Wonderful work, and excellent topic to be addressing. Space, of all places should be free and open to everyone, yet sadly we are not past our deficiencies as a country and a society to view individuals from another country as being a valuable contributors to the great US of A.
Only Russians can become cosmonauts so why wouldnt only Americans become Astronauts? If someone were Mexican, they could either legally become a citizen and then an astronaut or somehow start a Mexican govt space agency. Also there's the new privatized space industry which seems to be open to anyone (with a big enough wallet, anyway).