I'm particularly curious about TX - it's really impressive that a satellite would be able to pick out a signal coming from the tiny thing I'm holding in my hand.
It works for existing satellite messengers, and some of these are smaller and lighter than typical smartphones – and some even talk to geostationary satellites. These are almost 36000 km further away than your typical cell tower!
It’s all a question of data rates, transmit power, encoding, and (mostly in the geostationary case) large antennas on the satellite end.
