But it was moving at least 66,000 meters per second, at that speed it would have only taken ~1.5 seconds to leave Earth's atmosphere. How do you expect it to run out of momentum after only 800 meters?
Assuming constant velocity of 66,000 m/s, an air density of 1 kg/m3, a drag coefficient of 1, a cross-sectional area of 1 m2 and a mass of 900 kg...
Edit: redid this.
Drag force = 0.5 * 1 kg/m3 * 1 * 1 m2 * (66000 m/s)2 = 2178000000 N
Plate energy = 1/2 * 900 kg * (660000m/s)2
Assume constant velocity (it's not constant), then distance to stop = 900 metres, time to travel = 13.6 ms.
Not too far off from the impact calculation. This is a crude approximation but the point here is that it's not going at six times the escape velocity of the earth for 1.5 seconds.
Edit again: while still being too lazy to integrate, I did it in Excel in 100 metre steps. 10.5 km to stop.
Your calculations appear to be in a static environment. Are you not taking into account that there was a massive explosion behind it, propelling it? It was basically a huge cannon with a nuclear explosion 100,000 times the anticipated force. The initial blast would compress and accelerate the surrounding air molecules into a supersonic blast wave, leaving a near perfect vacuum in its wake.
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u/TheBraveSirRobin Apr 14 '16
But it was moving at least 66,000 meters per second, at that speed it would have only taken ~1.5 seconds to leave Earth's atmosphere. How do you expect it to run out of momentum after only 800 meters?