Gravity assists, SOI changes and minimizing dV

[NFunky]

Hey again guys,

I've just launched my first mission to land on minmus with KIDS set to real life. This makes dV a lot more precious, since it takes so much more fuel to achieve the same amount as in stock. I'm also not the world's best pilot, so I would like to give myself as much margin for error as I can. I've got a nice little Apollo style ship, with seperate reentry, service, and lander modules. The lander is also a two stager, just to give me that little bit extra to get back to orbit and to rendezvous more easily.

Anyway, my fuel margins are all really tight, so I'm trying to shave off as much as possible on the transit by using the Mun. However, I'm now doubtful if this is actually going to save me anything, or even cost a bit more. This is because my trajectory seems to change a lot in a pretty unpredictable manner when I cross SOI boundaries, even when I make sure to do this at 1x. I end up using almost as much dV to correct for these errors as I would save from the gravity assist.

So is it worth it at all to go for a gravity assist? Also, if anyone has any tips/suggestions as far as getting the most accurate trajectory which includes multiple SOI changes? Hell, I'd also appreciate any general advice on how best to pull this mission off.

Thanks

[Taki117]

unless you are playing RSS, going interplanetary and have a lot of time to dedicate to the calculations required, or the mission at hand, it's not worth it. The dV savings, while significant, require such a long mission time that it's not worth the savings for most people, and it's certainly not worth it if playing stock.

[The Yellow Dart]

I would definitely say when going to Minmus, a Munar gravity assist is not worth it. The difficulty in getting it lined up in such a way that it actually saves you dV outweighs any fuel savings you will find. I imagine you could save a little but I think it would probably be a matter of quicksaving and quickloading a lot of times to get it just right, and that spoils the fun in my opinion. I would look elsewhere for dV savings. Are you launching from Kerbin at the right time to minimize inclination corrections? Do you end up having lots of monopropellant left over? If I go very slowly, I can easily dock a small lander without any mono, just rotating and using the main engines to correct the trajectory, with the throttle limiter set around 10%. That will allow you to remove any mono tanks and empty it out of your crew modules.