How to surface attach a "merging" ship?

[paul23]

Well I have small drones/satellites that should be added to a big hangar-like generation ship used to travel between kerbin and the final destination of choice. In the vab, while editing the big ship, I tried to add the small satellites.

 

However they wouldn't attach to decouplers (surface attach). Even the root node won't.

 

How would I handle this where I have drones and wish to add (say) 12 to a mothership?

[bewing]

"Merge" mode has a lot of limitations. I think the answer is basically that you want to turn the satellite into a subassembly, from being a merged craft. I'm sure there are multiple ways of doing that, but my suggestion would be just to look for an open node on your generation ship's centerline. Merge the satellite, and attach it to the node. That will turn off "merge"mode. Then detach the satellite, and now it's a subassembly, and you should be able to attach it radially, onto any radial attachment point.

 

[paul23]

The merging ship satellite has no open nodes itself.

[bewing]

To merge a ship, the craft that is being merged *must* have an open node, and the part with the open node must be set as the root of the craft.

[Wobbly Av8r]

I've had a fair amount of success of using the Re-root tool on the grayed-out merge part before it is attached, to create a more convenient node from what appears to be an assembly with non-existent node.

As an example, if the top of a "Merge" assembly terminates in a nose-cone, select the part that the nose cone is attached to as the root - then it will attach and be manageable as @bewing described above.

[DeadJohn]

Try adding a temporary cubic strut to the big ship and to the satellite before merging. Do the merge between the 2 cubic struts as your open nodes. Then you can drag the satellite to your radial decoupler and delete both cubic struts.

[lemon cup]

Here’s how I would do it. Forget about merging anything. 

Fully build your generation ship minus the smaller ships and save it. Then clear the VAB and make your smaller craft. Now here’s the sort of convoluted part, but it’s a breeze when you get the hang of it. You need to make the entire thing a subassembly, complete with the appropriate decoupler (radial or inline depending on how that particular craft needs to mount to the generation ship) serving as the root part. 
 

The way you would do that is finish the smaller craft, then grab the appropriate decoupler and stick it on the craft precisely where it needs to be to successfully deploy from the mothership. Now stick something big and random on that decoupler, like a fuel tank, select the “Reroot” tool, and make that thing the root part. Then grab the decoupler, you’ll see this picks up the whole craft while leaving that thing that you just made the root part seperate.
 

Make it a Subassembly by clicking the double arrow icon all the way in the top left of the VAB menu, when the filter column pops out hit the green subassembly button, and drag and drop that whole craft into the hashed box there at the bottom. 

Finally, clear the VAB again and load your generation ship. Find the “subassembly” you just made and attach it to the generation ship however you see fit. If its got a radial decoupler, you can surface attach that small craft pretty much anywhere you want, and in symmetry too. If it’s an inline decoupler you can still freely put it wherever by placing a radial attach node on the ship first, but you could also attach it to the inside of a Mk.3 cargo bay for example.