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The break up of the previous Falcon 9 first stages on reentry was due to the fact that they were tumbling. Note that the recent launch of the F9 v1.1 followed the usual trajectory because it was only going to "land" on the water. And the first stage did at least survive the reentry. It turns out the greatest aerodynamic stress occurs lower down in the atmosphere not high up when the vehicle is moving at near orbital speed. This is because of the exponential drop off in air density with altitude. Also, the change in the staging point for the reusable two stage system is not coming from the need to reduce aerodynamic stress, but from the need to get the first stage back to the launch site. This is because the usual Mach 10 staging would take it too far down range. This is proven by the fact the recent flight of the F9 v1.1 did fly the usual trajectory, as it did not have to return to the launch site. Bob Clark
The break up of the previous Falcon 9 first stages on reentry was due to the fact that they were tumbling. Note that the recent launch of the F9 v1.1 followed the usual trajectory because it was only going to "land" on the water. And the first stage did at least survive the reentry.
It turns out the greatest aerodynamic stress occurs lower down in the atmosphere not high up when the vehicle is moving at near orbital speed. This is because of the exponential drop off in air density with altitude.
Also, the change in the staging point for the reusable two stage system is not coming from the need to reduce aerodynamic stress, but from the need to get the first stage back to the launch site. This is because the usual Mach 10 staging would take it too far down range. This is proven by the fact the recent flight of the F9 v1.1 did fly the usual trajectory, as it did not have to return to the launch site.
Bob Clark
