What does "Primary Docking Node" do?

[PyroPerc88]

I am about to go to sleep and was curious as to the function of "Primary Docking Node". Does it set which part is targeted when you Target a Vessal? Or something else? Whats the utility of this function?

[Okhin]

I think it has to do when you have more than one dock connecting two spaceship. The primary docking node is the one you use to "Undock" and separate both soaceships at once, while the non primary ones can only be "Decoupled" leaving the two spaceship connected if they have another docked port.

But I haven't tested it extensively, so can't be 100% sure.

[AHHans]

I've only seen that in the context of docking ports that are actually docked to something. And there the primary docking node is the one that has the "undock" option, the other one has the option to make it the primary one (which makes it have the undock option). And as far as I can tell, that's the only effect of that option.

1 minute ago, Okhin said:

I think it has to do when you have more than one dock connecting two spaceship. The primary docking node is the one you use to "Undock" and separate both soaceships at once, while the non primary ones can only be "Decoupled" leaving the two spaceship connected if they have another docked port.

Nope. When you have more than one pair of docking ports connecting two spaceships then you need to undock all of them to separate them. Yes, one of the pairs is the "primary" in the sense that the order which part is parent and which is a child to its connected parts goes through this, but when you undock this and there are other docked ports, then one of these other becomes the new "primary" until you undocked all of them.

This may have been different in earlier versions, but 1.8.1 behaves as I said. (At least in the test I just made...)

1 hour ago, PyroPerc88 said:

Does it set which part is targeted when you Target a Vessal?

This is set by the "control from here" function.

[Okhin]

That makes sense, they need one dock to be special to have a tree not a graph with loops (which you wanna avoid).

[Laie]

4 hours ago, PyroPerc88 said:

Whats the utility of this function?

There is an age-old bug where docking ports are stuck, with... oh, I can't recall really. Is it that neither is showing a undock or decouple option? Or that only one shows decouple and it doesn't work? Not sure.

The long and the short of it is that you cannot undock. The only known fix was to edit the save game, identifying the ports in question and altering their states. Either that, or relaunching the vessel(s) and hoping that you would have better luck next time.

Not too long ago, I had that happen to me. At that opportunity, I noticed the Make Primary Docking Node option for the first time... and after toggling it, first here then there, I could undock the ports in the usual manner.

TL;DR: Make Primary Docking Node will let you resolve the stuck ports problem. I don't know if it is the intended purpose, but I was sure happy that it could be solved so easily.