What method to get into Munar polar orbit?

[JenBurdoo]

It's pretty expensive delta-v-wise to get into polar orbit, which I'm trying to do in career mode to get max EVA science from Munar biomes. I can think of several ways of doing this:

- I can enter polar orbit of Kerbin, then do Munar injection from there instead of matching planes/Hohmann maneuver etc.

- I can circularize orbit and change my inclination at the descending or ascending nodes.

- I can land on the Mun, then launch into a polar orbit (going north or south).

- Or, I can extend my orbit's eccentricity, then change inclination at apoapsis, then circularize at periapsis.

The last three obviously apply to Kerbin as well.

Which of these is the most efficient?

Edited February 3, 2014 by JenBurdoo

[Rakaydos]

I managed a polar flyby of Mun when returning from minmus. Though I already had the equitorial bioms completed, there was no reason I couldnt have turned it into a polar orbit.

[Claw]

Do your normal burn to the Mun then play with a maneuver node that is roughly half way to the Mun. You can change your approach up or down to arrive above/below the moon to do your Munar orbital insertion.

Alternately, you can do your last option (highly eliptical) for ease of execution while still being efficient.

[astropapi1]

The last one seems like the best idea. When you're capturing into orbit, burn just enough to capture you into a Mun orbit, do the inclination change at apoapsis, and circularize when you come down.

[Woopert]

Either do midcourse corrections, such as burning ascending or descending nodes, or launch into a polar orbit around Kerbin then transfer over to the Mun. Check out this great video here by Darlock Ahe.

[JenBurdoo]

I hadn't thought of a midcourse correction. I like it, but would it waste more fuel than orbiting and re-inclining, given that normally I'd head for the leading edge of the moon to get gravity-assisted slowdown into orbit?

The ship I'm planning on has, I think, fuel to spare, so I can probably try several different options.

[Jimmy Jazz]

The farther away from the body you're orbiting you do the plane change, the less dv you'll lose. Also, you would be wise to do a mun injection

at about 1000km and at the same time a plane change maneuver, just play with the node a bit, and you'll get it. That way you'll lose less dv

compared to doing them separately.

[Taki117]

What I tend to do is plot an intercept for the mun from an equatorial Kerbin orbit. Make sure that you intersect the Mun (No periapsis) then when you enter the Muns' SoI burn either heading 000 for North or 180 for south Once you have the proper inclination put your periapsis where you want it (I usually do about 10km, but if your mapping 100km is better) then circularize at periapsis.

[Claw]

What I tend to do is plot an intercept for the mun from an equatorial Kerbin orbit. Make sure that you intersect the Mun (No periapsis) then when you enter the Muns' SoI burn either heading 000 for North or 180 for south Once you have the proper inclination put your periapsis where you want it (I usually do about 10km, but if your mapping 100km is better) then circularize at periapsis.

This is what I do now too. It's super easy once you figure it out, but when I was figuring it out it was confusing as heck.

I tend not to do a polar orbit around Kerbin first because I dislike waiting for the orbits to line up.

[PlonioFludrasco]

For my map satellites, I usually put them in a near-equatorial LKO, with few deg of inclination respectively to the Mun. Then I plan my intercept in a way that the capture mark is in the further position respectvely to the orbital nodes (ascending and descending). The result, after few corrections, is a good polar orbit.

I don't think that departing from polar LKO is a good solution because first it takes more delta-V to be reached, and then you have to make a very accurate capture burn.

[ShadowDragon8685]

When I do it, I find that the most practical method is to do a circular, equatorial Kerbin orbit (6 degrees if I'm heading to Minmus instead,) launch for the satellite of my choice, and when I have my encounter, adjust my inclination immediately, then circularize at the desired height.

[KN_Namida]

The most efficient way to achieve a Munar polar orbit is to work it out with manouver nodes right from the start: before leaving Kerbin orbit, once the Mun is in the right spot, place a manouver node and extend your orbit until you get a Mun SOI intersection. Right after that, grab the markers which are placed vertically and pull them just a bit, until you see that your trajectory will pass over one of the poles.

