I worked 10 years at JPL in Pasadena (SIR-C 1 and 2, Kidsat, DS1, and Cassini). It is very diverse with regards to ancestry, gender and sexual orientation. Mostly Chinese, followed by Hindi, Korean, Pakistani.
the reason for the high population of immigrants is simple: hard to get security clearance in the defense industry when you weren't born here, so those with an advanced degree in the sciences or engineering go into the space program.