For anyone wondering how to install this this is what you need to do.
1. Download the pack
2. Go into the custom solar systems folder and create a copy of the example folder
3. Rename this folder whatever you want
4. Extract the pack zip file and copy the planet, heightmap, and texture files of the objects you want from this pack into the respective folders in the new folder you just made.
5. Once you have moved all the data for the objects you want into the correct folders, open the game and use it just like a normal custom system and it should work.
Hope this helps as I've seen a lot of people saying to install it like a normal system when you don't do that.