Stepping Up The World of Satellite Phones

As the world of terrestrial cellphones radically expanded, a branch developed that was entirely different in its hardware but served a similar purpose.  Satellite phones were pioneered by Inmarsat and the Motorola Iridium program in the late 1990s but the field has changed since then.  Motorola is gone (although the Iridium service based on their original satellites appears to be there) and other companies have joined in.  The field, like much of satellite communications, has divided into satellites in Geosynchronous Earth Orbit (GEO) so that the satellites service small areas of the globe but are there all the time, and satellites in Low Earth Orbit (LEO) that move across the sky and don't give continuous coverage to any place.  The phones are different from the conventional cellphones most of us carry around with us, and the inescapable physics of communicating from GEO to the ground means they sometimes don't do much for you, like only providing one way messages or texts.

All of that is on the cusp of change as startup company AST SpaceMobile is moving to put more conventional cellphone base stations in LEO and allow anyone anywhere to connect to the network by going through space.  This is still preliminary as they have only done some testing of their concepts so far, so don't expect it Real Soon, Now, but they announced this week that they've signed agreements with SpaceX to launch the next level experiments of their satellites.  In addition to the planned launch this summer of their Blue Walker 3 prototype satellite (BW3), the agreement covers the launch of the first BlueBird satellite and provides a framework for future launches. 

AST SpaceMobile rendering of their BW3 satellite.

The BW3 satellite is slated to launch from Cape Canaveral on a Falcon 9 vehicle. The satellite has an aperture of 693 square feet and is designed to communicate directly with cell phones via 3GPP standard frequencies.

As you can see in their drawing, the antenna is a phased array or flat panel style antenna.  The antenna needs to be folded in a complex origami-like way to fit in the Falcon 9, so this is a major test of that operation.  Which is vitally important because the production BlueBird satellites will carry an antenna that unfolds to 4800 square feet.  The constellation of these BlueBird satellites that they're planning is nowhere near as big as the Starlink constellation but is still a respectable 243 satellites being planned.  

Thanks to those massive antennas, though, AST says its BlueBirds will theoretically be able to “reach over 700 million unconnected people,” though it’s less clear how many users the constellation – or a single satellite – will be able to simultaneously support.  

I found it interesting to note that AST said it has already demonstrated the space-to-ground connection by doing it backwards.  They launched what was basically a modified (to be controllable) mobile phone made into a CubeSat and then used that orbiting phone to connect to a simulated BlueBird satellite on the ground.