Reentry Heating (For Science!)

[Superfluous J]

1 hour ago, Scarecrow71 said:

I always go engine first (retrograde) so I can burn off any fuel I have remaining as I get near Pe.  This helps reduce speed AND decreases Ap.  Once fuel is burned, I jettison the engine and tank, letting the ablator do its job.

It's your choice of course but you could try - instead of just turning heat off - changing the way you do it.

Instead of burning in atmo, do it in space NEAR atmo. You can pinpoint your Pe to the meter by making your maneuver node use up all fuel, and avoid the problem you're having that we are not.

[The Aziz]

52 minutes ago, Scarecrow71 said:

I always go engine first (retrograde) so I can burn off any fuel I have remaining as I get near Pe.  This helps reduce speed AND decreases Ap.  Once fuel is burned, I jettison the engine and tank, letting the ablator do its job.

Of course. But like I said above, you better run out of fuel before hitting 70km mark. And just in case you're comparing your current experience with what you're used to in KSP1 (like some do), lemme show you something:

Spoiler

This is my very old station around Kerbin. Circa 2017. It really is just a random mix of unprotected parts docked together. I decided to deorbit it.

And here it is, in the middle of reentry, tumbling through the atmosphere, still very much in one piece.

And after "landing".

Lost pieces? The lab, and whatever was attached to it on the other end, and the pieces that were sticking out, all lost by impact, not reentry heat. Well, that may have affected solar panels, wow.

 

Few years later, actually in January this year, I had another station in LKO. About 100km orbit. You can see it below already accelerating through the upper parts of the atmo. (The gigantor panel was lost on earlier collision, nevermind that)

And here it is, after reentry. 95% intact.

Both of these were on default stock physics settings, 100% heating in stock Kerbolar system. If anything, this tell me that the reentry in the predecessor was WAAAAAAY too delicate.

The atmoshperic heating is supposed to be deadly and should be treated as such. I would expect these stations to be completely obliterated or broken to tiny pieces in KSP2.

 

[Vl3d]

5 hours ago, Scarecrow71 said:

I always go engine first (retrograde) so I can burn off any fuel I have remaining as I get near Pe.  This helps reduce speed AND decreases Ap.  Once fuel is burned, I jettison the engine and tank, letting the ablator do its job.

You don't need to burn the fuel, just PE ~33 km, decouple before entering the atmosphere and watch the fireworks. Worry not, the shield can take the heat even when returning from Eeloo without the need to slow down.

[Pthigrivi]

18 minutes ago, Vl3d said:

You don't need to burn the fuel, just PE ~33 km, decouple before entering the atmosphere and watch the fireworks. Worry not, the shield can take the heat even when returning from Eeloo without the need to slow down.

Wow 33km? Im much more used to an 80km Ap to 55km Pe reentry. I'll have to do more dangerous testing. Out of the gate I'll say I think we need more bow-shock buffer around heatsheilds' shadow (like a 1.25m shield has a 1.5m shadow) but I should do more test-to-destruction to be sure.  

Edited December 28, 2023 by Pthigrivi

[Vl3d]

30 minutes ago, Pthigrivi said:

Wow 33km? Im much more used to an 80km Ap to 55km Pe reentry. I'll have to do more dangerous testing. Out of the gate I'll say I think we need more bow-shock buffer around heatsheilds' shadow (like a 1.25m shield has a 1.5m shadow) but I should do more test-to-destruction to be sure.  

If you aim for ~42 km you can do a safe direct Laythe entry at 8900 m/s in KSP 1. Have to retest for KSP 2.

Edited December 29, 2023 by Vl3d

[Pthigrivi]

42 minutes ago, Vl3d said:

If you aim for ~42 km you can do a safe direct Laythe entry at 8900 m/s in KSP 1. Have to retest for KSP 2.

