i got rejected after the onsite at SpaceX about 6 weeks ago. writing this up because i couldn't find many honest post-mortems from people who didn't get the offer.
the loop i went through recruiter screen, a technical phone screen with an engineer (python + some systems questions), then a 4-hour onsite: 2 coding rounds, 1 systems design, 1 behavioral.
what i think happened coding: i passed the two rounds i thought i passed. no ambiguity there, the interviewers were signaling positively.
systems design: this is where i think i lost it. they asked me to design a data pipeline for telemetry from a rocket launch. i defaulted to a generic distributed systems answer. kafka, flink, s3, the usual. what i didn't do was ask enough clarifying questions about the actual constraints: latency requirements, what happens if the comms link drops mid-flight, how you handle the time gaps in data. those aren't standard web-company concerns. i was answering the question i'd studied, not the question they were asking.
behavioral: i'd prepped STAR stories but the one question that tripped me up was something like 'tell me about a time you pushed back on a deadline that you knew was unrealistic.' i gave a mediocre answer because i was tired and it was round 4. the story was real but i rushed it.
what i'd do differently for the systems design, i'd study embedded/real-time/aerospace constraints specifically, not just web-scale distributed systems. they are not the same domain. i'd put my behavioral round first in terms of mental energy management. it matters more than people think at SpaceX. i'd ask more about mission-specific context in the problem statement. they're not trying to trick you with aerospace stuff but they will notice if you treat the domain as irrelevant.
no offer. the recruiter gave me a 'not the right fit at this time' and left the door open to re-apply in 6 months. i believe that's real and i'm going to try again.