If the smoke was that far away, that very well may have been the sonic boom after all. Makes the timing work out. If so, that was a much bigger boom than the sonic boom I experienced.
Moral of the story? For your next interplanetary war forget explosives. Just use mass drivers.
Hence the theory behind the Navy's railgun program. Goal is 40lb projectiles hitting at Mach 7. No warhead needed.
Herb
You don't think size and speed matters? I would think how solid the object is and how it withstands the atmosphere would matter but speed and angle would also determine the outcome of the shock wave.
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2006 Ford 6.0PSD EB-50/E-PH SMB 4X4 Rock Crawler Trailer