[1.12.*] Deadly Reentry v7.9.0 The Barbie Edition, Aug 5th, 2021

[Jashin]

Thanks for the reply ! I'm using DRE 6.2.1 and RealChute 1.2.5.3. I've barely managed to get a few chutes running, with intensive tweaking of the RealChute part settings. However, drogue don't work like they should : they instantly snap at high velocities (>700 m/s, it's a rough estimate since I haven't had the time to check at other speeds) instead of slowing the craft down a bit. The only reliable solution is to set the chute to partially open at 3km and open at 500m like Taki117 suggested. However, this is sometimes hard to do given the time needed for the deployment to occur, heavier crafts might not like that setting. In addition, the drogue function is completely lost, and I haven't found a way to properly use a drogue with the new DRE settings.

EDIT : I just checked the deployment of real chutes in an Apollo reentry configuration and I'm stupid for thinking chutes wouldn't snap at speeds higher than 700 m/s. I'm sorry for bothering you about this, I suppose DRE is now set for maximum realism, which I'm fine with (however, may I suggest a nicer default option ? it's quite a step away from the previous settings). I will experiment with higher altitude drogue deployment, it seems that IRL they are often used as high as 13 km.

Edited October 14, 2014 by Jashin

[Starwaster]

700 meters per second is ~700 degrees Kelvin. My guess is you were actually doing closer to 775 m/s. So outside your ship is a plasma shockwave of 775 K. That's like 502 Celsius.

That's 25% of the max temp of the chute part. That's what that 0.25 means in the settings. Max temp of the part is 3100. 25% of that is 775 so chute failure occurs at 775. However density of the atmosphere is an issue. I've safely deployed a chute at very high altitudes (15-20km) but they fail when the air is dense enough to conduct a lot of heat.

IRL nylon melts at 521 K. Approximately. Assume the chute is nylon and that's a generously high failure temperature.

[Jashin]

I'm totally satisfied now that I have these numbers in mind. I will try to tweak RealChute presets to reflect the new DRE settings since it doesn't make sense anymore to have drogues deploy at 30-25 km like they used to. I will now have them deploy at about 11 km and see if that works with the new settings. I might also post something on the RealChute thread, but it seems things have been getting a bit out of control there lately...

[NathanKell]

*All* parachutes are to be deployed subsonic. That means < 300m/s.

Even if the heat doesn't get you, a supersonic shockwave will rip the chute apart. RealChute (let alone stock) parachutes are not designed for supersonic deployment.

(BTW the numbers cited are a bit off; DRE sets parachute parts to maxtemp 1250 IIRC, so 1/4 of that is 312. However, that is compared with shockwave * density^densityExponent, so at 15km you're talking, what, density .1 or .2? So something like .14-.25 * shockwave temp)

[Starwaster]

Thanks Nathan for the correction on chute max temp!

However, chutes have been tested at supersonic speeds IRL. Curiosity's chute was tested at Mach 1.5 before it was sent to Mars where it was deployed hypersonic.

(And I'm thinking maybe parachute multiplier should be part of the difficulty settings....)

[Jacke]

Ever since I upgraded to DR 6.2+, to avoid supersonic deployment on Kerbin landings I've learned to set my stock parachutes to pressure setting 0.5 atmosphere (the maximum) which means they semi-deploy about 3500m (formula '-5000m * ln pressure in atmosphere' from reversing the pressure formula in the wiki). If the spacecraft comes down on higher altitude land, at the full-deploy altitude (set to default 500m) they full-deploy straight from armed. Haven't lost a spacecraft yet from the opening shock but you can't have everything. Multiple parachutes with slightly different full-deploy altitudes could deal with that.

Edited October 14, 2014 by Jacke

[Starwaster]

Well, the conversations today have me wondering if it might not be a good idea to whip up a MM config file which changes the defaults for known parachute systems. 7km should be do-able too.... 3km is definitely safe as you've demonstrated.

[Galileo Kerbonaut]

I am just dropping a line to say thanks. I realized I've never done that although I've been using it for a long time. Don't even want to play the game without DR.

So... thanks!

[NathanKell]

Other than CORONA etc film buckets, which are caught in mid-air, 7km is about the highest I'm aware for drogues on returning capsules.

Starwaster: at what altitude? (Also, IIRC it wasn't using any of the materials RC uses)

[Starwaster]

Starwaster: at what altitude? (Also, IIRC it wasn't using any of the materials RC uses)

You didn't say anything about altitude before, only that a chute couldn't withstand supersonic opening. Anyway, I don't know the precise altitude. The test started at 130,000 feet at which point a rocket was fired to propel the chute part to Mach 1.5. AFAIK it fired straight down. There was some tearing but it was caused by the case, not the shockwave.

The canopy AFAIK was nylon, presumably one of the stronger ones. The lines were technora.

[Taki117]

For those of you having issues with chutes being ripped off during descent here is a "Proper" chute staging sequence resulting in a safe landing anywhere.

