Achieving Munar orbit: Do you first need to set the Munar orbit as a target?

[Echo__3]

Maybe some videos will help you better visualize things.
Getting to the Mun before unlocking maneuver nodes.

How to get to the Mun

Getting to the Mun early in career mode

 

[MetricKerbalist]

Hi Echo_3,

Thank you for showing me these videos.

The commentator goes awfully fast, so following the presentation is difficult.

Still, I appreciate your showing me these.

Stanley

[herbal space program]

14 hours ago, modus said:

The Mun will never 'just' capture your spacecraft. You have to slow down (burn retrograde, ideally at Mun periapsis) first in order to be captured.

I swear that there was one time  in some version that I actually found myself in orbit right after entering Mun's SOI, but it was probably some bug that happened near the boundary condition. As I understand it however, if you make a perfect entry into another body's SOI, i.e. you have no or nearly no motion as you cross in, you could in theory put yourself in a stable orbit for what amounts to an infinitesimal amount of dV.

[herbal space program]

10 hours ago, Echo__3 said:

<snip>
Getting to the Mun before unlocking maneuver nodes.

</snip>

That's easy! Now rescuing a stranded Kerbal before you have maneuver nodes or RCS or the ability to set distant targets, that's just a little hard!

[MetricKerbalist]

Hi KSP colleagues,

I have now achieved Munar orbit!

Here is one photograph:

And here is a second picture:

I am so grateful to all my KSP colleagues for assisting me with this.  For this particular accomplishment, I am especially grateful to @Zhetaan, who has been extraordinarily helpful.

Again, I thank all of you knowledgeable people.

Stanley

[Curveball Anders]

11 hours ago, herbal space program said:

I swear that there was one time  in some version that I actually found myself in orbit right after entering Mun's SOI, but it was probably some bug that happened near the boundary condition. As I understand it however, if you make a perfect entry into another body's SOI, i.e. you have no or nearly no motion as you cross in, you could in theory put yourself in a stable orbit for what amounts to an infinitesimal amount of dV.

I haven't run the numbers (or even tested it it) but could it be possible to get such a perfect rendezvous that you'd get a gravity assists from the moon to actually achieve orbit?

 

[Zhetaan]

1 hour ago, Curveball Anders said:

I haven't run the numbers (or even tested it it) but could it be possible to get such a perfect rendezvous that you'd get a gravity assists from the moon to actually achieve orbit?

In real life?  Surprisingly, yes.  However, that's dependent on the fact that there is no such thing as a perfect rendezvous and that gravitational interactions are affected by tidal forces from the sun, non-uniform mass distribution of the celestial body, and other perturbations.  Comet C/2012 S4 (PANSTARRS) has a calculated aphelion of something around 8 light-years--though that owes more to the error in measurement than to astrophysics--but it is not escaping.  It is listed as a near-parabolic comet.  The technical term for deviation from a Keplerian orbit (since Kepler so unhelpfully took the term anomaly for himself) is osculating orbit, and the osculations can absolutely perturb something into a capture (or an escape, or a crash--which is the eventual fate of nearly everything in low-Earth orbit).

In KSP?  Also, surprisingly, yes--but it depends on exploiting the nature of the game.  It's not a true gravity assist, and on paper, gravity assists cannot do what you want.  Essentially, you can get very, very close to a perfect rendezvous, but there is a recalculation when you cross the sphere of influence boundary.  If you get the right precision error in the floating-point mathematics, then you lose a few bits in the orbital energy and what was a near-capture hyperbolic orbit becomes a near-escape elliptical one.  However, I have not seen this in years--it was never common anyway, and I believe that the devs changed the sphere boundary calculation to avoid unwanted perturbations, as well.

[herbal space program]

3 hours ago, Curveball Anders said:

I haven't run the numbers (or even tested it it) but could it be possible to get such a perfect rendezvous that you'd get a gravity assists from the moon to actually achieve orbit?

the way I figure it with my mediocre math skills is that no matter how you enter Mun's SOI, you're going to have at least enough gravitational potential energy to put you back to that altitude after your PE. Any net motion towards Mun that you have as you enter will add to that potential energy, and by definition you can't enter Mun's SOI with a net motion away from it. So the best case is crossing the boundary with an infinitesimal amount of radial motion towards Mun, in which case only an infinitesimal amount of retrograde boosting at PE is required to keep you from going back out.  In my case, I think what happened is that I just grazed Mun's SOI on its inside boundary at the AP of my ship, moreover from a PE that was considerably higher than LKO, which allowed me to enter it with a motion that was small in the sideways dimension and minuscule in the radial one, just enough to avoid unplanned lithobraking.  If you manage to enter the Munar SOI with that type of motion, I can see how a rounding error might put you directly into orbit, as @Zhetaan described above. But that was I-don't-know-how-many versions ago, so it doesn't surprise me that they've since cooked up some kind of a kludge to make achieving orbit due to a rounding error impossible. In any event, I'm pretty sure that trying to shoot for that is never going to be the most efficient way to get into orbit, because you can't do it from an Oberth-friendly PE that is much lower than your point of entry.

[imcute]

mechjeb->manuver planner->hohman transfer(bielliptical)->target->create and execute