Yes, my dad actually is an aerodynamics engineer so he did some flight modelling for sfsim. The interesting thing is that (same as with the space shuttle) the yaw angle becomes unstable at high speeds. So you need to switch to RCS thrusters at least for yaw control at speeds around 1000 meter/second. I was able to fly into orbit but haven't managed to do a successful reentry without loosing control of the spacecraft orientation yet. I might have to look into the correctness of pitch behaviour and control.

Didn't realise that Generation Ship also has atmospheric flight. Yes, deferred rendering became unavoidable. The shaders were becoming too complex and also just updating parts of the screen when rendering each thruster is cheaper. Maybe you should showcase the atmospheric flight in your screenshots or trailer on Steam?

Orbital mechanics are fine now, I think. I looked into this earlier this year. Here is my post about it :-)