KSP atmosphere density gradient?

[The_Rocketeer]

Are atmosphere densities in KSP linear (atmo density directly proportional to altitude) or are there bands of sudden thickening as in Earth's atmosphere?

If the latter, is there anywhere I can find graphs plotting atmosphere density against altitude for the various atmospheres of KSP?

p.s. I know I could find this out by exporting barometric data but I'm feeling lazy...

Edited October 24, 2014 by The_Rocketeer

[Starman4308]

Are atmosphere densities in KSP linear (atmo density directly proportional to altitude) or are there bands of sudden thickening as in Earth's atmosphere?

If the latter, is there anywhere I can find graphs plotting atmosphere density against altitude for the various atmospheres of KSP?

p.s. I know I could find this out by exporting barometric data but I'm feeling lazy...

There is a wiki, you know.

[DeMatt]

As I understand it, pressure (and therefore density) is exponentially related to height. The wiki has the following formula for Kerbin's atmosphere:

P = (1 atmosphere) * e ^ (-altitude / 5000)

[Red Iron Crown]

It uses a scale height calculation, so it's exponential in nature.

Are atmosphere densities in KSP linear (atmo density directly proportional to altitude) or are there bands of sudden thickening as in Earth's atmosphere?

What do you mean by bands of sudden thickening in Earth's atmosphere?

[capi3101]

Kerbin's atmospheric pressure decreases exponentially with height, just like Earth's. In fact the profile is almost exactly like Earth's, assuming the mesopause is the "top" of the atmosphere at 70 kilometers. DeMatt's given you the formula for calculating Kerbin's atmospheric pressure with height; you can generate a graph with that in a program like MS Excel or OpenOffice Calc.

[Jovus]

There are thermoclines and pressure equipotentials in Earth's atmo because it's not an ideal fluid. So no, KSP's atmo is not just like Earth's. (Not that I'm complaining. Simplifying assumptions that don't do violence to the underlying truth make the game run faster and are easier to play.)

[cantab]

Neither, it's an exponential decay.

While Earth's atmosphere has complicated details, I'm pretty sure that on a gross level it also exponentially decays.

[capi3101]

There are thermoclines and pressure equipotentials in Earth's atmo because it's not an ideal fluid. So no, KSP's atmo is not just like Earth's. (Not that I'm complaining. Simplifying assumptions that don't do violence to the underlying truth make the game run faster and are easier to play.)

I meant in regard to the pressure profile; the programmers have used the notion of "ideal atmosphere" in that regard. Kerbin doesn't have weather in the stock game (obviously) and that's probably a good thing - you'd wind up with a bunch of complications that wouldn't add much to gameplay (besides frustration, I mean). Though trying to land a spaceplane in the middle of a severe thunderstorm with 50 knots of wind shear might be interesting to try once or twice.

[The_Rocketeer]

Thanks for your answers.

Yes I know there's a wiki. There's also a community.

[bakanando]

You get the first non-zero reading with the barometer at about 48km. IIRC ISP won't get lower until about 36km(going down). At 22-23km you get the 0.01 of the parachutes. At 18km the LV-N nuclear engine is at ISP 780+.

[The_Rocketeer]

What do you mean by bands of sudden thickening in Earth's atmosphere?

This pretty much sums up what I'm getting at:

There are thermoclines and pressure equipotentials in Earth's atmo because it's not an ideal fluid.

[NathanKell]

If you are using FAR, then density is calculated based off pressure, temperature, and gas constants. If you click ABS in the main FAR window, it will switch from relative to absolute density (in kg/m^3).

If you are using stock, density always equals pressure_in_atmospheres * 1.22231 (or pressure in pascals divided by 82843.125). Pressure, in FAR and in stock, can be computed in pascals as 101325 * e^(-height_in_km / 5), with it clamped to 0 when e^(-height_in_km / 5) == 0.00001.

[Nuke]

There are thermoclines and pressure equipotentials in Earth's atmo because it's not an ideal fluid. So no, KSP's atmo is not just like Earth's. (Not that I'm complaining. Simplifying assumptions that don't do violence to the underlying truth make the game run faster and are easier to play.)

yea thats why we have the standard atmosphere:

http://en.wikipedia.org/wiki/International_Standard_Atmosphere

this is what i used in my simulator (and models exist for mars, venus, etc). however since the part that matters for drag/lift calculations (pressure) its a pretty simple curve that can be approximated by a simple function, it can be used instead. temperature vs altitude is a less simple curve, but unless you want to simulate heating and cooling of objects at different altitudes with any precision you can exclude it from your calculations.

Edited October 25, 2014 by Nuke