Overheating RTG's and batteries

[xtoro]

These things always pop up as overheating, even in space. I realize that RTG's actually do produce heat, but for spaceplanes, it kinda sucks. It I stick RTG's and/or batteries in a cargo bay, they're the first to overheat, and even they explode. Even though the rest of the plane is fine and nothing else explodes, they usually do.

Anyone find a way to keep them cool without adding some dragging rads to the fuselage? Do radiators in cargo bays work maybe? Or RTG's on the outside?

[Snark]

Disclaimer: I don't fly spaceplanes in KSP, so rationales below are physics-based rather than gameplay-based; I'm not well-calibrated around what is or isn't fun for spaceplanes, or what appropriate tradeoffs are between gameplay and realism for them.

- RTGs do make heat, it's a fact of life. (I kinda like that they're not just magic-electricity-with-no-downside anymore.)

- They generate heat that you can't turn off. It's their primary distinguishing characteristic IRL.

- Radiators inside a closed container shouldn't work. Dunno how KSP models this (as I mention, I don't do spaceplanes), but they really shouldn't work because there's nowhere to radiate to.

- Putting them in a container that you then open ought to work (at least in terms of realistic physics): they should be able to rotate through the open cargo door (or whatever), though I'm not sure whether KSP models this.

As for a lightweight solution for your spaceplanes: Have you tried putting deployable radiators in a service bay? Fly to space, open the bay, extend radiators.

[xtoro]

Thought of that but the real issue is when I'm reentering the atmosphere. If I left the cargo bay door open with a radiator sticking out, I imagine it would tear off

[Snark]

So they overheat so fast that they blow up in the interval between hit-atmosphere-too-thick-to-keep-the-bay-open and landing?

Well, since I'm a rocket guy and not a spaceplanes guy, the obvious answer is "jettison the RTG before reentering if it's a problem."

However, if your goal is to recover everything (which SSTO folks usually want to do), I guess you'd be better off talking to someone who does spaceplanes.

[xtoro]

So they overheat so fast that they blow up in the interval between hit-atmosphere-too-thick-to-keep-the-bay-open and landing?

Well, since I'm a rocket guy and not a spaceplanes guy, the obvious answer is "jettison the RTG before reentering if it's a problem."

However, if your goal is to recover everything (which SSTO folks usually want to do), I guess you'd be better off talking to someone who does spaceplanes.

Yeah, plane starts getting reentry heating burning effects, and then the RTG and batteries get orange bars, then red, then they blow up. They don't cause anything else to blow up, but yes, I do want to recover, and reuse everything.

[Signo]

Are your RTGs connected directly to the cargo bay? I noticed that the RTGs that are not connected directly to the bay do not overheat.

I have a 2 bay reentry vehicle, a RTG powered rover is stored in the first, the second one is the ship "service" bay carrying batteries, a couple of RTGs and stuff like that. The RTGs in the service bay usually explode while the one attached to the rover does not even overheat.

[Streetwind]

Wasn't precisely this just fixed in 1.0.3?

From the changelog:

"Added a tuning factor to conduction between parts with different shielded states, so a cargo/service bay won't conduct much to parts within it. Since radiation is disabled for parts within bays, they'd just increase in temperature with no way to cool during reentry, and parts in bays would be the first to blow up on reentry."

xtoro, if you are still on 1.0.2, try updating KSP. If you are already on 1.0.3+, try posting in the support forum, referencing the above patch note. If there is a bug, I bet Squad will want to hear about it.

[rofltehcat]

I had something similar happen to me: I had some 4 reaction wheels (don't judge me!) stacked in a cargo bay and they overheated pretty quickly. This was in 1.0.2 though.

My guesses were: Either they are very bad at conducting heat and thus the stacking is the problem. Or they were somehow attached to the wrong part/node, either to the part in front of the cargo bay or to the outside node of the cargo bay.

Either way, I rebuilt the thing with 2 wheels in the forward position and 2 in the back and it worked afterwards. Maybe it was the stacking, maybe it was the wrong node, don't know.

[xtoro]

Happened in 1.0.2 but it's worse in 1.0.3. In fact I only posted this AFTER trying it in 1.0.3.... I even tried putting cubics in the cargo bays and attaching things to those, but still, the rtgs explode. I said screw it and decided to land my plane anyways, and all the science parts in the cargo bay blow up later on as well! After RTG's, the Thermostat blows, then the Gravioli, then everything else.... What's the point of the cargo bay? Do we need a shielded cargo bay now?

