[1.3.1] Ferram Aerospace Research: v0.15.9.1 "Liepmann" 4/2/18

[Sokar408]

45 degree entry is really steep. So that seems about right. Remember that the steeper the entry the lower total heat (peak heat may be higher but the time spent heating is more important), but the higher g forces become.

This is not true. You don't get less heat, more G. You get more heat and more G. This is because the TOTAL amount of energy that needs to be removed going from orbital speeds to standing on the ground speed, is constant, regardless of how fast or slow you're descent.

However going in steep means that all that energy needs, and will, be dissipated much faster, thus higher temperatures are reached, and the same goes for G-force. This is why shallow reentries are better, both for G-force, and temps, as a shallow entry allows you dissipate the over a longer period. Also ablator only gets used after you get to a certain temperature, so in theory, with enough shallow passes, you should be able to get the pod down without losing any ablator at all.

tl:dr Steep angle = Higher G-forces, AND higher temps

[futrtrubl]

This is not true. You don't get less heat, more G. You get more heat and more G. This is because the TOTAL amount of energy that needs to be removed going from orbital speeds to standing on the ground speed, is constant, regardless of how fast or slow you're descent.

However going in steep means that all that energy needs, and will, be dissipated much faster, thus higher temperatures are reached, and the same goes for G-force. This is why shallow reentries are better, both for G-force, and temps, as a shallow entry allows you dissipate the over a longer period. Also ablator only gets used after you get to a certain temperature, so in theory, with enough shallow passes, you should be able to get the pod down without losing any ablator at all.

tl:dr Steep angle = Higher G-forces, AND higher temps

That is incorrect. As I said, peak heat does increase, but total absorbed heat decreases. This is why reentry corridors are narrow, too shallow and you cook, too steep and you squish. BRB, getting sources.

Edit: ok http://www.slideshare.net/IngesAerospace/space-vehicle-design-6-atmospheric-entry-10879586 page 299, second paragraph after definition of units and onwards. Figure 6.11 on page 307 shows this very well.

Edited May 17, 2015 by futrtrubl

[ferram4]

Alright, so first point:

Memory "leaks": Some additional memory will be allocated over time as you need more voxel chunks. This is not a leak, this is on purpose, and those chunks will still be used. The memory is allocated and not released because otherwise you'd all be complaining about hitching during voxelization because of the garbage collector. All of my tests indicate that the only memory leak I can find is a steady 10-20MB leak every editor -> flight -> editor cycle, which can be reproduced using a purely stock game. In addition, maximum memory usage of chunks on a FAR-default-settings install is capped at ~63 MB total, ever. If you're leaking above that, it's not me, it's the stock game.

Second, yes, I just heard about the save file madness, I'll fix that. This is what I get for trying to fix save settings by doing something that I thought was safe. Did you know that forcing the game to save on scene changes actually causes bad things to happen?

@DuxDucisHodiernus: I haven't gotten to it because, though you may not have noticed, other people using the mod are having complete and utter gamebreaking issues. These are higher priority than your issue right now, and continuing to report the issue doesn't make it higher priority. It will be fixed, but nagging doesn't speed it up; in fact, it makes me take my time so as to not reward such nagging.

Edit: on heatshield testing with the Mk1 pod; a hop up to 800 km that reentered at about 2.5 km/s at a 45 degree angle burned off 60 ablator from the shield and heated up the pod itself somewhat substantially. Given how tall the pod is and the small size of the shield, this seems about right for a hyper-aggressive reentry to me. My previous tests were using the 3-man pod with a higher velocity, but much more shallow reentry.

Edited May 17, 2015 by ferram4

[Ser]

ferram4, I'm reposting here from Deadly Reentry thread:

It's definitely FAR. All the issues are coming from Conv Flux parameter. I've made some tests and had the same issues of plasma "jumping" over shields and everything to the parts that must be covered from it thus rising the Conv Flux factor in some misterious way. I have removed DRE and tried FAR with stock reentry and problem persisted. Once I removed FAR and kept DRE, everything was obscured from heating like it should: while having parts in a good cover Conv Flux dropped to 0 for them. So I'm sure the issues has been caused by FAR's voxel model somehow.

