If I may ask, how does one get "thrown into writing a simulation model for an attitude determination and control system with no prior exposure to orbital mechanics"? I always wanted to write software that deals in some way with spacecraft, but always thought one needs to have some physics degree for that.

Right place, right time. My career path has been a little weird. I got into the aerospace industry because after leaving the Army in 2006, I had a 4-year old CS degree and no work experience - but I did have a clearance, so I was able to land an entry-level SW job with a small aerospace company working on 3D visualization stuff. After a couple of years with that employer, I was hired on with a huge aerospace company working on a large satellite program.

As to the how, consider that if finding good software engineers is hard (debatable), finding them with clearances is even harder (definitely true). The interviews for defense and aerospace jobs are easy compared to your standard technical interview at Netflix, Google, et al. They really don't want to risk screening folks out for trifling things like "competence" when they have billets to fill (because they're selling man-hours of labor to the govt, even a mediocre engineer can be profitable).

But you should also know, that while working on a large satellite program may sound cool, the maddeningly slow and byzantine bureaucratic development processes (I'm currently on a waterfall-driven project) inherit in such programs will suck every last ounce of joy out of your working life. So, there's that...