Houston, the heat shield's overheating!

[ZentroCatson]

So, today, I made a Apollo-style Mun mission in Sandbox, just for fun. The mission went flawless but that's not the interesting part. On reentry, I noticed an orange temperature gauge pointing to the heat shield. Here's a pic of that:

(sorry for the large size)

I used KER to check wich part has critical temperature, and apparently, it was the heat shield  This is just too funny. A heat shield overheating. Think about it. Oh, and apparently there's another heat shield floating in a eccentric solar orbit 

[FancyMouse]

Not funny at all. Time to learn:

 

[Streetwind]

It is perfectly logical for a heatshield to reach a high temperature. Even for an ablating one.

Think about it: the higher the temperature climbs, the faster the heatshield ablates. In reverse, that means that the lower the heatshield's own temperature is, the slower it ablates. Now, in order to manage a certain heat load, ablator needs to burn off at a certain rate. And because of the relationship just explained, that means that the heatshield must reach a certain minimum temperature itself, or the ablation process could not run fast enough to counter the incoming heat load.

Thus, for every given heat loading scenario, there exists a specific temperture that the heatshield reaches and stabilizes itself at, because that is the temperature at which the ablation rate exactly cancels out the heating rate.

[ZentroCatson]

33 minutes ago, Streetwind said:

It is perfectly logical for a heatshield to reach a high temperature. Even for an ablating one.

Think about it: the higher the temperature climbs, the faster the heatshield ablates. In reverse, that means that the lower the heatshield's own temperature is, the slower it ablates. Now, in order to manage a certain heat load, ablator needs to burn off at a certain rate. And because of the relationship just explained, that means that the heatshield must reach a certain minimum temperature itself, or the ablation process could not run fast enough to counter the incoming heat load.

Thus, for every given heat loading scenario, there exists a specific temperture that the heatshield reaches and stabilizes itself at, because that is the temperature at which the ablation rate exactly cancels out the heating rate.

Yep, that does make sense. I just wanted to show my recent discovery, and as I'm not an aerospace engineer, it seemed quite amusing to me that a heat shield can overheat. Well, now I know better, but it's still funny 

[Octa]

1 hour ago, ZentroCatson said:

Yep, that does make sense. I just wanted to show my recent discovery, and as I'm not an aerospace engineer, it seemed quite amusing to me that a heat shield can overheat. Well, now I know better, but it's still funny 

I found the same when i tried to ablate a fully stocked heatshield. I guess it's not possible to use 100% of the ablator on kerbin in one turn without heating up. Maybe multiple aerobreaking turns from interplanetary speeds might utilize that much ablator. But within LKO missions, you could reduce the ablator to something between 20% or 50%, depending on your safety margin.

[Pecan]

In 1.0.5 I was mainly doing exo-atmospheric stuff for the past several months so, obviously, not using heat-shields.  Now in 1.1 I'm starting from scratch and have noticed something which seems odd to me.  I hope this is an appropriate place to get others' comments on it:

Launching causes high temperatures and I saw that my heat-shield was ablating before even reaching orbit.  Now during launch it's both facing backwards and has a shroud fitted from the decoupler just below it.  Since ablator adds mass I was trying to carry as little as possible and this meant there was insufficient for re-entry (although the rest of the ship managed to take the remaining heat-load) Is this ablating during launch correct behaviour?

Edited April 28, 2016 by Pecan

[Brofessional]

1 hour ago, Pecan said:

In 1.0.5 I was mainly doing exo-atmospheric stuff for the past several months so, obviously, not using heat-shields.  Now in 1.1 I'm starting from scratch and have noticed something which seems odd to me.  I hope this is an appropriate place to get others' comments on it:

Launching causes high temperatures and I saw that my heat-shield was ablating before even reaching orbit.  Now during launch it's both facing backwards and has a shroud fitted from the decoupler just below it.  Since ablator adds mass I was trying to carry as little as possible and this meant there was insufficient for re-entry (although the rest of the ship managed to take the remaining heat-load) Is this ablating during launch correct behaviour?

It's not really "correct" behavior, but with how the thermal system in the game works it does happen. It's usually negligible though, assuming you're not using the heatshield in an unusual way.

In general if you're heating up that much during launch you need to lower the throttle or head back to the VAB and adjust the thrust limiters on your SRBs.

Edited April 28, 2016 by Brofessional

[Raideur Ng]

If you push your luck, coming in fast enough will pop that heat-shield, just like any other part. The ablator doesn't even have a chance to work.

[TheKosanianMethod]

Now I want to take a ship up to the edge of Kerbin's SOI, get the periapsis just into the atmostphere, and as soon as I start hitting air, I will have SRBs that will make me go as fast as I can into the atmosphere, and burn up all of my ablator. 

 

"Put the spurs to 'er, Chuck!"

Anyone get the reference?

Edited April 30, 2016 by TheKosanianMethod
Wondering

[razark]

I'm using DRE here, but thanks for letting me know, I guess.

[Guest]

"Houston, the heat shield's overheating"

Jokes on you, spacecraft cannot communicate during reentry due to plasma around it or something like that. Houston wouldn't even know.

Edited April 29, 2016 by Guest

[razark]

4 minutes ago, Aperture Science said:

Jokes on you, spacecraft cannot communicate during reentry due to plasma around it or something like that. Houston wouldn't even know.

So, that means that we would only know if the heat shield were to overheat not during reentry.

Which makes the situation somewhat even more terrifying.

[Guest]

2 minutes ago, razark said:

So, that means that we would only know if the heat shield were to overheat not during reentry.

Which makes the situation somewhat even more terrifying.

Yes. Overheating on Eeloo's surface, for instance. I'd be worried.

[Streetwind]

8 hours ago, TheKosanianMethod said:

Now I want to take a ship up to the edge of Kerbin's SOI, get the periapsis just into the atmostphere, and as soon as I start hitting air, I will have SRBs that will make me go as fast as I can into the atmosphere, and burn up all of my ablator. 

 

"Put the spurs to 'er, Chuck!"

Try a retrograde solar orbit, encountering Eve...

[N_Molson]

To make yourself an idea of the "reentry terror", watch the final scenes of Apollo 13 (Ron Howard, 1995). Quite a realistic movie.

[TheKosanianMethod]

15 hours ago, N_Molson said:

To make yourself an idea of the "reentry terror", watch the final scenes of Apollo 13 (Ron Howard, 1995). Quite a realistic movie.

I've seen Apollo 13 three or four times, and those scenes are still amazing to me.

[mrclucks]

I'm still on 1.0.5, but I've noticed that during re-entry my heat shield will very quickly show up as yellow in the heat debug menu and KER will show it around 70% to critical temperature or something, however it doesn't budge from there.  It makes sense that the heat shield has too heat up to burn off ablator, but I'd hardly call it overheating since its not exploding or anything

[Mjarf]

No wonder it's heating up when you're entering the atmosphere at such high velocity. It's probably a more fuel efficient way of re-entry, but it's also a quite scary and risky one. I prefer to to first enter a ~100km orbit before re-entry to keep the velocity down, barely need a heat shield when doing it that way.

[TheKosanianMethod]

On 4/29/2016 at 3:26 AM, Streetwind said:

Try a retrograde solar orbit, encountering Eve...

Burn, baby, burn!

[ExtremeSquared]

The ridiculous thing is when the thermometer overheats and explodes from radiative heat. I'm glad that wasn't a manned mission.