Reentry heating - are you kidding me?

[Agost]

Hi all,

I'm trying a bit the 1.0 before modding it, since I'm waiting for all mods I want to use to be compatible ( and I have some exams to do... )

I put 110% heating at the beginning of the career, hoping it was good enough, but I was wrong. Coming back to Kerbin at 3 km/s with a debris ( falling engine side ) and from 2000x10 km sub-orbital trajectory... nothing burning.

I'd like to have a real concern when I'm coming back from orbit, but I'd like to avoid DRE, since reentry heating is now stock. How can I make it more deadly? Put to 120% and edit settings in .cfg files/ debug menu? At which settings?

Thanks in advance

[Superfluous J]

Yes it is ridiculous. I recently returned to Kerbin at 6.3km/s and all I lost was 3 of my 4 solar panels. I had no heat shield or fairing or anything. Just a ship with all the parachutes stuck to the outside.

You can do 2 things:

1) Wait for 1.0.3. No guarantee it will balance it better, but that is - I believe - one of their goals.

2) Install DRE.

[Geschosskopf]

I advise caution before tweaking reentry heat settings based soley on experience operating in LKO/Mun/Minmus. Don't forget the need for interplanetary aerocaptures where speeds are WAY higher. These are quite dangerous already with stock/default settings. If you jack reentry heating up so that landing from LKO is dangerous, you might preclude yourself from doing any aerocapturing at all.

[John FX]

Myself I find reentry at kerbin very mild yet aerobraking or aerocapture at Eve or Jool very very hard. There seems to only be a band of around 5km where it is feasible yet I can slam into Kerbin almost without care.

This may be due to design, Kerbin is where all new players learn and an unforgiving heat model may put them off.

[Warzouz]

Yes, don't forget this is a game. New player's first Mun fly by is already hard enough.

Even though, I burnt a entire ship while aerobraking around Kerbin ; I made a peek into Kerbol SOI. It was a MK3 passenger return ship with airbrake and heatshield (no wings). I was just coming at a 3km/s and even bleed speed to 2500m/s after 3 pass.

My fault was to keep a retrograde orientation (unpowered). I think. I didn't had any problem since then.

[Geschosskopf]

Myself I find reentry at kerbin very mild yet aerobraking or aerocapture at Eve or Jool very very hard. There seems to only be a band of around 5km where it is feasible yet I can slam into Kerbin almost without care.

This may be due to design, Kerbin is where all new players learn and an unforgiving heat model may put them off.

I think the issues with other planets' atmospheres are unintended consequences. I suspect Squad focused almost entirely on Kerbin when doing the new aero stuff and tailored the new rules specifically for its conditions. Thus, applying those rules to planets with different gravity and atmosphere values gives strange results.

[RoverDude]

It's actually a balancing act - making Kerbin challenging without making Eve impossible, etc.

[Agost]

Well, I have a lot of exams to do, I can wait for 1.0.3 balancing

[Snark]

A side note, for the specific case of Jool: Consider doing your aerobraking on Laythe, rather than on Jool itself. (That is, do an aerobrake pass on Laythe in order to capture to Jool.)

Reasons this is friendlier:

- You won't be going as fast. Laythe is considerably higher up in Jool's gravity well than Jool's surface is, so you don't have as far to fall.

- Quite aside from matters of reentry heating: by aerobraking at Laythe instead of Jool, you'll wind up in a much less eccentric orbit (since your periapsis will be up at Laythe's orbit, rather than down at Jool's surface). This, in turn, means you'll need a lot less dV to rendezvous with the various moons.

[MokieMan]

I dont think the new reentry effects were intended to destroy your entire craft. unless you are traveling unprotected at anything above 3000 m/s.

but to instead destroy more important items such as science stuff or parachutes. meaning that your crew will most likely survive (unless you loose your parachutes) but all of that hard work and effort will be lost. Note: keep your parachutes safe by storing them in service bays.

[Superfluous J]

I dont think the new reentry effects were intended to destroy your entire craft. unless you are traveling unprotected at anything above 3000 m/s.

Sounds good to me. That's why this bugs me:

Yes it is ridiculous. I recently returned to Kerbin at 6.3km/s and all I lost was 3 of my 4 solar panels. I had no heat shield or fairing or anything. Just a ship with all the parachutes stuck to the outside.

