Maybe... Maybe Not. The USSA seems to be more Military and an "Imperialist" organisation than NASA, which seems to fit the USA that existed in FO's universe better.
I suppose it could have also been a legal decision, like how in the new series of Doctor Who UNIT isnt the "United Nations Inteligence Taskforce" its the "Unified Inteligence Taskforce".
Another victim of political correctness, though actually that probably hits it right on the head. Actually, and you probably know better(being a UK Citizen), but I remember seeing a show on BBC America called "Red Cap"(about the British Army's Special Investigation Branch), where though there seemed to be some factual details, there were also quite a few liberties taken as it relates to some of the regiments mentioned etc.