[0.20] Deadly Reentry 2.3 - reentry heat, plus thermal and g-force damage to parts

[NathanKell]

there's no reason to wait to get below Mach 1.

G-force?

Seriously, the time between 3M and 1M for me, at least, is max-G. And then G falls off massively when subsonic. So if you're riding the redline, there's some good reason to wait on deployment.

[Lexif]

G-force?

Seriously, the time between 3M and 1M for me, at least, is max-G. And then G falls off massively when subsonic. So if you're riding the redline, there's some good reason to wait on deployment.

Haha, yeah, you're right. But I didn't look at my Mach number when i got the parachutes out -- I actually don't know what Mach 1 is at 6 km with far. Also, looking at my screenshots, for my reentry maximum g was about when the heat died down and my shield was ablated. The more I think about it, I usually just wait until I think that my decceleration is somewhat lacking and half-deploy the chutes at that point to help. (Or when I'm starting to panic... ) Never had any problems with that.

Edited to say: I guess it's better to get the chutes out earlier, at least for the simple "capsule reentry at high speed", their half-deployed drag is not that high, and the drag will help to lessen the shock of them fully deploying. But the drogue parachute is a good alternative if that isn't enough, as jrandom says. This radial drogue mod is quite the improvement for that.

Edited August 28, 2013 by Lexif

[NathanKell]

My decel isn't somewhat lacking until <1M

And that's actually a danger with drogues--the semi-deploy drag is 3, vs 1, so they actually have _more_ drag early than main chutes. Which can be Bad News if you're already near max-G. If you're really worried by G, pop mains first, then drogues when G lowers (5-10s later?). This should obviously be well above 2.5km though.

Gawd, deorbiting a spent booster stage, I think I popped my chutes at 1.8km once--survived, but barely. Wow that thing had low drag.

Then again I haven't launched a pod in some time--probes have such low drag that YMMV with pods.

[Jasmir]

Pod is a Mk 1-2 pod with a docking clamp, 2 radial shields, a tiny battery, an RTG, and a radial mono tank--total weight when the shield gives out is 5.3 tons.

You don't need all this stuff. Make it gone as you hit the Atmosphere. The only usefull parts on the reentry Pod are: Pod, Heatshield (personaly, i use the inflatable one), radial Cutes (i use 3). A maybe left upper docking clamp and -lets say- 3-4 RCS Thrusters are also ok. But massive things like batteries, tanks or RTGs will cause problems. Such things belongs to the ServiceModule that should decoupled at the edge of the atmosphere. The Pod has an internal batterie that contains more than enough charge to power the internal reaction wheels while the descent. If you come from the mun, aim for a 28km periapsis.

[Synthesis]

Has anyone else noticed that the shields don't exactly work on other equipment?

I've got what seems like a very reasonable reentry descent--60 km to 40 km--on stuck the shield on the B9 Mk5 cockpit (roughly the normal 2.5m component size). So, upon reentry, it explodes catastrophically upon as soon as it starts to heat up at 33 km.

I played around with the multiplier in the CFG file (not convinced that actually does anything), changing it from 25 to 2, since reentry at a few times the temperature of the sun's surface may not be necessary. I repeated the exercise, and thought things were going as normal...until at about 29 km, when my heat shield was 60% depleted but at 1200 degrees. It exploded, and then so did the cockpit.

Strangely, I've done this same reentry (in fact, much more severe) with the generic Squad cockpit module, angled the same, and survived no problem. This mod seems to be all over the place though (I recently reinstalled it, hoping that it would ease up on the bugs, but instead just made it seem worse).

Anyone have any idea what might have caused this?

[jrandom]

What is the impact tolerance on the Mk5 cockpit? I've brought that back from orbit without troubles (I think...).

[Jasmir]

Sometimes, some (non stock) parts are heatet to over 3000°C. Especialy Nuclearengines do so. But they don't explode. It's the neighbour part that explodes. Maybe you have an similar issue with a element next to your cockpit on reentry?

[BubbaWilkins]

Has anyone else noticed that the shields don't exactly work on other equipment?

I've got what seems like a very reasonable reentry descent--60 km to 40 km--on stuck the shield on the B9 Mk5 cockpit (roughly the normal 2.5m component size). So, upon reentry, it explodes catastrophically upon as soon as it starts to heat up at 33 km.

I played around with the multiplier in the CFG file (not convinced that actually does anything), changing it from 25 to 2, since reentry at a few times the temperature of the sun's surface may not be necessary. I repeated the exercise, and thought things were going as normal...until at about 29 km, when my heat shield was 60% depleted but at 1200 degrees. It exploded, and then so did the cockpit.

Strangely, I've done this same reentry (in fact, much more severe) with the generic Squad cockpit module, angled the same, and survived no problem. This mod seems to be all over the place though (I recently reinstalled it, hoping that it would ease up on the bugs, but instead just made it seem worse).

Anyone have any idea what might have caused this?

