How to find the altitude from a given atmospheric pressure?

[AlmightyR]

I know how to convert a given altitude into it's Kerbin's atmospheric-pressure value, thanks to the wiki's pages on Atmosphere mechanics and Kerbin.

I want to know how to do the reverse; How can I convert a given atmospheric pressure to an altitude value?

[EDIT:]

Answer: For Kerbin, multiply the Natural Logarithm of the Pressure by the Atmospheric Scale, with one of those values (the result of the Logarithm, or the Atmospheric Scale) negated (reversed signal); The result is the Altitude of that specific pressure.

Thanks to Razor235, SnappingTurtle and UmbralRaptor. You guys are awesome!

Edited August 18, 2013 by AlmightyR
Question is answered.

[Razor235]

Fill in all the variables that you know, including the value for p, and solve for H.

Edited August 18, 2013 by Razor235

[SnappingTurtle]

Reversing the equation in Kerbin's wiki gives:

-5000 * ln(pk) = altitude

[UmbralRaptor]

You can take the pressure equation and solve for altitude.

On Kerbin: -ln(pressure)*scale_height

On other bodies: -ln(pressue/datum_pressure)*scale_height

[AlmightyR]

Sorry for me being a math's dummy, but what operation does the "In()" mean exactly? I tried Google'ing "math in()" and such, but it returns all sorts of unrelated trash.

[SnappingTurtle]

LN, the natural logarithm. AKA log subscript e.

[AlmightyR]

Oh, I know that from Java programming as "Log()", not "Ln()"...Now that I actually Google'd Natural Logarithm, I finally noticed the scientific notation is different!

Well, there is only one thing better than learning something: Learning more than just one something!

Question is answered!

Thanks a lot guys! It's nice to see KSP's community being as awesome as ever!

One (two) extra question(s) for @UmbralRaptor:

What is "datum_pressure" and how can I find it's value?

Edited August 19, 2013 by AlmightyR

[SnappingTurtle]

log is log base 10 which is distinct from ln or log base e.

[AlmightyR]

log is log base 10 which is distinct from ln or log base e.

In programming, or at least in the Java programming language, Log() is a function that returns the Natural Logarithm (Base e).

[UmbralRaptor]

In()

Ln()

I've seen log() used for both base 10 and base e logs, but it seemed like it was more commonly used for base 10...

What is "datum_pressure" and how can I find it's value?

The pressure at datum (that is, 0) altitude. On planets/moons with water, this is sealevel. The values are on the KSP wiki.

[AlmightyR]

Fixed that "In" (->"Ln"); Thanks for pointing out.

And about datum; Third new knowledge of the thread!

Hail the masters!

\o/ <(Thank) _o_ <(You) \o/ <(Once) _o_ <(Again!)

[numerobis]

"log" is whatever logarithm the speaker feels like using that particular moment. It's usually base e or base 10, but sometimes base 2, and sometimes the speaker doesn't feel like spelling out which one exactly. You can get away with that because converting from one base to another is just a constant factor.

ln is always the natural log.

lg is always log base 2.

log_x is always log base x.

Anything else is confusing. In some communities you can know what log means, but switch communities and you can start a flame war for using it and meaning a different one than what they expect.

[tavert]

Though in most programming languages I've used, log(x) tends to mean natural log, there will sometimes be separate log10 and/or log2 functions or a 2-argument logarithm so you can specify an arbitrary base.

[Zeroignite]

I made a thread with these graphs a while ago, but the Big Forum Lithobraking Event seems to have destroyed the thread.

They may be helpful.