Heating - what is it about the 60s?

[JoeSchmuckatelli]

Anyone else noticing that the 60km range gets things extra hot?

A while back I wrote about descending into the atmosphere with several parts getting hot in the 60-65km range.  Parts that had higher thermal limits in the VAB were inexplicably getting hot and exploding - while others were fine.  At the time I thought it had to do with the shape of the part.

In a recent launch attempt I underpowered and got a 65km AP on a launch (by the time the NavBall was horizontal).  Planned on coasting to the low AP and then burning from there to raise PE (which was abt 14km) and then doing another burn at the new AP (burn AP to raise PE to 75-80km = new AP, then burn again to circularize).

However, while waiting to get to the AP several of my components got hot and exploded.  Decided to revert.

Anyway - it got me to thinking... is there something going on in the 60km range that's unexpected?

[Mikki]

This looks like a accurate depiction of the thermosphere, i think it is okay.

[The Aziz]

12 minutes ago, Mikki said:

This looks like a accurate depiction of the thermosphere, i think it is okay.

I've been saying this from the start, nobody listened.

[Vl3d]

9 hours ago, JoeSchmuckatelli said:

Anyone else noticing that the 60km range gets things extra hot?

At what speed?

[hatterson]

5 hours ago, Mikki said:

This looks like a accurate depiction of the thermosphere, i think it is okay.

I dunno. The ISS seems to do totally fine in Earth's thermosphere without blowing up due to heat and it's going at orbital velocity.

The main issue is that the heat transferred to your craft in the upper atmosphere is *much* higher than would reasonably be expected given how thin the atmosphere is there and how little your spacecraft is actually interacting with it (slowing down due to drag).

In practice, what that incentivizes is much steeper re-entries. Shallow re-entries are bad because you end up spending a ton of time at high velocity really high up generating a bunch of heat, but not slowing down at all. On a steeper re-entry you get to the thick parts faster and slow down faster so there's less time for heat to build up.

I'm not an aero engineer or anything but communicating to the player that the optimal reentry is "just slam into the thick atmosphere asap so that heat doesn't have time to build up" doesn't seem ideal, much less realistic.

[JoeSchmuckatelli]

59 minutes ago, Vl3d said:

speed

I have not paid that close attention 

What seemed odd to me was that I was coasting and below the altitude nothing seemed that hot but within a 60-65km band certain parts got hot when others did not 

[Vl3d]

11 minutes ago, JoeSchmuckatelli said:

I have not paid that close attention 

What seemed odd to me was that I was coasting and below the altitude nothing seemed that hot but within a 60-65km band certain parts got hot when others did not 

At what speed?

[The Aziz]

8 minutes ago, hatterson said:

The ISS seems to do totally fine in Earth's thermosphere without blowing up due to heat and it's going at orbital velocity

It's also going at much higher altitude, much closer to the upper end.

But considering that Kerbin atmo ends precisely at 70km, what we're experiencing is ionosphere (part of thermosphere with enough ionized particles to cause heating, but not enough to cause a ball of plasma around the vehicle). I'd still say that's fairly accurate considering the limitations of hardcoded atmo border.

[PDCWolf]

IRL, the atmosphere extends up a lot. The Karman line is a general accepted boundary, but in reality you're hitting atmosphere particles all the way up to 10000km. Even up to 1000km, atmospheric drag is considerable, and causes tangible orbital decay, but that same density of air is not enough for super heated particles up there to heat up anything in a non negligible way.

In game, we have to make do (LCD Pandering) with an atmosphere that ends at 70km, to not have atmospheric decay and having to juggle with station keeping every low orbit. This however also means atmospheric density is very compressed, and even at 69.999km you're hitting enough atmosphere to heat up.

It is unexpected an unintuitive, but it is more a concern of game balancing than a bug or something "done wrong". It is definitely not a thermosphere though, it's way too low for that. In fact it can't be related to any realistic term, as Kerbin is not realistic, it's density curve vs altitude isn't realistic, and thus heating effects aren't entirely realistic either.

[The Aziz]

5 minutes ago, PDCWolf said:

In fact it can't be related to any realistic term

Like I said, ionosphere. It starts low enough, and the particles in it are hot, even when sparse. And it had to be compressed to work in scaled universe.

We'd have to see an atmospheric diagram to know for sure. Or have experiments that show actual values.

[Pthigrivi]

There is also some bugginess happening which will hopefully get resolved in the not-to-distant future. So far it's seemed that when things are functioning properly (heat shields and fairings occluding as they should) soft equipment stays protected and things don't explode. In KSP1 I used to jettison the fairing on launch in the mid 50's and you can't really get away with that anymore. Since IRL launches don't drop the fairing until 130km I think KSP2 is probably closer to the mark. 

