Dealing with high inclination on return to Kerbin

[Pthigrivi]

This has been a continuing little irk for me but I still haven't found a way to really optimize my returns from places like Eve and Moho and constantly find myself coming in on steeply inclined approaches. This comes up a lot when capturing asteroids as well. This was no big deal when I used to just parachute in anywhere and recover, but now that I've been doing much more aerocapturing and reusing equipment it's started to seem like a huge waste to make a big inclination burn to get back into an equatorial orbit so that I can rendezvous with my station and refuel. Anyone know the best way to deal with this?

Edited February 6, 2015 by Pthigrivi

[pellinor]

You can do a small aerocapture into a highly eccentric orbit, then correct your inclination somewhere far out, and lower the AP afterwards. With asteroids I try to manouver/aerobrake into a trajectory that crosses the orbit of the mun and then wait for gravity assists to change the inclination.

[NASAHireMe]

Just like when you're traveling to other planets, you should adjust your inclination at the AN/DN on your way back to Kerbin. Or, if it's too late and you're already going to end up in a highly-inclined orbit: aerocapture, then raise your equatorial AN/DN (having some other craft in an equatorial orbit that you can target may prove useful here), adjust your inclination at the AN/DN, then use aerobraking to return to a circular orbit.

[pellinor]

having some other craft in an equatorial orbit that you can target may prove useful here

To see your equatorial AN/DN you can also target the mun.

[Foxster]

I've no idea if this is a good way to do it but what I do is... Get some kind of elliptical orbit, usually with some huge Ap and the Pe near Kerbin above 70K. Then I adjust the inclination at the Ap. I think this seems to take less dV compared to, say, trying to adjust the inclination in low circular orbit.

I'm sure someone who understands this stuff will be along with a better answer soon.

[Laie]

The important bits have been said, but here's all of it as step-by-step instructions:

1. target the the station that is the final destination.
   
2. if you don't see AN/DN: place a maneuver somewhat behind your Kerbin PE and pull retrograde until it shows a closed orbit (and AN/DN show up).
   
3. now adjust your incoming trajectory so that your Kerbin PE will be as close to either AN or DN as possible; when in doubt, PE slightly behind the AN/DN is better than slightly before.
   
4. aerobrake (or retro-burn) to an orbit with as high an apoapsis as you dare.
   

This should put you in an orbit where either AN or DN is close to a high apoapsis. A planechange at this node will be as cheap as it gets.

Often (but not always) it is cheaper and easier to change your PE not from a few weeks out, but just after you entered Kerbin SOI. Don't be afraid to use tiny nudges from RCS for fine-tuning.

[Guest]

Generally correcting for inclination requires less delta-V the further out you are, so doing it at AN/DN on your way back is preferable, but it is also fairly cheap right before after you enter SOI. I wouldn't bother doing it after aerocapture because you would need much more fuel to make the inclination change.

[Laie]

Correcting inclination in solar orbit isn't exactly cheap. At the apoapsis of a very eccentric Kerbin orbit, however, I've done a 180 degree turn for 30m/s. But that was extreme, with the apoapsis at the very edge of the SOI. If memory serves, twenty degrees at a Mun-like apoapsis should be on the order of 100m/s.

The trick is to make the apoapsis line up with an ascending or descending node, at least approximately. An apoapsis somewhere over the poles will do you no good if your destination is circling the equator.

[Yakky]

The trick is to make the apoapsis line up with an ascending or descending node, at least approximately. An apoapsis somewhere over the poles will do you no good if your destination is circling the equator.

If it doesn't, you can circularize a highly eccentric orbit (one that extends out nearly to the edge of the planet's SOI) for not too much delta-v. That will then allow you to then adjust the inclination without too much delta-v spend.

The key is always to be going as slowly as possible when you change your inclination. You do that by orbiting far away from the planetary body, either in a highly eccentric orbit or if necessary in a great big circular orbit.

[Pthigrivi]

Guys this is killer, thank you so much. I'd tried things along similar lines (adjusting inclination with a high apoapsis only removes one component) but figuring out when was the most efficient time to rock the AN/DN to come in level to begin with was what I was missing. I like the idea of moving the apoapsis to match.. I'll have to play with that.

I take it getting that right would be ideal, and circularizing high is a decent backup plan?

Edited February 6, 2015 by Pthigrivi