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Best Way to Enter Munar Polar Orbit


sardia
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What's the lowest delta v budget to enter a polar munar orbit from Kerbin? What about if you just got an encounter with the mun and entered it's SOI? I thought I could burn right away, but being in flyby orbit makes it complicated. I ended up making an orbit at PE with my AP really far out. Then I changed my inclination from there. 

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9 minutes ago, Starhawk said:

The lowest dV cost is to burn normal/antinormal about half way between Kerbin and the Mun.

^ this ^

Make your ejection burn from low Kerbin orbit as you normally would if you were aiming for an equatorial munar orbit.  However, instead of aiming for a close encounter just above Mun's surface as you would if you were planning an equatorial orbit, I like to aim for an approximate dead center impact with Mun.  Then, when about half way to Mun, make a normal/anti-normal burn to alter the trajectory so that you will pass just over one of Mun's poles.  Perform your orbit insertion burn at Pe just as you would in any other circumstance.

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Best way to get to a polar Mun orbit is to add a slight inclination to your ejection burn at Kerbin.

Plan your manoeuvre as usual, and pull normal/antinormal (purple thing on the navball) until your planned trajectory ends up slightly above (or below) the Mun instead of along the equator (focus on the Mun while moving around your node to properly see where you're going). Then play around with prograde/retrograde to get a proper polar encounter. Finally, when you arrive at the Mun,  burn retrograde at periapsis to circularise are normally.

I can upload a few screenshots if you wish.

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The lowest dV cost is to burn normal/antinormal about half way between Kerbin and the Mun.

If you've already entered the Mun's SOI, then your best bet is to do exactly what you did.  Barely capture into a highly elliptical orbit and adjust your inclination out at your apoapsis.

Happy landings!

Edited by Starhawk
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1 hour ago, fourfa said:

Half way point because why?  You have minimum speed there relative to both Kerbin and Mun?

it would be fun if MJ had an option for Hohmann transfer to polar orbit :)

Yea, that's what threw me off. I was fiddling with all the maneuver planning options until I gave up and just did an elliptical burn.

Thanks for the explanation guys. 

Edited by sardia
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1 hour ago, fourfa said:

Half way point because why?  You have minimum speed there relative to both Kerbin and Mun?

it would be fun if MJ had an option for Hohmann transfer to polar orbit :)

When you burn normal/anti-normal, the greatest change in position occurs at 90 degrees and 270 degrees from where you burn.

Therefore you burn half way between your origin and destination.

Happy landings!

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1 hour ago, fourfa said:

Half way point because why?  You have minimum speed there relative to both Kerbin and Mun?

it would be fun if MJ had an option for Hohmann transfer to polar orbit :)

I guess halfway because that is the middle between going too fast (so needing more dV for the manoeuvre) and being too close to the Mun (higher angular delfection, so more dV).

But I still believe that doing the inclination change at your ejection burn is cheaper in dV (thanks to keeping a Hohmann transfer and using the Oberth effect)

Edited by Gaarst
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39 minutes ago, Gaarst said:

But I still believe that doing the inclination change at your ejection burn is cheaper in dV (thanks to keeping a Hohmann transfer and using the Oberth effect)

The Oberth effect only works when you burn prograde or retrograde.  It does not help when you burn normal/anti-normal.

And, of course, when plane-matching, it's preferable to burn at the node (ascending or descending) which is farthest from the orbited body and where your craft is moving more slowly.

Happy landings!

Edited by Starhawk
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52 minutes ago, Gaarst said:

But I still believe that doing the inclination change at your ejection burn is cheaper in dV (thanks to keeping a Hohmann transfer and using the Oberth effect)

If your transfer is efficient, an inclination change on ejection will have virtually no effect on the latitude of Pe on your arrival, since it will be 180° later. You will arrive at the Mun coming in at an angle, but Pe will still be at the Mun's equator.

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