way into orbit, bleeding off any remaining propellant through the Space Shuttle Main Engines, which would have been "left open". One such test had been scheduled, but was canceled after the 1986 Space Shuttle Challenger disaster dramatically changed safety rules. The ET would have provided a huge working space, and one major problem with various wet workshop designs is what to do with all of it. The oxygen tank, the smaller of the two tanks inside the ET, was itself much larger than the entire Space Station Freedom. Additionally, getting access to the interior was possible though "manholes" used for inspection during construction, but it was not clear if realistic amounts of building materials could have been inserted into the tank after reaching orbit. Nevertheless, the problem was studied repeatedly. A similar concept, the "Aft Cargo Carrier", was studied by Martin Marietta in 1984. This consisted of a large cylindrical cargo container bolted onto the bottom of the ET, which offered the same volume as the Space Shuttle orbiter's cargo bay, but would be able to carry wider, bulkier loads. The same basic layout was also used as the basis for a short-duration station design. Although not a wet workshop in the conventional sense, the station piggybacks on the propellant tank and is therefore related to some degree. Space Launch System-derived concepts NASA contractor Brand Griffin has proposed to the Marshall Space Flight Center's Advanced Concepts Office the building of a station from a spent Space Launch System hydrogen fuel tank, to be placed at the Earth-Moon L2 Lagrangian point and named Skylab II in honor of the original Skylab. Commercial space station application NanoRacks, after finalizing its contract with NASA, and after winning NextSTEPs Phase II award, is now developing its concept Independence-1 (since renamed from Ixion), which would turn spent rocket tanks into a habitable living area. References External links Source Abstracts of External Tank Technical Reports Proposed space stations