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Leozaur

Heat shield mass added to pod, heatshield physicsless

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This is probably a bug with heat shield. The info on the part says its mass is 0.3, bug when I place it it doesn't affect center of mass indicator at all. Yes, my ship isn't that heavy, placing small girder that is just 0.125 on the same spot shifts the indicator a bit.

Testing whether it really is treated as 0 weight by physics is tricky for me, but it certainly seemed like the center of mass was where it was shown in the editor - just above geometry center which caused the ship to flip during descent back to Kerbin despite my attempts to hold it retrograde.

There are no fuel tanks on that stage either.

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Thanks for that!

My pleasure. I hope it helps people out :)

I'm not 100% convinced that's the actual problem btw, as your direction of travel still seems *slightly* offset with physics turned on in a way that I'm not entirely certain is intentional. At the very least, it does however sufficiently mask the problem to serve as a good workaround until we get a more official solution.

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Why is this tagged as "not a bug/intended"? If this fundamentally breaks reentry, then there is no way it was intended to be that way. This is clearly a bug/unintended consequence.

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Why is this tagged as "not a bug/intended"? If this fundamentally breaks reentry, then there is no way it was intended to be that way. This is clearly a bug/unintended consequence.

Right, I'd venture to say that their coding was intentional. But the consequence of that coding had an unforeseen affect on game-play, and is therefore a bug.

I'm sure the specifications for the design do not say "User should not be able to successfully re-enter Kerbin atmosphere with a heat shield."

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i believe it has to be [Heatshield*]:Final

Otherwise it may not work

No. The partnames are "HeatShield1" etc, with capital S. ModuleManages is case-sensitive.

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I gave it a couple of tries as is. Was unsuccesful with Science Junior or service bay attached I would lose them around 25K, really just did not have enough control. I had the difficulty at 120%, with just the pod and heatshield I needed to pay real careful attention to orientation during reentry. If not the heatshield may be ineffective. If I let it go on it's own with or without SAS it would angle itself so the heatshield was not protecting the whole pod.

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This might be because the center of lift is too low.

In mk1Pod.cfg I changed:

CoLOffset = 0.0, -0.35, 0.0

to

CoLOffset = 0.0, 0.35, 0.0

and now the pod is stable on reentry.

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i believe it has to be [Heatshield*]:Final

Otherwise it may not work

Final shouldn't be necessary as their aren't other ModuleManager patches being applied here. The changes are straight to the original .cfg files.

I believe Final only affects the order in which patches are loaded, not how they're applied to the original files.

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apollo.jpg

http://infoscience.epfl.ch/record/200444/files/thesis_ermina.pdf

Simulation of Apollo reentry.

I think the attitude might actually be closer to right than I thought… it's the shielding modeling that is wrong. They use a ray-trace, right? The shock heating is far more complex than that, so they either need to fix that, or alter the preferred orientation of the pod.

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You'll see this with the batteries too, the gear as I mentioned and some other parts, they add their mass to the parent but still act normally for things like drag :)

Which is completely unfair, and buggy. A part should be set up so that it either DOES, or DOES NOT get used in physics calculations. To have it get used in half of them but not others, especially in cases where there is a delicate balance between those calculations, is precisely what is causing the problem here. To make the heatshield so it DOES drag but does NOT move the center of mass, is exactly what is causing the flipover. When an object has one section that is dense and another that is very sparse, but both have equal drag, then when under a wind it will flip so the dense part faces into the wind and the sparse mass part flips to the lee side. You can't get much more sparse in mass than having zero mass but still having drag. That makes it behave like a sail, or a parachute, or like paper - high drag with low mass has a very profound effect - it behaves like an aerodynamics anchor.

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Good news: Apparently this has been confirmed by Squad as a bug, and they are aware of it, despite the "Not a bug" in this thread title ;)

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Roverdude, author of the heatshield .cfgs, has confirmed via Skype on DasValdez's stream tonight that this was a mistake on his part and it will be fixed in the next release. No word on when that will be.

