Mun slingshots.

[Fraston]

On 6/21/2018 at 5:57 PM, Eriksonn said:

With n-body physics you can do mun to mun assists and save a bunch of deltav

This trip from lko to circular mun orbit took only 220 deltav(after the initial ~800 from lko), i know that i can optimize it to an elliptic mun orbit with 0 deltav but that is for another day...

N-body orbits are fun stuff 

Even though if KSP used n-body sim for planets, vall would be shot out of the jool system in a few days. 

[pincushionman]

The reason most people don’t do it is threefold (and the first two…folds have been mentioned already):

1) The precision needed to use it effectively makes it difficult for most players.

2) The ammount of dV saved is marginal compared to said effort, with the exception of Jool-system gravity braking. Jool assists would be more useful (as we use Jupiter in real life), except there aren’t any more outer planets to go to using it.

3) Most importantly, it’s astonishingly easy to over-dV your ships in KSP, and outside of self-imposed low-dV challenges, there’s little incentive to do otherwise.

[Nich]

On 6/23/2018 at 8:53 AM, Laie said:

Half of the deal is knowing what a good assist looks like -- schematics showing a 180° U-turn are misleading, like @5thHorseman it didn't click for me until I got an accidental assist. Before, that, I've tried it from a wrong angle (heh), getting me nowhere. Example of a munar assist saving ~90m/s:

In order to set it up, I like to use a "marker" probe that has an ordinary direct burn for a maneuver.  My trajectory, post- assist, has to run very nearly parallel to that of the probe; this allows me to do most of the tweaking without constantly zooming and and out on the map.

For the benefit of @MisterKerman: that's a totally different problem. If you start from a munar orbit, going through a low Kerbin PE is indeed the way to go, that's true. But it has nothing to do with gravity assists.

Problem here is you are only transferring to eve and your turning angle is already reduced to 45 degrees.  As you add velocity to go further this angle becomes smaller and your 90 m/s becomes 45 m/s or 15 m/s.   Not to mention you have already spent 4153 dv so an extra 90 is only 2.2%  How much extra dv is required for correction burns?

[Laie]

2 hours ago, Nich said:

Problem here is you are only transferring to eve and your turning angle is already reduced to 45 degrees.  As you add velocity to go further this angle becomes smaller and your 90 m/s becomes 45 m/s or 15 m/s.

Yup, munar assists aren't very powerful to begin with, and the faster your already are, the less you can get from the mun. Wether it's worth the hassle to set up is up for debate... then again, if i can do it, why not?

2 hours ago, Nich said:

How much extra dv is required for correction burns?

In that case, "nothing". Mission video shows that I must have spent 6m/s between Kerbin departure and Duna arrival, but for my standards that's normal, regardless of how I got underway. I can't remember when or where, but as I know myself, it was probably for fine-tuning the PE for aerobraking.