Talk to me like I'm a child - how to read this Delta V chart?

[jpinard]

This is the chart I'm referencing.  It is beautiful but I don't understand how it works.  Where does it tell me how much delta V I need to get into Kerbin orbit, and then how much to go from there to Mun, and then to capture Mun orbit, and then back to Kerbin etc?

 

[Aegolius13]

For that trip, you will start from the bottom where it says Kerbin, go up one stop (to LKO), and then follow the gray path leading to Mun.  Now let's read it!

Going from the launch pad to an 80km LKO orbit takes 3,400 m/s.  Of course, this is a lot higher than orbital velocity, but that's due to the drag and atmospheric losses.  Pretty straightforward so far. 

Then imagine you burn from the correct point in this orbit to make an encounter with the Mun -- which means you have to get your apoapsis up to the Mun's altitude.  This takes about 860 m/s.  

Now, if you just did that burn and stopped, you'd end up with just a flyby of the Mun.  So the next step would be to circularize your orbit, by burning retrograde at your munar periapsis. The chart says this will take 310 m/s to get into a 14km circular orbit (we can therefore work backwards and understand that the flyby periapsis the chart had in mind was also 14 km).  

Finally, to land at the mun takes about 580 m/s.  This is a little higher than the amount of orbital velocity you need to shed, again because of gravity losses.

So, if you add these all up, the chart says you'll need (3400+860+310+580) = 5,150 m/s of delta-v on the pad in order to land on the Mun.

For the return trip (if there is one... sorry kerbals), you can just reverse the numbers, because the maneuvers are symmetrical.  The one exception is on planets with atmospheres.  As you probably know, you don't need to spend delta-v landing at Kerbin (beyond a small deorbit burn), since the atmosphere soaks up that energy for you.  The chart denotes this with the little triangle pointing the way you can use aerobraking (i.e, to reenter Kerbin, but not to leave).

Edited July 4, 2019 by Aegolius13

[Pecan]

7 hours ago, Aegolius13 said:

(we can therefore work backwards and understand that the flyby periapsis the chart had in mind was also 14 km)

Nicely explained, tiny typo correction for you.

[linuxgurugamer]

It was a good question, and has a great answer.

[OhioBob]

Step 1 - Select the celestial body you want to visit.
Step 2 - Select what type of encounter you want when you get there, i.e. intercept (flyby), low orbit, etc.  These are identified by the different types of icons at each body.
Step 3 - Starting at Kerbin, follow the lines until you get to your end point, and add up all the numbers as you go.

For example, let's say you want to send a probe to Duna and enter low orbit.  The starting point is Kerbin and the ending point is the "low orbit" icon near Duna.  Follow the lines and add up the numbers... 3400 + 950 + 130 + 10 + 250 + 360 = 5090 m/s.  Note that the number 10 is printed off to the side of the main line.  This is the maximum amount of plane change that might be required.  It could be as little as zero, but it's probably a good precaution to add it in until you gain the experience needed to minimize it.

As Aegolius explained, for the return you just follow the lines back to Kerbin in the reverse direction and add up the numbers as you go.  To get from Duna orbit to an intercept with Kerbin, we add up... 360 + 250 + 130 + 10 = 750 m/s.  Note that we didn't add in the last two numbers, 950 + 3400.  This is because we only need an intercept with Kerbin.  We can do a direct atmospheric reentry and use drag to slow down rather than propulsion.  However, if you plan to enter orbit around Kerbin upon your return (rather than perform a direct reentry), then you'll require some or all of the 950 m/s (depending on how much, if any, aerobraking you do).

The same is true with Mun and Minmus.  Getting to Mun orbit requires, 3400 + 860 + 310 = 4570 m/s, but getting back requires only 310 m/s.  To return you only need to break Mun orbit and set up an intercept with Kerbin (placing the periapsis inside Kerbin's atmosphere).

Be advised that some of the numbers in the delta-v map are aggressive.  You should add in a generous safety margin until you get good at it.

[FloppyRocket]

Note that the delta-v numbers in the chart are all vacuum delta-v, not the atmospheric delta-v you'll see by default in the VAB. You'll need to adjust the setting in the VAB's DV menu so that is shows vacuum delta-v as you design your rocket.