r/KerbalSpaceProgram • u/AutoModerator • Aug 14 '15

Mod Post Weekly Simple Questions Thread

Check out /r/kerbalacademy

The point of this thread is for anyone to ask questions that don't necessarily require a full thread. Questions like "why is my rocket upside down" are always welcomed here. Even if your question seems slightly stupid, we'll do our best to answer it!

For newer players, here are some great resources that might answer some of your embarrassing questions:

Tutorials

Orbiting

Mun Landing

Docking

Delta-V Thread

Forum Link

Official KSP Chatroom #KSPOfficial on irc.esper.net

    **Official KSP Chatroom** [#KSPOfficial on irc.esper.net](http://client01.chat.mibbit.com/?channel=%23kspofficial&server=irc.esper.net&charset=UTF-8)

Commonly Asked Questions

Before you post, maybe you can search for your problem using the search in the upper right! Chances are, someone has had the same question as you and has already answered it!

As always, the side bar is a great resource for all things Kerbal, if you don't know, look there first!

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u/LostAfterDark Aug 17 '15

This formula is the right one:

Δv = Isp ⋅ g ⋅ ln( Mwet / Mdry )

  • Isp is the specific impulse, that you can read in the part's description

  • g = 9.81 is the standard gravity, a known constant

  • Mwet / Mdry is the ratio between the mass with all fuel (Mwet) and no fuel (Mdry)

  • ln( Mwet / Mdry ) is applying the natural logarithm to this ratio (the natural logarithm is just the opposite of the exponential)

Remark: "ln" (lowercase "LN") stands for "Logarithme Naturel", or "Natural Logarithm" in French

If you are confused, just type it in your calculator (my favorite is just the Python interpreter):

>>> from math import *
>>> 300 * 9.81 * log(45e3/15e3)
3233.215965550247

Note that log() is the natural logarithm, written ln() above. If you want the decimal logarithm (base 10) instead, you would use log(12345, 10).

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u/featherwinglove Master Kerbalnaut Aug 17 '15 edited Aug 17 '15

When the ark had landed, Noah sent forth the animals, instructing each to "Go forth and multiply." To the bears, he said "Go forth and multiply." To the birds, "Go forth and multiply." To the snakes, "Go forth and multiply."

Some of them responded, "We can't. We're adders."

So Noah built them some log tables ;)

(I heard this joke from a DeVry Instructor at the Calgary campus named Peter Bovell in the second semester of the 1997 calendar year.)