I open sourced my open space game. It’s on Github: 

https://github.com/andytriboletti/openspace-swift

If you’re looking for something to do, you could find public domain images of views from space for the International Space Station, or views of Earth.

You can email them to me at andy@greenrobot.com or submit a pull request.

Happy to report I’ve used a tree data structure for the first time other than job interviews / college. SceneKit for iOS has a concept of nodes, and children nodes and parent nodes, etc. I wrote a recursive system to highlight the international space station 3d model when tapped. NASA provides a 3d model for free. It has lots of different components / levels.

https://solarsystem.nasa.gov/resources/2378/international-space-station-3d-model/