Oh. Continuing the trend of space settlement being way easier than ground-based life, it seems slaves are entirely docile while out in space. No rebellion or escape attempts at all. It would make sense if they tried to escape normally, it's not like there's anywhere to run... except they have an easily accessible escape route in the form of a passenger shuttle.
So I guess if you ever wanted a massive slave empire without needing to handle the inevitable rebellions and escape attempts, this is a way to do it. Hell you can even have armed mamluke troops at absolutely 0 revolt risk. Pretty neat.