How to use a Delta-V map.

[Admiral Fluffy]

Whenever I look at a delta-v map like this:

Spoiler

It makes no sense. For example, on the Mun part of the map, by 5120 does it mean the total Delta V to get there, or something else?
Help would be greatly appreciated. Thanks!

[Superfluous J]

FIRST NOTE: These numbers are suggestions and will vary in reality based on your skill, rocket, and how you do each burn. But given a typical rocket and correct burns, they should be pretty close. I like to keep a 10% margin for error in my tank, especially for landing on airless worlds.

You need to think of the map in sections. There's a "get into orbit or land from orbit" section of flight, a "circularize orbit from interplanetary or go from circular orbit to interplanetary" section. Each trip includes one or more of these and they're not all together.

Let's take a simple one, getting to Mun.  First you get into orbit (3400m/s, which I'll skip from now on and assume we're in orbit of Kerbin to start) and then there's the "go to Mun from circular orbit" which is 860. When you're done with that burn, you should have a periapsis around Mun at around 14km. You won't, but a tiny mid-course correction should do it. Then when you're at that Pe you need to do the "circularize at mun" burn which is 280. Then to land from there you need 580.

Reversing that, you need 580 to orbit Mun, 280 to eject back to kerbin, 860 to brake at Kerbin back into a circular orbit, and 3400 to land back at Kerbin. However, those last 2 can utilize aerobraking so you can do them all for free, assuming you can stand the heat

Okay now for the harder part (don't worry it's not much harder), getting to Duna. Duna has more numbers than Mun after the initial 3400 to reach orbit. you've got 930, 130, a little '10' off of that 130, 250, 360, and finally 1450. Whew, what to do?

Remember, there are only 2 actual ways to spend fuel: landing/takoff, or circularize/eject. So, we're in orbit of Kerbin and we want to eject to Duna, so we just add up all the numbers to achieve that. Note the little flyby icon in the Mun trip we did. We want to add all the numbers to Duna that reach that same flyby icon. That's 930 + 130 or 1060. You do that burn (at the right time and in the right direction) and your ship will encounter Duna, or at least be really close, and you may need up to 10m/s mid-course to fix your angle. You also will need a tiny bit to tweak your flyby so your periapsis is 60km away.

Now you're at that Pe and you want to circularize, so you need to burn 250+360 to do that. if all you want to do is get into ANY orbit (say, you're going to Ike instead of Duna) you'd need to at least burn 250. But to land on Duna, you need an extra 360. You do those at once though so need 610, but if you're daring you can use Duna's atmosphere to do them for you.

Then to land you need 1450, though really you can do it for almost nothing and let the air slow you down most of the way. Returning, though, you need 1450 to get back into orbit, 610 to eject back to Kerbin, 1060 to slow down at Kerbin back into a circular orbit, and 3400 to land at kerbin. As before, those last 2 can be reduced to almost 0 via aerobraking.

And that's basically it, all other planets are similar to Duna.

Edited July 8, 2021 by Superfluous J

[king of nowhere]

6 hours ago, Admiral Fluffy said:

 

It makes no sense. For example, on the Mun part of the map, by 5120 does it mean the total Delta V to get there, or something else?
Help would be greatly appreciated. Thanks!

yes, it means total (vacuum) deltaV to get there from Kerbin's surface.

Assuming reasonable efficiency on manuevers, and no gravity assists.