Edited January 6 by Pthigrivi

[hatterson]

17 minutes ago, Pthigrivi said:

There is also some bugginess happening which will hopefully get resolved in the not-to-distant future. So far it's seemed that when things are functioning properly (heat shields and fairings occluding as they should) soft equipment stays protected and things don't explode. In KSP1 I used to jettison the fairing on launch in the mid 50's and you can't really get away with that anymore. Since IRL launches don't drop the fairing until 130km I think KSP2 is probably closer to the mark. 

Yea I’m good with fairings being basically required in atmo, I just don’t think it’s a good gameplay experience to have shallow atmospheric entries be significantly harsher than steeper ones.

[PDCWolf]

3 hours ago, hatterson said:

Yea I’m good with fairings being basically required in atmo, I just don’t think it’s a good gameplay experience to have shallow atmospheric entries be significantly harsher than steeper ones.

Technically, holding your craft at speed at any altitude would cause enough heat buildup. The Apollo capsule dived very shallowly and skipped out to cool down between braking dives, because as shallow as you might want to come in, you'll still heat up beyond the capacity of whatever thermal management system if you just stay toasty for long enough.

 

[Mickel]

9 hours ago, The Aziz said:

We'd have to see an atmospheric diagram to know for sure. Or have experiments that show actual values.

There is something of an irony here, given the generic nature of science as it sits.  If this is a feature, rather than a bug, and there is a representation of the ionosphere, shouldn't this be a biome that we can go and do science in to find out what's going on?  Then this information could result in Keri telling us that after a long night of coffee drinking, our physicists have worked out that to stop bits leaking off our ascent stages we need to XXX, and to stop our descent stages melting we need to YYY.  There is a potential thread that unlocks a tutorial that people can use to guide them through it.  And it gives us a reason to send probes to other bodies.  I know some would find this dumb and/or frustrating, and would rather brute force their way through.  Others might find it an interesting little corner to delve deeper into.

If it's a bug; fine, fix it.  If nothing else, the fairings are because they aren't effective.

If it's a feature, we're currently left blind, which is silly.

Edited January 7 by Mickel

[Jeq]

Thermosphere doesn't destroy most thermal resistant parts first in real life.

9 hours ago, PDCWolf said:

Technically, holding your craft at speed at any altitude would cause enough heat buildup. The Apollo capsule dived very shallowly and skipped out to cool down between braking dives, because as shallow as you might want to come in, you'll still heat up beyond the capacity of whatever thermal management system if you just stay toasty for long enough.

 

Not sure how cooling works at vacuum that fast. there is no thermal conduction happening without air.

14 hours ago, The Aziz said:

Like I said, ionosphere. It starts low enough, and the particles in it are hot, even when sparse. And it had to be compressed to work in scaled universe.

We'd have to see an atmospheric diagram to know for sure. Or have experiments that show actual values.

Are you saying konosohere decides to destroy most heat resistant parts first. And destroy parts if they are protected by heatshield but let uncovered parts alone?

[Jeq]

it is nothing like thermosphere

Upper edge of thermosphere is hot, this is where magnetic field of earth fights radiation of sun and vacuum. (500k to 2000k)

Lower edge of thermosphere is very cold.

Lower edge of thermosphere is called Karman Line, This is considered to be line of outerspace and satellites can orbit above this line, in KSP this line is 70km.

Hot thermosphere if it was simulated in KSP, it would be at 500km altitude. 

ISS and crewed stations are at 300km, in middle of thermosphere, because it is just enought to keep station warm and nice.

Some people now claims that upper atmosphere (70km) should be hot, but this is not the case in real life. It is false information and it seems to spread and i hope it stops soon.

Edited January 7 by Jeq

[Jeq]

IRL: The longer the vehicle spends at high altitude, the thinner the air is and the less heat is conducted

KSP: High altitude heat conduction peak.

Edited January 7 by Jeq

[The Aziz]

Every single diagram on the internet shows different values, the only constant thing in those is the Karman line at 100km.

8 hours ago, Jeq said:

Are you saying konosohere decides to destroy most heat resistant parts first. And destroy parts if they are protected by heatshield but let uncovered parts alone?

No, I'm saying that heating is to be expected even that high up because of it. How it affects covered/uncovered parts is another matter (probably of a bug, not game design)

[Jeq]

2 minutes ago, The Aziz said:

Every single diagram on the internet shows different values, the only constant thing in those is the Karman line at 100km.

Yes values varies but it is know that temperatures rises gradually above that line, they don't peak on that line. 

