From: del@branta.demon.co.uk   
      
   On Fri, 21 Jan 2005, in sci.space.tech,   
   John Smith  said:   
      
   >James Nicoll wrote:   
   >>Although the idea of being able to convert angular momentum into   
   >>linear with actually throwing stuff is an old  one in space: didn't   
   >>both Tsiolkovsky _and_ Oberth briefly toy with that before seeing the   
   >>obvious problem?   
   >   
   >As a bit of whimsy - how about two long thin contra-rotating masses,   
   >with an electric motor at the pivot point that makes them   
   >contra-rotate.   
   [...]   
   >One goes one way, one goes the other.  The probe carries out useful   
   >science, and the dummy mass causes a catastrophe somewhere two thousand   
   >years later.   
      
   I think that's equivalent to a rocket in some deep sense that a   
   practical steam engine is equivalent to an ideal Carnot engine.  And in   
   the same way, I think you optimise mass and energy use at the expense of   
   a lot of impractical faffing around.   
      
   So I expect we'll continue to see rockets in preference to this sort of   
   device.  After all, properly designed for their mission, rockets aren't   
   as inefficient of mass and energy as they're made out to be.   
      
   --   
   Del Cotter   
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