Reentry Heating (For Science!)

[tstein]

People are still ignoring the  measurable fact that  the heat generated at 68 km is almost same as the heat at 40 km This is completely WRONG.  The heat  due to drag shoudl be a logarithm function of height but it is  a lineat function  with  a very big B component.

[RaccoonTOF]

It's also possible that the COOLING mechanics are not working as intended, contributing to some of the perceived HEATING effect issues.  My last launch, I was riding the very edge of part immolation with my nose-mounted docking port during ascent (fairings still being useless, and no shielded ports available yet in the tech tree).  After finally achieving orbit, I expected it to cool off within a few orbits or so at most - but instead it was still giving glowing orange (though not red) overheat warnings all the way through TLI and well through the actual flight, only finally cooling off a few hours before Mun INTERCEPT...definitely seems to be holding heat much longer than it should be.

[Wheehaw Kerman]

11 hours ago, Kerbart said:

If you're talking about the lander can... that one is OP in KSP1. Ironically the description in KSP1 lists not for atmospheric use (assuming it's similar to the LM it has 1mm thick aluminium walls, after all). But it does fine in the game. The KSP2 one doesn't have it in the description but behaves more realistically during atmospheric reentry. Curious.

I avoided using the Lander Can  for re-entry in KSP1 for exactly that reason - the sides overhanging the heatshield just looked like a recipe for flaming catastrophic disaster.  I’m glad it doesn’t work anymore.

[JoeSchmuckatelli]

Question  - (what am I missing?) - The Mk-1 'Tin Can' has a max temp of 850k, while the FL-T200 fuel tank has a max temp of 1000k.

Why is it that the FL-T200 heats up and explodes at around 62km (shallow, suborbital launch with an ap of 72km)?  Shouldn't the tank have less likelihood of overheating and exploding than the can?

(Just looking at the numbers, I decided to try to use the tank as an impromptu heat shield for a Science Jr (which has a max temp of 600k).

Also - if I'm not seeing reentry heat with the Tin Can until I'm in the atmosphere - why is the empty fuel tank exploding?

[JoeSchmuckatelli]

Okay - well, I just confirmed something for myself.  Ran the mission again and this time inserted to orbit with a really low pe (58km) that was technically 'in space' (by the altitude bar) just to see if the atmo was being calculated, even if thin... and yes, that altitude is dragging down my ap.  So, theoretically it could be atmo heating.   However, the engine bell is showing no heat (can is retrograde).   Just for funzies I saved the game and ditched the engine (still have a small fuel tank) and it immediately got hot.

So... now if I flip the whole ship back to prograde, the parachute doesn't get hot - and the fuel tank cools slowly.

This tells me the occlusion mechanic is working - but not why the tank is heating precipitously, when nothing else is.

Even odder, I can hang out with the craft at normal/antinormal or radial in/out and no heating occurs; it's just when the tank is leading (ship retrograde).

Tank heating occurs at any altitude below 70km... but only when leading. 

Ran through the pe marker with the ship facing radial in and neither the lander nor the tank got hot, but Science Jr. did.

Clearly heating is working - but none of this explains why a part with a 1,000k Max Temp is heating up faster than the 850k part

Edited December 24, 2023 by JoeSchmuckatelli

[JoeSchmuckatelli]

After continued testing - it looks like the parts have more granularity than I thought.  The sides of the fuel tank have plenty of reentry heat resistance - but the open end?  Not so much.

Pretty much what you would expect from a part shaped the way it is; but I was expecting simple 'the whole part has the same temp resistance' regardless of what the model showed.

Not confirmation, just an educated guess.

[Periple]

13 minutes ago, JoeSchmuckatelli said:

After continued testing - it looks like the parts have more granularity than I thought.  The sides of the fuel tank have plenty of reentry heat resistance - but the open end?  Not so much.

Maybe the open end just generates more heat (and drag?)

[The Aziz]

4 hours ago, JoeSchmuckatelli said:

After continued testing - it looks like the parts have more granularity than I thought.  The sides of the fuel tank have plenty of reentry heat resistance - but the open end?  Not so much.

Pretty much what you would expect from a part shaped the way it is; but I was expecting simple 'the whole part has the same temp resistance' regardless of what the model showed.

Not confirmation, just an educated guess.