7KM - Drogue Chutes Semi-Deploy

5KM - Drogue Chutes Fully Deploy

3KM - Main Chutes Semi-Deploy. Drogue Chutes Cut (optional but reccomended)

500-700M Main Chutes Fully Deploy.

[Jacke]

Well, the conversations today have me wondering if it might not be a good idea to whip up a MM config file which changes the defaults for known parachute systems. 7km should be do-able too.... 3km is definitely safe as you've demonstrated.

I think a MM config to change defaults would be a good idea.

I used to use pressure 0.2 for semi-deploy, about 8000m, as I didn't realise parachutes would full-deploy straight from armed. On some reentries that lead to parachute loss due to speed still being too high. Thus the shift to using 0.5.

For those of you having issues with chutes being ripped off during descent here is a "Proper" chute staging sequence resulting in a safe landing anywhere.

7KM - Drogue Chutes Semi-Deploy

5KM - Drogue Chutes Fully Deploy

3KM - Main Chutes Semi-Deploy. Drogue Chutes Cut (optional but reccomended)

500-700M Main Chutes Fully Deploy.

Here's what pressures would have to be set for every body with an atmosphere (Kerbin, Eve, Duna, Laythe, and Jool) to get 7000m and 3000m semi-deployment. They are very different for the 5 bodies. For Eve and Jool, they can't be set in the VAB and I suspect they aren't the best ones for them.

Body Scale Ht (m) 0m Pres (atm) 3000m Pres (atm) 7000m Pres (atm)

Kerbin 5000 1 0.55 0.25
Eve 7000 5 3.26 1.84
Duna 3000 0.2 0.07 0.02
Laythe 4000 0.8 0.38 0.14
Jool 10000 15 11.11 7.45

With stock parachutes, they have an altitude setting for full deployment which can be set in the VAB to 50m, 300-4750m in steps of 50m, and 5000m. But a pressure setting for semi deployment which can be set in the VAB to 0.01-0.47atm in steps of 0.01atm, and 0.50atm. Defaults are 500m and 0.01atm, except for Mk25 drogue parachutes which have 2500m and 0.007atm set (which isn't available in the VAB).

[Starwaster]

As far as other planets go, it's just got to be up to everyone properly plan for the planet they're trying to land on if it's not Kerbin. Kerbin's got to be the default.

[NathanKell]

Huh! I thought it was metallic, actually. Shows how good my memory is.

But yeah, sorry, I meant "at normal chute-opening altitudes." M2 at 130k feet does sound survivable (equivalent KSP at ~28km I think), and if you're only doing 450m/s at 28km, go ahead, pop a chute.

[Starman4308]

So, quick question: what factors influence how quickly ablative shielding wears away? I've noticed on my past two re-entries that I use 20% of my ablative shielding is used for 90% of the descent, with the rest of it consumed in maybe 30 seconds once I hit ~25 km (using the 6.4x config of RSS), despite the fact that velocity and temperature are both declining by that point.

[endl]

hi all, im new to this mod and im having a problem where my landing legs are burning up on re entry, is this intended or do i have to somehow shield them. how is this normally done?

[ArcFurnace]

hi all, im new to this mod and im having a problem where my landing legs are burning up on re entry, is this intended or do i have to somehow shield them. how is this normally done?

Do you have a picture of what you're trying to land at the moment? The exact method depends on how your ship is set up. The short answer is you take one of the disc-shaped heat shields from the Structural tab, put it on the bottom of your craft, and make sure the landing legs (or anything else you don't want fried) doesn't peek out from behind it when descending. The shields all have integrated decouplers, so you should be able to drop it once you're down to a safe velocity and deploy your landing legs. Note that this means the shield should be wider than your craft's core stack, given that landing legs are radially attached. It'll look a little weird, but there's nothing wrong with it.

[Starwaster]

So, quick question: what factors influence how quickly ablative shielding wears away? I've noticed on my past two re-entries that I use 20% of my ablative shielding is used for 90% of the descent, with the rest of it consumed in maybe 30 seconds once I hit ~25 km (using the 6.4x config of RSS), despite the fact that velocity and temperature are both declining by that point.

That's normal. The reason is density of the surrounding atmosphere. Even though the temperature is lower by the time you you hit the mid to lower atmosphere, the air is much denser which means it can transfer more heat. 28km seems to be where heating really starts to pick up because you still have a good amount of heat and more atmosphere to convect it into your ship.

[Starman4308]

That's normal. The reason is density of the surrounding atmosphere. Even though the temperature is lower by the time you you hit the mid to lower atmosphere, the air is much denser which means it can transfer more heat. 28km seems to be where heating really starts to pick up because you still have a good amount of heat and more atmosphere to convect it into your ship.

