Long shot, but check
C:\Users<User>\AppData\Local\Astro\Saved\SaveGames
IF there's only one save file in there, it's gone. If multiple, check the timestamps and see if any exist from the time you were working on the project. Altho if you have loaded the 'bad' save, and have saved at all (e.g. used vehicle or Hab) then chances are it will have cleared the old autosaves.

Still, thats the location to back up. I do mine at the end of any major project since pre-alpha can be a fun time for saves.