Kerbal Space Program - Can I transfer Parts to another in-orbit vessel?

I have a few satellites and stations orbiting my planets, but I'd like to add onto them. I've seen numerous videos on using docking clamps to attach my new ship to the existing station, but can I do that on a part-by-part basis? For example, I take an extra fuel tank up there, can I attach just the tank to my station, then send my vessel back to Kerbin? I'm not talking about refueling, but rather transferring individual parts from my ship to the station in orbit.

I'd prefer to not have to use an unmanned probe and jettison everything but the desired part in space after docking if possible, but if that's the only way I guess I don't have a choice.

Solution 1:

Kerbal Attachment System gives you a limited ability to do this, but probably not to the extent that you want. You can only move and attach parts that are Kerbal sized or smaller, and are radially attachable. Unfortunately, this doesn't include fuel tanks (other than monopropellant and xenon). The only other option that I know of is to use docking ports.

Solution 2:

When you want to dock with a vessel which hasn't got docking ports, you can use the Advanced Grabbing Unit. This gadget can grab onto any part of other vessels and then works just like a docking connection. You can use this to transfer resources or gain control of an uncontrolled vessel.

You can also use this to add new parts to an existing ship, as long as you are OK with having the AGU as an adapter. Here are instructions for how to attach a new fuel tank to an existing ship:

1. Build a new ship with a detachable fuel tank and add an AGU to the tank.
2. Rendezvous with the target.
3. Arm the AGU
4. Attach the AGU to the target ship by tenderly pushing it onto a surface
5. undock the tank.

You now have the tank attached to the ship with the AGU in between.

Supply-ship approaching target with armed claw:

Supply ship exchanging fuel with target through claw:

Supply ship decouples the fuel tank with the AGU. The tank keeps being attached to the target:

Unfortunately the fuel in the tank won't be used automatically because the AGU doesn't provide automatic fuel crossfeed, but you can pump the fuel from the new tank to the existing one manually. Also, this craft has some issues flying straight due to the asymmetrically attached mass of its new tank. But besides these minor inconveniences, it works.