For what they are doing, a very strong background in data structures and memory management is required, at least in so far as the code running on the rocket itself.
Very few people learn that on their own, and even fewer learn it to the proficiency level they need.
I'm going to go out on a limb here and ask if you think that because you've had very, very few people without a degree apply for that kind of position? Your ad is ensuring that you'll never see the people that have learned it. As a self-taught programmer, I don't apply to listings with this requirement, even if I have everything else they're looking for, because it's just as much an indicator for me as it is for you. I just want you to be aware that you're excluding a very special niche group that could do wonders for any business.
I don't have application demographics in front of me, but I'd wager that you're correct, most people without a degree don't apply to that position.
However, that doesn't actually speak to what I was saying. My claim refers to the population of non-formally educated developers as a whole.
You might fall into the small portion of the population where you do have the requisite knowledge and skill. However, I think you're missing key element to recruiting, that took me a long time myself to understand.
Recruiting is a numbers game. Finding good people is hard, but the best way to find them is A) have competitive compensation, and B) volume. If the signal to noise ratio of college educated applicants is 50:1 and the ratio for non-college educated applicants is 100:1, then as long as there isn't a shortage of college applicants, it improves the recruitment process to require a college degree.
I think you're missing fapjacks point. its not that you're not letting a few people in that are just as capable, its that you're not finding all of the top talent possible. looking around my organization I would say of the people that one out of every 50 people who are hired are observably way more talented than all of the other engineers in the org (ignoring years of experience and strictly speaking about talent + measured output). half of those do not have degrees whereas 90% of engineers in the org do.
so if youre looking for top talent, you are limiting yourself by a significant amount by only looking for people with degrees. looking further into this, if the top talent you do have doesnt have many people to challenge them, then they will leave because they either feel like they arent progressing or feel like they get frustrated by the others not being able to contribute at a level that they expect.
Very few people learn that on their own, and even fewer learn it to the proficiency level they need.