So I guess that's how it should work? If you face the atmo with a pointy end, it'll probably heat up to some level but not much and not slow down because of aerodynamic shape. If you face it with flat end, it'll heat up a lot because of large surface facing the air, but also slow down a lot because of the drag. If you face the air with a side of a cylinder, it'll be halfway from both. Large enough to generate drag, but also somewhat aerodynamic shape to dissipate heat to the sides (see: plans for Starship)

Maybe, just maybe, the planets now have a proper* thermosphere?

 

*Considering the hard edges of the atmosphere, it probably starts at upper line, and ends somewhere just before the plasma effects start to appear.

[ArmchairGravy]

I'm enjoying the heat physics. Seeing a craft lit up like a Christmas tree because of heat transfer between parts makes aerobraking way more entertaining. I'd show the neat picture except I lost it somewhere.   Having to adjust launch profiles depending on the delicacy of the part is EXACTLY what I want to see!

There needs to be a "too hot" animation for the Kerbalnauts when their entire craft is glowing red.

The cooldowns need tweaked a teensy bit. Seriously, just a smidge. Heat is hard to dissipate. 

This thermal system is currently pretty darn good. It's way better than I expected it to be as an initial implementation. 

[Aodhan]

9 hours ago, JoeSchmuckatelli said:

(Just looking at the numbers, I decided to try to use the tank as an impromptu heat shield for a Science Jr (which has a max temp of 600k).

Samples and data seem to be stored in the pod so now I just ditch everything but the command pod with a heat shield and reentry is fine.

My main chute ripped apart if I kept the science part (1t) and rogue chutes are not available at the beginning.

Never encountered anything exploding though, even with direct reentry from the mun with 30km Pe

[Scarecrow71]

Ok, so I'll retract my earlier statement about the lander can.  I came back from Minmus in the 3-seater capsule, and with a heat shield it survived re-entry very nicely.  So it's not the heat system, but rather my choice of re-entry capsules.

However, I'd like someone to explain to me why the fuel tank itself overheats and explodes at 60km, but none of the landing legs, radial tanks, or the 6 Ant engines I've got on this thing did:

Spoiler

That shot is the lander on Minmus, and I flew that thing back home to Kerbin.  The medium tank overheated, but none of the radial parts did.  At 60km.  Why does that happen?

Edited December 24, 2023 by Scarecrow71

[Periple]

Because the part thresholds need more tuning?

[The Aziz]

I think I may have guessed it a little earlier. The tank is essentially a flat circle facing the air at high speeds. The engines should technically survive higher temperatures because they're designed to operate at high temperatures (I wonder how the monoprop engines would cope here). The radial tanks in retrograde position still have a shape that directs some of the heat outwards (a ball has a higher chance of surviving reentry than a cube if you know what I mean by that). The legs, I dunno about their heat resistance, but chances are, they're so narrow that the not much of the air particles is actually hitting them.

[JoeSchmuckatelli]

2 hours ago, Scarecrow71 said:

Ok, so I'll retract my earlier statement about the lander can.  I came back from Minmus in the 3-seater capsule, and with a heat shield it survived re-entry very nicely.  So it's not the heat system, but rather my choice of re-entry capsules.

However, I'd like someone to explain to me why the fuel tank itself overheats and explodes at 60km, but none of the landing legs, radial tanks, or the 6 Ant engines I've got on this thing did:

That shot is the lander on Minmus, and I flew that thing back home to Kerbin.  The medium tank overheated, but none of the radial parts did.  At 60km.  Why does that happen?

Did the tank overheat with or without the heat shielding? 

 

And put stuff in spoilers!

[Scarecrow71]

52 minutes ago, JoeSchmuckatelli said:

Did the tank overheat with or without the heat shielding? 

No shield on the tank itself.  So I expected it to heat up...just not at 60km.

52 minutes ago, JoeSchmuckatelli said:

And put stuff in spoilers!

Why is it that I'm the only one getting called out here?  I'm following what others have done.

[JoeSchmuckatelli]

2 hours ago, Scarecrow71 said:

No shield on the tank itself.  So I expected it to heat up...just not at 60km.

Why is it that I'm the only one getting called out here?  I'm following what others have done.

In the old days random posting of anomalies was a no no.  You just happened to be here - not singling you out. 

... 

