"I'm burning through the sky, yeah!" (atmosphere thoughts)

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Greetings fellow Kerbals!

I'm burning through the sky yeah!
Two hundred degrees, That's why they call me Mister Fahrenheit 

I do not know if this is just a rant or a question... :confused:

I was just fiddling with my kOS scripts, which are mostly adapted from the mission toolkit ( ...  yes I have tried for a long time... this one are just much better than mine). It brings me to the conclusion that our atmosphere is still a little bit ... soupy or just hot .. I got the most dV left at the end (100k AP/PE  0.35% discrepancy) when I targeted the end of the grav-turn at 28km (below that point things getting too hot there) .. which feels nice, but it looks horrible during ascent. 



I have tried to change many parameters during the ascent, but all parameters which provides  an ascent, which doesn't looks like a torch being shot in the sky, left me with less dV and less discrepancy to the targeted AP/PE in space..

So do I have just to accept it, that our atmosphere is something special, or are the visuals just to important? 

(here some original lyrics.... ) 



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The atmosphere isnt soupy, it just ionizes very easily.


The issue is that Kerbin is tiny but has a huge atmosphere.


Orbital velocity is 1/4 Earths, but the atmosphere is 4/5.  Really plasma effects wouldn't happen at these speeds, but they are forced in so that you get them on the way down.

Following an optimal path put you at near Kerbin orbital velocity quite low, where as on Earth you would still have a lot of burning to do

Just ignore unless your ship is melting.

Edited by Rhomphaia

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12 hours ago, WeirdCulture said:

So do I have just to accept it, that our atmosphere is something special, or are the visuals just to important? 

It's just like @Rhomphaia says. A rocket on Earth will naturally end up much higher up in an ideal gravity turn, because if it turned over as hard as rockets in KSP can, it would fall out of the sky long before obtaining enough sideways velocity. The only reason you can even target the end of your gravity turn at 28km in KSP and survive is because Kerbin is so tiny and lets you get away with a much smaller amount of sideways velocity. And the only reason you're on fire at that point is because the atmosphere is not quite as tiny as the planet itself. If it was, flying planes wouldn't be much fun.

If you're interested in verifying this, you can actually do so relatively easily. Just download Sigma Dimensions, and try some of the following:

- Enter a 0.2x multiplier for atmosphere scaling. That'll make the atmosphere around 14 kilometers thick, which is comparable to Earth's atmosphere downsized to Kerbin's level. You should now no longer be on fire during ascent, even if the smaller atmosphere lets you target your gravity turn even lower.
- Enter a 2.0x multiplier for atmosphere scaling, and a 11x multiplier for size scaling. This will make Kerbin as large as Earth, and extend the atmosphere to 140km. These are, IIRC, roughly the values that Realism Overhaul is using (though they also edit a whole lot more than just that!). If you launch a rocket here (remember, > 9km/s dV required to orbit), you'll find that even with engines putting out 4 to 5 g of acceleration at stage burnout, you must target your gravity turn so high up that you don't get a flame sheath on ascent either.
- Enter a 1.0x multiplier for atmosphere scaling, and a 2.0x multiplier for size scaling. That'll create a situation where Kerbin's atmosphere is at 70km as normal, but your required sideways velocity is 50% higher than before. Wonder what happens here?

In case 3, you're probably still going to get some flames. The atmosphere is still oversized in respect to Kerbin, meaning you will spend a larger portion of the ascent inside it than you would on Earth. And because you're accelerating towards 3300 m/s instead of 2200 m/s, there's plenty of plasma sheath potential. This is where we get into the area where KSP fudges its physics in favor of gameplay.

As mentioned before, at the low velocities in stock KSP, you'd barely ever see a plasma sheath at all (only on aggressive interplanetary aerobraking at Jool, perhaps). So KSP has multipliers in place that pretend that, for the purposes of drawing the plasma sheath, the velocity you are going at is quite a bit higher than it actually is.

In your KSP root directory, find physics.cfg and open it. Near the top, you'll see the physics constants used for aeroFX (which is both condensation/mach effects and plasma/reentry effects). Find 'AeroFXVelocityExponent'. This number, defaulting to 3.5 in stock KSP, is the physics fudging factor that makes plasma effects show up at much lower speeds than natural. For example, if you set this value to 3.0 instead, you will find that a standard LKO reentry on stock Kerbin (100km AP, 0km PE) does not produce any flames at all (though the craft still heats up as normal). In my setting up my latest play instance, I found that putting it at about 3.33 was suitable for a 2x sized Kerbin.

While you're at it, you can also play with 'AeroFXDensityFadeStart', which controls how close to the edge of the atmosphere you can get plasma effects. In stock KSP on a normal reentry they start at about 51km, which I found to be a little low. So I tweaked it to be around 56km instead. It's really up to individual taste, and has a lot to do with how you set the velocity exponent. And then there is 'AeroFXStartThermalFX' and 'AeroFXFullThermalFX', which are the mach numbers at which condensation effects start/finish transforming into plasma effects. If you increase these mach numbers, you will see more white effects during ascent, and less red ones. Of course, you'll also see the plasma sheath fade sooner during reentry as well... I went with 3.0 and 4.5 here, to account for the higher speeds on my upscaled Kerbin.

Hope that provides some insight :)

Edited by Streetwind

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In the options menu I have atmosphere effects slider at the minimum. Fixes things for me. 

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