Comment by orochimaaru

You have to be a US citizen and not a citizen or permanent resident of any country that is embargoed for the project. The DOD embargoes run by project (at least where my wife works they manage it that way). You also have to file for permission to travel outside the US. It’s usually not an issue but will be denied if you are traveling to a country that is on the embargo list for the project you’re on.