Ah, exactly, this is correct, and dealing with those floats is a big issue for me. The physics is custom and is using doubles now, but the engine is float based, so a conversion happens before rendering. Being honest, my game won't be as realistic and good as the Orbiter engine is - I'm a long time Orbiter player and I have a huge respect for what Orbiter has made, including this community. Once I get support for doubles, a lot of my issues will be solved but it will take a while to get there I assume.
I have a few dev-phases in mind, where I'm currently focusing on the core features of the engine and the planned mission flow (such as landing on the Moon). Once I have these I will revisit the internal systems again, before starting on content, polish and graphics.
At one point I was thinking that these panels I have been making (the models) could be used for an Orbiter add-on. I know it's possible to create working 3D panels in Orbiter, but I don't know the details.