Heat shield mass added to pod, heatshield physicsless

[Leozaur]

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.

[sal_vager]

Most likely an oversight, not all parts are counted to mass.

[lajoswinkler]

I can confirm this bug. Heatshield does not move the center of mass at all and thus the capsule loses its inherent directional stability during reentry. SAS therefore must be kept on and it barely holds its retrograde orientation, making every reentry extremely dangerous. Normal reentry does not require SAS, it's stable by itself.

[Quorthon]

I can confirm this bug. Heatshield does not move the center of mass at all and thus the capsule loses its inherent directional stability during reentry. SAS therefore must be kept on and it barely holds its retrograde orientation, making every reentry extremely dangerous. Normal reentry does not require SAS, it's stable by itself.

I was very irritated when I experienced the same issue.

I already wanted to write a bug report about this. I'm glad the reason for this bug was found so quickly.

[smjjames]

I wonder why this bug wasn't found during testing though? Maybe people didn't do gemini/mercury/apollo reentries.

[sal_vager]

Oh wait, I know what's happening here, it's adding the mass to the parent CoM.

This was deliberate on some parts such as undercarriage to prevent unwanted CoM issues

[lajoswinkler]

It happens with Mk1 capsule only because its CoM is not low enough as Mk2's. All capsules should sport a bit lower CoMs.

[sal_vager]

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

[WOODY01]

Came here to report the problem myself. The capsules handle great with nothing attached, but when I tried bring a capsule back with a Science Jr and Service bay with two goo canisters it fought to go nose first and won. My second attempt was with a servicse compartment with two goo conisters protected by a heat shield same, tried Scince Jr alone with heatshiled same. As soon as those parts blew up the pod orientated nose up and bottom down nicely.

I also tried adding extra parts for ballast but could not seem to be able to add enough weight to counteract the pods nose first preference with any thing attached.

[Boamere]

Is this getting fixed?

[blspblackdeath]

I can confirm this, too. With heatshield I can't reenter properly it wants to go nose first. I with Science Jr I can't hold it even with SAS.

[Jouni]

According to the in-flight mass indicator, the heat shields are entirely massless. If physicsless parts add their mass to the parent part in 1.0, the ship info display hasn't been updated to handle this.

Also, I don't believe that this is intended behavior:

The craft consists of a Mk1-2 command pod, a Mk16-XL parachute, and a 2.5 m heat shield. During reentry, the aerodynamically stable angle of attack varies between 30 and 40 degrees. That's high enough that the heat shield can't entirely protect the parachute. Unless the reentry angle is very shallow, the parachute overheats and explodes.

[Leozaur]

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

Come on, this can't be exactly the way it was intended to be. I understand there are compromises to be made to not overengineer something not really that important, but it's forcing us to make contraptions to shift CoM on return stage. Which is especially tricky when you're just starting career and have very low limits on mass/number of parts, not to mention added drag and weight you have to lift to get to places. And without this foolishness you can't bring anything more complex than just a pod back from orbit. There must be another way.

[Treveli]

A work around I found by accident during my first 1.0 reentry attempt (the sixth or seventh revert of the attempt) is to deploy a Mk16 chute during reentry. Keeps the nose pointed in the right direction, but looks frelling odd having it out with reentry flames around it.

[biohazard15]

Oh wait, I know what's happening here, it's adding the mass to the parent CoM.

This was deliberate on some parts such as undercarriage to prevent unwanted CoM issues

These "unwanted CoM issues" would actually make re-entries easier and more realistic - just like it was with FAR+DRE in 0.90. You didn't need SAS to keep your capsule in the right direction - in some cases, it could even right itself up and do a proper re-entry.

First "fairings", then this - how many more fails do you keep inside, KSP 1.0?

[Beduino]

Really this should be fixed because mk1 capsule is flippy happy with the COM so high.

[lajoswinkler]

This simply must be repaired. Blunt bodies such as capsules have to be in a state of stable equilibrium during reentry.

Compare with a ball resting on these surfaces.

Stable, unstable and indifferent (neutral) equilibrium. Capsule needs to have the first one.

[Wintersdark]

Well, this certainly makes early career mode extremely challenging. I've got all these sciency parts, but can't use them in my early flights due to the resultant flip 'n burn.

Ah well, I'll figure out something I guess.

- - - Updated - - -

Ok, as I posted in another thread, I can offer some confirmation that popping a Mk16 parachute basically as soon as you reenter the atmosphere works to keep the craft aligned properly and quickly bleed off speed. I brought along a pair of Radial Mounts Parachutes as well, but didn't need them.

This is in a capsule>service bay(2xGoo)>Science Jr>Heat Shield configuration. No SAS used, the chute kept the ship aligned to retrograde nicely.

It didn't tear off, and fully deployed at 500m as normal.

[FlowerChild]

There is definitely a bug involved here. There's a lot of discussion going on about it in this thread:

http://forum.kerbalspaceprogram.com/threads/116895-One-way-stock-1-0-heat-shielding-is-a-bit-unfair-versus-old-DRE-mod-s-heat-sheilding

Where I also presented what seems to be a temporary workaround:

If you look in Kerbal Space Program\GameData\Squad\Parts\Aero\HeatShield\HeatShield1.cfg you'll see this line:

	PhysicsSignificance = 1

Changing that 1 to a zero should turn physics back on for that part. I'm going to give this a try myself right now, as yeah, heatshields seem quite broken right now making reentry with them next to impossible to survive, which is obviously not what one would expect

Which seems to largely fix it.

Could a moderator please remove the "Not a bug" label from this thread? It definitely is one, and it's a rather significant problem, especially if you're playing with reentry heat turned up and thus need a 1.25m shield on a Mk1 command pod to survive reentry. Without the above fix, it will constantly veer out of the airflow and your capsule will most certainly explode without heavy and constant control input to compensate (assuming you have enough battery power left to operate your reaction wheels).

Edited April 27, 2015 by FlowerChild

[tater]

This is a BUG, period.

Here is a 100% stable reentry.

Minus the heat shield… the bottom of the capsule points prograde, as it should. This is a fundamental error, and breaks, well, everything. New career players will have their first craft run out of EC trying to hold retrograde heading with SAS… did anyone actually play early career to test this?

[celerystick009]

I tried FlowerChild's suggestion, and it seems to work for me. Placing a heat shield now moves the yellow CoM ball, and makes a chute+capsule+Science Jr.+heat shield combo go through reentry mostly as expected. I noticed that it still wanted to be a tad off-center, but it was very manageable and nothing blew up.

[biohazard15]

You might also want to increase heatshield mass - it would move CoM down further and make the capsule even more stable.

Someone should make a temporary MM patch.

[Bedwyr]

Observed the same behavior on a couple tests. Capsule points correctly retrograde and stabilizes incorrectly at an angle with the heat shield, causing the capsule to burn up. This may be intended behavior, but it is also a bug.

[Dunbaratu]

Please change the label. "Adding a heat shield causes the capsule to flip point first and burn, thus doing the exact opposite of its intent of helping you survive re-entry" is emphatically a bug. And that's exactly what this misconfiguration causes.

Incedentally, turning physics on for the heat shield, via Part.cfg, fixes the bug entirely, so it shouild probably be made that way in the default install.

[FlowerChild]

Someone should make a temporary MM patch.

There you go:

@PART[HeatShield*]
{
	@PhysicsSignificance = 0
}

You will of course need ModuleManager installed for this to work, which can be found here:

http://forum.kerbalspaceprogram.com/threads/55219

Install MM, drop the above into a .cfg file in your GameData directory, and you should be good to go.

Edited April 28, 2015 by FlowerChild