[KyleofKerbin]

I don't exactly like the idea of stock re-entry up front, but once I start playing the game(especially without any mods) it doesn't really change much. I can come in from Mun at 1500 m/s and be cheese-grated, but coming in from a less than 1,000km flyby of Kerbol, going at speeds over 7000 m/s flattens my spacecraft like a goomba on the surface, yes, but re-entry doesn't do anything; if something does impact me, it's the aerodynamics. They blow off my solar panels, tear off my parachutes, and Kerbin's aerodynamics have even disassembled my craft going less than 1000 m/s, keeping in mind that I haven't seen flames in any of these occurrences.

[tutike2000]

Also, engines and everything attached inline with them seem to be immune to reentry heating.

Radially attached parts do explode much more often.

[Geschosskopf]

Also, engines and everything attached inline with them seem to be immune to reentry heating.

Radially attached parts do explode much more often.

It seems that rockets actually get hotter at the trailing end than the leading end. I seem to recall reading a while back that what happens is that the 1st part to hit the air heats the air, so anything radially attached further back on the ship gets normal reentry heat plus this preheated air. This yields the silly result that the radial parts away from where the actual heat is being generated and in the boundary layer that isn't moving as fast anyway, burn up before identical parts on the leading end of the ship that are facing the full brunt of the entry.

You can demonstrate this for yourself fairly easily. Make a tanker out of an orange tank with a Sr. docking port on the end that will hit the air first. Attach more Sr. docking ports radially to the orange tank near the middle or other end. The port on the end will survive a pass that burns off the radial ports.

[tater]

The problem is scale.

3000m/s? LOL. I tested kerbin up to about 12 km/s with a 20 km periapsis. Even at that velocity reentry is not troublesome. This is a situation that shows where realism is a better benchmark. Have a tiny system, with exaggerated gravity, and pulled from thin air atmospheric settings, and trying to balance things becomes impossible if a goal is for kerbin reentry to be even a little dangerous.

i will test using RSS tonight and see if at real scale reentry has some dangers. My thought is that the default orbital velocities are higher, and the time of reentry exposes the craft to longer heating.

Edited June 19, 2015 by tater

[justidutch]

Have you ever tried re-entry with large ships? Last night I exploded two different ones, using flight profiles I've successfully used with small landers. Both of these ships were coming from orbits of 190km, periapsis lowered to ~25km. Flames, then BOOM. It exists, it happens. But I wonder, maybe re-entry heating affects larger ships more than smaller ones?

[tater]

Maybe it's because I don't reenter anything that doesn't look like it shouldn't reenter. Actually, I recently tested a craft from another thread (a Mun lander, basically) that should have not made it, and it landed just fine.

[haltux]

Have a tiny system, with exaggerated gravity, and pulled from thin air atmospheric settings, and trying to balance things becomes impossible if a goal is for kerbin reentry to be even a little dangerous.

I don't see any balance issue when reentry is constantly too easy. Make all stuff fry at 30% lower temperature does not sound like a complex modification.

[tater]

I tend to agree, but people who expect to aerobrake at jool or eve in one pass would scream

[Superfluous J]

I don't see any balance issue when reentry is constantly too easy. Make all stuff fry at 30% lower temperature does not sound like a complex modification.

Then everybody will complain that their spaceplanes explode during orbital entry.

I wonder, though, how DRE managed it. None of these discussions occurred (to my knowledge) in that thread.

[tater]

I forgot about spaceplanes since I don't make them. Yeah, huge issue since they are in this regime far longer, and have lots of bits sticking out.

This is again why starting as realistically as possible is best since things that are hard in RL are hard. Generally speaking spaceplanes in ksp are too easy, but that's compared to earth, from fantasy mini-earth (kerbin) maybe it's ok.

[SAI Peregrinus]

Then everybody will complain that their spaceplanes explode during orbital entry.

I wonder, though, how DRE managed it. None of these discussions occurred (to my knowledge) in that thread.

In two ways:

First, most DRE users were FAR users. The combination of FAR aero (with nice occlusion) instead of the old souposphere + DRE meant that things balanced out reasonably if you just took a heat shield on everything.T

The second aspect is that DRE users are the kinds of people who willingly install a mod with the word "deadly" in its title. It made Kerbin re-entry mildly difficult, if it had made Eve re-entry easy THEN we'd have complained. Whereas with stock aerodynamics adding heating you've got a lot of the kind of people who don't want "deadly" in the title, so making anything without incredible care put into the construction/piloting blow up when entering Eve/Jool atmospheres is not the desired behavior.

