Atmospheric density/pressure graphs for 1.05

[KerikBalm]

Its been a long time now that the atmosphere of Kerbin hasn't followed a simple scale height equation.
In this last update, they made further changes to the atmospheres of multiple bodies.
In particular, Laythe and Duna have had even their surface pressure changed quite significantly: Laythe's atmosphere is only 75% of what it used to be at the surface, and Dunas is a mere 33% of what it used to be at the surface.

Yet... I just hyperedited a craft to Laythe, and surprisingly, my SSTO overheated after going full throttle from an altitude where it could go full throttle on Kerbin... which surprised me, because an altitude on laythe should correspond to a much higher altitude on kerbin.

On top of that, I noticed my rapiers kept producing thrust well above 30 km on Laythe... above 35km even... whch doesn't happen on kerbin.

It seems at ~30 -38 km the atmosphere of laythe is denser than the atmosphere of kerbin at 30-38km

I'd really like to see a graph of atmospheric pressure vs altitude for these bodies... I'm quite confused as to what exactly the atmospheres are like now.

[Starhawk]

The change to Laythe's atmo was made back in 1.0 IIRC.

Happy landings!

[KerikBalm]

Well, the Duna change is new...
I had sent a probe to Laythe in 1.0-1.04... but it was in career, and the probe is still on its way as I was doing other stuff in the meantime... like setting up my duna base, and I know the Duna atmosphere wasnt a mere 6% of kerbins.

By the way, do you know what game file specifies these things?
I've heard there was a file that even specifies the average molecular weight of the atmosphere's gas... but I can't seem to find it

[Starhawk]

Yeah, the Duna change is brand new. I haven't had a chance to check out the new Duna atmo for myself yet.

Laythe's atmo has a very different pressure curve than Kerbin's.

Unfortunately, I'm not sure where that data is stored. I was just wondering that myself.

Happy landings!

[monophonic]

[quote name='KerikBalm']By the way, do you know what game file specifies these things?
I've heard there was a file that even specifies the average molecular weight of the atmosphere's gas... but I can't seem to find it[/QUOTE]

[CODE]
~/KSP_linux$ grep -r -l Laythe *
GameData/Squad/Resources/Ore.cfg
GameData/Squad/Resources/ScienceDefs.cfg
KSP_Data/sharedassets0.assets
Launcher_Data/settings.cfg.bak
readme.txt
settings.cfg
settings.cfg~
~/KSP_linux$ file KSP_Data/sharedassets0.assets
KSP_Data/sharedassets0.assets: data
[/CODE]
The KSP_Data/sharedassets0.assets looks like the main suspect. It seems to be in some kind of Unity proprietary format. Strings bring out all sorts of interesting stuff from it, but strangely no "Laythe" even though grep finds the file with that word. 4.6.4f1 looks like the Unity version in case you feel like trying to find the tools to examine the contents.

[OhioBob]

There are tables in the Wiki that give pressure vs. altitude (which has been updated for 1.0.5). At[FONT=Calibri][SIZE=3][COLOR=#000000] 30 km the pressures on Kerbin and Laythe are 401 Pa and 1507 Pa respectively. [/COLOR][/SIZE][SIZE=3][COLOR=#000000]Laythe is also colder, so that will make the air even denser. [/COLOR][/SIZE][SIZE=3][COLOR=#000000]Both have the same molecular weight, so that’s not a factor.[/COLOR][/SIZE][/FONT]

[URL]http://wiki.kerbalspaceprogram.com/wiki/Kerbin[/URL]
[U][COLOR=#0066cc][URL]http://wiki.kerbalspaceprogram.com/wiki/Eve[/URL]
[/COLOR][/U][URL]http://wiki.kerbalspaceprogram.com/wiki/Duna[/URL]
[U][COLOR=#0066cc][URL]http://wiki.kerbalspaceprogram.com/wiki/Laythe[/URL]

[/COLOR][/U]

[Kerbart]

Sad face.

So here's an opportunity to actually go out and do some REAL SCIENCE. Equip a ship with a barometer, make it travel through the atmosphere (either rocket powered or by parachute) and make readings.

FOR SCIENCE!

[KerikBalm]

actually, before i saw ohiobob's post, I did just that for duna... a lot of the stuff on the wiki is out of date, it still says you need over 10km/sec of dV to lift off from Eve sea level for instance, the atmosphere graph hasn't changed. The chart with numbers... is that for 1.0 or 1.02 or 1.04 or 1.05? I can't tell

I didn't get around to doing it on Laythe because my spaceplane for laythe I had been toying with had the barometer in a service bay, and it tended to have contents overheat if opened during many parts of a reentry/ascent.

