Reuse of fuel tanks as habitats?

Question

So, we've got this huge, hermetically sealed tube of metal nearly to orbit, just to push another huge hermetically sealed tube into orbit, and then we let the first tube fall and burn in the atmosphere... seems like a big waste to me.

Of course all the "furniture" would need to fly in another launch, and the project would need to foresee the dual use - equip the rocket with at least stubs for all the necessary infrastructure. But the heaviest part - the strong walls, the structural reinforcements, the airtight sealing, plus a lot of tubing seems to be viable for reuse once in orbit, as actual structure of the station - habitats, greenhouses, even dumb structural parts like trusses.

Would it be possible - is there any research or projects - of reusing fuel tanks of rockets as structural parts of a space station?

Answer 1

This is known as a "wet workshop". This was one of the options looked at for Skylab: the S-II second stage would place itself plus a payload into orbit.
Once in orbit, the payload (containing all the equipment for the station: life support, experiments etc.) would be inserted into the S-II hydrogen tank once piece through a large hatch.