[Geschosskopf]

I tend to agree, but people who expect to aerobrake at jool or eve in one pass would scream

Or Laythe for that matter, or returning to Kerbin from anywhere else. But those who have tried these things are already screaming with things as they are. Send a small probe and no real problem, provided you've got it in a fairing. But send a big ship and things get quite tricky. If you come in low enough (and "low" at Jool is in the vicinity of 190km, just 10km inside the atmosphere) to capture into the most elliptical orbit possible, you'll probably burn something up. So you pretty much have to plan on burning about 600-1000m/s for such ships to capture at Jool intact after just barely aerobraking at like 198km, depending on your arrival speed. I believe this is all because of fundamental flaws in both the heat system and the new aero system.

The new aero system, which I think was designed especially for Kerbin without much consideration of its effects elsewhere, is really weird in that atmospheric density is much greater, ridiculously so, at higher altitudes than it was pre-1.x. This is why all aerobraking altitudes are considerably higher than before for the same planets. I suspect this was done to remove the incentive for airhogging with SSTOs, along with jet thrust curves that make thrust suddenly die at about 25km even though there's still plenty of air. And also to reduce the amount of wing area required, so that drag would be low enough to get supersonic. But this has all sorts of strange effects on other planets. It essentially makes any substantial atmosphere nearly a brick wall at interplanetary speeds. In addition, it has made Duna's atmosphere totally friendly in all respect. Used to be, Duna's atmosphere was like Mars', aptly described as "too thin to be any use but too thick to ignore". Now it's the opposite. Thin enough to ignore if you so choose, but thick enough to be extremely helpful if you want it to be. Parachute landings are now totally easy on Duna, even at high ground elevations, with much less chute area than before. And you can fly airplanes there no problem at all, nearly as well as on Kerbin, when before this was extremely difficult. But at the same time, there's no heat to reentries at all, not even coming from Kerbin, and taking off requires less dV than before, just like on Kerbin.

Then there's the wrongness of the whole heat system. First and foremost is the fact that it has more massive objects heating up faster than lighter objects, which is back-asswards to reality. Second is the way the rear parts of the ship experience more heat than the front parts, which is also at odds with reality, so the longer the ship, the hotter it gets. And the bigger the ship, the faster it heats up. Thus, the odds are stacked against anything much bigger than a small probe.

All in all, the full silliness of the 1.0.2 system cannot be judged simply by how pods reenter from LKO. You have to see it all across the solar system to fully "appreciate" it.

The bottom line, however, is that nobody's happy. Some say it's too easy at Kerbin, other say it's too hard elsewhere, and a few say it makes Duna the easiest place ever. Making things harder at Kerbin will necessarily make things impossible elsewhere (or when returning to Kerbin). Making things easier at other planets (or returning to Kerbin) will make things at Kerbin super-easy. I think that's a pretty good indication that both the heat and aero systems need to be rebuilt from the ground up because arguably it's currently broken everywhere in the solar system. Individual users can't alter settings to make 1 place more to their liking without making everything else worse. I hope that some of the working being done for 1.0.3 is aimed at this.

[SignalCorps]

That picture you have of that horrendous rock with wings and a crazy-ass kerbal on top...please tell me you made that, and it actually is flyable.

[Crzyrndm]

The new aero system, which I think was designed especially for Kerbin without much consideration of its effects elsewhere, is really weird in that atmospheric density is much greater, ridiculously so, at higher altitudes than it was pre-1.x. This is why all aerobraking altitudes are considerably higher than before for the same planets. I suspect this was done to remove the incentive for airhogging with SSTOs, along with jet thrust curves that make thrust suddenly die at about 25km even though there's still plenty of air...

...Then there's the wrongness of the whole heat system. First and foremost is the fact that it has more massive objects heating up faster than lighter objects

IIRC there was a thread around showing that atmospheric density with 1.0 was actually lower in the upper atmosphere than it was prior. Atmospheric drag being different shouldn't surprise anyone given the entirely new system that doesn't just assume a coefficient of 0.2 for everything.

The decreasing thrust at altitude is to my knowledge approximating atleast two things. The decreasing mass flow rate and the change in compressor efficiency. Combustion engines can't run on the extremely thin air in the upper atmosphere so it needs to be run through a compression stage first to bring it into operational densities. That compressor is going to have a limit past which it can't do it's job effectively enough to feed the engine even if the total flow would be high enough.

Larger objects heating up faster is actually somewhat to be expected. Larger objects generally experience a lesser drag force per unit mass (mass is ~cubic with size while frontal area is ~size squared) leading to them decelerating slower and carrying greater speed into the denser parts of the atmosphere. Heating rate is most likely proportional to atleast speed² if not a higher power, so even a slight increase in speed would have a dramatic impact on the generation of thermal energy. Focus that into only a couple of parts that receive the brunt of the airflow and you get more explosions with the heavier vessel