[img]http://i.imgur.com/dGz5JHr.png[/img]

[img]http://i.imgur.com/qgJiMHc.png[/img]

Log scaled:
[img]http://i.imgur.com/f1lvj2I.png[/img]

My raw data:
50km = atmo start
40km = 0.0049
35km = 0.0152
30km = 0.0326
25km = 0.0925
20km = 0.2432
15km = 0.7111
10km = 1.7875
7.5km = 2.6728
5km = 3.7889
2.5km = 5.1378
0.75km = 6.2393
0.5km = 6.4072
0.0km = 6.6667


Ok, using the wiki data:
[img]http://i.imgur.com/IQrDY6X.png[/img] Edited November 17, 2015 by KerikBalm

[OhioBob]

[COLOR=#222222][FONT=Verdana][quote name='KerikBalm']The chart with numbers... is that for 1.0 or 1.02 or 1.04 or 1.05? I can't tell.[/QUOTE]

The tables that give pressure at varies altitudes is up to date for version 1.0.5 (I just edited it a couple days ago). The numbers are based off the curves used to compute pressure within the game, so they should be spot on accurate.[/FONT][/COLOR]

[OhioBob]

[quote name='KerikBalm']...[COLOR=#3e3e3e][FONT=Verdana] and Dunas is a mere 33% of what it used to be at the surface.[/FONT][/COLOR][/QUOTE]
[FONT=Verdana][COLOR=#000000]This is true, but the molecular weight of the gas has tripled, so the air density is the same as before. [/COLOR][COLOR=#000000]For some reason the old atmosphere had a molecular weight of 14, which didn’t make any sense for such a small planet.[/COLOR][COLOR=#000000] It is now 42, but with 1/3 the air pressure. [/COLOR][COLOR=#000000]With the same air density, lift and drag should be unchanged.
[/COLOR][COLOR=#000000]
[/COLOR][/FONT][COLOR=#222222][FONT=Verdana][quote name='KerikBalm']By the way, do you know what game file specifies these things?
I've heard there was a file that even specifies the average molecular weight of the atmosphere's gas... but I can't seem to find it[/QUOTE]

There is a file that contains this data but, unfortunately, it is not readable as a separate config file.[/FONT][/COLOR]

[KerikBalm]

Curious... the MW of Eve's atmosphere is 43 according to the wiki, so it is more than 5x as dese as kerbins atmosphere at the surface now, right?
Many of the aerodynamic calculations actually account for atmospheric density, rather than simply pressure, as in older versions, correct?

[OhioBob]

[COLOR=#222222][FONT=Verdana][quote name='KerikBalm']Curious... the MW of Eve's atmosphere is 43 according to the wiki, so it is more than 5x as dese as kerbins atmosphere at the surface now, right?[/QUOTE]

Don’t forget that Eve is hotter too. Density is given by the formula,

ρ = (PM)/(RT)

where ρ is density (kg/m[SUP]3[/SUP]), P is pressure (Pa), M is molecular weight (kg/kmol), R is the universal gas constant (8314.4621 J/kmol-K), and T is temperature (K).

Kerbin’s air pressure at sea level is 101325 Pa, the molecular weight of its air is 28.9644 kg/kmol, and its globally averaged temperature at sea level is about 287 K. Therefore,
[/FONT][/COLOR]
[COLOR=#222222][FONT=Verdana]ρ = (101325*28.9644)/(8314.4621*287) = 1.230 kg/m[SUP]3[/SUP]

Eve’s air pressure at sea level is 506625 Pa, the molecular weight of its air is 43 kg/kmol, and its globally averaged temperature at sea level is about 408 K. Therefore,[/FONT][/COLOR]
[COLOR=#222222][FONT=Verdana]
ρ = (506625*43/(8314.4621*408) = 6.422 kg/m[SUP]3[/SUP][/FONT][/COLOR]

[COLOR=#222222][FONT=Verdana]
[quote name='KerikBalm']Many of the aerodynamic calculations actually account for atmospheric density, rather than simply pressure, as in older versions, correct?[/QUOTE]

[/FONT][/COLOR][FONT=Verdana][COLOR=#000000]The aerodynamics forces of drag and lift are a function of density, not pressure.[/COLOR][COLOR=#000000] Through pressure does effect things such as the thrust of an engine.[/COLOR][/FONT]