Looks like for long vessels reententring with FAR the heat is able to get around shields and affect parts behind them. I'm still not sure if that's wrong, but if it's right then we have no way to solve that besides tuning debug settings for heating physics to relax them.

If I go on reentry with that LV-T30 pointing forward, then the fuel tank receives much of the Conv Flux heating factor despite it's obscured by the engine from the flow. After it collapses, the next are the material bays, especially the one closest to the front despite it is obscured by the shield, service bay and decoupler from the flow. Not much changes if I flip the vessel around.

Without FAR all the parts that are obscured by anything immediately become safe from Conv Flux.

What do you think of this?

Edited May 17, 2015 by Ser

[ferram4]

I think that sounds perfectly reasonable. There is a good reason why reentry vehicles aren't super-tall. It's because the heat flux can get around the sides of it.

Probably what's happening is that those parts are wider than the heat shield, which helps get them more heating. This seems like an excellent accidental feature to me, to be perfectly honest.

[Ser]

There's some other concerns in DRE thread for example for parachuttes burning behind a crew pod.

So what's the solution? Only to have a bigger shield? Don't think that solves the problem as heat gets around anyway.

Edited May 17, 2015 by Ser

[ferram4]

No, wait, I just tried it with a much large heat shield and it didn't protect it. Alright, I'll look into that more. Probably something wrong in me setting areas for heating because the heating code has the most confusing area names I have ever seen and doesn't make a whole lot of sense in how it's laid out and what does what.

[jab136]

question related to FAR and RealChutes, with the new stuff that FAR added, how does it interact with RealChutes, and is it nescessary if I have RealChutes, I am trying to minimize memory as I have a crapton of mods and am trying to figure out what I don't need. thanks

[Ser]

ferram4, One more thing I've noticed: the Conv Flux for the fuel tank is 2 times higher than for the engine in front of it despite the exp. area is exactly the same.

[ferram4]

@jab136: It simply includes it's own super-light version of RealChute to replace the stock behavior that FAR basically nuked out of existence. It'll play fine with RealCHute, but you don't need it.

@Ser: Yeah, and I found the issue. This is what happens when I don't bother transforming the part's orientation wrt the airflow properly for the stock heating. Derp. Fixed on master, along with the save issue.

[B15HOP_xmen]

I think that sounds perfectly reasonable. There is a good reason why reentry vehicles aren't super-tall. It's because the heat flux can get around the sides of it.

Probably what's happening is that those parts are wider than the heat shield, which helps get them more heating. This seems like an excellent accidental feature to me, to be perfectly honest.

What about people like me who build huge 200 tonn craft.

[Ser]

ferram4, thanks. You're fast like a meteor.

[werk62]

Thanks for the quick reply on my post about debug options not saving between game sessions! Unfortunately the new update made it worse, and now I have to set the options every flight Here is my ksp.log file. I cut out 24,768 lines of part and addon loading to help make it more digestible. https://drive.google.com/file/d/0BzmXDSSKR2fsbHZBUjFnOVlYVEU/view?usp=sharing

No rush though, this is not a very important bug. I understand you have a lot more on your plate to deal with

[jab136]

thanks ferram4

[kcs123]

Plenty of stock bugs are still present in game that cause those memory leaking and it is hard to pinpoint exact reason for memory leaks is it from mod or from stock game.

Good to know that is not FAR fault afterall.

Until SQUAD release more stable verion of KSP only thing you can do is to monitor used memory and save game before it CTD.

Thanks for quick fix on save issue, I will give it a try to see if there is anything else troublesome.

