Delta V

[Henakk]

Before I get yelled at to use search this is not a thread on how to calculate Delta V in KSP.

I know how to calculate my Delta V in KSP and it's actually really helping me. However I was wondering if you fine folks could help me with something. If I already know how much Delta V I need is there a way to figure out how much ISP I need or how much fuel in terms of weight I'll need? I was never good at math and could not turn around equations.

Basically I want to try and solve for ve (ISP) or ln*mo/m1

[vetrox]

Your total delta v will take your ISP, weight and fuel into account?

Maybe i misread your post.

However delta v is fairly simple to work out.

EDIT:Actually heres a link to all the calculations

http://wiki.kerbalspaceprogram.com/wiki/Tutorial:Advanced_Rocket_Design

All the info on each specific part IE weight, isp etc is listed alongside each part in ksp.

[Henakk]

I know how to solve to get my delta v, instead i'm trying to solve for ISP or weight (whichever is easier) already knowing my delta v to try and build a rocket around how much thrust I need or if I have my thrust than how much it can weigh.

[mhoram]

The question how much ISP you need is a bit blurry.

ISP describes the efficiency of the propulsion system. So you are asking how efficient your propulsion system needs to be. That is a question that can in my opinion not be calculated by itself, but must be answered by the rocket-designer.

I think you should rather ask how much TWR you need.

For rocket-liftoff a TWR>1 is necessary and a TWR of roughly 2 while in atmosphere helps to keep your velocity near terminal velocity.

In vacuum the TWR simply states how much time is needed for a course correction. I usually try to have a TWR>=0.5, except for scannig probes that are inteded for only small Delta-V course corrections.

If you have an AddOn installed that displays the ship's Delta-V values, then it already accounts for the weight of the fuel.

Edited November 28, 2013 by mhoram

[Ralathon]

Before I get yelled at to use search this is not a thread on how to calculate Delta V in KSP.

I know how to calculate my Delta V in KSP and it's actually really helping me. However I was wondering if you fine folks could help me with something. If I already know how much Delta V I need is there a way to figure out how much ISP I need or how much fuel in terms of weight I'll need? I was never good at math and could not turn around equations.

Basically I want to try and solve for ve (ISP) or ln*mo/m1

dV = ISP * g * ln(m_wet/m_dry)

If you already know your ISP you can figure out the mass fraction via:

e^(dV/(ISP*g))=m_wet/m_dry

If you already know mass fraction your ISP is:

dV/(g*ln(m_wet/m_dry))=ISP