From: kymhorsell@gmail.com   
      
   On Tuesday, April 18, 2023 at 5:00:31 PM UTC+10, phister wrote:   
   ...   
   > I dont know what altitude sonic bangs cease to occur, but many people    
   > guess the elevation of various UFO sightings to a few thousand feet. They    
   > then describe these objects as moving off silently at extremely high    
   > speed. Maybe there is a mechanism where a vacuum corridor can be produced    
   > in the atmosphere ahead of any object movement, but surely that would also    
   > make some noise.   
      
   About about 11 km sonic booms generally dont reach the ground.   
      
   There are many (logically ;) possible  ways to go fast inside an atm. In water   
   there are ideas of using cavitation -- causing bubbles to form in the water --   
   to reduce drag and go fast. I dont know about going faster than the speed of   
   sound in water, but    
   it surely can't be impossible.   
      
   The same kind of idea might work in air. Even back in the 50s and 60s I heard   
   tell of using ionisation of air near the surface of an object and magnetic   
   fields to push the ionised air out of the way to allow very high speed travel.   
      
   I think the current hypersonic aircraft and rockets just use brute force. The   
   Russian hyp missiles create a sonic boom but a side-effect of bulling your way   
   through the air at mach 5 focuses the boom ahead of the rocket and it doiesnt   
   reach the ground.   
      
   NASA was working on a quiet SS aircraft "QUEST" but it was more focussed on   
   trying to just absorb some of the sound using special materials that turn the   
   boom into a "thud" they say.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)