AST SpaceMobile plans to deploy massive satellites with 64m² antennas to provide direct-to-phone 5G coverage. Is this technically feasible, or are the physics of space-to-ground cellular communication fundamentally limiting?

Additional Context

Link budget calculations for satellite-to-phone communication are brutal. Power limitations, antenna gain requirements, and atmospheric losses make direct satellite cellular incredibly challenging. AST's satellites would be among the largest ever deployed - can they generate enough signal strength?