Why do my aerospikes overheat?

[Delrey]

I have 2 on a spaceplane and when I activate them they immediately overheat. Any ideas?

[Sampa]

Delrey, we might need a little more information than that! At what altitude are you at? How fast are you going? Can we get some pictures to better see what is going on?

[Taki117]

The most likely reason is that you are going too fast too low. What I would do in this situation is kill throttle, kill jet engines, activate aerospikes. and then slowly increase throttle being careful about overheating. Do you have any mods installed?

[Laie]

The way overheating is handled currently has some quirks.

That said, I only know of two ways of making them overheat. But first off: merely seeing an overheat bar is not a problem. Engines work as expected even when very hot; only when they get too hot will they break/explode. Now, how do you get them to become too hot?

a) too many too close. But you need a quadcoupler worth of aerospikes to destroy them; a tricoupler still works, even if the overheating indicator looks scary. Unless your two are mounted very close together (maybe even overlapping), that should not be a problem.

mounted to a big tank. Because of $reasons, engines that tend to overheat will overheat much more when mounted directly to the largest tanks. IIRC only the orange tank and large Kerbodyne can have this problem, all others should be fine. You can solve the issue by putting a smaller part between the engine and the large tank: a battery, a small tank, whatever. Just don't mount the engines directly to a large tank and you should be fine.

[LordFerret]

The way overheating is handled currently has some quirks.

That said, I only know of two ways of making them overheat. But first off: merely seeing an overheat bar is not a problem. Engines work as expected even when very hot; only when they get too hot will they break/explode. Now, how do you get them to become too hot?

a) too many too close. But you need a quadcoupler worth of aerospikes to destroy them; a tricoupler still works, even if the overheating indicator looks scary. Unless your two are mounted very close together (maybe even overlapping), that should not be a problem.

mounted to a big tank. Because of $reasons, engines that tend to overheat will overheat much more when mounted directly to the largest tanks. IIRC only the orange tank and large Kerbodyne can have this problem, all others should be fine. You can solve the issue by putting a smaller part between the engine and the large tank: a battery, a small tank, whatever. Just don't mount the engines directly to a large tank and you should be fine.

I have a thread here on the forums where I tested some 'solutions' for the quadcoupler and Rapiers / LV-Ns ... and pretty much the same can be applied here. This is a static test I just did, 4 aerospikes on a quadcoupler - with small tanks as a buffer. Full throttle, burning nearly a full orange tank ... note the overheat level.

[Streetwind]

I have 2 on a spaceplane and when I activate them they immediately overheat. Any ideas?

Note: just seeing the "overheat" bar is actually not a problem. There are several engines which burn so hot that they always do this. However, they will stabilize themselves somewhere near the middle or upper end. The LV-N for example goes all the way to 85% or something.

But your engine doesn't actually take any damage from the heat until the bar is at 95%. So you can let them run all day long with the overheat bar showing and there is absolutely no downside whatsoever. Only when it fills up completely will you start seeing explosions.

[Delrey]

I'll post a pic tonight. I have 2 on a Mk2 bi-coupler. I'm going about 1200 -1300 m/s at about 25000 m.

I have some mods; the craft is mainly stock with the exception of a 5-way RSC and 6.25 radial tanks from modular fuel tanks.

They overheat and explode as I'm trying to climbing out.

Nick

[DeMatt]

I have some mods;

Would one of them be Deadly Reentry, perhaps?

[Delrey]

Yes I am using DRE.

[DeMatt]

Yes I am using DRE.

There you go. Aerospike heat production + poor heat dispersion (two aerospikes attached to one bicoupler) + DRE saying "burn!" = destroyed aerospikes.

Try using different engines. LV-909's are the same form factor, LV-T45's offer similar thrust, Rockomax 48-7S's are light and easily clustered. None of these heat as much as aerospikes do.

Alternatively, fly a steeper trajectory. Less horizontal speed and more altitude out of your jets, then allot more rocket fuel for the remaining flight.

[Delrey]

I switched to LV-30's using the RSC for control for the lack of gimballing. I'm sticking with the same flight profile though. I can now do an orbital rendezvous pretty easily.