To see how we will react, just like the 9/11 hijackers took commercial flights while carrying box cutters in the months leading up to the date of the attack to

To see how we will react, just like the 9/11 hijackers took commercial flights while carrying box cutters in the months leading up to the date of the attack to verify that they could get through security repeatedly with the devices before they used them as planned. As for what a balloon can do that a satellite cannot... how about making a controlled descent once it gets into a designated geofence? Beyond that... it's up to anyone's imagination.