moon

after launching the rocket, open access to the moon, extract various resources there and send them to earth,
to send to earth, you need to send a lot of resources to the moon to build a lunar base, the rocket capacity is small as in reality, and it is difficult to transport a resource from the moon to earth,
it is profitable to build factories on the moon to process the resource there and send it to earth, but not any factory will work on the moon because there is no air there, and workers somehow need to live there, and somehow send them there, that is, they will also be there die of old age
in general, the idea is to add the moon and make it 100 times more economically difficult to master
further mission to mars
to implement this, you will have to add algorithms for simplified calculation of offline progress so that the moon does not load the computer, but calculates interactions during the absence when entering the moon, which means that only part of the processes work offline