2.5 Heatshield Exploded due to overheating.

[Daveroski]

As subject.

To reproduce;

2.5 pod +2.5 heatshield +2.5 Decoupler + Orange 2.5 Tank + Skipper (I had a 1.5 battery, Large Drogue + 4 Radial Parachutes on the Pod)

Orange Tank has 4 Winglets? for stability

Launch go to 25 degrees wait for fuel to run out.

Drop orange tank.

Go a few hundred thousand meters to ap and back to atmosphere.

Turn to Retrograde and wait watch the ablative shielding on the heat shield.

Heatshield doesn't lose most of its ablative shielding but it blows up due to overheating.

I would have posted this in unmodified but I use Engineer.

Isn't the ablative coating supposed to burn off before the heatshield blows up?

[Ryds]

What's your PE for reentry? The sweet spot seems to be around 22 kilometers. If you spend too much time in atmosphere with a high PE then you'll burn up due to heat build up over time. If you come in too steep you'll burn up due to excess velocity being transferred to friction heat.

[mikegarrison]

What's your PE for reentry? The sweet spot seems to be around 22 kilometers. If you spend too much time in atmosphere with a high PE then you'll burn up due to heat build up over time. If you come in too steep you'll burn up due to excess velocity being transferred to friction heat.

I think his point is that the HEAT SHIELD shouldn't blow up because it got too hot. Heat shields are supposed to get hot. If there is any ablation material left, it's supposed to ablate (and carry the heat away with it when it does).

[sal_vager]

If your Physics.cfg failed to update you can have incorrect values for heating, KSP has internal values but reads that file to check for any user modified settings (via debug menu or hand edit), so renaming or deleting that file will reset heating values to the current defaults.

[Daveroski]

I think his point is that the HEAT SHIELD shouldn't blow up because it got too hot. Heat shields are supposed to get hot. If there is any ablation material left, it's supposed to ablate (and carry the heat away with it when it does).

Bravo! It's good to be understood!

And your post is most welcome.

You sir, can have some rep!

[Starwaster]

Even real life heat shields have a maximum amount of heat they can handle.

Thermal management for a space craft means more than just slapping a heat shield on it.

You need a proper reentry profile or you will die.

Or to put it in the words of a certain famous starship captain.... "Hey, space is a tough place where wimps eat flaming plasma death!"

(sorry... couldn't resist)

[Daveroski]

Even real life heat shields have a maximum amount of heat they can handle.

So heat can bypass the ablation and go right to the shield and destroy it? seems a pisspoor invention to me.

I might expect the ablation to get rapidly blown away and then destroy the shield but ignoring the ablation and just destroying the thing as whole? No I have to have a little logic with my science or it's just not fun any more.

Edited June 25, 2015 by Daveroski

[Padishar]

The ablation process can only take heat away at a certain rate, if heat is getting put in faster than that then the temperature will rise. Too much and it will not protect whatever it is attached to (the heat will conduct through to it). The problem is that everything fails (explodes) in the same way in KSP even parts that would never actually explode. I think the heatshield should probably have a significantly higher temperature limit so that if it does get "overloaded" then the part it is attached to will overheat and fail instead, e.g. the pod would explode before the heatshield...

[Green Baron]

So heat can bypass the ablation and go right to the shield and destroy it? seems a pisspoor invention to me.

That's *not* personal, but i'm wandering and can't understand why people are having problems with choosing an appropriate perapsis for aerobraking. And why it's so difficult to understand that plummeting through the atmo @3km/s with a too steep angle doesn't leave the heat enough time to dissipate and heat storage capabiltiy of parts is limited. That's expected and accepted, or not ?

Adapt the flightpath is so easy and then even parts that stick slightly out of the heatshield stay alive :-)

And i would really appreciate if squad wouldn't change it over again, because they can *never* make it right for everyone. It might be a nice idea to stick a post on top explaining what to do in physx.cfg to avoid heating dramas ?

k

Edit: partly ninjad ba padisher :-)

[Daveroski]

The ablation process can only take heat away at a certain rate, if heat is getting put in faster than that then the temperature will rise. Too much and it will not protect whatever it is attached to (the heat will conduct through to it). The problem is that everything fails (explodes) in the same way in KSP even parts that would never actually explode. I think the heatshield should probably have a significantly higher temperature limit so that if it does get "overloaded" then the part it is attached to will overheat and fail instead, e.g. the pod would explode before the heatshield...

