Hi. I've been playing SE for 5+ years now. and in all that time I've never seen anyone try to make this block. I've seen attempts, like the docking ring mod, and VCZ's Airtight Connector mod. but nothing that truly embodies a ship-to-ship airlock.
I would like to see the modding community try to make a fully functional telescoping airlock. that have the functionality of a piston, which is hollow, and a connector. which should be compact enough to not take up too much space, be able to extend to at least 5 meters. and be usable for both large and small block grids.
the pic is an example of the type of airlock system I'm talking about.