adapter" , insulating the engine from other parts.

Burn times with those kind of tugs where only like 3 minutes..

I think its not a good idea to stop the engine from spreading heat to nearby fuel tanks. Better spread the heat to fuel tanks and insulate crucial parts like pods, batteries behind a "firewall" (docking ports, brand adapter, ...).

Im currently testing a triple NERV tug with 16min+ burn time on the launchpad:

Still experimenting though..

Edited April 29, 2015 by spaceBrezel

[blowfish]

spaceBrezel: HyperEdit (or launch) that into space and see how long you can get the engine to run. I doubt it will be nearly as long.

[Temeter]

Seems like struts dont move heat anymore, and thermal mass gets lower when fuel tanks loose fuel.

Im currently testing a triple NERV tug with 16min+ burn time on the launchpad:

Keep in mind cooling is around a million times better on the launchpad. The issue with spacecraft is that they are in empty space, meaning there is nothing really to give off heat too (mostly air) and they need to rely on heat radiation.

[Brotoro]

You do realize that nuclear engines overheat in space much faster than they do in the atmosphere, don't you?

[Frozen_Heart]

As the above two posters pointed out. Try burning that in space and it will overheat in seconds...

[Temeter]

I'm actually using hyperedit right now to check how efficient heat mass/wing cooling in space is.

[Frozen_Heart]

Testing replacing the LV-Ns on my capital ships with LV-T45s. I only need half the amount and still get double the thrust. The massively lower weight means that the dV is pretty much unchanged.

And no overheating issues at all.

I'm honestly not understanding the point of the LV-Ns as they are. Other parts can do the same job better.

[jshier]

I don't like this general heat engine. Reentry heat was a nice additional challenge since you had to use the right parts to avoid blowing up and not reenter too steeply, but the system was pretty forgiving. With this, we've got just waste heat from parts, which was not a fun part of the interstellar mod at all. So we have to add all of these additional parts, whether they're intended to be radiators or not.

[Red Iron Crown]

I'm honestly not understanding the point of the LV-Ns as they are. Other parts can do the same job better.

If you can tolerate a lower TWR they can produce more dV. They're not the ideal solution for every situation, but they are very, very good in some situations.

[Lord Crc]

This is a petty cosmetic thing, but I really wish the thermal display's color spectrum was blue for cold parts, transitioning to red, then yellow, then white. It's just odd for cold parts to be red.

Please no! They're using the physically correct colors (well roughly). I would hate for them to change it into some arbitrary color scheme.

[Frozen_Heart]

If you can tolerate a lower TWR they can produce more dV. They're not the ideal solution for every situation, but they are very, very good in some situations.

I prefer a pretty high TWR. Previously it was pretty close but nuke won out. Now chemical engines are doing slightly better. They don't have overheat issues either.

[eddiew]

If you can tolerate a lower TWR they can produce more dV. They're not the ideal solution for every situation, but they are very, very good in some situations.

The frustrating factor is that LV-N's are low thrust already; and then the heating kicks in and 50kN has to come down to 20, and it's just painful

Not that this will stop me using them on the back end of my SSTOs however, I'm just gonna whine and moan about the annoyance of it for the next 12 months

[regex]

I'm just gonna whine and moan about the annoyance of it for the next 12 months

1.0.1 will be out sooner than you think (no, I don't have a crystal ball, I just suspect that) and, if it isn't fixed, a simple ModuleManager script will deal with your woes.

[Temeter]

I DID IT!

I've got a heat neutral vessel without any extra 'cooling/radiation' parts, in contrary it works because I did remove them. It's not a joke ship either, but a serious test:

Fuel distribution, only unused exidizer in the cargo dummy. Mind the fuel locks, no cheating here.

And it stalls around 2060 temperature, I expect it to burn the full 3600 delta-v on the sunside of a planet without explosions. I did most of the burn, but lost flight computer. The cargo are two locked fuel tanks, around 27 tons, full T/W is 0.32. Very inefficient ship, but already more efficient than you would ever be with normal engines. Mind the fuel tanks above the engines are working at half weight, giving every 3 ton engine around 7,2 tons of fuel in a oversized 2 ton container. Not to mention the empty middle tank.

One thing was very important: Let the head spread through the ship (bringt it to space and use that heat coloration)! In my first version those outer tanks were connected by the midsize girder, which effectively isolated the middle compartment and causing a heat congestion in the 4 engine/tank sections and killed the engines after ~1200 dv (which is enough for most burns). Connecting the tanks directly to the empty middle tank did cause the heat to spread nicely up through the mid-stack.

Another thing to keep in mind are the more sensitive equipment and probes. In my example the heat spread to well, killing my core and one or two electricity parts. Interestingly enough, the other 6 batteries and panels survived. Isolating them via girders is probably the best choice. It's also a question if you want to try to spread some heat to your cargo. In my case the cargo was isolated.

So yeah, heating is an issue than can be solved and nukes are still more efficient than everything else. Have to see how it plays out, but I like it until now. Looks like you really want to properly design/reuse your nuclear driven motherships in future. As a fun fact, crafts like the apollo space ship are similarly build to spread and radiate heat as much as possible to avoide overheating. That's why apollo 13 got so cold after shutting of the heating.

Edited April 29, 2015 by Temeter

[RocketPilot573]

In the meantime I'm just going to use the next best engine: The Poodle.

[Brotoro]

I've started testing with my old nuclear Tugs (since I have a lot of them out in space on missions).

The engines are thermally isolated from the rest of the Tug because they are mounted on radial decouplers along with an extra shadow shield part and a parachute so that the nukes can be dropped and recovered in case of launch failure...which seemed like a prudent design at the time).

At 100% power, the nukes explode after 75 seconds. They hardly have time to heat up other parts (just the plate they are mounted on).

At 50% power, the nukes explode just shy of 3 minutes.

At 33% power, the nukes explode at 6.5 minutes. One of my typical burns for Jool could take almost an hour at that power level, and would need to be done in over ten burns.

At 25% power, the nukes reached an equilibrium temperature of 2418° and were still going after 20 minutes. Of course, a Jool burn for my typical payloads would require something like 72 minutes at that thrust level...and would need to be done in several burns anyway at consecutive periapses.

[Temeter]

You want to put those nukes as close as possible to the big fuel tank so it can soak and further distribut heat. Maybe even decrease the central tanks size and put the 4 nukes on radial tanks. Keep in mind those radial tanks will be the 2nd hottest part of the ship, so they need to withstand a lot (=try bigger tanks if the small ones break). Electrics also need to be isolated somehow.

Well, the old ships won't work anymore.^^'

Edited April 30, 2015 by Temeter

[Brotoro]

I see that Temeter was reading my mind while I was gone.

Below is a test of a new Tug. It uses all liquid fuel (the Rockomax X200-8 tanks have been tweaked to remove their oxidizer). The X200-8 tanks are hard-mounted to the sides of the big tank, so no more option of dropping the nukes (the environmentalists will just have to bit my shiny Plutonium ass).

Will a full fuel load (and therefore the maximum thermal mass to soak up the heat), the nukes can run at 100% power for 7 minutes before explosions. And, as expected, it's the X200-8 tanks that explode.

Sure, the old ships will work. They just need to be kept at low throttle (but I'm not going to throw away useful nukes already in space).

[juanml82]

Ok, so then the issue wasn't so much about the nukes overheating, but of players trying to attach them in the old fashioned way?