Just because the parts are the same size doesn't mean they have the same stats. I'm guessing you're exceeding the structural limits of the Mk5 cockpit utilizing it like that. The B9 stuff has different breaking values than the stock parts even if they have the same impact rating.

[Synthesis]

Sometimes, some (non stock) parts are heatet to over 3000°C. Especialy Nuclearengines do so. But they don't explode. It's the neighbour part that explodes. Maybe you have an similar issue with a element next to your cockpit on reentry?

That's entirely possible--I mean, the reentry section has four parts (Two radial parachutes, the shield, and the cockpit itself).

Most unusually, the failure report describes it as overheating, but I guess that shows up if it's a structural limit failure.

[Lexif]

Most unusually, the failure report describes it as overheating, but I guess that shows up if it's a structural limit failure.

No, if a part is destroyed because of the g-force limits, it should show up as such in the post-flight log.

[Metapher]

Or during flight if you press F3, right after the part exploded.

[aeroz]

Just installed this mod. It works great! Nicely done.

I haven't read through all the postings so someone may have made this comment already. My only concern is it's ability to interface with procedural wings. I saw that someone had commented about B9 Aerospace (which I also installed recently). All of those parts have a finite shape though. Procedural mods let you design the shape, so I'm unsure about the ability of the mod to accurately apply heating to the body. Just food for thought. I also haven't tried it yet to check, so my concern (however slight) may be entirely undue.

Regardless, this is a fantastic addition to KSP.

[BigNose]

Just installed this mod. It works great! Nicely done.

I haven't read through all the postings so someone may have made this comment already. My only concern is it's ability to interface with procedural wings. I saw that someone had commented about B9 Aerospace (which I also installed recently). All of those parts have a finite shape though. Procedural mods let you design the shape, so I'm unsure about the ability of the mod to accurately apply heating to the body. Just food for thought. I also haven't tried it yet to check, so my concern (however slight) may be entirely undue.

Regardless, this is a fantastic addition to KSP.

I use Deadly Reentry and Procedural Fairing&Wings since they were playable, and I never noticed any problems in heating or anything. The Fairing shield the payload from heating correctly and the wings break due to high-g-loads or excessive heating normally.

[aeroz]

Thanks for the verification. Like I said, I hadn't tested it yet, just crossed my mind.

[Specialist290]

I don't know about Procedural Wings, but Procedural Fairings tend to have pretty high heat tolerance. I'll sometimes use them as an aerobraking "shell" just in case my craft's weight isn't balanced like I thought it was. They don't have ablative shielding like the heat shields do, but they work well enough for my purposes.

[taniwha]

As a foreword, I do not disagree with the concept of acceleration damage. What I disagree with is DRE's implementation.

I've gotten a little tired of arguing that DRE's g-force damage is bogus and people trying to use Newton's three laws to prove that the g-force damage is not bogus, so I did up a diagram (by hand and scanned in. strokes inconsistent because I use a fude-pen).

(click for a larger version)

A bit of an explanation:

• The numbers started out as from-memory values for some parts, but the math produced unpleasant numbers, so the values were tweaked to avoid too many decimal places.
  
• Other than the 8.5t payload, both rockets are identical.
  
• All parts in the rocket have exactly the same acceleration. If they did not, the rocket would either pull apart or collapse in on itself. That is, a is the same for the rocket as a whole and each part of the rocket.
  
• Newton's second law (F=ma) is used for both the overall rocket acceleration (100m/s² and 50m/s²) and for calculating the force required to accelerate the parts of the rockets.
  
• The upward force at the bottom of each part is the force required to accelerate the part and all parts above it (ie, m is the sum of the masses of all parts above the arrow. For the engine, the force is the thrust of the engine.
  
• The downward force at the top of each part comes from Newton's third law, and thus is the same as the force on the part above, but in the opposite direction. For the top-most part, there is no mass above it (operating in a vacuum) and thus the force is 0kn.
  
• "accel" is the numeric difference (vector sum) of the two forces on the part and if divided by the mass of the part will give the correct acceleration.
  
• "compress" is the numeric sum (sum of force.displacement) of the two forces on the part and provides the stress experienced by the part. Lie on your back: fairly comfortable. Get someone who weighs the same as you to lie on you: not so comfortable.
  
• There is no such thing as "g-force". It is an illusion caused by Newton's first law. We feel like we are being pulled into the seat as the car accelerates, but really it is the seat being pushed into us. The skin of our cheeks is not being pulled back by anything, but rather it is being pulled forward by our noses.
  

So, on to why DRE's g-force damage is bogus (ignoring the illusory nature of g-force). All parts in the rocket to the left are experiencing lower forces (even looking at only the accel forces (except the engine)) than the same parts in the rocket to the right, less than half for the forces other than accel, despite the acceleration of the rocket on the left being twice that of the rocket on the right. Despite that, DRE will destroy the rocket on the left before it will destroy the rocket on the right. And yes, I have had DRE destroy rockets just because the TWR got too high as the fuel drained. If the part can't stand the forces with an empty tank above it, it should not be able to withstand the forces with a full tank above it.

