Duna transfer orbit

[Chiron0224]

I'm currently trying to pass that next great milestone in every KSP player's career: my first landing and return from another planet.  In this case the planet is Duna, but here's my problem.  Whenever I do my interplanetary transfer and encounter Duna I end up with a periapsis well below or above Duna.  This means that I would have to expend a ton of fuel to achieve an equatorial orbit.  Is there a better way to do this?  Is there a way to angle my ejection burn so that I match Duna's orbital inclination or do I have to do a mid-course correction (not looking forward to the dV required for a plane change with an orbit that size I can tell you)?

[Starhawk]

After you leave Kerbin's SoI place a maneuver half way between Kerbin and Duna.  Click on Duna in map view and focus on it.  Now gently adjust the maneuver node while zoomed in on Duna to see exactly how the changes will affect your trajectory.

You should be able to adjust your arrival as needed for a very small amount of dV.

Happy landings!

[Chiron0224]

Thanks, I'll give this a try tonight.  If successful I'll post an album of my mission

[Aegolius13]

As I look at it, there are two kinds of solutions.  As described above, you can burn pretty much anywhere to PUT an ascending our descending node right on the target.  This means you'll hit the target mid-planet, but at an incline.  Then you can either land, fix the plane in orbit, or just continue with an inclined orbit.  

Or, you can burn AT a node to match planes exactly.  This is the more complete solution, but can be expensive.

All things being equal, it's better to adjust a plane while moving slowly.  For example, if you have to correct plane in orbit of a planet, you can burn at peri just enough to capture, then plane change at the far end of the orbit, then burn again at peri to enter your parking orbit.

It's often possible to save some on the plane change cost by including it in your ejection burn.  (Like the sides of a triangle, it's cheaper to go diagonally then straight in one direction and then straight in another).  In an ideal situation, if you eject while Kerbin is at a node, you can plane match exactly for very cheap.  One method for going to Moho calls for doing this, rather than using launch windows based on phase angles.  But that's excessive for Duna.

In some systems, including Duna, you can also use a trip around a moon to level out your plane.

[DerekL1963]

Honestly, so long as you perform the burn as soon as you enter Duna's SOI, it doesn't cost all that much d/V to change your inclination.   Doing it once you're in orbit, as Aegolius13 suggests can be risky at Duna because of Ike.

[Chiron0224]

It was a success!!!  By the way, if some of the captions seem obvious it's because I also shared this album on my facebook so people who don't play the game might also see the album.

http://imgur.com/a/7JWCJ

Edited September 28, 2016 by Chiron0224

[Starhawk]

3 hours ago, Chiron0224 said:

It was a success!!!  By the way, if some of the captions seem obvious it's because I also shared this album on my facebook so people who don't play the game might also see the album.

http://imgur.com/a/7JWCJ

Congratulations!

Nice mission.  The slides in the imgur album are out of order, though.

Happy landings!

[Plusck]

3 hours ago, Chiron0224 said:

It was a success!!!  By the way, if some of the captions seem obvious it's because I also shared this album on my facebook so people who don't play the game might also see the album.

http://imgur.com/a/7JWCJ

Excellent - but maybe you could re-organise the album images 'cos they're all out of (chronological) whack. : D

For the question of exactly where to make the mid-course correction burn, you're right that doing it on AN/DN will get you lined up with the destination orbit best. However, that won't get you into an equatorial orbit around the destination (except if the designation is Kerbin or the Mun) because the north pole of all planetary bodies (afaik) is at zero inclination compared to Kerbin's orbit. Also, whether it is the most efficient option will depend on several factors... very much like going to Minmus in fact:

