From: nuny@bid.nes   
      
   On Tuesday, April 4, 2017 at 7:18:50 AM UTC-7, 0something0 wrote:   
   > I thought that a pure antimatter-powered nuclear-pulse was a interesting idea   
      
     A quick Google doesn't inspire me with its practicality.   
      
   > that deserved a thread all of its own. So, here is a question that begs to be   
   > asked:    
   >    
   > How do we calculate the thrust and the Isp of an antimatter-powered nuclear   
   > pulse?   
      
     The general idea is to mix small amounts of antihydrogen with a larger mass   
   of ordinary hydrogen. The implementations so far suggested (per the Wiki and   
   other sources) don't seem to me to be particularly efficient.   
      
     You either load a kilogram or so blob of cold hydrogen plus a microgram of   
   antihydrogen in a sacrificial Penning trap and allow them to mix Orion-style   
   then get thrust against a non-sacrificial magnetic field that makes up the   
   "exhaust bell", or inject    
   pellets of antihydrogen into a continuous stream of hydrogen producing   
   individual bangs of variable yield depending on how wide open the hydrogen   
   throttle happens to be at the moment, again getting thrust by reaction against   
   the engine's magnetic field.   
      
     In the first case, as Luke Campbell points out, much of the reaction   
   products don't actually provide thrust (because they ignore the engine's   
   magnetic "bell"), and some are actively hazardous to the engine structure and   
   presumed crew (do it just right    
   and it's a neutron bomb). You get individual pulses of thrust just like the   
   original Orion. How much? Total released energy minus the unusable part that   
   ignores the magnetic bell. It seems to me that it gets very handwavy depending   
   on how quickly the    
   reactions proceed vs. confinement time in the bell. The engine dimensions will   
   be critical.   
      
     In the second case, the continuous hydrogen stream can contain some of the   
   non-thrust products (decaing neutral pions)leading to more heating and   
   presumably more thrust, but does the stream stay hot enough to keep fusing   
   between pellets? If so there    
   will be a constant thrust component with the pulses superimposed on top of   
   them. You could get variable thrust by opening the hydrogen throttle and   
   injecting the pellets more often while keeping the constant thrust-pulse   
   thrust ratio constant.   
      
     I *think* the continuous stream approach will be more efficient but that   
   also depends on confinement time vs. reaction rate, but only if the engine is   
   big enough to allow the stream to capture and utilize the "wasted" products   
   before they escape.   
      
     Deducing Isp is beyond me. I'll have to think about it a lot more.   
      
      
     Mark L. Fergerson   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)