XPost: rec.arts.sf.science   
   From: twhall@netvigator.com   
      
   Russell Wallace wrote:   
      
   > I'm designing an O'Neill habitat for use in a game scenario, [...]   
   >   
   > I'd ideally like to point it at the sun [...]   
   >   
   > But in that case, it seems that a quarter orbit later it'll be side on   
   > to the sun, another quarter orbit the opposite end will point at the   
   > sun etc, since conservation of angular momentum will tend to keep the   
   > spin axis pointing in the same direction relative to the rest of the   
   > universe, not relative to the sun.   
   >   
   > Is there any way to change that ...   
      
      
   Noordung addressed this problem as early as 1930 in his "wheel station"   
   concept.  O'Neill adopted the same strategy in 1974 for his "Model 1"   
   colony.   
      
   Arrange two cylinders side-by-side, slightly "above" and "below" the   
   orbital plane, with their axes parallel to the plane and with opposite   
   spins (as if geared together).  Put connecting structures between the   
   end caps, from cylinder "A" to cylinder "B", at each end.  Give the   
   assembly an initial torque around the "vertical" axis (perpendicular to   
   the orbital plane) to set up the desired star-pointing motion.   
   Ordinarily, this torque would reorient the spin axes of the cylinders   
   away from the orbital plane, in opposite directions due to their   
   opposite spins.  But, the connecting structures restrain them, with   
   tension in one structure and compression in the other.  These   
   structural forces in turn provide just the torque needed to keep the   
   cylinder axes pointed at the star.  O'Neill calculated that a mere 60   
   pounds of force in the connecting structures would be sufficient to   
   keep his "Model 1" colony pointed at the sun.   
      
      Oberth, Hermann (1957).  _Man into Space_ (p. 160-165).  Translated   
         by G. P. H. De Freville.  Harper and Brothers.  Published in   
         Germany under the title _Menschen im Weltraum_.   
      
      O'Neill, Gerard K. (1974 September).  "The Colonization of Space."   
         _Physics Today_, vol. 27, no. 9, pages 32-40.  American Institute   
         of Physics.   
      
      O'Neill, Gerard K. (1977).  "The Colonization of Space."  In   
         J. Grey (Ed.), _Space Manufacturing Facilities (Space Colonies):   
         Proceedings of the Princeton / AIAA / NASA Conference, May 7-9,   
         1975_ (p. A5-A11).  American Institute of Aeronautics and   
         Astronautics.  Appendix A consists of the Proceedings of the May,   
         1974 Princeton Conference on Space Colonization.   
      
   --   
      
   Ted Hall   
      
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