Man o man that’s insane. I think part of it is in KSP1 Id gotten used to having modded aerocapture trajectories visible so Ive seen how every km matters and planned on maxing my capture altitude with the understanding that this would be a multi-pass approach. By the time I was doing crewed Joolean moon missions Id also have stations and tugs in LKO so I could reuse interplanetary equipment, and designed interplanetary vessels with reuse in mind. Crew would never descend to Kerbin in the same capsule they left in. They’d aerocapture to LKO and then transfer to a purpose build shuttle to return them home. 

Edited December 29, 2023 by Pthigrivi

[Vl3d]

1 hour ago, Pthigrivi said:

Man o man that’s insane. I think part of it is in KSP1 Id gotten used to having modded aerocapture trajectories visible so Ive seen how every km matters and planned on maxing my capture altitude with the understanding that this would be a multi-pass approach.

You worry less about where the Duna rover will land when you aim directly from Kerbin orbit and just send it. Spot on accuracy! Well.. almost - you have to account for planet rotation. Long live Trajectories mod - we NEED it in KSP 2.
https://core.ac.uk/download/pdf/10573539.pdf

[The Aziz]

What we need is a stock implementation. I ended up 20km short from the Kapy Rock despite aiming my Pe beyond it. And the Minmus monument always runs away from under me thanks to the rotation of the moon. Can't imagine aiming for colony landing pads without it.

[SolarAdmiral]

I haven't had any trouble with spaceplanes to and from low kerbin orbit, or simple stuff like a pod with a heat shield. But I'm finding Laythe's atmosphere very punishing for entering. Even with a plane that can steeply reenter at kerbin with no extreme heat, with the wings with the highest max temp, and first lowering the orbit to just above Laythe's atmosphere before entry, almost as soon as hitting Laythe's atmosphere all the wings instantly burn off. It isn't a big or heavy craft either, under 20 tons. So far I haven't found a way to get wings to survive through Laythe's atmosphere, has anyone else had any success?

[cocoscacao]

I tried Duna aerocapture... First, nuclear engines at the bottom. They exploded. Then, I tried the same path with command pod (and parachutes) first. They exploded too, but they lasted a lot longer. That doesn't sound right to me....

[asmi]

On 12/23/2023 at 9:22 AM, Scarecrow71 said:

My big issue here is that it's happening really high up in the atmosphere, and it's happening before anything else overheats.  There is also very little warning that it's happening; you look at the craft, it's fine, you look away, it's exploded.

This is actually the way it works in real life. It's all about heat flux, heat shields can only absorb/dissipate so much of it, once it's overpowered, things go south really quickly. Most people think that reentry heating works kind of like frying pan on a stove - it slowly builds up the heat. And it's hard to really blame them, as most people don't really have experience dealing with high heat flux. In reality it's more like aiming a 3000+°C welding torch into the middle of a said pan - the torch provides much higher flux than pan can wick away and dissipate, and as a result you will very quickly have a hole in the middle of the pan. The only unrealistic part of it is that in KSP (both 1 and 2) there is a hard cut-off of the atmosphere, while in reality it's very gradual, if you watch some of RL reentry videos, you will see that windows get charred waaay before they feel any significant G-load.

This whole dynamics is actually pretty accurately modelled by late versions of KSP1 (if my memory serves me well, it was implemented in 1.12 when some of modders were hired by Squad to work on the core game), but it is very non-intuitive to most players so it was heavily toned down in stock variant, but since the actual simulation is still there, it can be made realistic with mods. For KSP2 devs decided that it's too complicated for players (which is true), and so they introduced severly simplified system instead which only looks at the temperature of entire vessel as a single unit by postulating that any temperature gradient which is present in vessel will eventually even itself out. The funny part is that reentry (and atmospheric flight in general) is one of flight regimes when this statement is absolutely FALSE, infact the very reason heatshields work is because such gradient exists and can be maintained on purpose (by keeping the heat away from sensitive parts of a vessel), so it's principally impossible to simulate real-life behavior with such approach. What I suspect they've done is basically manually tuned system parameters such that it would work the way they wanted in some finite number of flight scenarios, but since the model they use is fairly crude, you can't really expect it to function realistically.

