Re: O'Neill habitat spin axis

From: Theodore W. Hall (twhall_at_netvigator.com)
Date: 08/26/04 

To: sci-space-tech@moderators.isc.org
Date:  Thu, 26 Aug 2004 12:05:07 +0800

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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