I'm trying to add mods and other planets but I don't know how. I'm on mobile and I am using file manager +
On mobile you cant add mods, however to add a planets you simply need to go to your game files, like this:
Android>data>com.StefMorojna.SpaceflightSimulator>files>Custom Solar Systems
Then you copy the Example folder and edit the planets as you want. If you want to have a planet pack in the game, download it and move it's file to the Custom Solar Systems folder the same way as i instructed you.