But then again, most players have no idea how this works in the real life, so an argument can be made that maybe they made a right call for majority of players. But of course those who bothered to learn it will not be happy with such approach, and wasn't learning things being marketed as one of purposes of this game?

Edited December 30, 2023 by asmi

[Vl3d]

24 minutes ago, asmi said:

they introduced severely simplified system instead which only looks at the temperature of entire vessel as a single unit by postulating that any temperature gradient which is present in vessel will eventually even itself out

So you are saying that parts obstructed by a fairing are heating up because the total heat flux gets distributed to all the vehicle parts?

[Periple]

2 hours ago, asmi said:

KSP2 devs decided that it's too complicated for players (which is true), and so they introduced severly simplified system instead which only looks at the temperature of entire vessel as a single unit by postulating that any temperature gradient which is present in vessel will eventually even itself out.

No they didn't. The heat for each part is simulated individually. 

The main differences with KSP1's system are:

• Surface and internal temperatures are not simulated separately, they're rolled into one value
• There is only one heat system; the "core temperature" system used by ISRUs and drills isn't there
• Heat conduction between parts isn't simulated

Additionally, I think the current radiators work like the deployable TCSs with core heat in KSP1 -- plumbing is implicit and they dissipate heat from the entire vessel regardless of placement. I don't think there's anything inherent in the system that precludes parts that only dissipate heat from adjacent parts, like KSP1 radiator panels with core heat, or all of the radiators with the other thermal system.

[cocoscacao]

On 12/28/2023 at 6:46 PM, The Aziz said:

How is going engine first into atmosphere a standard procedure 

It was in KSP 1. Since my Duna mission failed (melted), I did some basic tests in K's atmosphere. One thing that bother's me:

Falling from Mun's orbit, with prograde orientation, doesn't show temperature gauge, except one millisecond before explosion:

Orienting capsule retrograde (no heatshields), the temperature gauge was shown (it increased quickly as expected). The craft exploded at ~32Kms.

Oddly enough, the engine survived all the way down...

[The Aziz]

6 minutes ago, cocoscacao said:

It was in KSP 1.

As shown in earlier post, KSP1's reentry heating was too forgiving for what it was.

[cocoscacao]

17 minutes ago, The Aziz said:

As shown in earlier post, KSP1's reentry heating was too forgiving for what it was.

Not saying that it's bad. Duna aerocapture was way too trivial in the original. I'm saying UI needs some tweaking in certain scenarios (shown above). I want the game to tell me "you're about to die in 3...2...1..." Not just give me an instant *pufff*

[Mikki]

20 hours ago, cocoscacao said:

I tried Duna aerocapture... First, nuclear engines at the bottom. They exploded. Then, I tried the same path with command pod (and parachutes) first. They exploded too, but they lasted a lot longer. That doesn't sound right to me....

Engine bells are cooled while running, aluminium starts melting at 650° celsius, steel keeps melting  at 1`400° celsius, titanium at  1`700°. All is well in the KSP fact check...

Remember, 340 m/s is Mach 1, - 680 m/s is Mach 2, - 1`020 m/s equals Mach 3  (Aluminium starts to get mushy)... and so on. Mach 5 and higher allready melts steel away by the way... ("Hypersonic Area*)

Entering Jool at a common 8`800 m/s orbital velocity is how fast? Yes, way over Mach 25, equals 31`680 km/h or imperial  19`685 Miles per hour.

I would like to see mach number and km/h or mph for US people, it does confuse me all the time how fast the vessel is since we have no better other clues to determine the speed. Easy.

And friction by drag inreases squared, which makes this discussion quite obsolete since it is implemented by an engineer at the devs iirc. Like double the speed, friction increases squared... let this sink in or read about it...

