Retrogade Orbit and Launch Windows

[lugge]

So, my Kerbals successfully planed a flag on Duna and got back to LDO. There, they abandoned their MAV and transfered to the Kerbin-Return-Stage. This stage has about 2250 dv. Launch windows for Kerbin opens up in 11 days, ejection needs about 1650dv. I have strong heatshields on my MK-2-pod, thus, I guess I don't need to get back to Kerbin orbit but can directly hit atmo from interplanetary speed. Thus, lots of spare dv.

Well, that was the idea.

Now I realized my return stage is in a retrogade Duna orbit...When I set up my manoever node for ejection burn, I miss Kerbin at about 180° because my craft is going in the wrong direction! Shame on me!

I tried to raise my AP until Duna SOI edge. There I can reverse orbit for about 30-40ms, then circularize again. However, this will take about 50 days. My launch window is gone and I have not enough dv for Kerbin transfer left. Until I wait in high Duna orbit for about 600 days until a new window opens.

I hate to fast forward the game. I don't want my Kerbals hanging in HDO for so long.

Any suggestions? Is there a way to use the abcoming (11 days) window to get home?

Maybe raise AP not till SOI edge but till Ike, then reverse orbit there?

Any fancy space manoever?

 

[Reactordrone]

A retrograde orbit around Duna really shouldn't make much difference to a Kerbin return burn. As long as your ejection burn away from Duna is retrograde to Duna's orbital direction it doesn't matter whether you're coming off the inside or the outside of the planet.

 

[FungusForge]

If you're only on a retrograde Duna orbit (meaning you are going against Duna's rotation) then it shouldn't really make much difference.

[lugge]

Well, thats strange.

I set up my manoever as alexmoon's calculator told me.

I finetuned the node until my orbit intersects Kerbin orbit. Then you get the two marks "Target destination at intersect...". And these marks told me Kerbin is on the opposite side of Kerbol at intersect (~ 180°).

Thus, I thought this is due to my retrogade Duna orbit. Doesn't mean retrogade Duna also you are going retrogade Kerbol when you leave Duna SOI?
 

[Callmedave]

As above states, plan your maneuver on the other side of Duna (180° from where you were going to do it) and you should be golden!

[Reactordrone]

Odd, where are the planets relative to each other? Looking down on the system, if Duna's in the 6 o'clock position Kerbin should be just past the 8 o'clock position.

[mk1980]

it's possible that the mod that shows the launch window is just wrong. I'm using Kerbal Alarm Clock and it displayed wrong launch windows occasionally. funny enough, that was also a return trip from duna and the launch window was also... inverted? or something. basically, it showed a window where kerbin is at the opposite side of the orbit.

i ended up doing the return trip the old fashioned way (by "eyeballing" the correct phase angle of ~ -75°).

also, 1650 m/s seems excessive? i'm pretty sure my transfer burn back to kerbin was somewhere around 670 m/s