From: mikkelhaaheim@gmail.com   
      
   Le mercredi 21 septembre 2016 18:50:47 UTC+2, elie....@gmail.com a écrit :   
   > >So far, H2 is still superior... but at this point, heat capacity becomes a   
   disadvantage, as it takes 7x the amount of energy to heat gaseous H2 as it   
   does to heat water vapour.   
   >    
   > I am not sure how this is a disadvantage. Given that the ship has weeks,   
   months or even years of coast time, low acceleration is not a problem: small,   
   constant acceleration is about as good as high point acceleration, as seen   
   with probes using ion    
   drives.   
   > In specific short-duration missions, or on the outer reaches of the system   
   where solar-thermal simply don't have enough energy, higher thrust may be   
   needed for the entire course, though. Maybe Kuiper Belt models would use water   
   for that reason. They    
   might still keep liquid hydrogen to cool the hull down, though.   
      
   I just considered another factor:   
   Although the latent heat of vaporisation of H2O is about 5x that of H2, which   
   makes it a better heat sink at the mtime of boiling, but requires more energy   
   to boil; the expansion of water during boiling is 22x greater than that of H2.   
   Assuming that you    
   are ejecting both (as thrust) at their respective boiling points, H2O provides   
   a clear advantage over H2.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)