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Which is completely unfair, and buggy. A part should be set up so that it either DOES, or DOES NOT get used in physics calculations. To have it get used in half of them but not others, especially in cases where there is a delicate balance between those calculations, is precisely what is causing the problem here. To make the heatshield so it DOES drag but does NOT move the center of mass, is exactly what is causing the flipover. When an object has one section that is dense and another that is very sparse, but both have equal drag, then when under a wind it will flip so the dense part faces into the wind and the sparse mass part flips to the lee side. You can't get much more sparse in mass than having zero mass but still having drag. That makes it behave like a sail, or a parachute, or like paper - high drag with low mass has a very profound effect - it behaves like an aerodynamics anchor.

Yeah, I'd have to agree here. It's really unintuitive for parts to be used in physics calculations in some ways but not others. Obviously this needs to be fixed for the heatshield as it has a profound impact on gameplay. But honestly it should probably be fixed with batteries/landing gear/etc as well - or we might see more unintended derpy behavior from the drag and mass models being out-of-sync.

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Yeah, I'd have to agree here. It's really unintuitive for parts to be used in physics calculations in some ways but not others. Obviously this needs to be fixed for the heatshield as it has a profound impact on gameplay. But honestly it should probably be fixed with batteries/landing gear/etc as well - or we might see more unintended derpy behavior from the drag and mass models being out-of-sync.

The biggest other problem at present with this seems to be fairings. Apparently they don't shed any mass when you eject them, because they're also defined as physicsless, and all their mass ends up residing in the base as a result.

Obviously, this is less than optimal, as it kinda defeats the purpose of ejecting fairings. And yes, I agree: I have no idea why this physicsless thing is still a thing.

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Which is completely unfair, and buggy. A part should be set up so that it either DOES, or DOES NOT get used in physics calculations. To have it get used in half of them but not others, especially in cases where there is a delicate balance between those calculations, is precisely what is causing the problem here.

Sal might have misspoke when talking about mass and drag for physicsless parts.

Drag does get calculated for physicsless parts and that drag is added to the parent part. You can toggle both of these options in the Debug menu if you wish. (see pic)

Mass is supposed to get calculated for physicsless parts, and added to the parent part. This looks like it might not be working for some parts, or maybe all parts (I'm not sure which).

Cheers,

~Claw

6bB9h1E.jpg

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Mass is supposed to get calculated for physicsless parts, and added to the parent part. This looks like it might not be working for some parts, or maybe all parts (I'm not sure which).

This came up in another thread, but it appears that the problem is that the mass is being applied to the parent part, but the COM isn't being moved by it. This seems to create instability in this particular case with the heatshields.

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http://i121.photobucket.com/albums/o222/tatersw/KSP/apollo.jpg

http://infoscience.epfl.ch/record/200444/files/thesis_ermina.pdf

Simulation of Apollo reentry.

I think the attitude might actually be closer to right than I thought… it's the shielding modeling that is wrong. They use a ray-trace, right? The shock heating is far more complex than that, so they either need to fix that, or alter the preferred orientation of the pod.

Sorry to interrupt a bugfixing thread, but the mk1 pod "stock" reentry attitude is incorrect and resemble the apollo reentry by chance. In that case the pitch was maintained low thanks to a CoM offsetted from the central axis with unsymmetrical distribution of hydrazine in certain side tanks. This allowed the pod to generate more lift and have a less steep reentry and splasdown in american waters of the pacific ocean, but it is not required to do a reentry and the CoM was still very low. If heatshields have mass (use flowerchild patch) you can replicate this with some monoprop side tanks. The mk1 pod with heatshield has the CoM too high and is way more unstable.

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http://i121.photobucket.com/albums/o222/tatersw/KSP/apollo.jpg

http://infoscience.epfl.ch/record/200444/files/thesis_ermina.pdf

Simulation of Apollo reentry.

