>>82185349
>astronomy, rts
Have you tried Terra Invicta? It's a (non-RTS) strategy game about aliums invading da urf (you can choose whether to help them or not).

It's got some flaws but I think it's worth checking out just for the cool model of the solar system alone. It's not perfectly 1:1 or anything crazy, but I had fun plotting ambushes on the aliums, and determining what moon or obscure asteroid is most efficient to set up water extraction/refueling site, and what have you.