From: gcowan@eagle.ca   
      
   Parallax wrote:   
   >   
   > I have a question that may have an obvious answer but I have lost too   
   > many brain cells for it to be obvious to me.   
   >   
   > isp is given as the thrust produced/quantity of fuel/sec used.   
   > Pounds/(Pounds/sec) gives units of seconds for ISP.  Do the same in   
   > MKS (metric) units and you get:   
   >   
   > Newtons/(Kg/sec)=Kg*m/sec^2/(Kg/sec)=meter*seconds.   
   >   
   > Why do I never see isp expressed in MKS units?   
      
   Newtons per (kilogram-per-second) to me seems to boil down thus:   
   kg m s^(-2) per (kg s^(-1)) --->   
   kg m s^(-2) times (s kg^(-1)) --->   
   m s^(-1),   
      
   not metre-seconds as you have it.   
   But metres-per-second is the dimension of the effective jet velocity,   
   aka the propellant expulsion speed.   
   It probably has several other names.   
      
   I'm curious whether any merit has been seen   
   in reusable first stages that lift straight up just a few km,   
   then fall straight down again, using half their delta 'V'   
   to match speed with the ground just as they get to it,   
   maybe decelerating a little later and more roughly   
   if at their apogee they weren't able to get rid of the upper stages.   
   Expelling a whole lot of very cool reaction mass.   
      
      
   --- Graham Cowan   
   http://www.eagle.ca/~gcowan/boron_blast.html --   
   fireproof fuel, real-car range, no emissions   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)