I went too far back in my KSP world
Solution 1:
There's a rolling backup of the persistant save in your KSP save folder
<KSP Folder>\saves\<World save>\Backup
Take one by one back into the parent folder and call them with the Alt+F9 key.
When you found the one, do a Alt+F5 to put a big checkpoint in your main game, the persistent.sfs which contains the current game will automatically be overwritten.
Good luck!