AST SpaceMobile had great news for investors today. So why are they selling AST stock?AST SpaceMobile (ASTS -12.29%) stock tumbled 10.5% through 10:10 a.m. ET this morning on what -- one would think -- was actually some pretty good news. (And as we'll see, that may be the problem.)Overnight, SpaceX successfully launched five AST BlueBird satellites into orbit from its launch pad at Cape Canaveral. Once set in their orbits, says AST, it will begin offering "approximately 100% nationwide coverage from space w ...