A wet workshop is a space station made from a spent liquid-propellant rocket stage. Such a rocket stage contains two large, airtight propellant tanks; it was realized that the larger tank could be retrofitted into the living quarters of a space station, while the smaller one could be used for the storage of waste. A large rocket stage would reach a low Earth orbit and undergo later modification. This would make for a cost-effective reuse of hardware that would otherwise have no further purpose, but the in-orbit modification of the rocket stage could prove difficult and expensive. , no wet-workshop space station has been built or flown. A wet workshop is contrasted with a "dry workshop", where the empty upper stage is internally outfitted on the ground before launch with a human habitat and other equipment. It is not filled with propellant; instead the stage is launched into orbit by a sufficiently powerful rocket. The Apollo Applications Program of the 1960s studied using the Saturn V second stage S-II, and later planned to use the Saturn IB second stage S-IVB as a wet workshop, but cancellation of some Apollo program lunar landing missions made a two-stage Saturn V available to launch the station known as Skylab as an S-IVB dry workshop. Apollo-derived concepts Wernher von Braun proposed a wet workshop concept for launch on the Saturn V. His design modified the S-II second stage of the Saturn V stack to allow it to be used as living space once reaching orbit. Since the S-IC lower stage of the Saturn V cannot reach orbit on its own, the S-II would have to fire, and then vent out any remaining propellant once it reached orbit. To allow this, the floors of the station would be made of an open grid which allowed the propellant to pass through easily to the piping at the bottom of the tanks. The structure also presented convenient hand and footholds. Since the entire propellant load would be needed to reach orbit, additional life support equipment could not be stored inside the S-II during launch. von Braun's design placed all of this ancillary equipment in a large cylindrical carrier, which would be carried on top of the S-II stage in place of the S-IVB normally placed there. After reaching orbit and venting, a large access hatch in the top of the S-II's hydrogen tank would be opened. The