[DancesWithSquirrels]

Have you tried putting a couple of surface mount radiator panels on top of the fuselage of your spaceplane? They should be shielded from reentry and able to dump any excess heat. According to other discussions the mechanic is like RCS or xenon, and they don't need a direct connection to hot elements.

[xtoro]

Have you tried putting a couple of surface mount radiator panels on top of the fuselage of your spaceplane? They should be shielded from reentry and able to dump any excess heat. According to other discussions the mechanic is like RCS or xenon, and they don't need a direct connection to hot elements.

I have a rad on each side of the cargo bay and 2 on the bottom. Maybe I'll try flipping the bay around so the rads are on top. Perhaps the rads on the bottom make heating worse?

[DancesWithSquirrels]

Radiators work best when they emit to colder directions, like space - the ones directly facing reentry heat may make matters worse. Remove the bottom radiators and put some on top of the cockpit, the fuselage, the top of the wings, or if they are large enough, the sides of your vertical tail(s).

[xtoro]

Yeah I wasn't sure how realistically they were in the sense of drawing in heat as well. Then I thought "I can't put them on top because of the cargo bay doors!" Duh... Flip it around so the doors open on the bottom lol will try it tonight.

[xtoro]

Rads on top not helping... Anyone else having issues with RTG's in cargo bays blowing up on reentry?

[steve_v]

Yeah, and not just RTGs either. The issue is due to another shortcut in the heating system: Parts can't radiate any heat at all when in a cargo bay. Why one would do this I don't know, physics fail.

Parts in a cargo bay should radiate, heat be absorbed by the bay walls and re-radiated out into space, possibly via external radiators. Disabling radiant heat in a closed cargo bay is just stupid.

Considering the number of "illogical heating / exploding" reports coming in, I guess we'll have to wait for yet another emergency patch for a poorly tested system. This is getting ridiculous.

Edited June 25, 2015 by steve_v

[Streetwind]

Radiation wouldn't solve this problem.

The issue is that shielded parts get a large amount of heat dumped into them in a very short time, to the point of exploding. And while all parts in stock KSP are unrealistically good radiators, the ability to radiate is still exponentially related to part temperature, and linearly related to surface area. Parts need to get extremely hot in order to radiate significant amounts of heat, especially when they're small... unfortunately, batteries and RTGs and science experiments are very small. And to make that worse, they generally have very low maxTemp values.

If you put one of these parts at 99% maxTemp, then it has a certain radiation flux value that it gives off. That value is equal to the value of conduction flux that the part can receive without further increasing its temperature, which would result in an explosion. Because the part has low maxTemp, default emissiveConstant and a tiny surface area, the value is very small.

However, since the part manages to spike all the way from space ambient temperature to explosion during the short period of reentry heating, this implies that the conduction flux it receives is significant. It's therefore reasonable to assume that it exceeds the ability of the part to radiate heat away. If the part was able to radiate while shielded, it might buy itself an extra 5-10 seconds lifetime, but it would not actually prevent overheating.

Rather, this behavior is a bug. Cargo bays are not supposed to conduct any noticable amount to shielded parts in 1.0.3 according to the patchnotes; however, the opposite seems to have happened. The bays actually conduct more, not less. That's the reason that this happens, and Squad must fix the conductivity.

[xtoro]

Yep, not just RTG's. I placed the RTGs on the outside, on the wings. They survived, but all my science gear in the bay exploded. So basically, cargo bays are now useless for storing things on reentry?

[Signo]

I think it is a matter of heat transfer from the bay to the first part directly connected to it. RTGs directly connected to the bay will blow up pretty soon, while on the other hand a RTG in the bay connected to a jr docking port, connected to a cubic that finally connects to the bay is apparently safe.

[A_name]

Yep, not just RTG's. I placed the RTGs on the outside, on the wings. They survived, but all my science gear in the bay exploded. So basically, cargo bays are now useless for storing things on reentry?

This would really suck.

[xtoro]

I think it is a matter of heat transfer from the bay to the first part directly connected to it. RTGs directly connected to the bay will blow up pretty soon, while on the other hand a RTG in the bay connected to a jr docking port, connected to a cubic that finally connects to the bay is apparently safe.

LOL yeah, the problem is with that many parts, it doesn't leave much room for my little probes that I launch with the plane...

[A_name]

Xtoro, have you found a solution to this?

[xtoro]

Xtoro, have you found a solution to this?

Sorta. The only way they survive is if I put the RTGs on the outside, and in the cargo bay I have cubics with the science parts on those. Not really a fix though, just a workaround.