So, if I'm understanding it right, at the tail end of your reentry, temperature is lower but thermal energy flux (heat flow) is greater because there is that much more air slamming into your heat shield, even if it's not as hot, and because ablation rate is (presumably) proportional to thermal flux instead of raw temperature, that's when you lose most of it?

[Wanderfound]

Did anything happen in the last release to aggravate the tendency of RAPIERs to overheat? I'm finding that they're cooking up to explosive levels after a very short time at full throttle in closed-cycle mode.

They were always a bit prone to heating, but previously it was "don't leave them at full throttle for several minutes". Now it seems to be "don't leave them at full throttle for more than a few seconds".

This is the ship in question:

...and, although all three engines are overheating, it seems to only be the side-mounted ones that are doing the "explode in ten seconds" trick. Something about being mounted near a cargo bay perhaps?

(the overheating is happening whether the doors are open or shut, BTW)

Edited October 15, 2014 by Wanderfound

[Matrix Aran]

Did anything happen in the last release to aggravate the tendency of RAPIERs to overheat? I'm finding that they're cooking up to explosive levels after a very short time at full throttle in closed-cycle mode.

They were always a bit prone to heating, but previously it was "don't leave them at full throttle for several minutes". Now it seems to be "don't leave them at full throttle for more than a few seconds".

This is the ship in question:

http://i1378.photobucket.com/albums/ah120/craigmotbey/Kerbal/screenshot219_zps0f18a776.png

...and, although all three engines are overheating, it seems to only be the side-mounted ones that are doing the "explode in ten seconds" trick. Something about being mounted near a cargo bay perhaps?

(the overheating is happening whether the doors are open or shut, BTW)

I am also having this very same problem. While I can handle the in atmo heating, I have no idea why the engines have a persistent desire to overheat 10 times faster in closed cycle mode than they do in airbreathing mode. I've experimented with only placing one engine on the craft, but even then the engine will explode if run at full throttle for more than a few seconds. What's more they insist on exploding like this even outside an atmosphere.

[lajoswinkler]

Yes, rapiers will overheat. SSTO's I've tried to build don't work so I gave up. I don't care, though.

[Starwaster]

So, if I'm understanding it right, at the tail end of your reentry, temperature is lower but thermal energy flux (heat flow) is greater because there is that much more air slamming into your heat shield, even if it's not as hot, and because ablation rate is (presumably) proportional to thermal flux instead of raw temperature, that's when you lose most of it?

Did anything happen in the last release to aggravate the tendency of RAPIERs to overheat? I'm finding that they're cooking up to explosive levels after a very short time at full throttle in closed-cycle mode.

They were always a bit prone to heating, but previously it was "don't leave them at full throttle for several minutes". Now it seems to be "don't leave them at full throttle for more than a few seconds".

This is the ship in question:

http://i1378.photobucket.com/albums/ah120/craigmotbey/Kerbal/screenshot219_zps0f18a776.png

...and, although all three engines are overheating, it seems to only be the side-mounted ones that are doing the "explode in ten seconds" trick. Something about being mounted near a cargo bay perhaps?

(the overheating is happening whether the doors are open or shut, BTW)

I can't think of anything that would be affecting RAPIERs in particular. Reentry is going to be a little hotter on everything but your problem seems to be just with running them.

Do you have anything else that affects them like Real Fuels? Have you tried running just stock + DRE to see how they behave?

As a workaround, try putting a small fuel tank between the RAPIER and the long fuel tank. The way heat transference works in KSP, more heat is transferred to shorter parts than longer parts. (literally measured from the attachment node to the part's center)

[NathanKell]

If you define more as "some, rather than none"

If the two parts' origins are > 4.5m apart, *no* temperature will be transferred.

[Matrix Aran]

I can't think of anything that would be affecting RAPIERs in particular. Reentry is going to be a little hotter on everything but your problem seems to be just with running them.

Do you have anything else that affects them like Real Fuels? Have you tried running just stock + DRE to see how they behave?

As a workaround, try putting a small fuel tank between the RAPIER and the long fuel tank. The way heat transference works in KSP, more heat is transferred to shorter parts than longer parts. (literally measured from the attachment node to the part's center)

I've set up an install of KSP with nothing but the stock configuration, plus DRE. I also installed module manager 2.5.1 as the current version of DRE doesn't come bundled with a module manager .dll

I built a simple rocket in sandbox mode with nothing more than a probe core battery, fueltank and a bunch of intakes and one engine. With DRE installed, the engine will overheat extremely fast in closed cycle mode, so fast that should you not react in time to throttle back to 50%, the engine will detonate.

Without DRE installed, the rocket will still tend to overheat in closed cycle mode, but it will do so at a much slower rate, and only require throttling back by about 5-10%

Edit: After a happy accident when switching around parts, I've found a potential work around for the time being, albeit an ugly one. By using 8x symmetry strut connectors connected from the engine to a small fuel tank, you can apparently remove all overheating from the part, even at ground level, with DRE installed.

Edited October 15, 2014 by Matrix Aran