XPost: rec.arts.sf.misc   
   From: chakatfirepaw@gmail.com   
      
   On Sat, 01 Aug 2015 18:07:57 -0400, J. Clarke wrote:   
      
   > 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).   
      
   Yes, I know what the numbers get like for _any_ interstellar craft using   
   a reaction drive of _any_ kind.   
      
   There's a reason why the more serious ideas tend to involve sending   
   things no larger than a toaster.   
      
   >> > 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.   
      
   Given that I'm the one that brought up that efficiency issue, I was kind   
   of the one who got to specify what kind of efficiency I was talking about.   
      
   I even _specifically said_ that I was talking about power efficiency,   
   something that is important with things like electrically powered drives.   
      
   >> 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?   
      
   On the order of 3kW/N.   
      
   --   
   Chakat Firepaw - Inventor and Scientist (mad)   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)