As I understood it, the ablation process works by the friction of the hot air hitting it and gradually stripping it away. The heat comes from direct contact with the heated air. The ablative substances are terrible conductors of heat and are designed to be eroded by the contact of the hot air so that any hot ablative coating is removed and so does not conduct heat to the craft.

As the only heat source is the heat of the friction with the atmosphere that heat should not be able to go deeper than the ablative coating.

Once the coating is used up and gone. then the friction heats up the base of the heatshield and conductivity can cause it to get to the rest of the craft.

Which brings me to my point. While there is still ablation on the shield, it should continue to function until there is not.

If the friction and so the heat becomes more intense, more ablation is removed from the shield again until such a time as there is no more ablation left.

Are you seriously suggesting that there is a different heat source than the friction from the atmosphere? One which can be so intense as to bypass the heatshield altogether?

Please, I'm eager to learn. Do educate me.

[Green Baron]

As i understood, there is a max Temp. for each part (3000 for the heatshield) and a conductivity, the latter being just very low for the shield (0.01, whatver that means). Your craft explodes from shield to chute upwards "due to overheating" (F3 printout), meaning (for my understanding) that the part heats up too fast (in a second as from the gauges) for the shielding to take effect.

That behaviour is close to exactly what i would expect.

Solution: choose a shallower path and your fine.

:-)

k

edit: maybe it's easier if you see it that way: Even the shielding has a max Temp., though higher than the rest. To take effect it must slowly melt thus take the heat away. If its heated too fast it can't melt (change of state from solid to liquid takes time), it breaks from thermal stress. Ok ? :-)

Edited June 25, 2015 by kemde

[Daveroski]

That's *not* personal, but i'm wandering and can't understand why people are having problems with choosing an appropriate perapsis for aerobraking. And why it's so difficult to understand that plummeting through the atmo @3km/s with a too steep angle doesn't leave the heat enough time to dissipate and heat storage capabiltiy of parts is limited. That's expected and accepted, or not ?

Adapt the flightpath is so easy and then even parts that stick slightly out of the heatshield stay alive :-)

And i would really appreciate if squad wouldn't change it over again, because they can *never* make it right for everyone. It might be a nice idea to stick a post on top explaining what to do in physx.cfg to avoid heating dramas ?

k

Edit: partly ninjad ba padisher :-)

When testing the heatshield for Duna and Eve, I would like to test it thoroughly on Kerbin before spending hours building a mission and going to another world.

While Duna shouldn't present any real problems, Eve on the other hand has a much denser atmosphere and one can expect the heat from re-entry to be much greater and for a much longer duration than one can properly produce on Kerbin.

You are saying that the shield can be destroyed by a process we can't measure or test. That finding the pe on kerbin is the best solution. If I have to send mission after mission to Eve just to find the best pe, my career funds won't last very long.

Besides Quote "A Mk1-2 straight-in reentry to Eve starting at 6.5km/sec surface (more orbital) is just barely survivable (ablator fully depletes),"

Seems to me it's a good job I didn't wast a bunch of time trying that one eh?

- - - Updated - - -

As i understood, there is a max Temp. for each part (3000 for the heatshield) and a conductivity, the latter being just very low for the shield (0.01, whatver that means). Your craft explodes from shield to chute upwards "due to overheating" (F3 printout), meaning (for my understanding) that the part heats up too fast (in a second as from the gauges) for the shielding to take effect.

That behaviour is close to exactly what i would expect.

Solution: choose a shallower path and your fine.

:-)

k

The ablator is supposed to keep the temprature of the heat shield down to almost normal until the ablator is used up. No ablator = nothing to prevent the temprature increasing to 3000.

While you have ablator the temprature shouldn't get up to anywhere near the tolerance of what ever it's attached to.

