How to set up a münar free return trajectory using maneuver nodes?

[twol]

I'm trying to get from Kerbin to about 10km from the Mün, then come back. Easy peasy, except I want to save a whole bunch of fuel by going in the cismünar way so the Mün's gravity assist gets me back to Kerbin instead of into deep space. I can't seem to find a way of doing this with maneuver nodes, which only seem to show reaching the Mün at all if I go around the transmünar way and get the gravity assist into deep space. Is there something I'm doing wrong here?

Here's an graphic for the equivalent orbit in the Earth-Luna system:

 

Edited November 14, 2022 by twol
typo

[jimmymcgoochie]

It’s entirely possible to do a Munar free return trajectory, but it requires the trans-Munar burn to be a bit longer and at a slightly different time. Try adding an extra 5m/s prograde to the burn and moving the node around until you get the right periapsis, then repeat the process until the return trajectory comes back to Kerbin and not off into deep space.

Free return trajectories will always produce a retrograde orbit around the Mun so keep that in mind as well.

[king of nowhere]

you need to pass in front of mun, not behind it.

it's basic gravity assist theory: if you pass behind a planet, it will accelerate you, while if you pass in front of it, it will slow you down.

as for maneuver nodes not showing much in the future, indeed after a few changes of SoI the game stops showing trajectories. the workaround for that is to set up another maneuver node - keep it at 0 m/s, you don't want to actually make a maneuver there - forward into the future. in this case, you could make it in munar orbit. this will persuade the game to show you your planned trajectory a bit longer

[Streetwind]

What @jimmymcgoochie described is pretty much how I always did it as well. 1.) Plan normal Mun transfer, 2.) add some extra dV juice, 3.) move maneuver node counterclockwise around Kerbin until a new encounter shows up, 4.) finetune that encounter into a free return trajectory.

 

1 hour ago, king of nowhere said:

as for maneuver nodes not showing much in the future, indeed after a few changes of SoI the game stops showing trajectories. the workaround for that is to set up another maneuver node - keep it at 0 m/s, you don't want to actually make a maneuver there - forward into the future. in this case, you could make it in munar orbit. this will persuade the game to show you your planned trajectory a bit longer

You can also go into the game options in the main menu and use the slider there to configure how many SoI changes ahead the trajectory simulation allows. I think the default is 3, you can raise it to as much as 5.

[18Watt]

4 hours ago, Streetwind said:

You can also go into the game options in the main menu and use the slider there to configure how many SoI changes ahead the trajectory simulation allows. I think the default is 3, you can raise it to as much as 5.

I think doing this will help the OP visualize the resulting path better.   The default is indeed 3, but I always set that to 5.

I think this setting is in the general KSP settings.

[luz.tolentino1126]

I think it's pretty simple: The moment you pass by a central gravitational force like a planet, it accelerates you thus setting up the munar basis. It's rather easy to understand.