 

Edited December 30, 2023 by Mikki
aluminium, US, last sentence, typos sorry

[Mikki]

1 hour ago, cocoscacao said:

It was in KSP 1. Since my Duna mission failed (melted), I did some basic tests in K's atmosphere. One thing that bother's me:

Falling from Mun's orbit, with prograde orientation, doesn't show temperature gauge, except one millisecond before explosion:

Orienting capsule retrograde (no heatshields), the temperature gauge was shown (it increased quickly as expected). The craft exploded at ~32Kms.

Oddly enough, the engine survived all the way down...

And your capsule is going MACH 9, or better, 11`000 km/h. Might have a titanium shell on top. Altimeter shows 26`000 above sea ground btw...

Edited December 30, 2023 by Mikki
ground

[hikerchick29]

The visual scorching effect on heat shields is nonexistent for me.  Re-entry barely affects the ablative coating, even when landing at Kerbin at dangerously high speeds

[Pthigrivi]

On 12/28/2023 at 8:58 AM, Scarecrow71 said:

I am simply turning heat off for the time being.  Although some of the issues I'm experiencing are a direct result of the craft I'm building, there is ZERO reason for things to explode in a fountain of hot lava at 60km when attempting to aerobrake in Kerbin's atmosphere.  If I'm trying a direct descent at 6 km/s?  Yes, I should explode.  Trying to use the upper atmosphere to slow down and reduce Ap, using multiple passes and not dipping closer than 60km?  Shouldn't happen.

After several experiments I have to agree the high atmo (60+km) heat flux seems way overboard. Yeah Im going fast but intuitively you should just be hitting way fewer molecules and the friction should be much lower until you dip to 50km or so. I'd be curious the math on this vs real life reentry. 

[Kerbart]

26 minutes ago, Pthigrivi said:

After several experiments I have to agree the high atmo (60+km) heat flux seems way overboard. Yeah Im going fast but intuitively you should just be hitting way fewer molecules and the friction should be much lower until you dip to 50km or so. I'd be curious the math on this vs real life reentry. 

Not just high altitude. i have an Okto2 consistently blowing up once it passes 10k on ascent due to overheating. Going maybe 500 m/s at that point. It's inside a 2.5m fairing, if that matters.

Had to turn of heating to get it into orbit.

[Pthigrivi]

24 minutes ago, Kerbart said:

Not just high altitude. i have an Okto2 consistently blowing up once it passes 10k on ascent due to overheating. Going maybe 500 m/s at that point. It's inside a 2.5m fairing, if that matters.

Had to turn of heating to get it into orbit.

Yeah Ive noticed a few parts that seem to ignore fairings. Trying to build more concrete notes on that. Curious. 

[Kerbart]

14 minutes ago, Pthigrivi said:

Yeah Ive noticed a few parts that seem to ignore fairings. Trying to build more concrete notes on that. Curious. 

This was also at a velocity where heat should not be an issue. I'm not sure if the fairing is ignored or that it affects the heat flux of enclosed parts in some unexpected way.

[Superfluous J]

1 hour ago, Kerbart said:

Not just high altitude. i have an Okto2 consistently blowing up once it passes 10k on ascent due to overheating. Going maybe 500 m/s at that point. It's inside a 2.5m fairing, if that matters.

Had to turn of heating to get it into orbit.

 

35 minutes ago, Pthigrivi said:

Yeah Ive noticed a few parts that seem to ignore fairings. Trying to build more concrete notes on that. Curious. 

In another thread we came to the conclusion that it was always the root part. Maybe try changing the root part to a more hardy part like a heat shield.

[Kerbart]

10 hours ago, Superfluous J said:

In another thread we came to the conclusion that it was always the root part. Maybe try changing the root part to a more hardy part like a heat shield.

Yes that did the trick. Had some very interesting repercussions for staging, but I digress.