If it is supposed to be able to withstand a 6k+ straight down re-entry on eve, Kerbin Should be no problem at all.

[Green Baron]

while( not content ) {

F3, enter bodys soi, choose perapsis, watch your craft, F9

} // not content :-)

We don't have the means to calculate the periapsis for a given craft for an aerobrake/-capture. But there are allready hints on the forum about certain altitudes for aerobrake or even -capture.

:-)

[Daveroski]

while( not content ) {

F3, enter bodys soi, choose perapsis, watch your craft, F9

} // not content :-)

We don't have the means to calculate the periapsis for a given craft for an aerobrake/-capture. But there are allready hints on the forum about certain altitudes for aerobrake or even -capture.

:-)

I was expecting someone to say that.

[NathanKell]

Daveroski: Nope, ablation works more or less like a standard exponential-rate chemical reaction: slow to start, speeds up fast in the middle, rate of climb slows after a certain point. There are very definitely "peak" ablation rates that thermal protection systems (and reentry corridors) have to be designed around.

Let me give you an example: Mercury had approximately 250lb of ablator, IIRC. Only "a few pounds" were used on reentry. The peak skin temperature of the heat shield was around 2700F. Had the descent been all that much steeper, the shield probably would have locally burned through, despite having tons of ablator remaining.

This is one reason why lifting reentries are so useful: while the total heat load is larger, the peak heating rate is much lower, which means temperatures can be kept low and much heat reradiated.

[Daveroski]

Daveroski: Nope, ablation works more or less like a standard exponential-rate chemical reaction: slow to start, speeds up fast in the middle, rate of climb slows after a certain point. There are very definitely "peak" ablation rates that thermal protection systems (and reentry corridors) have to be designed around.

Let me give you an example: Mercury had approximately 250lb of ablator, IIRC. Only "a few pounds" were used on reentry. The peak skin temperature of the heat shield was around 2700F. Had the descent been all that much steeper, the shield probably would have locally burned through, despite having tons of ablator remaining.

This is one reason why lifting reentries are so useful: while the total heat load is larger, the peak heating rate is much lower, which means temperatures can be kept low and much heat reradiated.

If Quote "A Mk1-2 straight-in reentry to Eve starting at 6.5km/sec surface (more orbital) is just barely survivable (ablator fully depletes)," is true, then Kerbin should be easy.

Now it seems that the quote just is not true.

And mercury had a fat guy passenger there and back. That is so inefficient it beggars belief.

I would have thought that the ablator would have varied in speed of loss, greater friction, greater loss until it reaches a point where friction is so fast that it strips the ablator away really quickly and the heat shield then feels the real heat.

One would have thought that the formula for ablator would have improved since mercury and be much more efficient by now. One lives and learns.

Oh my, all those poor newbies to the game will come across this problem and won't know anything about mercury and the fat man. They will be forever thinking that the game is broken because it isn't working as expected and there is no info in game to tell them what is really happening. Suckers! they should all use the forum like us real players eh?

[Ryds]

If Quote "A Mk1-2 straight-in reentry to Eve starting at 6.5km/sec surface (more orbital) is just barely survivable (ablator fully depletes)," is true, then Kerbin should be easy.

Now it seems that the quote just is not true.

And mercury had a fat guy passenger there and back. That is so inefficient it beggars belief.

I would have thought that the ablator would have varied in speed of loss, greater friction, greater loss until it reaches a point where friction is so fast that it strips the ablator away really quickly and the heat shield then feels the real heat.

One would have thought that the formula for ablator would have improved since mercury and be much more efficient by now. One lives and learns.

Oh my, all those poor newbies to the game will come across this problem and won't know anything about mercury and the fat man. They will be forever thinking that the game is broken because it isn't working as expected and there is no info in game to tell them what is really happening. Suckers! they should all use the forum like us real players eh?

