Docking ports align but won't connect

[the_beholden_one]

I've got a munar lander that I'm trying to dock to my return vessel, and I've aligned them perfectly, come in at 0.1 m/s and the magnetic attraction has pulled them together. Despite this, the ports aren't connecting. It's as if there's an invisible layer between them holding them apart at 0.4 m. The ships are now held together magnetically and in stable orbit over the mun, but I can't transfer my crew to get home.

Also, I've docked in the past successfully. I don't believe that the ports are on backwards, as I had them connected when I launched.

I'm controlling from the lower port and have the target set for the upper one. There aren't any kerbals in the return vehicle, nor is there a probe. Could that be my problem? Has anyone else run into this?

[Snark]

Moving to Gameplay Questions.

Ports don't look backwards to me.

It's definitely not an issue with missing crew or probe core; docking works fine even with uncontrollable vessels.

Looks like you've got something clipped into a service bay? My guess is that you've got some kind of collision problem preventing the docking ports from being able to mate.

Assuming that to be the problem, can't you just work around it by EVAing the kerbals to the return ship?

Or... just fly them home as it currently stands. Even if you can't reenter and land, you could at least get to LKO where it's quick and easy to send a rescue ship.

 

[bewing]

I agree with snark -- some invisible part of ship1 is colliding with some part of ship 2 just before the docking completes, holding them apart. I'm going to bet on the terrier "tank butts".

So yeah, pop the doors open on your lander bay, EVA the kerbals with any data, fly them to a hatch on the return vessel, and get them aboard that way. If you were going to be trying to transfer science when you docked, it wouldn't have worked anyway. You can only transfer science during an EVA.

 

 

[Capt. Hunt]

if the ports are actually touching but not connecting, sometimes turning SAS off will get them to lock, but this looks like they're not even touching, so that tells me that there is a collision mesh in the way.

[HvP]

I'm not 100% sure about this, but I think the problem might be that the collision mesh for the lv-909 terrier engines on your return vessel could be colliding with the top of the service bay on your lander. The perspective on your screenshot doesn't show very well the clearance from the side of your engine bells to the side of the cargo bay, but it looks like your service bay has to slide in between them a little bit.

The physical boundaries of parts in KSP don't always coincide with the art as seen in the game. Some parts have collision surfaces well outside of the part of the model that you can see. As I understand it, the newest version of the Unity platform that KSP runs on doesn't allow any concave surfaces without the addition of extra shapes to the model. So, for the sake of simplicity and better performance some corners get cut, literally. Those areas at the top of the engine bell probably aren't really pinched in if you could see the invisible parts of the mesh model. It would be more like a truncated cone with the top chopped off -- the wide end at the top (base) of the engine butt and the smaller end at the exhaust nozzle.

This wasn't a problem when you launched because KSP doesn't calculate collisions for parts on the same vessel, and as long as it was docked together it was treated all as one. Now though they are two ships and will bump into each other.

The best solution at this point is as the others have said. EVA your Kerbals from the lander, don't forget to collect any science you have from it, and float them over to your return ship. On your next design iteration try to leave a little more room between parts that are going to be in close proximity when docking. And it's sometimes fun to take a page out of NASA's book and test the docking mechanism in near orbit before starting the long trip.

Edited May 9, 2017 by HvP

[Kryxal]

It might be worth saving, then using the lander to set the whole thing on a reentry course if you're able.  That lets you just timewarp and let things drift apart.