Calculating Delta V Needed

[sneezedr424]

Hi there!

I'm creating a station that I want to put in orbit around Duna. I have the thing basically built (need to add non-important things like solar panels as of yet), but my main concern is attaching a rocket to the end of it - well, attaching a big enough rocket. How would I go about finding out how much Delta V I need to accomplish my task? Thanks!

[imgur]u1qaa[/imgur]

Sneeze Edited November 16, 2015 by sneezedr424

[Red Iron Crown]

Use a delta-V map like those found here: [url]http://forum.kerbalspaceprogram.com/threads/96985-1-0-4-WAC-s-Delta-V-Map-continued-2-2-%28Aug-13th%29-Swash-transition[/url]

Add up the segments between LKO and low Duna orbit and you have your total dV required for the transfer.

[sneezedr424]

I guess I should have asked how to calculate the DV a rocket is gonna give me with the station attached to it. For example, if a tank+engine is going to give me 5000 m/s, how much is it going to give me with 27 tons of stuff in front of it? How would I calculate that?

[Gaarst]

[URL="https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation"]Rocket equation[/URL]. :wink:

[Red Iron Crown]

[quote name='sneezedr424']I guess I should have asked how to calculate the DV a rocket is gonna give me with the station attached to it. For example, if a tank+engine is going to give me 5000 m/s, how much is it going to give me with 27 tons of stuff in front of it? How would I calculate that?[/QUOTE]
Load up a copy of your station in the VAB (or any inert payload of the same mass) and attach the rocket to it, KER will do the rest. :)

[Snark]

The rocket equation, in KSP terms:

Take the total mass of ship including fuel.
Divide by the dry mass (i.e. mass without fuel).
Take the natural logarithm of that.
Multiply by your engine's ISP.
Multiply by 9.81 m/s2.

That's your dV in m/s.

[Venusgate]

Using less rocketpower will stretch out your dV for how much fuel you send up, but too little twr you might have to get tricksy with things like resonating de-orbit burns and aerobraking.

[Mastikator]

1330 delta-v to get to Duna and get into a highly eccentric orbit.
Lets say 1500 delta-v to cover for human error.

delta v equation is 800 x 9.82 x ln((26618+fuel needed)/(26618)), assuming you use one nuclear thruster, the fuel needed variable is how many kilograms of liquid fuel (not necessarily units)
Plugging in some numbers I got 800*9.82*ln((26618+5600)/(26618)) = 1500
A Mk 1 Liquid Fuel Fuselage has 400 units, weighs 2.25 tons full and .25 empty. So many 3 of those would be enough to counter the mass of the thruster and the empty tanks.

What you need:
[U]1 Nuclear thruster + 3 mk1 liquid fuel tanks[/U] ([B]not [/B]the fl-400 ones!)

[Violent Jeb]

TL;DR

In the stock game you either need to have experience in college level math and physics or a cheat sheet,

Otherwise, you can also use the mods KER or Mechjeb, both of which can generate these values in real-time, along with various other features.

[Gaarst]

[quote name='Venusgate']Using less rocketpower will stretch out your dV for how much fuel you send up, but too little twr you might have to get tricksy with things like resonating de-orbit burns and aerobraking.[/QUOTE]

This is not true: dV does not depend on thrust.
You lose dV when adding engines because you're adding mass through these engines. If you have a 1t engine with 10kN thrust or 1000kN, as long as the Isp is the same, the dV will remain the same; and putting a 2t engine with 1kN thrust will give you less dV.