I would have thought that the ablator would have varied in speed of loss, greater friction, greater loss until it reaches a point where friction heat build up is so fast that i̶t̶ ̶s̶t̶r̶i̶p̶s̶ ̶t̶h̶e̶ ̶a̶b̶l̶a̶t̶o̶r̶ ̶a̶w̶a̶y̶ ̶r̶e̶a̶l̶l̶y̶ ̶q̶u̶i̶c̶k̶l̶y̶ the ablator is not stripped away fast enough and the heat shield then feels the r̶e̶a̶l̶ full friction heat - which is transmitted to other parts in the vehicle - which why it is important to test my craft in order to find the optimal reentry profile - which is around 22-25k on Kerbin.

Kerbal Construction TIme is a great mod that allows you to run simulations of your craft from defined altitudes, as well as adding value to career. It's not really hyperedit as you can only run simulations on planets you've discovered.

http://forum.kerbalspaceprogram.com/threads/92377-1-0-x-Kerbal-Construction-Time-1-1-8-(06-18-15)-Unrapid-Planned-Assembly

Edited June 26, 2015 by Ryds

[Nigeth]

As it stands a capsule won't survive a 6.5 km/s reentry on Kerbin, regardless of angle of entry (I've accidentally had to try this with a craft that was on a return trajectory from Jool). Capsule will explode due to overheating. So I seriously doubt that it would survive a similar re-entry on Eve with its denser atmosphere.

The fact that this is exactly what Squad claimed you should be able to do (" a 6.5 km/s direct re-entry to Eve's atmosphere is barely survivable") just makes this more that more annoying. It's one thing to say that this won't work because it's too far from reality anyway and another to claim that it will work even though it doesn't.

[Daveroski]

Its seems it's supposed to work a certain way but it doesn't. Call it a bug or call it a coincidental simulation of reality.

It isn't intuitive.

Many haven't a clue about thermodynamics and won't understand the coincidental simulation of reality version.

To new players and older players who don't use the forums, there is no answer to the 'Why did my heat shield just blow up with all that ablator still on it?'

[stratvox]

I am reminded of something I heard once. "In theory, practice and theory are the same, but in practice, they differ."

There is nothing you can make that can't be overcome by nature's forces. That includes heat shields. Heat shields merely make successful re-entry possible. They don't make it certain. Just ask Vladimir Komarov.

Here's how I do re-entry. Returning to Kerbin I'll put my periapse at ~68km. When I get to periapse, I burn retrograde to bring apoapse down to ~40km. I now have a good long run of slow aerobreaking in the upper atmosphere to bring it in gently. One hundred percent survival rate, barring things like poorly designed aerodynamics of the re-entry vehicle.

- - - Updated - - -

As it stands a capsule won't survive a 6.5 km/s reentry on Kerbin, regardless of angle of entry (I've accidentally had to try this with a craft that was on a return trajectory from Jool). Capsule will explode due to overheating. So I seriously doubt that it would survive a similar re-entry on Eve with its denser atmosphere.

The fact that this is exactly what Squad claimed you should be able to do (" a 6.5 km/s direct re-entry to Eve's atmosphere is barely survivable") just makes this more that more annoying. It's one thing to say that this won't work because it's too far from reality anyway and another to claim that it will work even though it doesn't.

Actually, that's not necessarily true, and here's why. The pressure gradient of Eve's atmosphere is going to be different from Kerbin's because of its high gravity. That means that you'll have significantly more time for aerobraking before you hit the denser parts of the atmosphere where heat can rise quickly enough to bypass ablation... so when you get there you'll be travelling significantly slower than you would be entering Kerbin's atmosphere at that velocity.

[Daveroski]

I am reminded of something I heard once. "In theory, practice and theory are the same, but in practice, they differ."

There is nothing you can make that can't be overcome by nature's forces. That includes heat shields. Heat shields merely make successful re-entry possible. They don't make it certain. Just ask Vladimir Komarov.

Here's how I do re-entry. Returning to Kerbin I'll put my periapse at ~68km. When I get to periapse, I burn retrograde to bring apoapse down to ~40km. I now have a good long run of slow aerobreaking in the upper atmosphere to bring it in gently. One hundred percent survival rate, barring things like poorly designed aerodynamics of the re-entry vehicle.

Wow, what an amazing waste of fuel.

