Most efficient way to leave Minmus or Mun and return to Kerbin?

[Invader Jim]

What is the most efficient way to leave if you want to go home? Point a certain direction (which one?) and full throttle until your path includes an escape? Where should the escape SOI point be relative to the the bodies involved? Sometimes I have left the SOI but get caught back in the SOI again and then thrown into and orbit farther from Kerbin.

Edited October 1, 2015 by Invader Jim

[FungusForge]

You want your escape vector to send you to the moon's retrograde. If you eject prograde, you can get recaptured when trying to slow down to re-enter Kerbin, and it also takes a bit more fuel.

[mattssheep4]

Yeah, if you burn towards Kerbin when it comes up over the horizon, you'll get back pretty efficiently.

[FancyMouse]

Burn is a little earlier than retro so that ejection angle is almost retro, and upon entering kerbin soi, you should be roughly at apoapsis.

[GoSlash27]

^ This. It takes very little beyond escape velocity to get an atmospheric periapsis if you do it this way.

Best,

-Slashy

[OhioBob]

For Mun I typically set my maneuver node about 140 degrees to retrograde, and for Minmus about 100 degrees to retrograde.

[SpeedDaemon]

Assuming you're in an equatorial orbit of the Mun/Minmus:

Imagine you're looking "down" from the north pole (so your equatorial orbit is going counter-clockwise), with Kerbin at 12 o'clock.

From the Mun, you generally want to burn prograde when you get to about 2 o'clock in your orbit. I usually don't bother with maneuver nodes from the Mun, since its orbit isn't inclined. Just burn prograde until my Kerbin PE is where I want it.

From Minmus, you can wait until you get to 1 o'clock or so. Here, (or from an inclined orbit of the Mun, or if my dV budget is really tight) I usually will drop a maneuver node, because if you want to land at/near KSC, you'll probably want to fiddle the normal/anti-normal controls a bit to make your eventual Kerbin orbit have as little inclination as possible.

If you use a maneuver node, slide it along your orbit so that the exit vector is as parallel to the Mun/Minmus's orbit around Kerbin as possible. When you do this, you can easily see the effect it has on the required dV by watching your Kerbin PE change.

[Alshain]

For the mun in an equatorial orbit, wait till your craft is between Kerbin and the Mun and burn prograde, you can get into the atmosphere directly. Going the other way, wait till the Mun is between Kerbin and your ship. Polar orbits are done this same way but will require some correction after you leave the Muns SOI

[QuantumInc]

The thing to be aware of is that is that your velocity relative to Kerbin is equal to your velocity relative to the moon plus the velocity of the moon itself. To get closer to Kerbin you have to reduce your velocity relative. If you are moving in the opposite direction as the moon when you leave, the resulting velocity relative to Kerbin is your velocity relative to the moon MINUS the velocity of that moon.

The faster you are going when you leave the moon, the closer your PE will be to Kerbin. (If you go too far, you'll crash into Kerbin or end up orbiting in the opposite direction.) For the best fuel efficiency you will adjust it so that your planned orbit around Kerbin will bring you well within the atmosphere. I'm not sure the best number, but probably a PE of 10km to 40km. The downside is that you will absolutely need a heat shield to survive, and also you won't be able to adjust your landing point much.

[Reactordrone]

I usually place a manoeuvre node in roughly the right area on the orbit and pull the prograde handle until there's about 270m/s (170m/s for Minmus) on it and then move the node around until I have a tangential escape vector before fine tuning the periapsis for an aerocapture.

[OhioBob]

I'm not sure the best number, but probably a PE of 10km to 40km.

I don't know what other people do, but I usually target a Pe of about 42 km from LKO, about 30 km from Mun/Minmus, and about 25-30 km from deep space. The higher the entry velocity, the lower the Pe. These numbers came from experiments in which I sought to minimize the g-load and heating.