Wet workshop

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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. As of November 2024^[update], 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.^[1]

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.