Edited January 7 by Jeq

[StrandedonEarth]

10 hours ago, Jeq said:

Not sure how cooling works at vacuum that fast. there is no thermal conduction happening without air.

Radiative cooling. It might not be a lot, but apparently it was enough. And there is still air there, very little, but it's there

On 1/6/2024 at 6:56 AM, PDCWolf said:

IRL, the atmosphere extends up a lot. The Karman line is a general accepted boundary, but in reality you're hitting atmosphere particles all the way up to 10000km.

 

As I understand it, the Karman Line is where the velocity required to maintain enough aerodynamic lift for level flight exceeds orbital velocity, and can vary somewhat as the atmosphere expands and contracts, as Starlink found out....SpaceX just lost 40 satellites to a geomagnetic storm. There could be worse to come. | MIT Technology Review

[PDCWolf]

10 hours ago, Jeq said:

Thermosphere doesn't destroy most thermal resistant parts first in real life.

Not sure how cooling works at vacuum that fast. there is no thermal conduction happening without air.

Are you saying konosohere decides to destroy most heat resistant parts first. And destroy parts if they are protected by heatshield but let uncovered parts alone?

6 minutes ago, StrandedonEarth said:

Radiative cooling. It might not be a lot, but apparently it was enough. And there is still air there, very little, but it's there

As I understand it, the Karman Line is where the velocity required to maintain enough aerodynamic lift for level flight exceeds orbital velocity, and can vary somewhat as the atmosphere expands and contracts, as Starlink found out....SpaceX just lost 40 satellites to a geomagnetic storm. There could be worse to come. | MIT Technology Review

When the capsule raises back up, the ablative material keeps melting and ablating away, taking heat away with the pieces that fly off. You can read about that and radiative cooling in the apollo capsule here.

You're not in the thermosphere, that's just not how atmospheres work in the game.

As for the heatshield issue, if your heatshield is designed to whitstand 3000ºC and your capsule can only resist 1500ºC, and you keep both parts in 3000ºC heat for long enough, guess which one fails first...

Edited January 7 by PDCWolf

[Jeq]

I am right now just assuming that heating is bugged.

I don't think developers meant it to be complicated and thermosphere exist yet at this point if ever, without giving any information or tutorials about it.

[SciMan]

4 hours ago, The Aziz said:

Every single diagram on the internet shows different values, the only constant thing in those is the Karman line at 100km.

No, I'm saying that heating is to be expected even that high up because of it. How it affects covered/uncovered parts is another matter (probably of a bug, not game design)

OK, you keep saying "heating" but you aren't being specific enough.
The ISS exists in the thermosphere, nothing on the ISS explodes or gets red-hot.
Things in KSP, at 60-65km... are exploding, or getting red hot.
One of these things is not like the other. One of these is measurable physical phenomena that we have observed (IRL thermosphere).
The other one (KSP behavior) is a bug, plain and simple.

If they WERE trying to model the thermosphere (they're not), it wouldn't be exploding parts, because the devs don't want "Space is hard and you should feel lucky to make something get to orbit", they want "Let's make a fun game that isn't overly punishing for reasons that we aren't even going to explain to the player". What is happening right now is exactly "overly punishing for reasons that the developers haven't even tried to explain" which points me at "this is a bug" not "the devs are clever".

[The Aziz]

1 hour ago, SciMan said:

The ISS exists in the thermosphere, nothing on the ISS explodes or gets red-hot.
Things in KSP, at 60-65km... are exploding, or getting red hot.
One of these things is not like the other.

Exactly. One orbits at 400km where the particles can be nearly handwaved (aside from regular tasks to boost up the station's orbit because of decay. Quite a difference between 400 and 60, isn't it?

Plus if you didn't notice, in several posts I kept mentioning ionosphere, not thermosphere. So please read up. Perhaps, where it starts, and what's it made of.

And again, Kerbin's atmo doesn't extend to 10000 kilometers, it ends abruptly at 70km and everything above is pure vacuum. But below? Can't tell me that at 69999 vehicles enter the stratosphere straight away.

[Jeq]

3 hours ago, The Aziz said:

Exactly. One orbits at 400km where the particles can be nearly handwaved (aside from regular tasks to boost up the station's orbit because of decay. Quite a difference between 400 and 60, isn't it?

Plus if you didn't notice, in several posts I kept mentioning ionosphere, not thermosphere. So please read up. Perhaps, where it starts, and what's it made of.

And again, Kerbin's atmo doesn't extend to 10000 kilometers, it ends abruptly at 70km and everything above is pure vacuum. But below? Can't tell me that at 69999 vehicles enter the stratosphere straight away.

Atmosphere of 0.000001atm pressure