It depends on what you mean by "practical". It's probably possible to do if you throw enough money at it, but would probably not have any practical purpose. I

It depends on what you mean by "practical". It's probably possible to do if you throw enough money at it, but would probably not have any practical purpose. I don't think there's any open-source software for this, but the software isn't really the problem anyways. It's more about getting sensors that are accurate enough and actuators for thrust direction and power that are accurate and fast enough. I don't think there's anything off the shelf for this, and building and testing it, at that scale, is possible, but not cheap or easy. Once you get all of that together, the software is a relatively small and simple problem, and probably too specific to your exact setup for it to make sense to open-source. Probably the biggest problem is that model rockets use solid-fuel engines, which cannot be controlled once ignited and probably don't have the greatest consistency in thrust and time. Short version is you ain't gonna do a propulsive landing with that. You'd have to build your own micro-scale liquid-fuel rocket engine. I don't know that much about building rocket engines, but it sure looks like building ones on the scale to take commercially viable weights into orbit is very hard. I'm going to bet that building one on a micro scale would be substantially harder and probably require the services of several experts in the field. If you're interested in the area, see what info you can find about military missiles, like for MANPADS, guided anti-armor missiles, and some of the lighter AAMs. Every one I've heard of uses solid-fuel engines too, but they do have good control systems for guidance. I don't think any of them care much about the exact thrust levels, just get it going good and fast and the active guidance systems can handle the rest. But you're gonna need that precise thrust control if you want to land propulsively. Relatedly, if you tried to actually build your landable model rocket, I would expect the appropriate Government agency in your jurisdiction to take a very keen interest in exactly what you plan to do with these things. It may involve spending lots of time and money to convince them that you definitely won't give any of your stuff to whatever the relevant agency considers to be a terrorist group or rouge state.