So.. re-entry heating - hard mode?

[DJK]

Ok, so, seeing that the default setting for re-entry heating is quite forgiving for someone with a decent amount of hours into this game, i decided to set the slider for re-entry heating to 120% and see how it works.

I took a basic rocket with a mk1 pod with chute & decoupler to a sub-orbital trajectory with Ap @ 100km. Note that my usual sub-orbital trajectory has the Pe around 25km in atmosphere, so that the circularization burn takes < 100 m/s dV. Now, i did this flight only to see the re-entry heating so i did not circularize. On my way down, all fine & dandy, the shield ablated roughly 50% of the ablative coating.

Next, i took the same rocket - but this time without a heat shield. Roughly the same trajectory.. give or take. To my surprise i could re-enter even without the heat shield. Given the fact that it was just a sub-orbital flight, thats fine for me, since the temperature values were extremely close to the point where things blow up.

3rd rocket.. same design, but with 2.5 parts. Mk1-2 pod, chute & heat shield. Same trajectory.. In this case, the max temperature on the parts reached ~600 deg, which translates to about 300 deg. celsius.. which seems extremely low for a re-entry. Even a sub-orbital one. On top of that, the heat shield ablated just 1.5 of its ablative coating. 12 units out of 800. That feels a bit underwhelming in terms of re-entry danger. Even feels a bit like cheating.

EDIT #1: Just did another test run with the Mk1-2 pod + chute but without heat shield. Pod temperature peaked @ 1300 deg. - seems extremely effective :-/

EDIT #2: Re-entry coming from Mun with 25km Pe. Mk1-2 pod + chute. No heat shield. 120% re-entry heating. Was perfectly fine. Peak temperature @ 1700 deg. Definitely some part tweaking is order in my opinion.

5th run was with an airplane, which started blowing up @ 600-700 m/s - but i admit, i wasn't trying too much either. Also, i understand it is normal since the aircraft stays in atmosphere for a longer time.

Given those test runs, it appears that some parts kinda need a balance pass regarding re-entry heating and how they handle it. It seems that heat transfer and thermal mass has a strong effect on how much parts heat up during re-entry (and i'm referring to the 2.5m parts).

Anyone else noticed these behaviours or is it just me imagining / doing something wrong?

Cheers,

DJK

Edited April 30, 2015 by DJK

[rkman]

Reentry from suborbital is as slow as reentry can get. Even reentry from LKO is very modest at some 2000 m/s.

I test reentry from a 'Mun return' orbit, that gives a reentry speed of some 3000m/s.

I to have re-entry heating at 120%, and although it doesn't surprise me that reentry from suborbital does not do much, and i have not tested without heatshield, my impression is that reentry heat is quite forgiving even at highest difficulty.

[X-SR71]

I must be very bad at this game since everytime I get a solar panel and/or batteries exploding on reentries.. Communtrons tend to go too. The invincible chute is what's been saving me.

[DJK]

Reentry from suborbital is as slow as reentry can get.

Indeed. But at 120% re-entry heating, the mk1 & airplane was heating up as expected (can do a mk1 pod sub-orbital re-entry without heat shield, but very close to the limit - seems resonable), while the mk1-2 setup i tested was child's play even without a heat shield. And while i expected to be easy to re-enter from a sub-orbital trajectory, Mk1-2 @ 1300 deg without a heat shield is nowhere near a dangerous re-entry.

I test reentry from a 'Mun return' orbit, that gives a reentry speed of some 3000m/s.

I'm going to try that as well, but i'm affraid that with some easy "aerobraking" that would turn out the same..

my impression is that reentry heat is quite forgiving even at highest difficulty.

My point was exactly that some parts might need a balance pass regarding re-entry heating for maximum difficulty settings.

Edited April 30, 2015 by DJK

[EtherDragon]

I must be very bad at this game since everytime I get a solar panel and/or batteries exploding on reentries.. Communtrons tend to go too. The invincible chute is what's been saving me.

You'll have a lot of the weaker parts explode off your ship - which is why cargo bays and fairings become useful.

I wish that the two Command Pods had ablation built in. But as soon as they get 1.0.1 out the heat shields should no longer flip your stuff around on reentry.

[Enorats]

Yeah, those new service bays need to be used. I don't think I've launched a craft yet that didn't have one of those (or at least a cargo bay for Mk2/3 ships).

[DJK]

I must be very bad at this game since everytime I get a solar panel and/or batteries exploding on reentries.. Communtrons tend to go too. The invincible chute is what's been saving me.

The solar panels and batteries explode because their maximum temperature is 1200 deg. Can do so even if they are completely shielded by the heat shield, due to heat transfer between parts. Your best bet is to use the service bays, like others suggested or use a different re-entry trajectory.