Mine started heating up under 60 as well - so my guess is the sides are modeled to withstand 1000 k but the ends are not. 

Nothing else heats that high 

[Periple]

11 hours ago, Scarecrow71 said:

Why is it that I'm the only one getting called out here?  I'm following what others have done.

I’m sorry, it was nothing personal! I just saw your post and closed my eyes and skipped forward and didn’t notice the other one! I do appreciate you spoilering it as I haven’t had the chance to play 0.2.0 yet!

[Vl3d]

I do not doubt that there is some fine tuning needed to the parts heating, but I do want to stress that it's normal to heat up while going ~2000 m/s without a heat shield in the upper atmosphere. When posting information about altitude and max. temp, please also post what speed you had when heating up.

[ArmchairGravy]

11 hours ago, Periple said:

I’m sorry, it was nothing personal! I just saw your post and closed my eyes and skipped forward and didn’t notice the other one! I do appreciate you spoilering it as I haven’t had the chance to play 0.2.0 yet!

I just have to ask, what are you worried about being spoiled? I mean everyone already knows at the end Bob ends up being Jeb's father.

[JoeSchmuckatelli]

On 12/25/2023 at 12:51 PM, ArmchairGravy said:

Bob ends up being Jeb's father

Nooooo! 

(insert over-acting face) 

[Rylant]

On 12/23/2023 at 7:32 AM, Mutex said:

I get the vague impression the heating calculation isn't taking the altitude / atmospheric density into account. I dipped a probe into Eve's atmosphere and at 85km it was already toast. The very upper part of the atmosphere I'd expect to cause negligible heating because the air is so thin.

I agree with this. I built a satellite with a fairing and it had a lifter stage which purpose was to get almost to orbit.  Every time I launch it, I get to 60 or 65 thousand meters, and THEN the fairing heats up and is destroyed.  After the fairing goes, all of the other more sensitive components get destroyed.  It makes no sense that this would happen at the end of this stage when the air is so thin.  It's a really normal ascent profile too.  Something goofy is going on.

[Scarecrow71]

4 hours ago, Rylant said:

I agree with this. I built a satellite with a fairing and it had a lifter stage which purpose was to get almost to orbit.  Every time I launch it, I get to 60 or 65 thousand meters, and THEN the fairing heats up and is destroyed.  After the fairing goes, all of the other more sensitive components get destroyed.  It makes no sense that this would happen at the end of this stage when the air is so thin.  It's a really normal ascent profile too.  Something goofy is going on.

Check your TWR in the upper atmosphere.  Although I agree with you that this shouldn't happen, it does.  Pull back on the amount of thrust you are generating so that you aren't racing as fast as possible to orbit.  Stay < 2.0 on that ascent (TWR), and around 1.5 if you can.  That should help.

[Superfluous J]

I notice that under a fairing, the root part (for me right now, generally a probe core) gets heat, but nothing else does. Anyone else notice this? It's generally in the 2nd half of the ascent, when > 40km and my Ap is still in the atmosphere.

I've adjusted to the new heat system by making my launches slightly less efficient. Instead of turning under 1km up, I wait until I've cleared the cloud deck. And instead of trying to make my angle off the horizon 40 degrees when my Ap is 20km, I tend to wait until it's 30km or even 40km. I throttle down to keep my time to Ap roughly 1 minute, until I'm well over 60km.

Edited December 28, 2023 by Superfluous J

[Wheehaw Kerman]

So earlier this evening, I dropped a prob into Jool behind a medium heatshield and wrapped in a fairing - overall it was proportioned rather like a rifle bullet.  The thing promptly tumbled and stabilized point first, and when I tried to orient it properly it re-stabilized sideways on.  Imagine my surprise when it didn’t burn up - everything was still intact when the re-entry effects stopped and I jettisoned the fairing.

Given past experience I was expecting rapid overheating inside the fairing, but apparently not on Jool…

[18Watt]

16 minutes ago, Superfluous J said:

I notice that under a fairing, the root part (for me right now, generally a probe core) gets heat, but nothing else does.

Hmm.  Now I'm wondering if I make the fairing the root part, what happens?  Might have to try that tonight, after I boot the youngsters off the computer.

17 minutes ago, Superfluous J said:

I've adjusted to the new heat system by making my launches slightly less efficient.

That's what I'm currently doing as well.