-------------------------------------------------------------------------------
   Compute specific impulse from exhaust velocity
-------------------------------------------------------------------------------
   Form:
   iSP = V2Isp( v, g )
-------------------------------------------------------------------------------

   ------
   Inputs
   ------
   v           (1,:)  Exhaust velocity 
   g           (1,1)  Acceleration of gravity (9.806 m/sec^2)

   -------
   Outputs
   -------
   iSP         (1,:)  Specific impulse (sec)

-------------------------------------------------------------------------------