[DJK]

Oook.. just did a re-entry coming from Mun with 25km Pe. Mk1-2 pod + chute. No heat shield. 120% re-entry heating. Was perfectly fine. Peak temperature @ 1700 deg.

[klesh]

I've had some re-entries burn 150 of my 200 ablations.

I've had others, including a return from the Mun last night, burn 1 of the 200.

Clearly, there is a right and wrong way to go through the atmosphere. I probably could've gone through the 2nd re-entry without a shield; the first, no way.

[DJK]

The problem i see is not with the shields.. I understand that they need a certain temperature & air flow to start ablating, so to speak. The problem is that the Mk1-2 pod is extremely heat resistant, due to its high thermal mass, making heat shields useless in your day-to-day kerbal re-entries. Also note that every test i did was with the re-entry heating slider set to maximum - 120%

The 2.5m heat shield does not ablate because the pod soaks up all the heat.. acting like a huge heatsink.

Thats not necessarily a bad thing for some people.. but for those that lean towards a more.. "real" gameplay, its not fun at all. And from my understanding, that is why there is a slider, to adjust the re-entry heat difficulty to suit your gameplay, but that is quite underwhelming at the moment due to the fact that some parts aren't quite balanced (personal opinion). I'm not expecting this to be a 100% accurate representation of what happens in real life, but then again, not too far either, specially when we have difficulty options.

[arq]

Yeah there is a definite need for a thermal rebalance of the parts. For example, the Mk2 Cockpit (not the inline, the nosecone version) can't help but explode from reentry heat, even on a modest descent from LKO. Meanwhile, another plane I built with a ram intake into a Mk1 Inline cockpit came in on a more aggressive descent without any serious heating.

[goduranus]

The problem is the parachute. You can open them at re entry speeds, slowing you enough that you never hear up.

[lajoswinkler]

I use 120% and it's extremely forgiving. I still don't understand how people get 75% of their shield ablated. I barely reach 90% or so, usually 95% is left after the landing.

Heatshields need few changes and the one that concerns this topic is that their heat conductivity must be set very low so that they don't bleed much heat away.

[goduranus]

Did you open parachutes above 20km?

[lajoswinkler]

I don't cheat with buggy parachutes. I use a shallow periapsis and do a proper reentry.

[DJK]

Indeed conductivity is at fault here.. or so i've concluded while playing around with the new thermal options in debug menu. Or better yet, the way conductivity is handled. Lowering the conductivity flux worked fine for mk1-2 pod + heat shield (high thermal mass). The shield heated up and ablated properly.. but at the same time, with the same conductivity value, the mk1 pod + heat shield (low thermal mass) wasn't working properly anymore. The heat shield was indeed heating & ablating, as in previous tests, but there was absolutely no heat transfer from the shield to the pod. Apart from that, i am assuming that conductivity flux regulates all heat transfers, so it is pointless to tweak it.. that would render the Nerv engine, mining drill & space planes pretty much useless.

At this point i'm pretty baffled of what is going on with re-entry heating.. but i'm sure that its not properly balanced.. specially for a maxed out difficulty setting. I actually want to have stuff blow up during re-entry rather than doing ridiculous re-entries with no heat shields and no worries.. that kinda defeats the purpose of having a thermal re-entry effect

I hope Squad takes notice of this and at least tries to fix it somehow..

EDIT: Also, heat shields ablate from the sun while in space.. which to my knowledge is impossible (i might be totally wrong though) and when they reach 0 ablator they stop transfering heat to the other parts, if said parts are shielded from the sun by the actual heat shield.

Edited May 1, 2015 by DJK

[larkvi]

I don't get it. I am using hard mode, and a mk 1-2 pod with only a chute and a heat shield explodes with only about 20 shield ablated, in a relatively easy 100 x 30 re-entry. I can't imagine coming in from the Mun.

1.0 has all been bugs and explosions for me, and I am used to playing with DREC and FAR.

[DJK]

I've heard alot of people complaining about blowing up.. but truthfully.. i re-entered with both mk1-2 and mk1 coming from mun with 25k Pe @ kerbin.. perfectly safe, with or without shields. 100x20 again, perfectly safe.. sub-orbital perfectly safe. If i put heat shields on mk1-2 and do an 100x20 re-entry it ablates nothing.. 0.. or maybe 1 unit at max.

I also did a fresh install of the game when 1.0 came out and currently have no mods, except engineer, hyper edit (to make the tests easier) and visuals. Nothing to interfere with the aero/thermal system.

The only way i could heat up the mk1-2 pod + heat shield was coming down from Mun at a 90 deg. angle relative to kerbin's surface.. basically falling out of the sky.. and even then nothing blew up.. the pod just smashed into the ground at 1800 m/s. Heat shield did heat up to 2000 deg. and ablated roughly 50% though.

