From a size standpoint, an ET outfitted as a lab or whatever is an attractive proposition on the surface. It has not been done because of cost.<br /><br />It is still less expensive to build modules that are ground processed and checked out than to outfit one in orbit. For one thing, experiment racks, stowage lockers, etc would have to be sent up for installation on later missions.<br /><br />The early ideas consisted of getting the tank to orbit on a shuttle mission. This would be the least expensive method of getting an ET to orbit however. Modifications would be required to get the ET to a stable orbit. Currently, the ET is jettisoned just below orbital velocity.<br /><br />Orbital velocity being 17,500 mph, ET jettisoned at around 16,500 mph.<br /><br />To send an ET to orbit via SDHLV would require the ET to be atop the LV if its launched wet. There would be no reason to do this unless the ET served as an upper stage which would require mods to the bottom bowl shaped end and the top. The bottom mods to allow an economical interface to the stage the ET sits upon and engines. The top because the wet ET would be wet in order to loft some useful payload sitting on top of it to orbit.<br /><br />The foam could be done away with because like the Saturn rocket, an ET atop an SDHLV would not require foam insulation. Other mods as shown on my crude graphic include eliminating the installation of shuttle attaching hardware and SSME plumbing. The tank itself would require an airlock to gain access to the inside. A passageway would have to be provided between the LH2 and LOX tanks to make use of both.<br /><br />Because there is always residual propellant in the tanks, safety precautions would be required, especially for welding operations within the tank.<br /><br />There is really no logical reason to send up a dry ET atop an inline LV. It would actually be more economical to gear up ET production lines to build ETs as payload carriers rather than propellant tanks. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>