About those ET's

Let's see: Van Pelt's book discusses artificial gravity.  From that discussion, I show four External tanks bolted together and then rotated at 2 rpm would give you an approximation of Mars gravity.  It would need a docking facility and some habitation modules.  It wouldn't need the internal tanks, so those can be melted down.  The metal could be used as shielding.

Just bolt the external tanks together with the docking facility in the middle of the station at the center of gravity.

The docking facility would need to be a fancy bit of hardware, though.  As the station is rotating, there would be a need to avoid putting torque on the docking spacecraft. It may also need a braking device so as to stop the spacecraft from spinning when with the rotation of the station when departure is desired.  Perhaps a clutch- this to keep the docking facility stationary so as to allow docking.  It could be released after the transfer in order to allow everything to spin with the station.  When departing the station, "push in the clutch" to disengage the rotation of the station, then apply brakes to stop the spacecraft from spinning, and then undock and then depart.

Update:

A need for those rocket engines must be found.  Otherwise, they may to get melted down or deorbited.  I was thinking, why not detach them from the "bottom" of the tank and reattach them somewhere so they can be useful in moving the station.  A good spot to reattach could be at the center of gravity on the opposite side of the docking port.

In addition to propulsion, there needs to be a climate control feature for the station.  The side facing the sun will be hot and the opposite side will be cold.  Just set up a Stirling engine to redistribute the heat and generate electricity for the station.

By the way, this topic is interesting to me, so I'll keeping adding to it from time to time.  As a reminder, all posts here are classified according to topic, so as to make it easy to locate similar posts.  Just click on the label at the end of the post in order to see all posts related to this or any other topic.

Update: 12/16/10

Trent Waddington at QuantumG's Blog proposed a tether which will enable artificial gravity of .1 g.  I was thinking, it would be a lot easier to wet workshop these external tanks if they were tethered and separated thusly.  When the construction was completed, they could be reconnected and then spun to Mars gravitation.