Edited May 1, 2015 by DJK

[Urb4n0ninj4]

I've heard alot of people complaining about blowing up..

Me too, and I cannot get my craft to blow up at 120% no matter how hard I try.

I ran a test yesterday, dropping an MK1 command pod with a heatshield, and mk16 parachute straight down through the atmosphere at 3,000+ m/s

I got to about 1,000 meters above sea level before I pulled the chute. Heatshield deteriorated to about 44 units of 200, the parachute had no problems taking it down from 1,200 m/s to 40 m/s in roughly 3 seconds. Kerbals would have been TOAST.

I love the update overall, but I look forward to some tweaking.

Right now i'm toying with the cheat menus thermal physics, hopefully that will provide more advance trials for us more seasoned KSPers.

And on that note...

"Solar Luminosity at home"

and

"Solar insulation at home"

mean in the debug?

[FlowerChild]

Heatshields need few changes and the one that concerns this topic is that their heat conductivity must be set very low so that they don't bleed much heat away.

...

Indeed conductivity is at fault here..

AHA! Thanks so much guys. I was having a huge head-scratching fest going on with regards to why heatshield behavior seemed so erratic based on what was attached to them. Had some Munar free returns almost completely deplete a 1.25m shield, while ones from Minmus (and Munar returns with different vehicles) didn't even make a dent in it. Am also playing at 120% settings, because yes, reentry heat is a joke at present, and I wanted a more challenging experience (which it isn't really providing).

This all makes sense now thanks to the above comments

Edited May 1, 2015 by FlowerChild

[DJK]

I have not fiddled with those two options yet.. but i'm assuming its something related to the sun's radiation and / or light levels (for solar panels)? Just a wild guess.. But i did fiddle with conductivity flux & others.. there is no point in trying.. at least for me, tweaking them fixes something but makes something else worse.

[FlowerChild]

BTW, in case it helps, I just noticed this commented out line in the .cfg file for the mainsail:

	// heatConductivity = 0.06 // half default

Not sure if it'll work, that may be a way to reduce conductivity specifically for the heatshields without affecting other parts.

EDIT: Yup, I think it would work. Just found an active line like that in airbrake.cfg:

heatConductivity = 0.06 // half default

I strongly suspect adding something similar to the heatshield .cfg files will reduce their conductivity without affecting other parts.

Here's a little ModuleManager cfg for anyone that wants to play around with those values for all heatshields simultaneously:

@PART[HeatShield*]
{
	@heatConductivity = 0.06 // half default
}

Edited May 1, 2015 by FlowerChild

[DJK]

I was having a huge head-scratching fest going on with regards to why heatshield behavior seemed so erratic based on what was attached to them.

Thats basically because some parts have more thermal mass than others.. in my tests for example, the mk1-2 pod has enough thermal mass to keep the shield nearly below ablation temperature.

Also, that heatConductivity line on the mainsail might be useful, but i'm under the impression that there are more variables that needs tweaking (to which there is no access thermalMassModifier in the parts .cfg file).. like thermal mass calculation. Because lowering conductivity yields no heat transfer between parts with very low thermal mass, while working ok for higher thermal mass parts.

In any case, thats a good find, ty for sharing.

Edited May 1, 2015 by DJK

[xXIndestructibleEVAXx]

*snip*

Okay, what would you suggest setting this to?

[FlowerChild]

Thats basically because some parts have more thermal mass than others.. in my tests for example, the mk1-2 pod has enough thermal mass to keep the shield nearly below ablation temperature.

Also, that heatConductivity line on the mainsail might be useful, but i'm under the impression that there are more variables that needs tweaking (to which there is no access thermalMassModifier in the parts .cfg file).. like thermal mass calculation. Because lowering conductivity yields no heat transfer between parts with very low thermal mass, while working ok for higher thermal mass parts.

In any case, thats a good find, ty for sharing.

No worries. I've also seen values for thermal mass btw, like the solarPanels have:

	thermalMassModifier = 2.0

So that's likely tweakable on a per part basis as well.

Okay, what would you suggest setting this to?

No idea. I haven't even tried it yet

If the .cfg files are to be believed, 0.12 conductivity is the default for parts, and a number of them are set to 0.06 with comments saying that's half default.

So, since the heatshields have no such line by default, I would assume that in stock they're normally at 0.12, and the .cfg I provided sets it to half that as a starting point to see if it has desirable results.

I'll likely be tweaking these values to get a more hardcore reentry experience for my mod, and will be happy to share whatever I come up with, but it may be awhile before I get to that, as I have a ton of other stuff to take care of for this update.

Just really happy to have a clue as to what's going on with reentry in stock right now, so I'll have an idea of what I need to adjust there.

Edited May 1, 2015 by FlowerChild