I would like to know if it is playable solo.
An extremely crunchy d6-based hard sci-fi table top roleplaying game. · By
The closest this game comes to that is A Lot of Zeroes which allows you to create star systems and worlds on those star systems.
But the creation process is tied to the game systems across the other books - you’re not just creating worlds for flavour, but because you need to survey them in order to build a factory (core rules), visit or run a colony (This Space Intentionally), or steal something from them (A Facility with Words). And the world creation process is obsessively focused on getting the details for these specific activities right, instead of more generic flavour (the trade goods for all colonies of the same spectral type are the same, for instance).
If you’re looking for inspiration for sci fi ideas on the other hand, every page of every book is packed full of them. Have a look at the screen shots.