1. if AN/DN is "high" away from the major body (i.e. high above the sun and closer to Duna, for a transfer to/from Duna) then most definitely do the correction burn near to it;
2. if AN/DN is "low" (i.e. close to Kerbin) then it will probably be more efficient to make the mid-course correction a lot later, and spend a few percent more of your capture burn straightening out the orbit;
3. if you perfectly match planes, you should hit the destination SOI exactly on the equator. However, in this case, the difference in orbital velocity between you and the destination will always make you "miss" the equator at Pe: it is therefore impossible to obtain a truly equatorial orbit if you start on the same inclined plane;
4. combining point 3. with 1. or 2., you're actually wanting to over-correct the plane change (i.e. burn after AN/DN) or under-correct it (i.e. burn before AN/DN), depending on whether you're heading outwards or inwards relative to the major body: if you start closer to the sun, you want to over-correct (to increase the normal/anti-normal component of velocity when the SOI comes up from behind and hits you, therefore maximising the "equatorialness" of the resultng orbit), and vice versa when starting from a higher sun orbit. This is good news in a sense, since you'll always want to make the plane-change burn during the "slow" part of your transfer orbit;
5. if you plan to swing past Ike on the way in (it can help a touch for the capture burn if you pass very close), you can also use it to reduce inclination;
6. if you're aerobraking, you can use body lift/drag to correct the plane.

[Chiron0224]

 

3 hours ago, Starhawk said:

Congratulations!

Nice mission.  The slides in the imgur album are out of order, though.

Happy landings!

Dang it!  I spent so long re-arranging the pictures.  What gives imgur?  Oh well

[Andiron]

7 hours ago, Chiron0224 said:

It was a success!!!  By the way, if some of the captions seem obvious it's because I also shared this album on my facebook so people who don't play the game might also see the album.

http://imgur.com/a/7JWCJ

Well done !

[Norcalplanner]

Takes me back to my first Duna landing. Well done!

[Chiron0224]

13 hours ago, Plusck said:

Excellent - but maybe you could re-organise the album images 'cos they're all out of (chronological) whack. : D

For the question of exactly where to make the mid-course correction burn, you're right that doing it on AN/DN will get you lined up with the destination orbit best. However, that won't get you into an equatorial orbit around the destination (except if the designation is Kerbin or the Mun) because the north pole of all planetary bodies (afaik) is at zero inclination compared to Kerbin's orbit. Also, whether it is the most efficient option will depend on several factors... very much like going to Minmus in fact:

1. if AN/DN is "high" away from the major body (i.e. high above the sun and closer to Duna, for a transfer to/from Duna) then most definitely do the correction burn near to it;
2. if AN/DN is "low" (i.e. close to Kerbin) then it will probably be more efficient to make the mid-course correction a lot later, and spend a few percent more of your capture burn straightening out the orbit;
3. if you perfectly match planes, you should hit the destination SOI exactly on the equator. However, in this case, the difference in orbital velocity between you and the destination will always make you "miss" the equator at Pe: it is therefore impossible to obtain a truly equatorial orbit if you start on the same inclined plane;
4. combining point 3. with 1. or 2., you're actually wanting to over-correct the plane change (i.e. burn after AN/DN) or under-correct it (i.e. burn before AN/DN), depending on whether you're heading outwards or inwards relative to the major body: if you start closer to the sun, you want to over-correct (to increase the normal/anti-normal component of velocity when the SOI comes up from behind and hits you, therefore maximising the "equatorialness" of the resultng orbit), and vice versa when starting from a higher sun orbit. This is good news in a sense, since you'll always want to make the plane-change burn during the "slow" part of your transfer orbit;
5. if you plan to swing past Ike on the way in (it can help a touch for the capture burn if you pass very close), you can also use it to reduce inclination;
6. if you're aerobraking, you can use body lift/drag to correct the plane.

 

15 hours ago, Starhawk said:

Congratulations!

Nice mission.  The slides in the imgur album are out of order, though.

Happy landings!

 

Alright, here's the corrected album http://imgur.com/gallery/BCeWu

[Kelderek]

Nicely done!  Grats on a mission well executed!

[Chiron0224]

1 hour ago, Kelderek said:

Nicely done!  Grats on a mission well executed!

Yes, and now to apply what I've learned to do the same thing in my career save and rescue the Kerbals I've stranded in LDO. lol