The book says that the explorer can affect only the Fellowship bonus number of npcs with a roll, the Air of authority adds 1d10 + bonus. A player of mine ask why the limit of npcs if the crew (non-player) are a lot of people. Or is it explained in another part of the book? Maybe someone can clarify this? Thanks.

IIRC Master Orator makes that x10. Given proper xhain of command this should be enough to insure proper order propagation.

THANKS! Is all clear now.

Or, if you aren't too finicky about following rules, you could Rule Zero it and just be like "You yell into the vox-casters, the officers hear your command and they relay it to all necessary personnel."

Yeah, in my game, we only use it when there isn't a proper and established chain of command in place to deal with the dissemination of orders. Such as when the Rogue Trader tried to rally and take command of a fleeing group of Imperial Guardsmen. (Who he'd never met before, and had no official authority over.)

Yeah you shouldnt really need to make Command tests on your own ship outside of the Extended Actions that require it - its always been used more to boss about NPCs in an orderly way (subservient factions or basic civilians usually, doesn't work on peers or more powerful factions).