Strange, just yesterday I was wondering when the next one of these was going to come down as I was reading John and Mary Gribbin's "Fire On Earth".
In 1947, another space rock hit Siberia about 3000 miles East of the Tunguska, this time it was smaller, but still had many times the power of Hiroshima.
Remember the giant fireball that missed the Earth in 1972? It sliced through the atmosphere from the US rockies to Canada, then headed back out into space. It was estimated at many times the size of the Tunguska object.
Whoever is shooting at Siberia is closer than 47 light years!
My calculations were a little silly anyway, as I had the rocks flying to earth at light speed. A strict "No no!"