[ma2rten]

Would that not be illegal? Or is SpaceX required by law to do so?

The law prohibits employers from hiring only U.S. citizens or lawful permanent residents unless required to do so by law.

http://www.eeoc.gov/laws/practices/inquiries_citizenship.cfm

[TorKlingberg]

They are probably required to. Space launchers and intercontinental ballistic missiles are pretty much the same thing after all.

[grhino]

SpaceX is guiding rockets into space which I'm guessing is a lot like guiding missiles. SpaceX is probably required by law to guard some, if not most, of their technology.

[pound]

there may be a need for clearance.