XPost: rec.arts.sf.misc   
   From: j.clarke.873638@gmail.com   
      
   In article , chakatfirepaw@gmail.com says...   
   >   
   > On Sat, 01 Aug 2015 08:51:03 -0400, J. Clarke wrote:   
   >   
   > > In article , chakatfirepaw@gmail.com says...   
   > >>   
   > >> At _best_, what they have here is a highly power-inefficient photon   
   > >> drive.  Note, photon drives are reaction drives and don't get the whole   
   > >> "infinite propellant with a mass ratio of 1," thing.   
   > >   
   > > You only get "infinite propellant" if you have free energy.  Otherwise   
   > > you are still expending mass to make energy.   
   >   
   > You don't need free energy, you just need to avoid carrying your fuel.   
   > For instance, you could use a beamed power setup.   
      
   Might be ok for stationkeeping on a satellite but it's not going to get   
   you to Alpha Centauri (yeah, I know there are schemes to do that--if you   
   decide to run the numbers on them be sure to swallow your drink before   
   you look at the results).   
      
   > > Discussing the efficiency   
   > > of space engines for which the means of energy production is separate   
   > > from the means of thrust generation is not something that lends itself   
   > > to a simple figure of merit.   
   >   
   > The power required for a given thrust is a very simple and useful   
   > measure.   
      
   I'm not talking about the "power required ror a given thrust", I'm   
   talking about the mass consumed to generate a given increment of delta-   
   v.   
      
   > Note that I was specifically referring to the power efficiency,   
   > (an ideal photon drive requires 300MW/N, the claimed figure for the EM   
   > Drive is about 1GW/N).   
      
   And how much does kerosene require per newton?   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)