[MatterBeam]

Thanks for the quick reply on my post about debug options not saving between game sessions! Unfortunately the new update made it worse, and now I have to set the options every flight Here is my ksp.log file. I cut out 24,768 lines of part and addon loading to help make it more digestible. https://drive.google.com/file/d/0BzmXDSSKR2fsbHZBUjFnOVlYVEU/view?usp=sharing

No rush though, this is not a very important bug. I understand you have a lot more on your plate to deal with

Can you explain what you did for us plebs?

[BudgetHedgehog]

What about people like me who build huge 200 tonn craft.

A, why are you re-entering 200 ton crafts and B, if you are doing that, re-enter very gradually.

[werk62]

Can you explain what you did for us plebs?

What would you like explained?

[MatterBeam]

What would you like explained?

In fewer, simpler, words, if I should install the file you posted

[werk62]

Oh, no this isn't a fix lol. I just gave ferram4 my log file so he could try to fix the bug. I'm just as much of a pleb as you are haha.

[Kitspace]

As promised an example of the strange airspeed behaviour.

There are no special reproduction steps.

This kind of thing is observed constantly.

It does not seem to depend on anything.

Just an image of the airplane.

http://postimg.org/image/4e9bxnah5/

Standing on the ground with brakes set.

http://s18.postimg.org/b40oqaktl/image.png

Just taxiing along the runway at constant speed.

http://s28.postimg.org/n1kffcgdp/image.png

http://s11.postimg.org/me9r6c2mb/image.png

http://postimg.org/image/6iklo4t81/

Fast cruising over the ocean.

Sorry for the time between the screenshots but I needed some time to save them during which the plane was unattended and fluctated somewhat.

I think the speed and altitude are stable enough.

http://s24.postimg.org/4lxaetlj9/image.png

http://s7.postimg.org/ozg7f62az/image.png

http://s2.postimg.org/r3qdz4h55/image.png

Taking into account that the atmosphere is thinner than the real life the altitude could be considered even higher than it is.

If that would help this anyhow I can provide some realistic data from real life examples in similar flight conditions.

Thank you.

Edited May 17, 2015 by Kitspace

[futrtrubl]

What about people like me who build huge 200 tonn craft.

Then you have 3 options.

a. Don't build 200 ton craft.

b. Disable reentry heating.

c. Build your 200 ton craft in such a way that it can survive reentry heating. Which is difficult and requires a lot of drag and shielding.

[blub01]

I'd like to use FAR's better aerodynamics model, but my knowledge about aerodynamics is.. limited to say at best. is there a guide explaining how it works somewhere?

[Sokar408]

That is incorrect. As I said, peak heat does increase, but total absorbed heat decreases. This is why reentry corridors are narrow, too shallow and you cook, too steep and you squish. BRB, getting sources.

Edit: ok http://www.slideshare.net/IngesAerospace/space-vehicle-design-6-atmospheric-entry-10879586 page 299, second paragraph after definition of units and onwards. Figure 6.11 on page 307 shows this very well.

Just looking at that makes my head spin. Are you sure the total heat absorbed isn't that of the craft in total. Because I have not been talking about heat absorption, I have been talking about ablator used, and the higher the temps, the more ablator will be used, as natural convection isn't enough to lose the heat to the atmosphere. Thus bringing me back to, shallow angle = less ablator used, as the over all temps are lower, and more heat is lost to the atmosphere instead of the ablator, where as steep angle = more ablator, as the temps are higher, and less of it gets to be dissipated in the atmosphere, and those more needs to be dissipated through the ablator.

If what I'm saying is still wrong, then something very fundamental is wrong with my understand of physics (I will admit, its very rudimentary, so this is very likely), and doesn't explain how going in at shallow angles = less ablator used, and steep angles = more ablator used.

[mockingking]

I'd like to use FAR's better aerodynamics model, but my knowledge about aerodynamics is.. limited to say at best. is there a guide explaining how it works somewhere?

This, please. My stubbornness will only take me so far.