From: mikkelhaaheim@gmail.com   
      
   Le jeudi 15 septembre 2016 17:57:19 UTC+2, Mikkel Haaheim a écrit :   
      
      
   > Once detected, you need processing power to identify a source as a   
   "legitimate" target. You need to eliminate all background sources. To   
   understand how many sources have to be eliminated: someone had calculated that   
   a "torchship" (fusion powered rocket)   
    at full thrust would have a magnitude of +12 (he did not specify if this were   
   absolute magnitude, or apparent magnitude at 1 AU or so, so I will assume   
   apparent, which would actually yield a brighter absolute). This roughly   
   coincides with the detection    
   limit of a 5" to 10" telescope. Now, consider the hundreds to thousands of   
   stars visible to the naked eye on a clear, dark night (the milky way)... and   
   consider the tens to hundreds of thousands of stars and galaxies that become   
   visible with a 5"    
   telescope. This is the background you have to elliminate before detecting an   
   unsheilded fusion drive.   
      
      
   Right. I actually have a little more precise information.    
   I found a source that reports 156 182 070 295 stars catalogued with apparent   
   magnitudes of 12 or brighter. Remember, this is the magnitude calculated for   
   an unshielded fusion rocket engine at full thrust. Multiple this value by 4 to   
   find the number of    
   stars including magnitude 13 (2/5 the brightness, so it is what you have to   
   sort through if your sensor sensitivity is increased by 5/2). Double that   
   value for the count of catalogued stars going to magnitude 14. Double again if   
   you want to go to    
   magnitude 15 (each magnitude requires 5/2 the sensitivity to observe than the   
   magnitude before). All these stars are observable by Hubble sized telescopes.   
   Remember that Hubble is not sensitive enough to observe IR emissions less than   
   kW levels at over 1    
   AU. This does not include the planets, nor reflected light from asteroids or   
   meteoroids.    
   Note that the count is taken from stars catalogued as of 1997. also note that   
   astronomers are STILL going through photographic plates up to 50 or even 80   
   years old trying to catalogue these stars (there are actually many, MANY more).   
      
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