Of course, doing mid-course corrections is a bit easier, but if you don't have much fuel, the most efficient way to get a polar orbit around the Mun is to achieve one right from the transfering burn

[Padishar]

...the most efficient way to get a polar orbit around the Mun is to achieve one right from the transfering burn

I would agree with that. The most efficient way is to get it as correct as possible as early as possible. However, to hit perfection from LKO, it can be quite awkward to set up the node accurately enough and your final orbit around the Mun is unlikely to be exactly where you want it. A mid-course correction can then usually be done using RCS translation (orient your ship logically, i.e. prograde and roll to match the map view) or a very small burn. Then, during the capture burn, check the inclination again and if it is a long way off then leave the orbit very elliptical and adjust it at apoapsis as needed before finishing the circularising the next time round. The more elliptical you leave the orbit, the slower you will be going at apoapsis and the less dV you will use for the plane change (again probably small enough to do with RCS) though the orbit will take longer.

[Steve-S]

I'm trying something now and it looks like it will work fantastically. I used my mid course correction to have me pointed directly at Mun, collision course. Upon Mun SOI I set a node to send me over the pole to just under 60k (alt of choice) and then at apoapsis I circularized. My orbit is polar passing through the current Mun's orbital plane on it's orbit line, 90* to Kerbin. Might make the return trip interesting if I can't loiter long enough to be pointing at Kerbin. I still have 452 Liquid and 552 Oxidizer, 91.1 Mono at 19.54t. I'm using BTSM & DR as my only mods. I'll edit with return status if, er um when I make it.

Made it. Had the plane of orbit pointed at Kerbin and burned for a Periapsis and then corrected at appoapsis for re-entry. Didn't even skip and had 200 fuel left to burn to assure no skip. I like this flight profile.

Hope this helps y'all.

Edited February 6, 2014 by Steve-S

[sciguyCO]

I hadn't thought of a midcourse correction. I like it, but would it waste more fuel than orbiting and re-inclining, given that normally I'd head for the leading edge of the moon to get gravity-assisted slowdown into orbit?

From my understanding, if you're not leaving the Mun's SOI, there's really no concept of a "gravity assist". You can use the Mun's gravity + orbital velocity to change your Kerbin orbit by encountering it "in front/behind" the Mun, but if you're doing an orbital insertion, the amount of delta-V required is pretty much the same regardless of which side your peri-Mun sits.

And I'm also pretty sure that radial/normal burns have the biggest effect when you're 90* in your orbit from what you're trying to move (in this case your Munar periapsis), so doing those mid-course seems the most effective to me. Prograde/retrograde burns have the largest effect 180* around your orbit.

In general, the latitude under your periapsis before your orbital insertion is what determines the inclination of your final orbit. So I try to get that roughly where I want it during a mid-course correction, then do final tweaks just after the SOI switch. I used this method to put some scanning satellites around the Mun and Minmus for Kethane and ScanSAT, aiming my periapsis as close to a pole as I could long before the insertion burn.

[Shna_na]

I have a unique suggestion here that I'm yet to test but believe to be the most efficient:

1. Burn from equatorial Kerbin orbit as you would for a normal Mun intercept burn, but slightly early so that you go past it and arrive from 'behind' as it passes.
   
2. When you reach apoapsis, make your Kerbin orbit polar. This will be extremely efficient, as you will only be moving at possibly less than 100m/s.
   
3. If your orbit no longer intercepts the Mun, correct for this. It shouldn't take much fuel.
   
4. When you've entered the Mun's SOI, circularise your orbit at the desired altitude.
   
5. Profit - in the form of science!
   

Maneuver nodes will help massively for steps 1-4.

Let me know if it's any good, I might use it .

[cantab]

My first thought for making polar Munar orbit was to go from polar Kerbin orbit, but it quickly became clear that's not the way to go. You'll be waiting ages for an encounter, for one.

Now I think the way to go is with a mid-course correction after you've set up the encounter. Earlier needs less delta-v I believe, but later demands less precision. Tab through to focus on the Mun, set the manouver node, then zoom in and angle the camera so you can play around with the node, including the radials, while getting a close-up view of the Mun encounter and periapsis. Keep that same camera position when you make the manouver itself.

