When you encounter another planet and are in a clockwise orbit...

[OscarJade]

...Instead of counter-clockwise, how best to correct this? In .90, I found I could not get a successful return encounter with Kerbin from Duna from a clockwise orbit - frustrating, since it had been an otherwise successful

landing mission.

Edited June 13, 2015 by OscarJade

[klesh]

You can still get a return from a clockwise orbit, I am sure I have done it.

The easiest way to flip your orbit is to raise your AP very high and once you get there thrust backwards. The orbit will flip for much less cost than doing it in low orbit. Then when you get back to your PE, you can lower your AP. Or, in the case of wanting to leave, you can continue the flip burn until you escape int he other direction.

[kurja]

You determine your inclination around a body when you approach it, changing it 180 degrees later on costs much more fuel. But direction of your orbit around Duna shouldn't really matter hardly at all for your return to Kerbin, please tell more what difficulty you had there?

[OscarJade]

Even using Mechjeb, I could not set up an encounter. Now, post 1.0 and planning a manned Duna mission, I want to do it right. I have landed an unmanned probe there from a clockwise orbit, which is fine since it isn't coming back

I assume that, once in Duna's SOI, I generate a maneuver node and tweak it with a combination of retrograde and normal/antinormal moves?

Edited June 13, 2015 by OscarJade

[kurja]

well I usually decide the orbit earlier than that - when approaching Duna, further out the better delta-v wise, when you have an encounter just put a maneuver node in front of you and then focus the the view on Duna. Now start adjusting the node and see which way your trajectory shifts when pulling on the 'handles', using a maneuver node like that it's really easy actually.

But for your return it should not matter if you're orbiting along the planet's rotation or the other way round really, it's the same ordeal returning to Kerbin either way.

- - - Updated - - -

I assume that, once in Duna's SOI, I generate a maneuver node and tweak it with a combination of retrograde and normal/antinormal moves?

assuming you're approaching with little or no inclination it's really the radial vectors you are interested in, you shouldn't need to touch normal unless you want to change your inclination during the approach.

[Empiro]

If you're already captured into orbit, then you want to raise your AP as high as possible, flip your orbit at the AP, and then bring it back down.

Otherwise the best way is to enter the SOI in the correct place. All it takes is a slight burn when you're far away to determine which direction you'll be orbiting the planet.

Also, it really doesn't matter which direction you're orbiting if you want to transfer back to Kerbin. I've never used Mechjeb, but perhaps it doesn't handle retrograde orbits properly or something, but it isn't too hard to do it by hand.

[magnemoe]

Even using Mechjeb, I could not set up an encounter. Now, post 1.0 and planning a manned Duna mission, I want to do it right. I have landed an unmanned probe there from a clockwise orbit, which is fine since it isn't coming back

I assume that, once in Duna's SOI, I generate a maneuver node and tweak it with a combination of retrograde and normal/antinormal moves?

Yes, once inside the SOI you can do an ormal/antinormal burn, just add burn, drag it to center of planet and continue to burn to you get Pe on right side.

Note that if you enter on the left side of planet mechjeb set Pe will set you up for retrograde.

You can focus on the planet in solar orbit and adjust the trajectory here, mechjeb fine tune distance will set you up for an right side past, however has limited accuracy over many years travel.

Main issue with Duna is Ike messing upp stuff. this can also be checked if you focus on planet before entering SOI, doing an small braking or acceleration combined with normal / antinormal to compensate will let it pass.

[Starhawk]

The direction of your orbit is irrelevant when transferring to another planet.

The direction of your orbit changes nothing except which side of the planet you are on when you make your burn. Transfer window, ejection angle, delta-v required, etc. are all exactly the same.

I do not understand the difficulty you had with setting up your transfer, but it's not due to the direction of your orbit. Perhaps if you explain the problem in more detail we could help pin down the exact cause.

Happy landings!

[Geschosskopf]

Even using Mechjeb, I could not set up an encounter. Now, post 1.0 and planning a manned Duna mission, I want to do it right. I have landed an unmanned probe there from a clockwise orbit, which is fine since it isn't coming back

Well, it's pretty simple to do right. Even if after several course tweaks en route you still have a retrograde (clockwise) orbit when you enter Duna's SOI, it still costs very little dV (on the order of 50-80m/s) to switch it to prograde (clockwise) if you do this as soon as you enter the SOI. The easiest way to is to burn radial inwards and just pull your Pe all the way through Duna and out the other side to the desired altitude. It's best to do this without a node, just point radial inwards and burn at like 1/4 throttle while watching your Pe move. When you get very close to the desired altitude, fine-tune it with RCS.

Of course, the above only matters if your Duna lander has to dock with a mothership after landing, in which case it's important that the mothership be in a prograde (counterclockwise) orbit. If you don't have to dock and the lander is going to fly home by itself, then the direction of its orbit prior to landing doesn't matter. Once on the ground, you can take off towards the east and be in a prograde orbit.

[Snark]

The direction of your orbit is irrelevant when transferring to another planet.

The direction of your orbit changes nothing except which side of the planet you are on when you make your burn. Transfer window, ejection angle, delta-v required, etc. are all exactly the same.

I do not understand the difficulty you had with setting up your transfer, but it's not due to the direction of your orbit. Perhaps if you explain the problem in more detail we could help pin down the exact cause.

Happy landings!

+1 to this, was thinking the exact thing while reading this thread.

Techniques for reversing the orbit are all well and good... but you don't actually need to, in the situation described by the OP.

[Kryxal]

assuming you're approaching with little or no inclination it's really the radial vectors you are interested in, you shouldn't need to touch normal unless you want to change your inclination during the approach.

Actually, radial in/out can be useful in conjunction with prograde/retrograde to adjust arrival times ... a real lifesaver when you're 10 days out from Duna and Ike wants to play...

As for returning to Kerbin from Duna, it's still the same sort of burn, probably about 30 degrees on the day side (since you're looking to eject Duna-retrograde) and just play with it from there.

[Warzouz]

If you arrive clockwise, you can always land then take off counter-clockwise. Your orientation change would nearly be free and don't need specific and costly burns. But maybe your mission didn't include landing ?

MJ sometimes mess up maneuver planing. I've experienced it a lot around Jool moons. It wasn't rare that MJ wanted me to dive into the planet crust to do a simple transfert to another moon...

[KerikBalm]

Of course, the above only matters if your Duna lander has to dock with a mothership after landing, in which case it's important that the mothership be in a prograde (counterclockwise) orbit. If you don't have to dock and the lander is going to fly home by itself, then the direction of its orbit prior to landing doesn't matter. Once on the ground, you can take off towards the east and be in a prograde orbit.

While its true that for a lander, it doesn't matter which direction you de-orbit, its not true that your mothership needs to be prograde.

As previously said:

The direction of your orbit is irrelevant when transferring to another planet.

The direction of your orbit changes nothing except which side of the planet you are on when you make your burn. Transfer window, ejection angle, delta-v required, etc. are all exactly the same.

The ony reason for prograde orbits is that you save some dV during ascent/descent.

For Kerbin, this is significant... for Duna (or Mun for that matter), due to its smaller radius and longer rotation period, it doesn't matter so much.

Also on an unrelated note, Warouz:

it may be "transfert" in French, but its only "transfer" in English.