Free return trajectories and retrograde orbits

[Alistair]

Hello everybody,
Just wondering, when you do a free return trajectory your encounter would be retrograde so that you are in front of the body and can be pulled in the retrograde direction. So I have a mission going to the Mun, and it's encounter with it means that it's going retrograde because its a free return trajectory. And then when I do my orbit insertion, the orbit will be retrograde.
Anyway, I was just thinking - would this have been how, say, the Apollo missions did it; would they have gone in a retrograde orbit around the moon?
Thank you very much

[GunsForBucks]

Never heard the term before but ... a retrograde orbit would mean going against the rotation. At least in KSP as all moons and planets spin the same way. So if your intent is landing you would just be adding to your DV.

But if you intend to scan/ survey you might cover more ground going opposite. I suppose it depends on the mission.

That said though our moon rotates once a monthish so how much difference could it be?

Definitely don't want to enter Jool the wrong way if you are heading for a moon there ha ha.

[GunsForBucks]

I kept wondering what "free return trajectory" might mean...

The only thing I can think of is that you are a bit confused on what it means?

It sounds like you burn out to in front of it and then the mass pulls you to slow you down from its orbital speed and that would put you more retrograde to the Muns motion around Kerbin. This would make for an easier return or possibly a "free" return if you hooked it right with the gravity assist.

This situation is to your advantage if you are doing a flyby and not going into orbit around the Mun.

So it isn't for a retrograde orbit around the Mun but to apply a retrograde vector relative to Muns orbit around Kerbin.

If I am understanding the whole "free return" thing properly.

[Wobbly Av8r]

If I understand your question correctly, this is a link you might be looking for:

https://astronomy.com/news/2018/05/why-apollo-flew-in-a-figure-8

[Alistair]

Originally posted by GunsForBucks:

I kept wondering what "free return trajectory" might mean...

The only thing I can think of is that you are a bit confused on what it means?

It sounds like you burn out to in front of it and then the mass pulls you to slow you down from its orbital speed and that would put you more retrograde to the Muns motion around Kerbin. This would make for an easier return or possibly a "free" return if you hooked it right with the gravity assist.

This situation is to your advantage if you are doing a flyby and not going into orbit around the Mun.

So it isn't for a retrograde orbit around the Mun but to apply a retrograde vector relative to Muns orbit around Kerbin.

If I am understanding the whole "free return" thing properly.

Yeah, I do think that that is what a free return trajectory is. Basically my plan was that if something goes wrong on the way to the mun (which it wouldnt because of QUICKSAVES!) then I would just fling around the mun and it's gravity would pull me in the retrograde direction which means that I would end up just flying back to Kerbin.
My problem is, I'm going around the mun in the retrograde direction. Or as the article above put it (thank you by the way) around in the trailing edge (I think).
So this means that when I do my orbital insertion, I am doing it on the trailing edge of the mun which means that the retrograde vector of my orbit is facing in the direction the mun rotates.
So as I do the orbital insertion, I burn retrograde which means that I'm slowing myself down in the direction of the muns rotation. So the prograde vector is in a direction OPPOSITE the muns rotation, therefore orbit is retrograde (when I look at orbital info it says inclination is around 180 degrees). But would this have been how the apollo missions did it? They would have gone around the trailing edge of the moon and surely must have done their orbital insertion there as this is where their perilune would have been, right? So then the same thing would have happened that would have happened in KSP and their orbit would be retrograde.
Sorry if I'm being confusing, it's just something that's been bugging me a bit recently.

[Alistair]

I'm really really sorry, I just took ONE MINUTE doing a bit of googling and I believe that the apollo missions did indeed have a retrograde orbit, so I am sorry if I was wasting your time or something.
Thank you very much :)

https://forum.kerbalspaceprogram.com/index.php?/topic/48448-effect-of-retrograde-mun-orbit-for-apollo-styled-mission/
I found this conversation on the forums

[GunsForBucks]

Originally posted by AngusRetriever:

I'm really really sorry, I just took ONE MINUTE doing a bit of googling and I believe that the apollo missions did indeed have a retrograde orbit, so I am sorry if I was wasting your time or something.
Thank you very much :)

https://forum.kerbalspaceprogram.com/index.php?/topic/48448-effect-of-retrograde-mun-orbit-for-apollo-styled-mission/
I found this conversation on the forums

No need to be sorry for anything.
Always interesting to have something to think about.
So thanks!

[Alistair]

Yeah, thank you. Have a great day

[MAD]

yes
the Apollo missions used a free return trajectory because there was concern about the Luna engine reignighting. If it failed the crew could safely return to earth.