Formula questions

[price.michael79]

Setting up my calculations so I can do more than just build something that looks cool and hope it gets into orbit. For the delta-V equation, one must use the gravitational constant, which for Kerbin is 9.81. When would you change to another celestial body's gravitational constant? I am assuming when you are within that body's sphere of influence, but didn't know if anyone else had thoughts on the subject. Been a while since I was in college for this stuff...

[K^2]

No. For the delta-V computation from I_SP you always use 9.81m/s². The reason for that is that I_SP is impulse you get per weight of fuel. But it's always weight on Earth/Kerbin. It's really just a terrible definition that results in that.

A better definition, and indeed, what Tsiolkovsky used, is to define impulse per mass of propellant. In which case, you end up with I_SP measured in m/s instead of seconds. It also ends up being equal to average exhaust velocity. And then you don't have to carry around a convention constant. Alas, most of formalism on rocketry comes from U.S. engineers, and they have a funky way of dealing with weights, resulting in some weird constants you have to drag around. (Basically, it all comes down to pounds of weight and pounds of mass.)

[price.michael79]

The explanation of the Tsiolkovsky equation I found uses effective exhaust velocity, which uses the g conversion factor. Thank you for the explanation though. As long as I know it is always 9.81, I can plug it in rather easily.