Help on Orbital Plane(s)

[darthWes]

Two questions:

1) Im in polar orbit around Duna, I want to return to Kerbin. Mechjeb tells me I have to get an equatorial orbit in order to get home. This can't possibly be true, right? How hard is getting back to kerbin from a polar orbit?

2) The delta-v required to change from polar to equatorial is MASSIVE (according to Mechjeb). Is this right? What's the most effecient way to change your orbital plane (I dont have the fuel to do what mechjeb thinks is the best way)? It seems like MJ wants to kill all the vertical momentum, then burn horizontally. Couldn't I slowly make micro burns to change my orbit and save a ton of fuel?

[Traches]

You have a couple of options--

Burn prograde until you have an elliptical orbit and do your plane change at apoapse, which will cost less than the overall plane change.

Use a couple gravity assists from Ike to change planes (but I don't think Ike's gravity is strong enough for this to be a good option)

Or, time accelerate until your orbit lines up with duna's orbit around the sun, and leave duna in the retrograde direction like you normally would. Plan your ejection burn to push your periapse down to kerbin's orbit, to where you get the white approach markers. Time accelerate down to the white marker, place a maneuver node, and play with the pro and retrograde markers to try and get an intercept. If you're too far away, wait a year and try again till it works. The important thing is that you do your burns where your orbit intersects kerbin's-- so you'll always pass through that point, and you're adjusting how long it takes you to get there in order to meet up with the planet.

Good luck!

[TechnicalK3rbal]

To correct the inclination, set Ike as your target, than at the ascending/descending node, (whichever is closer) make a maneuver node to correct the inclination about half, than make another at the other AN/DN to fix it the rest of the way, your relative inclination should be 0. This is more efficient than correcting it from a solar orbit.

[Traches]

To correct the inclination, set Ike as your target, than at the ascending/descending node, (whichever is closer) make a maneuver node to correct the inclination about half, than make another at the other AN/DN to fix it the rest of the way, your relative inclination should be 0. This is more efficient than correcting it from a solar orbit.

I think he's asking if there's a way to do it more efficiently than that-- a brute force plane change like you describe will take tons of dV. You basically have to cancel out your orbital velocity in one direction and add it back in another.

[Guest]

One way to do it is to get a gravity assist from Ike. Put your orbital path right next to its equator as low as you need and you should get a free plane change. It may not be perfect but you'll save tons of delta-V on your way out (fine-tune your plane change after the Ike encounter before you've left Duna SOI). Of course, that also depends on how well you set up the transfer node because you'll probably also be using Ike to sling you out of Duna's SOI.

[Dave Kerbin]

This might not be the best answer for you, but if you goal is just to return to Kerbin (a parachute landing, no fancy orbit) then a direct burn from polar orbit should be entirely possible without losing much delta-v. You just need to plan it manually without mechjeb (mechjeb has a specific program for figuring out how to reach a goal and it will try altering everything else to fit that program instead of improvising - you can see this when it uses tons of monopropellent to dock).

Drop down a maneuver node, pull the prograde side out until it reads about 1500m/s, then zoom out to see Kerbin and set it as your target. Now move the node around until it shows you moving into a lower sun orbit instead of a higher one. Push or pull the prograde handle until you have a close encounter with kerbin (little grey arrows appear), then try fine tuning, first with the prograde handle and then with the inclination handle. You may need to move the node a bit too. Alternate between the two until you have a proper encounter. At that point you do the burn and wait until you are outside Duna's SOI. Now plot a much smaller maneuver node (or even just use RCS translation with trial and error) to lower the PE of your Kerbin encounter below 20km.

[capi3101]

I had a polar orbit last time I visited Duna (during the Constipation XI mission). I handled it by burning just enough to escape Duna's SOI - once in orbit around Kerbol, I set up a transfer back to Kerbin same as I would've had just left from Duna's equator.

[KSK]

Assuming that you can, it might be more fuel efficient to land on Duna and then re-launch into a more equatorial orbit.

[Kasuha]

There are several reasonable approaches and it depends on details.

If your polar orbit is along current Duna orbital movement direction, then just burn above south or north pole to eject. It's exactly as good as escaping the system from equatorial orbit.

Most of the time though, your orbit will not be along the Duna's trajectory.

Then one option is to wait till it will be.

Or you can adjust the direction by burning at the pole you'll be using to eject, raise your apoapsis above the other pole, then adjust the inclination at the apoapsis and finish the ejection at periapsis in the correct direction.

Or you can burn near equator and burn to make your distant apoapsis also near equator. That'll allow you to change inclination to an equatorial orbit quite cheap. Just make sure you raise the right end - you don't want to pull that apoapsis down again. You want to finish the burn and change your elliptic orbit to escape.

[Markus Reese]

Polar orbit and get back to kerbin? Easy! Just need to do your de-orbit burn so your pole becomes your gravity departure point. Usually this will be a bit before you are at the equator. You will slingshot out into a slightly off dunar orbit, but nothing slight burns while returning to kerbin wont fix.

The other way is to get yourself a really high altitude, almost escape orbit of Duna then correct to an equatorial, but where is the fun in that ^.^

[darthWes]

Thank you all for all the help. You have restored my faith in Kerbanity.

I was able to bring my Kerbals home! (BTW, does this game become "Put gas tanks into orbit" after you work through the learning curve or what?)

How would I mark this as answered?

[vexx32]

I got it for ya

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