How can I store subassemblies for reused on other vessels?

[Zeiss Ikon]

Several times, recently (in a sandbox game where I'm building up the knowledge and skill to consider taking on a career game, as well as putting together a library of my own rocket designs), I've wished I could take a stack of parts off an existing vessel and either convert them into a vessel in their own right, or mount them (or multiple copies of them) onto another vessel.

I know I can stash removed subassemblies aside in the VAB, but they vanish when I load another vessel.  Say I've got a booster design I really want to add to another, better core -- how can I do that without having to build the thing up from scratch again?  Or I finally got my lander figured out -- but because I built the vessel down from the command pod, I can't take off parts to leave just the lander; rather, I'm stuck with the "lander and everything above it" or, if I built up from a booster engine, "lander and everything below it."

i suspect, as is usually the case when I think there's something I'm not allowed to do in KSP, that there's a reasonably simple, reasonably efficient way to do this, else why would assemblies like landers appear in the premade vessels library in a freshly installed game?  That said, I haven't seen any reference anywhere to the ability to do this.  What am I missing?

[Gaarst]

Subassemblies already exist. Click the arrow at the very top-left in the Editor to bring the "advanced editor" and click on the green rocket icon to show the Subassemblies tab.

[astroheiko]

When I started playing the game, I also looked for it. The solution is the Bottun in the upper left.

I show the best with a few pictures.

Suppose we want a standard satellite, which we want to put on a rocket. So, for example.

You want to save as a subbassembly. To do this, press the button in the upper left corner. I marked it.

 

Then this bar appears. The yellow marked button is the subassemblies zone.

 

Now drag and drop the Satellite in this (red marked) Zone.

 

There appears a window where you can give it a name.

 

Then build or load a rocket. When you press the Subassemblies button again, you can simply select the satellite. He then hangs at the mouse. Put him on the top and ... bingo.

 

Make shure the root part has been set to the Decoupler before saving a Subassembly.

Alternatively, you can also connect a satellite from the VAB. You load the rocket and choose again "open". Then you can use "merge" to load an already existing object. You can connect that too.

I hope I could help

Greetings

 

Edited February 10, 2017 by astroheiko

[Zeiss Ikon]

Astroheiko, that's a very clear explanation.  Next time I have time to start the game, I'm going to open your answer and flip back and forth -- I've got a few pieces to save that will save me time and mistakes. 

For now, though, it's time for bed...