I very rarely burn retrograde at all on re-entry only to set pe. My guys always aero-brake and always survive.

I don't have any problems re-entering. I was commenting on tests I was doing with the heat shield.

We are not talking about natures forces, we are talking about a game. There is no theory it's all practical data. Garbage in...

About what the devs said we can do as opposed to what we can actually do.

[Zeo]

As I understood it, the ablation process works by the friction of the hot air hitting it and gradually stripping it away. The heat comes from direct contact with the heated air. The ablative substances are terrible conductors of heat and are designed to be eroded by the contact of the hot air so that any hot ablative coating is removed and so does not conduct heat to the craft.

As the only heat source is the heat of the friction with the atmosphere that heat should not be able to go deeper than the ablative coating.

Once the coating is used up and gone. then the friction heats up the base of the heatshield and conductivity can cause it to get to the rest of the craft.

Which brings me to my point. While there is still ablation on the shield, it should continue to function until there is not.

If the friction and so the heat becomes more intense, more ablation is removed from the shield again until such a time as there is no more ablation left.

Are you seriously suggesting that there is a different heat source than the friction from the atmosphere? One which can be so intense as to bypass the heatshield altogether?

Please, I'm eager to learn. Do educate me.

Hello!

Re-entry heating actually happens mostly because of pressure, not friction. Because of the very high velocity when entering atmosphere, the air in front of the ship gets compressed so much that it turns to super-heated plasma (high pressure -> high heat). Blunt shaped ships (surprise high friction!) work so well because the air can't escape from the front fast enough and it pushes this hot stuff away from the ship. Similarly, ablative heatshields block the heat by expelling gases and pushing the hot stuff away, no friction. I'm sure someone with proper education can explain this a whole lot better than me.

So yeah you can totally cook through the heatshield while it still has protective material left. Go too fast and the shield can't keep up. Or go too slow and you won't get enough heat for the reactions in the shield to happen and it becomes useless and your ship blows up (not in ksp thankfully).

In KSP universe things are of course scaled differently and work differently.

tl;dr It is pressure, not drag!

[Daveroski]

Hello!

Re-entry heating actually happens mostly because of pressure, not friction. Because of the very high velocity when entering atmosphere, the air in front of the ship gets compressed so much that it turns to super-heated plasma (high pressure -> high heat). Blunt shaped ships (surprise high friction!) work so well because the air can't escape from the front fast enough and it pushes this hot stuff away from the ship. Similarly, ablative heatshields block the heat by expelling gases and pushing the hot stuff away, no friction. I'm sure someone with proper education can explain this a whole lot better than me.

So yeah you can totally cook through the heatshield while it still has protective material left. Go too fast and the shield can't keep up. Or go too slow and you won't get enough heat for the reactions in the shield to happen and it becomes useless and your ship blows up (not in ksp thankfully).

In KSP universe things are of course scaled differently and work differently.

tl;dr It is pressure, not drag!

Its a game. The problem is with the game. It's not behaving like one would expect a game to behave. How do you people manage to keep confusing the two?

Please don't make assumptions about my education. Unlike Vladimir Komarov i don't have a parachute problem.

Am i going over 9000 m/s on re-entry? Plasma? I don't think so.

Please people all I want is an in-game explanation of why the heatshield might explode while carrying lots of ablator. Even a warning that it can happen and why, in the heatshield description, would be better than unplanned disassembly on decent.

[ExplorerKlatt]

I have a question for you? When was the statement about Eve made?

For an in-game explanation for why the heatshield fails with ablator left, the ablator is used at a constant rate, your re-entry is generating more heat than the ablator can dissipate, excess heat builds in the heatshield, heatshield is destroyed.

[Daveroski]

I have a question for you? When was the statement about Eve made?

It's in the notes for the 1.03 release. Didn't you read them?

For an in-game explanation for why the heatshield fails with ablator left, the ablator is used at a constant rate, your re-entry is generating more heat than the ablator can dissipate, excess heat builds in the heatshield, heatshield is destroyed.

Do you know what an In-game explanation is?

Guess where it would be?