I have done this . . . sort of. The job ad did not explicitly require a PhD, but it was the sort of position where one would be expected (notionally, a postdoc)

I have done this . . . sort of. The job ad did not explicitly require a PhD, but it was the sort of position where one would be expected (notionally, a postdoc). If the position is meant to be research, you are almost certainly going to need a PhD and a record of publication. Seriously, a PhD by itself isn't even worth much any more. However, there are plenty of job ads that ask for a PhD which are not research and do not really require a PhD. What I did was to contact the decision maker (sometimes it is easy to find out who that is, sometimes not), and then talk to him. You can ask if he is willing to consider someone without a PhD, and then give brief account as to why your skill set or experience is appropriate for the job. Keep in mind, this usually doesn't work. You may have misunderstood what the job entails, or the decision maker may simply be unwilling to consider someone without a PhD (rightly or wrongly), or there may be a whole line of better candidates who all have PhDs. You mention building "something that goes beyond NASA's Curiosity." This is a field that interests me, too. Most of the positions that actually build things are engineering or software. Most of them do not require PhDs, explicitly or otherwise. So, in short, I am not sure what position you are trying to get. If it involves building spacecraft, and asks for a PhD, it is almost certainly research, and it almost certainly really does require a PhD.