Let's talk about parachutes, drag and heat..

[Old Foxboy]

Hello,

1. As most of you already found out, parachutes are, well, powerful. Too powerful even when half opened.

However, does anybody know how to modify the parts database drag cube of the chutes to make them a little more realistic? The numbers in the part configuration file don't seem to do much.

2. Heating up is easy. Losing heat isn' t. Even when the craft has touched down and is sitting still (or floating in the ocean), the temperature still rises happily. Any ideas?

3. Atmosphere pressure curve: below 25k, it's definitely there and will kill you when going > mach2+, and above, it's nearly gone, leaving your capsule returning from the moon with > 3000 m/s nearly untouched. Meh.

Any quick fixes for someone like me who doesn't hesitates to edit a cfg file?

[FreeThinker]

It realy depends what you are used to. If you were a casual player not want to worry about reentry angle, I can imagin the change can be a bit dounting. If on the otherhand you are a FAR player, it feal like a dumb down arodynamic model

[KSK]

No idea about 1. I'm afraid, and haven't noticed any problems with 2. personally, although I've only been landing Mk1 capsules from Kerbin orbit so far.

With regard to 3. I am finding that I need to change my old re-entry profile quite a bit. I'm guessing that parachute drag will be changed at some point so I'm trying to get into the habit of flying 'sensible' re-entries from the start. Specifically, only deploying chutes once I'm through the fire and ideally through the aerodynamic shock effects too.

Setting my periapsis to about 30km and coming in shallow seems to work OK because it gives me more time to slow down before deploying my parachutes. That's for return from Kerbin orbit - I'll probably need to go shallower still for a return from Munar orbit.

[Poynting]

I too have been playing it sensible and not using parachutes until subsonic speeds after re-entry. They really should be ripped off/destroyed/over heated with all the other re-entry effects but they aren't low down in the atmosphere as they slow you down so quickly. Has anyone tried opening one before re-entry?

[Streetwind]

I agree that the way the craft's temperature (or well, the flux values, more accurately speaking) changes feels really weird and inconsistent in places. I played a lot with Deadly Reentry in the past and that always gave me smooth temperature increases up to a certain peak, followed by a smooth temperature decrease until space (where it's pretty cold).

Now we have a great and highly detailed vessel heat and temperature simulation that is leaps above and beyond in physical accuracy than Dealdy Reentry ever tried to be, but at the same time... the smoothness is gone. You have giant spikes or jumps in behavior when passing certain velocity or altitude marks - it feels like the atmosphere only knows 3 or 4 different, discrete states.

Example 1: try looking at external temprature just as you're passing the boundary from atmosphere to space. It drops from several hundred Kelvin directly to 4 Kelvin instantly. No gradual decline, not even over as little as a single meter - no, it just switches instantly the very moment you pass the boundary.

Example 2: This ---> http://forum.kerbalspaceprogram.com/threads/117230-Whats-with-the-insane-heating-spike-at-Mach-2

Now it's possible that some of what we're seeing is actually realistic and that the onset of certain types of shock heating really is that drastic - I wouldn't know, I'm not qualified to comment on that. But that can't explain all the sudden jumps (certainly not the one in example 1). And it just doesn't... feel smooth, you know?

Disclaimer: I like the new aero and heating systems and point out their flaws only because I care about them and think they could be even more awesome.

[Old Foxboy]

Okay, let me get more precise

I am a long term Orbiter player (if you know it) and have lots of experience in X-Plane, too. I am into realism, as far as it makes practical sense for a computer game like kerbal I don't have any issues with a real flight model. So, of course i played a modified version back in 0.9.

I don't mean a simple LKO return. Of course i've done that. Dozens of times, and never ran into issues - and i popped my chutes very low, like they should (immediate hyper high G force stop nevertheless, as you all know). The heating in LKO reentries shouldn't be a problem anyway.

But: When returning from the Mun, you have about 800 -900 m/s more speed. A "shallow" reentry will end up in a bounce back into space, followed by a dangerous steep reentry if you aren't able to do corrections. A steep reentry - well you all know.... So i aimed at about 25k-28k, and the capsule followed a nice Apollo-style flight profile.

Oops i forgot to mention i had a stack of 2 capsules and a service bay (they used up all of my heat shield).

On the parachute, and later on the ground, the attached thermometer didn't measured a falling temperature, but still rising. My question is if this is through belated conductive heating or if it's a bug.

Another thing i did see was that the mk 2 heat shield didn't lose any ablator when i tried to do a reentry with a hitchhiker container. But that's another story.

