What EXACTLY do delta-V requirments mean?

[Themohawkninja]

When it comes to space travel, I am aware that delta-V is the most important number that you have to think about, and I know that when it comes to how much of <something> you need to get to another celestial body, that <something> is delta-V, but how do you calculate how much delta-V is required, and what things are factored in?

-Are gravitational slingshots calculated in?

-Are the values based on a specific launch window?

[GJames]

Delta-V is just a change in velocity, so if my rocket had a dV of 3km, it would be able to go from a standing start to 3km/s once it had used up all it's fuel by burning in one direction. You can find out how much dV a rocket has with an equation called the Tsiolkovsky Rocket Equation. It looks pretty heavy but isn't that bad once you know all the variables, (dry mass of rocket, fuelled mass of rocket, rocket isp, etc.). I'm sure there is someone here with more experience who could fully explain it, as a lot of the information on the internet about it is fairly high level...

As for the last two questions, these are informed guess at most, but as most space missions travelling further out than Mars use gravitational slingshots, they would likely be factored in, but you should be able to see if they are or not by looking at the planned trajectory of the mission. Usually the values are for a specific transfer window and transfer type. If you want to use less dV, you can sometimes get a transfer that takes longer but is less expensive, and vice versa.

Hope this helps somewhat.

[Crush]

Gravity slingshots add delta-V to a vehicle (or remove it). They can be seen as another source of propulsion. Unfortunately you usually have to expend delta-v into a different direction than you usually would to tap into this source.

[tomf]

A quoted delta-v is for a specific mission plan. The values read from maps are for the most efficient simple plan, launching when the planets make the optimum angle to each other and using a hohmann transfer. They are based solely on the orbits and masses of the starting and ending bodies (and the mass of the sun). The maps ignore eccentricity and inclination. The maths for this isn't to hard, I wrote a post a while ago http://forum.kerbalspaceprogram.com/showthread.php/27171-Calculating-interplanetary-delta-v.

There is a calculator that will give you delta-v requirements for arbitrary departure dates taking inclination and eccentricity properly int account http://alexmoon.github.io/ksp/ but the maths of that are slightly beyond me.

Working out the delta-v requirement for a mission that is going to use gravitational slingshots is going to be harder still.

[Themohawkninja]

Delta-V is just a change in velocity, so if my rocket had a dV of 3km, it would be able to go from a standing start to 3km/s once it had used up all it's fuel by burning in one direction. You can find out how much dV a rocket has with an equation called the Tsiolkovsky Rocket Equation. It looks pretty heavy but isn't that bad once you know all the variables, (dry mass of rocket, fuelled mass of rocket, rocket isp, etc.). I'm sure there is someone here with more experience who could fully explain it, as a lot of the information on the internet about it is fairly high level...

Yeah, I know what delta-V is in respect to the rocket equation (which I have never been able to do correctly, since I get answers like 3=2). I just don't know what's factored in to delta-V requirements for missions.

[who-is-john-galt]

I only seem to get gravity assists when I don't need them. eg. when travelling to the mun.

[Person012345]

Yeah, I know what delta-V is in respect to the rocket equation (which I have never been able to do correctly, since I get answers like 3=2). I just don't know what's factored in to delta-V requirements for missions.

How much speed (or rather, acceleration) you need to get somewhere.

[Frederf]

The delta-v charts are almost assuredly made with the following assumptions:

1. Piecemeal calculations from all intermediary states.

2. No gravity assists or aerobraking.

3. Hohman transfers.

4. Ideal transfer angles.

5. Instantaneous impulses.

6. Minimum or average inclinations.

I'm curious what exactly the math is that the people used to derive these charts.

[tomf]

I did an example of the maths here http://forum.kerbalspaceprogram.com/showthread.php/27171-Calculating-interplanetary-delta-v