For acceleration damage to not be bogus, the forces on the parts need to be calculated and compared with the strengths of the parts.

All that said, Kerbals should indeed have an upper limit based solely on acceleration: they are consistent in size so the limit is knowable (but still direction based). That humans can't survive high acceleration for long periods (without a lot of support) while machines can just goes to show how frail the human body is. But really, the problem is the pressure required to pump blood uphill (our hearts will struggle long before our bones will), thus blackouts and red-outs.

[edit]Shortly after posting, I thought of a point (against me, or so I thought) that needs addressing. Using the rocket on the left:

As the fuel tank (the 2.25t part) drains the acceleration of the rocket increases and the forces on the parts do indeed change, but rather interestingly. The last-moment acceleration of the ship (now 6.5t) is 130.8m/s². The forces between the probe body (0.25t part) and the tank rise from 25kN to 32.7kN. However, the forces between the tank and the engine (bottom part) decrease from 250kN to 65.4kN.

Despite the rocket's acceleration increasing, the overall stress on the part decreases. However, that's not to say that the increased forces between the probe body and tank can't cause local damage, but the increase is still significantly lower than the forces in the rocket to the right.

Edited September 7, 2013 by taniwha

[Torminator]

I would say the simplest case against purely acceleratory damage is that if you have a fuel tank with two mainsails on each end firing at full thrust inwards, that tank is going to be under massive stresses, but 0 acceleration.

That said, even if we assume g force damage is proper, it's a bit wonky in DRE. I had an entire spaceplane go poof because it hit a bump on the ground after landing. The landing gear didn't break, the entire plane went, quite literally, poof. I also got the periodic "burned up on reentry" right after loading the rocket for launch but BEFORE the physics kicked in.

[taniwha]

Torminator: indeed, that dual mainsail argument is a very strong one against DRE's pure acceleration implementation. Very similar to my 10kN-><-10KN quip in the FAR thread.

Even if only a very naive approximation was used, I would be happy so long as the damage to a part was based on the forces on the part (as a sum of F.r (r as a unit vector? anyway vector from part origin to force application point)).

[a.g.]

One problem here is that to my knowledge it is impossible to read back forces acting on joints from the unity physics engine. The only thing you can do is set the breaking force, for the familiar "structural failure at whatever" outcome if the acting force exceeds it.

A purely acceleration based model would be appropriate for internal damage to a part, i.e. crew being killed, poorly supported wires and pipes tearing off, that kind of thing. In this case you are looking at forces acting between the structural frame of the object and all the stuff inside it, so you can ignore all the stuff outside and just assume the structure accelerates.

[taniwha]

Yes, internal stuff will have simple limits (though varying based on what that stuff is). I would be much happier if DRE's g-force damage was reduced to kerbal deaths. Pretty much anything else worth simulating would have too high an acceleration limit.

[KerbMav]

So, the rocket as a whole accelerates at the same rate, but the parts have different values at which they break? Meaning it is only the (positive or negative) acceleration that causes damage in DR, no matter at which angle the rocket "hits" the air or what maneuvers it flies?

Does the stock game cause any damage during atmospheric reentry at all? I think to remember a hard Eve aerobraking maneuver that ripped my ship apart and I am quite sure I only had FAR installed and not yet DR.

Is there a way to keep the heat damage and the cool structural sounds in DR - but take out the g-force damage (by editing a cfg-file)?

Edited September 7, 2013 by KerbMav

[taniwha]

So, the rocket as a whole accelerates at the same rate, but the parts have different values at which they break? Meaning it is only the (positive or negative) acceleration that causes damage in DR, no matter at which angle the rocket "hits" the air or what maneuvers it flies?

Heh, no, that's not what I'm saying. I guess part of the problem is some context got lost: DRE throws out the m in F=ma when doing damage by comparing the current acceleration against a semi-arbitrary value (computed from impact tolerance, but that's not necessarily a good source, though not necessarily bad, either).

Does the stock game cause any damage during atmospheric reentry at all? I think to remember a hard Eve aerobraking maneuver that ripped my ship apart and I am quite sure I only had FAR installed and not yet DR.

If the drag causes parts to be pulled apart with sufficient force, then the joints will break, but no damage is done to the parts themselves (except solar panels).

Is there a way to keep the heat damage and the cool structural sounds in DR - but take out the g-force damage (by editing a cfg-file)?

Not that I've seen. I just simply disabled the g-force checks in my local copy of the code and rebuilt the dll. Having no damage is preferable to having bogus damage (IMO).

[InfinityArch]

So has this mod been abandoned, because I'm still having issues with parts occassionally exploding upon loading while in an atmosphere, particularly on Kerbin.

[KerbMav]

So has this mod been abandoned, because I'm still having issues with parts occassionally exploding upon loading while in an atmosphere, particularly on Kerbin.

Thats what popped my Eve probe?

[The Lone Wolfling]

Can the G-force damage be configurable/disable-able in the next version?

I've currently got a local copy with it disabled, but it is a mite tedious to have to recompile the code every time a new version comes out. Configuration files exist for a reason.