[SRV Ron]

Do the equatorial orbit as normal. Do the Munar intercept burn as normal. Do a midcourse to change the intercept to come in a polar Munar orbit. Soon as you get into Mun's gravitational field, you can do a fine tune burn to get the orbit completely polar. That will be the most efficient.

[merendel]

I usualy just do a small correction right after the main transfer burn. Its technicly more dV than doing it during the transfer burn but since it only takes a couple m/s when your close to kerbin to enter a highly inclined orbit around the mun it shouldnt mater most missions. I tend to find small innacuracies in my burning of the node will nessesitate a small correction anyway. For the minimul fuel use for this manuver I think the extra cost is worth it.

[Jart]

What I tend to do is plot an intercept for the mun from an equatorial Kerbin orbit. Make sure that you intersect the Mun (No periapsis) then when you enter the Muns' SoI burn either heading 000 for North or 180 for south Once you have the proper inclination put your periapsis where you want it (I usually do about 10km, but if your mapping 100km is better) then circularize at periapsis.

Even if it is not the most efficient, this is my general method. I am rarely starved for fuel during Mun missions. Building for Kerbal Komfort

[architeuthis]

Since the delta-v to make a plane change is approximately dV=2*v*sin(theta/2), you want to do the burn when you are going as slow as possible. The best place to do that is at apoapse after being captured by the mun. This is generally what I do when I want to rendezvous with my Munar polar orbit space station.

Here is a handy guide from a 1970's era NASA technical document about reusable nuclear shuttles for lunar missions:

Edited March 8, 2014 by architeuthis

[Dave Kerbin]

The way I did it recently was from Kerbin orbit with another correction once I reached the Mun.

Starting from LKO with an inclination of 0 degrees I plotted an 879 m/s burn that was mostly prograde but added a small normal burn. I was basically eyeballing it to try and pass over the Mun with a low orbit PE for capture.

The better method would have been to do a correction earlier, once I was close enough to better see the line, but I had lots of fuel so it was easiest to just wait until I entered the Mun's SOI. From there I did a 116 m/s correction to get right on the pole, followed by 239 m/s to capture into low orbit for a total of 1234 m/s. If I had done the correction earlier it could have probably been done for about 60 - 75 m/s more then a normal trip to Mun orbit.

[MarvinKitFox]

It's pretty expensive delta-v-wise to get into polar orbit,

Going there, about 8m/s Thats how much your initial low kerbin orbit needs extra to be 2 degrees off equator, which supplies the right angle.

Circularizing around Mun from a polar approach, or returning form a polar orbit back to Kerbin, wastes another ~125 m/s, if you would otherwise have been using Mun's gravity to best advantage.

Not expensive at all.

- I can enter polar orbit of Kerbin, then do Munar injection from there instead of matching planes/Hohmann maneuver etc.

NONONONONO! worst possible idea.

- I can circularize orbit and change my inclination at the descending or ascending nodes.

Ummm, Wot? What exactly is the ascending node, when considering one spacehip, orbiting one celestial body?? AN/DN only compares two orbits around a third central body.

- I can land on the Mun, then launch into a polar orbit (going north or south).

Ok, apologies.. Polar orbit of Kerbin idea above is not the worst possible idea.

- Or, I can extend my orbit's eccentricity, then change inclination at apoapsis, then circularize at periapsis.

This works, and quite well. Better if you plan it ahead of time and do the equivalent *before* entering orbit. At as great a distance as you can manage.. How about as a mid-course correction halfway from Kerbin? How about Aiming 2 degrees north or south at launch time?

In practise, I usually do a combo of all these moves.

Start in a slightly off-inclination orbit, which results in approaching Mun from a bit to the north/south.

Mid-course tweak of exact approach angle & timing.

"circularise" to an enourmously eccentric Mun orbit, just barely in SOI at Apoapsis.

Tweak the approach a bit more, at Apo. Finetune exact orbit angle, and exact Periapsis now.

Circularize at Periapsis.

This style wasted time, a lot of it. But reduces delta-v quite handily.

Edited March 8, 2014 by MarvinKitFox