Maybe it's just that the Kerbin atmosphere resembles the earth's atmosphere, but it only reaches to 70km - and the planet is significantly smaller while having the same gravity. Coming from Orbiter, i am used to other dimensions. On Earth, you need 7000 m/s to reach LEO, as you probably know. So breaking this speed with Earth's atmosphere is a whole different story in terms of heating. With a real Apollo capsule, you brake with a maximum of 6g during reentry when coming from the Moon. You won't reach that value in KSP (without popping your chute, of course) I think that the relation of deceleration to heating is too far off in KSP.

[Fizbanger]

Yep, if you open it before re-entry it doesn't animate until you get to 25K and under, then they chutes pop and drag you to a stop at 10G without snapping off.

For me, I've changed my approach to gathering science - I will EVA and bring everything down in the capsule to get around the heat shield having no mass and everything flipping with it - but the parachutes are indestructible brakes at the moment.

Next I'm going to try the types of Lunar landers I would build in 0.90 for gather Mun science and then landing safely back on Kerbin and see how I go with these aero effects.

[georgTF]

I apologise for possibly going a little off-topic but i find the parachutes unrealistic only when the entry angle is too steep or too shallow. To be honest that's most of the time, and abolutely they need to burn up or break off when the player gets it wrong (and Kerbals need to be killed by huge G forces).

Initially i was irritated to see parachutes magically save Kerbals from certain death, but since i was trying to play permadeath i was also more carefull and kept re-entry speeds on my mind. I was pleasently surprised to find that in some cases parachutes worked exactly as you'd expect them to. They reduced speed very gradually and the g-force indicator hovered in the red zone but never maxed out. Visually it looked "realistic" as well. I guess these are the scenarios testers were using most of the time to see if things work as intended.

Long story short, when the angle is too steep the craft experiences extreme heat and g-forces and the parachute is unrealistically strong. It does not burn nor break off and can reduce speed very suddenly in ways that nature never intended. When the angle is too shallow, the craft accumulates heat for a longer period of time at altitudes where the parachute cannot deploy to slow it down. The parachute should be incinerated once it's deployed. If you get the angle right, the parachute deploys as the craft begins to heat up then gradually and almost gently bleeds off excess speed.

They are broken though, in the sense that they will allways do their programmed job, no matter what the speed, altitude or heat have to say.

I too have been playing it sensible and not using parachutes until subsonic speeds after re-entry. They really should be ripped off/destroyed/over heated with all the other re-entry effects but they aren't low down in the atmosphere as they slow you down so quickly. Has anyone tried opening one before re-entry?

Yes, i tried deploying chutes at the moment the craft enters the athmosphere. In fact i've begun staging chutes before the last decoupler on rockets that do not use heat shields. Of course they don't work until the correct athmospheric conditions but once deployed they get to work immediatley. They currently forgive unrealistic flying, though if you fly correctly they work more realistically.

Edited April 29, 2015 by georgTF

[rkman]

Fix for parachutes and many other 1.0 bugs:

http://forum.kerbalspaceprogram.com/threads/97285-KSP-v1-0-Stock-Bug-Fix-Modules-%28Release-v1-0-0-27-Apr-15%29-Misc-Utilities-%2818-Jan-15%29

[Curveball Anders]

2. Heating up is easy. Losing heat isn' t. Even when the craft has touched down and is sitting still (or floating in the ocean), the temperature still rises happily. Any ideas?

I don't know how it's coded.

But as I understand it heat transfer is a big part of the new heat system.

Transfer by contact (or radiation) means that any part of a construction with higher levels of thermal energy will try to dissipate this excess to it's surroundings .

So a hot engine will try to transfer it's excess energy (heat) to a cooler tank, and continue to do so until there's a balance of available energy.

If we take a standard capsule returning from space one would assume that the heat shield is sizzling hot while the capsule and other attached paraphernalia is cooler.

And while the heat shield can dump some (and most likely the majority) excess energy into the water, some energy will transfer to the capsule (and attached dodads).

So the entire craft will cool down, while at the same time some part (the initially cooler ones) will actually heat up.

It's not exactly rocket science, it's thermodynamics

- - - Updated - - -

The effects of heat transfer was shown in vivid detail by some glorious streamer during the launch weekend (I don't remember who, I blame myself for being drunk and watching streams for too many hours).

A Mk.1 capsule, with a heat shield and a Mk16 parachute, hitting re-entry by the book.

Heat shield doing it's job, glowing red and shedding mass to dissipate heat and suddenly boom goes the parachute.

...? Why did the gadget way out of the air stream and generated heat go boom?

The answer is heat transfer and heat tolerance.

The heat shield transferred a bit of it's excess heat to the capsule, and the capsule transferred a bit of that energy to the parachute.

And while the parachute had to deal with a fraction of the total heat, it has a much lower tolerance to heat than the heat shield or the capsule.