I think the attitude might actually be closer to right than I thought… it's the shielding modeling that is wrong. They use a ray-trace, right? The shock heating is far more complex than that, so they either need to fix that, or alter the preferred orientation of the pod.

From the paper you cited:

" The vehicle

followed a lifting trajectory with a nominal angle of attack of 25.5 deg during reentry."

40 > 25.5

I doubt the MK1 pod was intended to be a lifting body. Particularly when it wants to go 40 degrees in *any* direction, rather than toward a hypothetically intended lifting body offset CoG.

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There's nothing wrong with physicless parts in general adding their weight to the parent object; it's a reasonable approximation that saves a lot of processing.

But the idea that a heat shield should be treated that way is daft. They're heavy, and their mass is a fundamental part of how they work.

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Sorry to interrupt a bugfixing thread, but the mk1 pod "stock" reentry attitude is incorrect and resemble the apollo reentry by chance. In that case the pitch was maintained low thanks to a CoM offsetted from the central axis with unsymmetrical distribution of hydrazine in certain side tanks. This allowed the pod to generate more lift and have a less steep reentry and splasdown in american waters of the pacific ocean, but it is not required to do a reentry and the CoM was still very low. If heatshields have mass (use flowerchild patch) you can replicate this with some monoprop side tanks. The mk1 pod with heatshield has the CoM too high and is way more unstable.

I don't disagree, I know it is accidental. None the less, it does show that if they use ray-tracing for heat shielding, it is too simplistic for anything other than a aligned reentry.

- - - Updated - - -

From the paper you cited:

" The vehicle

followed a lifting trajectory with a nominal angle of attack of 25.5 deg during reentry."

40 > 25.5

I doubt the MK1 pod was intended to be a lifting body. Particularly when it wants to go 40 degrees in *any* direction, rather than toward a hypothetically intended lifting body offset CoG.

I wasn't saying it was right, I said it was "closer to right than I thought" (assuming an off center CM for the pods, since they stabilize, and the offset rotates with them). Since at first I thought it was 100% wrong, anything better than 0% right is closer.

The take-away from the image I posted was that ray-tracing along the velocity vector for heating effects is unrealistic, and can result in problems due to lack of a proper bow shock.

Edited by tater

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It is intended that the sciencejr and heat-shield add to its parent parts weight without changing the center of mass, making the capsule top heavy? It's not a bug?

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Drag chute to stabilise the craft during re-entry worked a treat, Val is safe and sound :)

One thing I noticed was that the new resource for the heat shield (ablator?) didn't diminish during the re-entry effects, is that a bug too or do you have to be really really aggressive to make a dent in it?

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Drag chute to stabilise the craft during re-entry worked a treat, Val is safe and sound :)

One thing I noticed was that the new resource for the heat shield (ablator?) didn't diminish during the re-entry effects, is that a bug too or do you have to be really really aggressive to make a dent in it?

Presumably this is for when coming back from Moho/Eeloo and you're really booking it, although I have yet to get that far out.

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Drag chute to stabilise the craft during re-entry worked a treat, Val is safe and sound :)

Fixing one bug by exploiting another doesn't appeal to me. And yes, he fact that parachutes live through heat just fine that tends to explode the main craft is certainly buggy. And if that's the way they wanted it then it's buggy by design rather than buggy by code, but still buggy. Broken as intended.

- - - Updated - - -

It is intended that the sciencejr and heat-shield add to its parent parts weight without changing the center of mass, making the capsule top heavy? It's not a bug?

The science jr doesn't have the bug. It's mass is being added properly and moving the CoM properly. For it, it's actually *correct* that it tends to throw off the balance by being a less dense part on the bottom. What's incorrect is how the heat shield does so even MORE than the science Jr does, because it's even less dense, with its mass of zero, and is thus acting more like an airbrake or a sail.

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