From: henry@spsystems.net   
      
   In article <402A2E6A.1050503@business.com>,   
   nafod40   wrote:   
   >We could send up water, then just let solar array-powered electrolysis   
   >slowly do its magic to make the fuel. Two years for a bag of fuel? No   
   >problem, no rush.   
      
   Such schemes have been looked at repeatedly, but unfortunately they tend   
   to require inordinately large amounts of power.  Water electrolysis needs   
   roughly 10kW-hr/kg, and that is a *lot* of power by space standards.   
      
   Electrolyzing 80t of water -- enough fuel for an Apollo-sized lunar   
   mission, nowhere near enough for a Mars expedition -- in a year requires   
   90kW of continuous power.  (Nearly double that if your electrolysis plant   
   runs only when the station is in sunlight.)  The full continuous design   
   power of ISS when completed, assuming no further major Russian   
   contributions, is under 80kW, and nearly half of that is required for   
   station systems.   
      
   >That way no volatile components in the launch. You could freeze the   
   >water, and use it as part of the structure of the launch vehicle to   
   >reduce weight.   
      
   Ice is not a good structural material, unfortunately.   
      
   >Alternate launch techniques such as rail guns? The   
   >payload would certainly tolerate the G's.   
      
   So would most any liquid fuel.   
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