So boom goes the parachute, annoying, but actually quite realistic.

[Old Foxboy]

Okay, that changes the drag modifier from 10 to 1 on semi deployed.

I fiddled with that number, too, didn't seem to do much, though. Don't know where the other numbers reside they played around with.

[Old Foxboy]

Ooookay, now i finally got the medium heat shield to shed some of it's ablator. In a standard reentry, i can do the reentry even without the shield. The craft (MK I-2) will survive easily, even if the parachute will slightly overheat (but not be damaged). With the heat shield attached, one has to fly a very brutal reentry to make it ablate some. I guess if you don't have "strings attached", namely a lot of heavy stuff (and not only a capsule...), the reentry is finished before the ablator even reacts... strange. The Mk I pod heat shield (the small one) loses between 25% and 75% of it's ablator (depending on reentry).

So maybe the difference between the two heat shields was the reason i was so confused about the heating. And maybe the med sized is a bit overpowered.

[panzer1b]

Drag?

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What drag, a EXPOSED 3.5m fuel tansk get under 6 drag at mach4!

[juanml82]

I apologise for possibly going a little off-topic but i find the parachutes unrealistic only when the entry angle is too steep or too shallow. To be honest that's most of the time, and abolutely they need to burn up or break off when the player gets it wrong (and Kerbals need to be killed by huge G forces).

According to wikipedia, humans can survive short exposure to over 50 Gs. You won't be able to pull more than 50 Gs without disintegrating from the heat, so it's a moot point. Being subject to 8-20 Gs will not kill an astronaut.

I don't care much about the parachutes. Yes, they seem overpowered. But if they weren't, I would be just slapping a lot of them, increasing part count, so as far as gameplay is concerned, I don't see much of a difference.

The heatshields can (and should) be modified so they aren't massless. That will help a lot in keeping them pointing towards the atmosphere. It won't stop a science jr behind them from reaching it's max temperature, blowing up and throwing everything off course, though. Not that it happened to me

That's not necesarilly unrealistic - it's likely that some equipment isn't meant to survive reentry heat unless it's specially protected.

[X-SR71]

Drag?

What drag, a EXPOSED 3.5m fuel tansk get under 6 drag at mach4!

That's a nice find, and it sucks part occlusion works in that dumb way. Keep building your huge, flat bases. Attach nosecones on top of it for every horizontal part, and you're done!

[Matt516]

That's a nice find, and it sucks part occlusion works in that dumb way. Keep building your huge, flat bases. Attach nosecones on top of it for every horizontal part, and you're done!

Well hopefully they'll be updating the occlusion model in future patches - the whole aero model is still new and I imagine they've still got some stuff on their wishlist, feature-wise.

[falloutaddict]

Here's my input if anyone cares.

Somebody in another thread mentioned that you could change the .cfg file for the heat shields by changing the "PhysicsSignificance" value to zero. This has helped keeping the craft retrograde on reentry. I also set my per around 20-25k for reentry from mun transfer and then deploy my chutes around 6-8k i am usually only going around 200-300m/s at this point. Took a couple tries to get the numbers right but this has worked for me no problems whatsoever.

[mikegarrison]

I don't know how it's coded.

But as I understand it heat transfer is a big part of the new heat system.

Transfer by contact (or radiation) means that any part of a construction with higher levels of thermal energy will try to dissipate this excess to it's surroundings .

So a hot engine will try to transfer it's excess energy (heat) to a cooler tank, and continue to do so until there's a balance of available energy.

If we take a standard capsule returning from space one would assume that the heat shield is sizzling hot while the capsule and other attached paraphernalia is cooler.

And while the heat shield can dump some (and most likely the majority) excess energy into the water, some energy will transfer to the capsule (and attached dodads).

So the entire craft will cool down, while at the same time some part (the initially cooler ones) will actually heat up.

It's not exactly rocket science, it's thermodynamics

- - - Updated - - -

The effects of heat transfer was shown in vivid detail by some glorious streamer during the launch weekend (I don't remember who, I blame myself for being drunk and watching streams for too many hours).

A Mk.1 capsule, with a heat shield and a Mk16 parachute, hitting re-entry by the book.

Heat shield doing it's job, glowing red and shedding mass to dissipate heat and suddenly boom goes the parachute.

...? Why did the gadget way out of the air stream and generated heat go boom?

The answer is heat transfer and heat tolerance.

The heat shield transferred a bit of it's excess heat to the capsule, and the capsule transferred a bit of that energy to the parachute.

And while the parachute had to deal with a fraction of the total heat, it has a much lower tolerance to heat than the heat shield or the capsule.

So boom goes the parachute, annoying, but actually quite realistic.

"Thermal soakback". Real world engineering issue.