The interview process is pretty demanding and thorough. It's a total of 4 interviews, the last one if you get there is in person. You are pitted against applicants at every turn, so be ready for that. The first interview is pretty straightforward. The interviewer asks some basic questions like tell me about yourself, why Spacex, 5 year plan, etc. They then go into a 20 technical question section where they see where you rank compared to other interviews and its about fluids, heat transfer, beam questions and material properties. They do tell you if you got it right or wrong though