I have 19 (2 MB worth!) uuencode'd GIF images contain charts outlining one of the many alternative Space Station designs being considered in Crystal City.  Mr. Mark Holderman works down the hall from me, and can be reached for comment at (713) 483-1317, or via e-mail at mholderm@jscprofs.nasa.gov.  Mark proposed this design, which he calls "Geode" ("rough on the outside, but a gem on the inside") or the "ET Strongback with integrated hab modules and centrifuge."  As you can see from file geodeA.gif, it uses a Space Shuttle External Tank (ET) in place of much of the truss which is currently part of Space Station Freedom.  The white track on the outside of the ET is used by the Station Remonte Manipulator System (SRMS) and by the Reaction Control System (RCS) pod.  This allows the RCS pod to move along the track so that thrusting can occur near the center of gravity (CG) of the Station as the mass properties of the Station change during assembly.  The inline module design allows the Shuttle to dock more easily because it can approach closer to the Station's CG and at a structurally strong part of the Station.  In the current SSF design, docking forces are limited to 400 pounds, which seriously constrains the design of the docking system.  The ET would have a hatch installed pre-flight, with little additional launch mass.  We've always had the ability to put an ET into orbit (contrary to some rumors which have circulated here), but we've never had a reason to do it, while we have had some good reasons not to (performance penalties, control, debris generation, and eventual de-orbit and impact footprint).  Once on-orbit, we would vent the residual H2.  The ET insulation (SOFI) either a) erodes on-orbit from impact with atomic Oxygen, or b) stays where it is, and we deploy a Kevlar sheath around it to protect it and keep it from contaminating the local space environment.  Option b) has the advantage of providing further micrometeor protection.  The ET is incredibly strong (remember, it supports the whole stack during launch), and could serve as the nucleus for a much more ambitious design as budget permits.  The white module at the end of ET contains a set of Control Moment Gyros to be used for attitude control, while the RCS will be used for gyro desaturation.  The module also contains a de-orbit system which can be used at the end of the Station's life to perform a controlled de-orbit (so we don't kill any more kangaroos, like we did with Skylab).  The centrifuge, which has the same volume as a hab module, could be used for long-term studies of the effects of lunar or martian gravity on humans.  The centrifuge will be used as a momentum storage device for the whole attitude control system.  The centrifuge is mounted on one of the modules, opposite the ET and the solar panels.  This design uses most of the existing SSF designs for electrical, data and communication systems, getting leverage from the SSF work done to date.  Mark proposed this design at Joe Shea's committee in Crystal City, and he reports that he was warmly received.  However, the rumors I hear say that a design based on a wingless Space Shuttle Orbiter seems more likely.  Please note that this text is my interpretation of Mark's design; you should see his notes in the GIF files.    Instead of posting a 2 MB file to sci.space, I tried to post these for anon-FTP in ames.arc.nasa.gov, but it was out of storage space.  I'll let you all know when I get that done.  -- Ken Jenks, NASA/JSC/GM2, Space Shuttle Program Office       kjenks@gothamcity.jsc.nasa.gov  (713) 483-4368