Aurora II is interesting, done a net search and the search for an open source project similiar but not identical to aurora leads to not very much
Steve is the designer and programmer for both Aurora and Aurora II. Aurora is written in VB6. Aurora II is being written in C#.
I do not think Steve has any intention of releasing Aurora or Aurora II as FLOSS projects. My impression is that he designed and programmed them for his personal satisfaction and enjoys retaining control of their direction and functionality. They are part programming exercise to learn or refresh his VB6 and C# skills, and part hobby based on his pursuit of war games like Starfire. However, if I am wrong, he will correct me.
I do not recall that there is a release date in mind for Aurora II. However, if you are really interested in seeing a FLOSS version of Aurora, you might politely ask Steve to release Aurora as a FLOSS project when he eventually releases Aurora II.
Other than Aurora and Aurora II, I am not aware of any similar projects, FLOSS or otherwise. Conversely, if you like in-depth strategy video games in a sandbox environment, I recommend Dwarf Fortress by Bay 12 Games. It is not a FLOSS project, nor is it science fiction, but it is incredibly fun.